Is the pumice prophylaxis omitted?

September 11, 1998
Dr. Heung-Youl Kim

The pumice prophylaxis has been recommended for achieving a strong enamel-resin bond. The acid-etching technique has been in use for a long time, but there still remains some doubt concerning the relevance of preliminary prophylaxis.

Silverston's study has shown little difference in the surface pattern of enamel, and several clinical trials have demonstrated favorable retention rates for bonded resin when the pumice prophylaxis of the tooth surface was omitted.

A rotating bristle brush with pumice paste is unlikely to clean the pellicle. The acquired pellicle is a tenacious layer of salivary glycoproteins linked physicochemical with surface hydroxyapatite of enamel and is not easily removed by pumicing.

Main (1983) stated that under laboratory conditions the acquired pellicle is completely removed by a standard acid-etching technique. The mechanism probably involves rapid diffusion of the acid through the pellicle and demineralization of the underlying enamel surface, allowing the protein layer to be easily washed off. Therefore the prophylaxis of the enamel surface prior to etching may not be necessary.

Donnan (1988) stated that the prophylaxis of tooth with pumice prior to etching contributes little towards retention, and this step can be omitted. The elimination of this step makes the procedure less involved and less time consuming for the operator.

The result of many studies did not provide any clear support for pumice prophylaxis as a prerequisite for achieving enamel etching. Some mechanism to clean the teeth before orthodontic bonding is still recommended, however, to remove gross plaque accumulation before brackets are placed.

References
1. Silverston LM. Variation in the pattern of acid etching of human dental enamel examined by scanning electron microscopy. Caries Res 1975;9:373-87.
2. Main C, Thompson JL. Surface treatment studies aimed at streamlining fissure sealant application. J Oral Rehabil 1983;10:307-17.
3. Donnan MF. A double blind clinical trial to determine the importance of pumice prophylaxis on fissure sealant retention. Br Dent J 1988;165:283-6.
4. Lindauer SJ. Effect of pumice prophylaxis on the bond strength of orthodontic brackets. Am J Orthod Dentofac Orthop 1997;111:599-605.

Use of the Chlorhexidine mouth rinse in orthodontic patient

September 18, 1998
Dr. Jin-Hyeong Cho

Periodontal problems occurred after the placement of orthodontic bands, brackets and arch wires are the result of inherent irregularities of fixed orthodontic appliances. These irregularities provide additional opportunities for the collection and retention of food and debris. The increased supply of substrate permits luxuriant bacterial growth and accounts for the increases concentration of bacteria in the plaque.

Dr. Zachrisson reported that most orthodontic patients slightly, but significantly show more loss of attachment clinically and hyperplastic gingivitis in good oral hygiene. But, severe gingivitis noted only in few patients with poor oral hygienes. We also can note significantly more alveolar bone loss radiograghically than did the untreated subjects. Especially the greatest alveolar bone loss was noted in the closed extraction space particularly on the pressure side of the retracted canines

As you know, thorough plaque control is very difficult in patients with fixed orthodontic appliances and the use of chemical agent, such as chlorhexidine in the form of mouth rinses, have been shown to be an useful adjuncts in plaque control for these patients. 0.12% chlorhexidine gluconate mouth rinse as an antiplaque and antigingivitis agent provides substantial clinical reduction in gingivitis occurrence, severity and bleeding in an orthodontic population.

The staining due to the use of chlorhexidine gluconate is significant to a mild degree, but it will be removed with a dental prophylaxis. The taste may be bitter to some, but the advantages of this drug far outweigh the disadvantages and make it an acceptable chemical agent for reducing plaque and gingivitis.

0.12% chlorhexidine gluconate is an important therapeutic agent in controlling gingival inflammation, gingival bleeding and plaque accumulation in orthodontic patients. Its best effect on these chemical parameters is achieved when it is used for the full 3 months of therapy.

The Advanced Nance Holding Appliance

September 25, 1998
Dr. Ji-Hyun Min

Nance designed an appliance to hold the molars distally.
The appliance can be used to stabilize molars that have been brought distally using headgear, as well as to retain the excess space between the deciduous molars and first permanent molar. The small heart shaped acrylic base of the Nance appliance, in combination with the molar bands, creates a stable and convenient anchorage.

In the first premolar extraction cases with molars, second premolars, and canines banded, no problems were encountered using a conventional Nance appliance and sectional arches to retract the canines. In cases in which second premolars were extracted, the first premolars tended to drift buccally during distal movement. The solution to this problem led to modification of the Nance Holding Appliance, which called the Advanced Nance Holding Appliance.

In second premolar extraction cases, the lingual framework of the Nance appliance is recurved forward so that a straight section of wire can be engaged in a narrow piece of tubing attached to the lingual of the first premolar band. This framework and a distal hook for elastics are soldered to the molar bands. The appliance is assembled by sliding the lingual tube of the premolar bands onto the straight sections of the Advanced Nance Holding Appliance framework. The appliance is then cemented passively.

The first premolars are retracted along the palatal bars of the Advanced Nance Holding Appliance, using power chain. Following completion of retraction of the premolars, the mesial end of the palatal bar is bent upward to retain the premolar position, and the canines are retracted. If necessary, power thread can be attached from Advanced Nance Holding Appliance framework to a cleat on the lingual of the canine to assist rotation.

Second molars did not remain stable by themselves. Therefore, the canines are included in the framework for increased anchorage.

Patients are not bothered by the small acrylic base of the Advanced Nance Holding Appliance ; in fact, they get used to it immediately. Also, histologic examination of the palatal mucous membrane under the appliance has never demonstrated the presence of pathology.

The advantages of the Advanced Nance Holding Appliance are in decreased chair time, appointments and costs ; and in no need for headgear or Class II elastics to support anchorage ; and no need for banding anterior teeth during retraction of canines or first bicuspids.

The Advanced Nance Holding Appliance provides intramaxillary anchorage in extraction cases, allowing bodily movement of the retracted teeth without headgear.

Surgical correction of the open bite

October 2, 1998
Dr. Hyun Kim

When we attempt to treat an open bite patient with the surgery, we should know the site of origin of the deformity. therefore, it is important to examine the cephalometric anatomy to determine the cause of the apertognathia. And, surgical orthodontic treatment planning of an open bite patient should not only be based on skeletal assessment of the deformity but also on the posttreatment stability, too.

The preferred surgical treatment has moved over the years from mandibular osteotomies to maxillary procedures. At present, surgical superior repositioning and tilting of the maxilla, with or without bilateral mandibular ramus osteotomies, is usually the treatment of choice. Procedures involving a Le Fort I osteotomy are less influenced by muscle force, and render more stable and predictable results than those obtained with only mandibular ramus osteotomies.

Studies on stability of the maxilla after surgical correction have provided various results. According to the study of Kahnberg et al on the stability of maxilla after Le Fort I osteotomy, no significant difference was found between groups in which wire fixation or rigid fixation was used to stabilize the maxilla.
According to the study of Hoppenreijs et al, patients who underwent a multisegment Le Fort I osteotomy stabilized with rigid internal fixation showed better transverse stability than those with intraosseous wire fixation and maxillomandibular fixation.

Bishara reported that after initial surgical superior repositioning, the maxilla continued to move superiorly and most of the upward movement occurred during the period of fixation. When compare the maxillary advancement surgery groups and impaction surgery groups from immediately after surgery to fixation, the absolute maxillary skeletal vertical change was greater in the advancement group, and the postsurgical absolute maxillary horizontal dental changes were greater for the impaction surgery. The stability of the surgical procedure was not influenced by gender, age, growth, orthodontic treatment, amount of surgical displacement at Le Fort I level maxillary segmentation, period of intermaxillary fixation, or additionally performed genioplasty.

Consequently, although the use of wire fixation provide satisfactory results, the use of rigid internal fixation appear to render better stability after surgery. And the tendency to relapse seems to decrease when using rigid fixation. However, dento-alveolar changes may result in posttreatment instability. Therefore, when we establish the treatment plan for the patient needing a maxillary advancement and who express minimal exposure of the maxillary incisors before surgery, care should be taken to avoid burying the incisors beneath the lip, since the maxilla moves superiorly an additional 2.0mm during fixation.

Ideal Tooth Preparation for Bonding

October 9, 1998
Dr. Ji-Hyeong Son

Every investigated product yielded relatively high bond strengths. Recently, similar results were reported in another study, with no significant difference between commercial products. Consequently, at present it seems more important to improve and simplify the clinical operating procedures rather than to increase the adhesive strength of the currently available adhesives. Moreover, an increased bond strength to enamel could provoke more damage of the enamel because of the difficulties in debonding. However, higher bond strengths could reduce the surface area needed for a strong bond, which ultimately result in the use of smaller brackets.

Preparing a tooth for bonding involves a mechanical procedure(prophy) and a chemical procedure(acid etching). First, any calculus should be scaled from the enamel. Then the prophy should be performed with a watery slurry of pumice. The teeth to be bonded should be thoroughly cleaned and rinsed prior to acid etching. The enamel should be air-dried and properly isolated. Then the etchant should be applied to the enamel with a dabbing motion. The acid should not be rubbed onto the enamel, as this may damage the enamel rods and reduce the surface area to be bonded. After etching for 15 to 30 seconds, each tooth should be rinsed for 10 seconds with a water-air spray (or for 15 seconds if a gel etchant is used). One should not etch for more than 90 seconds, because an insoluble layer of calcium phosphate salt may form on the surface and impair resin penetration.

Although some investigators indicate that after an etching time of 60 seconds or more the enamel etching pattern would be more uniform compared with a 15 second etch, this uniformity is not reflected in the values of the bond strengths. Several studies even indicate that increased bond strengths can be achieved with a reduced acid etching time.

There have been studies that seemed to indicate that a weaker etching solution and less etching time than traditionally used would be adequate. 15 second exposure with 37% concentration of phosphoric acid on normal permanent enamel is enough to produce the depth required for optimum bond strength (20 MPa).

The purpose of a thorough rinse is to remove soluble reaction product form the enamel, whose surface energy or clinical adhesiveness is now raised by the chemical conditioning. Each tooth should be desiccated with air free of oil, water, or other contamination. Saliva contamination of the enamel from this point on requires only re-etching. The preparation procedure chemically cleans the enamel, although the result cannot be seen with the naked eye, except for a frosty appearance. If the operator deviates from the prescribed method, there is no way to determine visually whether the surface is acceptable for bonding.

The Development of Maxilla  

November 6, 1998
Dr. Sung-Ho Han

Traditionally, nasomaxillary growth and development remodels in a predominantly posterosuperior manner as it becomes displaced in an opposite anteroinferior direction. This is similar with the mandible, but midface necessarily involves additional and significant developmental operations like palatal vault.

The horizontal lengthening of the maxilla is produced by remodeling at the maxillary tuberosity. The backward periosteal surface of tuberosity receives continued deposits of new bone while the endosteal surface of cortex within tuberosity is resorptive, The lateral surface of maxilla is similarly depository. Therefore, the cortex relocates progressively in posterior direction. Also, there exist many other basic sites of growth like palatal vault, various sutures, eyeballs, nasal cartilages etc.

The whole maxilla undergoes a simultaneous process of primary displacement in an anterior and inferior direction. The nature of the force that produces this anterior movement has been great controversy. One theory suggested that tuberosity push the maxilla. But it is aborted because bone's osteogenic membrane is pressure-sensitive. Another theory held that bone growth within the various maxillary sutures produces a pushing of bones. It is believed that the stimulus for sutural bone growth(remodeling) relates to tension produced by the displacement. Therefore, the whole maxilla is carried forward and downward by displacement.

Delaire thought that midface divide into two parts-anterior and posterior part. He assumes that there exits a specific development of anterior part in addition to maxillary primary displacement and tuberosity apposition-resorption. He claims that it is basis of face-mask therapy for class¥² malocclusion. He takes cranial vault as an example for anterior-lateral regions of maxilla. The cranial vault develops by compensatory ossification of the sutures, by superficial bony apposition-resorption, and by expansion of the external and internal cortex. Almost of maxillary growth in his article are similar to Enlow's explanation except expansion of external and internal cortex in antero-lateral region of maxilla after 10 years old. He told that there are two questions for antero-lateral growth of maxilla. And then, he answered himself for questions;

The first question: How can the anterior maxilla develop in the absence of movement of skeletal units and without superficial bony apposition?

The answer: The maxilla is a membranous bone, and so has a particular manner development like calvarium.

 

The second question: If a specific type of development does exit, why can it not be quantified in usual cephalometric analysis and method using Bjork analysis and metallic implants?

The answer: The classic points of reference and metallic implants used to measure this development are located on or implanted in the external cortex. And so they move at the same time in frontal and/or maxilla.

Therefore he suggested architectural analysis and superimposition of cephalometric radiology for antero-lateral regions of maxilla.

I think that this Delaire's new view compared to Enlow's explanation needs to be backing of many researches in regard to antero-lateral growth of maxilla.

Root Resorption After Orthodontic Treatment

November 13, 1998
Dr. Eun-Hee Kim

Apical root resorption is a common idiopathic problem associated with orthodontic treatment and has recently received considerable attention because of medicolegal exposure. Schwarzkopf in 1887 demonstrated resorbed roots in extracted permanent teeth. In 1927, root resorption was a subject of major concern to the orthodontic field.

Although most root resorption studies attempt to investigate the etiologic factors and predictability of this phenomenon, its origins remain obscure and root resorption, unlike alveolar bone resorption, is unpredictable. Individual susceptibility, hereditary predisposition, systemic, local, and anatomic factors associated with orthodontic mechanotherapy are commonly cited components.

Edward. Harris reported a heritable component for external apical root resorption in patients treated orthodontically using the sibling samples. So, if you are treating the sibling of a patient who had experienced greater-than-average levels of external apical root resorption, be aware that the sibling may also experience greater levels.

Reitan, Rygh, and Phillips enumerated the various major factors causing root resorption of permanent teeth. According to Rygh, the root resorption process seems to vary among persons and within the same person at different times. A high percentage(90.5%) of nonorthodontically treated permanent teeth displayed microscopic lesions of external root resorption that are clinically insignificant and radiographically undetected. Root resorption of permanent teeth is a probable consequence of orthodontic treatment and active tooth movement.

No weakening in the function and stability of the individual tooth occurs as long as the resorbed lacunae are confined to the marginal and middle thirds of the root. Only apical root resorption is an injury that can imperil the stability and normal function of the tooth. The problem is to avoid any increase in the resorption process that may shorten the root. This can be done by periodic radiographic examination of such types of tooth movement in which the orthodontist may expect an increased likelihood of apical root resorption. The followings are some of the types of tooth movement that may lead to apical root resorption.

1. Prolonged tipping, notably of anterior teeth
2. Distal tipping of molars, causing resorption particularly of the distal roots of the molars(Gradual tipping of these teeth by light interrupted forces may reduce the tendency to root resorption.)
3. Prolonged continuous bodily movement of small teeth, such as upper lateral incisors(Interrupted movement, or continuous movement with rest periods, may diminish the occurrence of this type of root resorption.)
4. Intrusion(It is important to initiate the intruding movement by forces as light as 25g. Frequent rest periods will prevent any extensive resorption.)
5. Extensive edgewise torque of anterior teeth in the more mature young and adult patients.

Goldin reported that the amount of root loss during treatment is 0.9mm/year. And most studies agree that the root resorption process ceases once the active treatment is terminated. Usually, extensive resorption does not affect the functional capacity or the effective life of the tooth.

There is no basis for the assumption that teeth with significant root resorption have a limited life expectancy. However, the patient or his parents must be informed that apical root shortening may be a consequence of orthodontic treatment and its incidence is highly unpredictable.

In the light of the orthodontists's liability of what is basically an unpredictable phenomenon, it is necessary that the specialty define this uncertainty and establish criteria of diagnosis, records, and informed consents to protect its members against unnecessary and unjustified litigation.

Thank you

Orthodontic treatment and temporomandibular disorders

November 20, 1998
Dr. Eun-Jeong Kim

The relationship between orthodontic treatment and temporomandibular disorders (TMDs) has long been of interest to the practicing orthodontist. Dibbets and van der Weele suggested that while patients who have received orthodontic treatment have a higher ratio of TMD problems than average, it should be remembered that they are also likely to have a higher ratio of dental and skeletal problems before treatment. But Sadowsky and Polson revealed that there were no statistically significant difference between the orthodontically treated and untreated groups.

Furthermore Dibbets' studies that looked at the specific type of orthodontic mechanism used, such as the Begg technique versus activator and chin cup also failed to show a relationship between intracapsular disorders and orthodontic treatment. Even the extraction of teeth as part of an orthodontic treatment plan does not increase the risks of TMD. Although these studies are comforting to the orthodontist, one also must note that the incidence of TMD symptoms in the orthodontically treated populations was generally no lower than that of the untreated population. Therefore these findings suggest that orthodontic treatment is not effective in preventing TMDs.

For a while, an important question that arises in dentistry is "What occlusal conditions are commonly associated with disc derangement?" It has been demonstrated that when an occlusal condition causes a condyle to be positioned posterior to the musculoskeletally stable position, the posterior border of the disc can be thinned. A common occlusal condition that has been suggested to provide this environment is the skeletal class II deep bite, which may be further aggravated when a division 2 anterior relationship also exists. One must be aware, however, that not all patients with class II malocclusions present with disc derangement disorders. Some studies show no relationship between class II malocclusion and these disorders. Other studies show no association between the horizontal and vertical relationship of the anterior teeth and disc derangement disorders. The important feature of an occlusal condition that leads to disc derangement disorders is the lack of joint stability when the teeth are tightly occluded. It is likely that some class II malocclusions provide joint stability, where as others do not. Another factor that must be considered is the amount of joint loading. Perhaps joint loading is more damaging with certain class II malocclusions. It becomes obvious that no simple relationship exists. It is vitally important, however, that when orthopedic instability exists it be identified as a potential etiologic factor.

It should also be noted that although these studies do not reveal a relationship between orthodontic therapy and TMDs. It would be naive to suggest that orthodontic therapy has no potential to predispose a patient to disc derangement disorders. Any dental procedure that produces an occlusal condition that is not in harmony with the musculoskeletally stable position of the joint can predispose the patient to these problems. This may occur secondary to orthodontics or prosthodontics or even surgical therapies. In conclusion, patients who receive conventional orthodontic therapy are at no greater risk for developing TMD than those who do not.

Surgically Assisted Rapid Maxillary Expansion

November 27, 1998
Dr. Wang-Sik Kim

In recent years, an increasing number of adult patients have been seeking orthodontic correction of their dentofacial disharmonies. Some of these patients require correction of a transverse maxillary deficiency as part of their treatment plan. Transverse maxillary discrepancies are routinely corrected in growing patients with appliance that separate the median palatal and associated maxillary sutures. However, this type of rapid palatal expansion is not feasible in adult because of the increasing resistance of the suture.

The indications of SRME are as follows. 1) maxillary transverse deficiency of greater than 5 mm by P-A analysis. 2) failed orthodontic, orthopedic expansion. 3) extremely thin, delicate gingival tissue or presence of significant buccal gingival recession in the canine-premolar region in the maxilla. 4) skeletal age of 15 years or older.

Prior to surgery, a rigid palatal expansion device is cemented to the maxillary first premolar and first molar teeth. Circumvestibular incision is made through the mucoperiosteum from the second molar on the left to the second molar on the right. Horizontal osteotomy is made through the lateral wall of the maxilla, approximately 4 to 5 mm above the apices of the teeth from the inferior lateral spect of the piriform aperture to the inferior aspect of the junction of the maxillary tuberosity and the pterygoid plate. Sectioning of the pterygomaxillary suture is unnecessary. Expansion of the anterior part of the maxilla can be started by malleting a thin osteotome between the central incisors. Following the osteotomy, approximate 10 turns were placed on the hyrex, until 2 mm of separation was obtained between the maxillary central incisors. Expansion was continued postoperatively by instructing the patients to turn the appliance twice daily, morning and evening. Patients were examined weekly until the desired expansion was achieved.

Expansions by SRME are more stable than those achieved without surgical assistance. Consequently, Dr. Kraut insisted that the addition of only 1.0 to 1.5 mm is necessary to compensate for relapse in surgically assisted maxillary expansion. According to Dr. Bay, the relapse is 8.8% in canine region, 1.0% in premolar region, 7.7% in molar region.

Surgically assisted rapid maxillary expansion is an extremely valuable operation that should be considered whenever maxillary expansion is need, especially in adults. The relative lack of complications and the excellent stability are important reasons for considering this procedure.

Implant for Orthodontic Anchorage

December 4, 1998
Dr. Jea-Chul Lee

Many partially edentulous patients being restored with implants as abutments for fixed bridges. If orthodontic treatment is needed for these patients, the implants may be used initially as anchors for tooth movement and later as abutments for fixed restorations. With an immobile implant in the bone, several types of tooth movement are possible. A tooth can be pulled toward the implant, pushed away from the implant, as well as intruded or extruded relative to the level of the implant.

Several factors are necessary to ensure success when using implants as anchors to move adjacent teeth. First is the planning process. By carefully determining the proper position of the implant before orthodontic therapy, it may be used as an anchor for tooth movement and also as an abutment for a fixed restoration following the completion of orthodontic therapy. The location of the implant before orthodontic therapy can often be confused. This is especially true if the teeth are moving toward or away from the implant during orthodontics. This precise positioning of the implant requires the construction of a pretreatment diagnostic wax set-up. The diagnostic wax set-up acts as a blueprint for proper implant placement.

Another crucial step in the process is to determine the appropriate time for placing the implant. In most situations, the implant is placed before the orthodontic treatment begins. However, occasionally the implants will be placed during orthodontic treatment. When tooth movement on either side of the implant may be unpredictable, it is best to begin the orthodontic treatment, align the teeth, and then make a set of progress dental casts and construct the diagnostic wax set-up on these casts.

Another issue related to timing is the age of the patient. Implants should not be placed in growing individuals. If no change in vertical facial development is detected, By comparing two cephalometric radiographs taken 12 months apart, the implants may be placed.

When there is insufficient bone buccolingually to place an implant, two options are possible. One option involved placing the implant and freeze-dried decalcified bone is placed over the implant threads, and the polytetrafluorethylene membrane is positioned over the bone and implant and the flap is sutured. Another option is to build-up the bridge before implant placement. In patients with narrow ridges, it is necessary to expose the bone, place freeze-dried decalcified or autogenous bone in the area, and cover the ridge with specially designed polytetrafluorethylene membrane.

When implants are used as anchors for orthodontic treatment, sufficient time must elapse before placement of the implant and application of orthodontic force. When restorations are to be placed on implant, generally a period of 4 to 6 months is recommended before uncovering the implant.

The Side Effects of RPE and Its Prevention

December 11, 1998
Dr. Jeong-Tae Kim

Rapid maxillary expansion procedures have been proposed since the past century by Angell and consolidated clinically by Haas. Rapid palatal expansion is recognized as a very successful orthopedic therapy to correct maxillary transverse deficiencies in growing patients. This procedure leads to an increase in the upper arch transverse dimensions by mainly skeletal alterations associated with dental alterations.

RPE increases the upper arch transverse dimensions mainly by separation of the two maxillary halves, followed by buccal movement of the posterior teeth and alveolar processes. However, the transverse forces delivered during RPE have been shown to create undesirable orthodontic and orthopedic side effects in patients exhibiting skeletal open bite tendency, large interlabial gap, or severe class II skeletal patterns, with long lower facial height and increased facial convexity. RPE causes rotation of the buccal alveolar segments and extrusion of the lingual cusps of maxillary posterior teeth. These changes cause downward and backward rotation of the mandible, reduction in the overbite, and an increase of interlabial gap, facial convexity and the vertical dimension of the lower face.Indeed, even a minor extrusion of only 1 mm at the maxillary first molar may result in an increase of 2 to 3 mm at the central incisors and lips. Therefore it may be beneficial to try to counteract the iatrogenic orthodontic and orthopedic side effects during RPE therapy.

Haas indicated that a high-pull headgear or a vertical pull chin cap might be used, coincident with RPE, to reduce vertical dimension in the posterior region and significantly improve dental and skeletal openbite. However, the use of a high-pull headgear to control buccolingual tipping seems to be much less effective when compared with the use of a high-pull chin cap. The point of force application of headgear, being buccal to the center of resistance of both the molars and the alveolar processes, will produce a moment that will tip the maxillary posterior teeth even more buccally. The use of a high-pull chin cap delivers more ideal force system. The application of an intrusive force at the lingual cusps of the maxillary posterior teeth during and immediately after RPE offers potential control of both the extrusive and buccal tipping side effects created by RPE.

Other factors involved in the successful control of side effects are the timing and force magnitude of the high-pull chin cap. It has been shown that force should be applied during expansion, when the tipping and extrusion are occurring, and possibly 7 to 10 weeks after expansion during the remodeling of the circummaxillary sutures. Favorable results seem to be achieved when the chin cap is worn 12 to 16 hours a day with a force level of 250gm per side.

Influence of Growth Hormone on Dentition

December 17, 1998
Dr. Byeong-Seok Lee

Growth hormone is needed for the development of teeth and bones. The action of this hormone plays an important role in the growth process of the craniofacial complex. Hormone deficiencies can affect the development of the dentition and facial skeleton and, therefore, may be initially detected by the dentist. The initial exam should appraise possible signs or symptoms of hormonal disturbances. Many a subclinical case of growth hormone deficiency has been pointed out to an unknowing patient by an alert orthodontist looking at the patient's teeth and investing tissues, plaster casts, head plates, and dental radiographs.

The recognition of short stature in children has been focussed on boys who have failed to attain the expected age-related height of their parents. Short stature has a varied etiology, and attention has been given to those children who have no recognizable disorder that may have contributed to a reduction in statural height. The term idiopathic short stature has been applied to these children. Advancements in recombinant DNA technology have increased the available supplies of biosynthetic growth hormone (somatotrophin). As a consequence, some short children, who do not meet the classic criteria of growth hormone deficiency, are now being selected for growth hormone (GH) substitution therapy. Preliminary studies of children with idiopathic short stature, who were treated with recombinant growth hormone, suggest that the majority have a significant initial increase in their statural growth rate. There have been some studies that examined the effects of recombinant growth hormone on dental development or craniofacial growth, notably Myllarniemi, Bevis, Poole, and Tapert.

Previous studies have reported that tooth formation and tooth eruption are retarded in hypopituitary dwarfs. This delay in tooth formation is primarily attributed to a deficiency in either growth hormone, thyroxine, but probably not gonadotropins. Although short statured children do not meet the criteria for classic growth hormone deficiency, some degree of growth hormone deficiency may still exist.

There are a number of hypothetical physiologic mechanisms that may explain idiopathic growth retardation, and also delay in tooth formation:

(1) Secretion of an endogenous GH with normal immunoreactivity but subnormal bioactivity
(2) failure to release endogenous GH in response to physiologic stimuli (especially slow wave sleep) despite normal release of the hormone during pharmacologic tests
(3) abnormality in cellular receptors to GH or somatomedins
(4) impaired production of polyamines, which are believed to mediate some of the cellular growth responses to GH and somatomedins
(5) inadequate GH production due to neurosecretory abnormalities.

Although tooth formation was generally delayed in the short statured subjects, the degree of delay in tooth formation was variable, with no relationship to the degree of reduction in stature. Keller reported a highly variable, but consistently significant, delay in skeletal maturation in 20 short statured children, as determined from calculation of bone ages. Initial dental delay was also variable, and unrelated to the degree of skeletal delay.

Recombinant GH treatment had a significant influence on acceleration or gain in stature in this sample of short statured children. These results are in agreement with previous studies of idiopathic short statured subjects who were treated with recombinant growth hormone.

Secondary bone graft in cleft

March 19, 1999
Dr. Jin-Hyoung Cho

The incidence of cleft lip and palate is quite high, and it is increasing. The effect of extensively early cleft surgery, such as palate repair and alveolar bone grafting, on craniofacial growth is controversial. The opponent of early surgery advocates delaying cleft closure to avoid scar-tissue formation and growth-inhibition. In contrast, proponent cites the need for early and proper development of speech mechanism and arch forms.

Closure of the alveolar cleft in infancy by what has been termed primary bone grafting or periosteoplasty is generally considered to cause inhibition of subsequent maxillary growth in the sagittal and vertical plane. In 1972, Boyne and Sands introduced a technique for bone grafting prior to the eruption of the canine. Alveolar repair at this age has been generally considered to cause minimal disruption to facial growth. Ross in 1987, noted that patients with bone grafts performed between the ages of 4 and 10 years showed a marked deficiency in anterior upper-facial height at age 15 years compared to ungrafted patients. in 1991, Brattstr m et al found the patients that included primary bone grafting to the alveolus resulted in inhibited anterior maxillary growth. The patients that included secondary bone grafting resulted in better maxillary development but were not as good as patients that omitted bone grafting altogether. however, in 1988, Semb found no stastically significant difference in either anteroposterior or vertical maxillary growth. In other words, mixed-dentition bone grafting did not seem to have any adverse effect on maxillary growth in the years following the procedure. Ross in 1997, concluded that bone grafting in the mixed dentition which was prior to the eruption of the canine on the cleft side did not appear to effect maxillary development.

Bone grafting in the mixed dentition of residual alveolar clefts in patients with cleft lip and palate has become well established, and the advantages can be summarized as follows:
(1) stabilization of the maxillary segments, (2) facilitation of tooth eruption close the cleft, (3) improvement of the bony support for teeth close to the cleft if the gap in the dental arch has to be closed orthodontically, (4) promotion of closure of an oronasal fistula, (5) enhancement of the aesthetic appearance of the alveolus, (6) support for the alar base of the nose to enhance facial appearance, (7) reduction of the need for a fixed bridge, (8) improves facial appearance through restoring facial symmetry. In addition, secondary alveolar bone graft resulting in satisfactory periodontal support for cleft associated canines, has been reported.

In my opinion, to achieve the best results, the secondary bone grafting should be done prior to canine eruption.

References

Ross EL Jr, Barbara ES, Mimi Y. Cleft Width and Secondary Alveolar Bone Graft Success. Cleft Palate Craniofac J 1995;32(5):420-7.
Carroll AT, Ross EL Jr, Sheldon WR. Comparison of Facial Form in Primary Alveolar Bone-Grafted and Nongrafted Unilateral Cleft Lip and Palate Patients: Intercenter Retrospective Study. Cleft Palate Craniofac J 1996;33(2):91-5.
Amin K, Jan L, Hans F. Bone Grafting at the Stage of Mixed and Permanent Dentition in Patients with Clefts of the Lip and Primary Palate. Plast Reconstr Surg 1994;93(4):690-6.
John D, Ross RB. Effect of Alveolar Bone Grafting in the Mixed Dentition on Maxillary Growth in Complete Unilateral Cleft Lip and Palate Patients. Cleft Palate Craniofac J 1997;34(5):455-8.

The use of implant as the anchor for tooth movement

March 26, 1999
Dr. Hyun Kim

In orthodontic tooth movement, one of the important concern is anchorage control. When maximum anchorage is desired, we can consider extraoral appliance, intermaxillary elastics, transpalatal arch, etc. But the effect of extraoral appliance such as headgear is mainly dependent on the cooperation of patients. In spite of the use of these methods, absolute or complete anchorage is usually impossible.

Today, as the number of adult patient increases, anchorage control is more important issue. Adult patients have often partially edentulous dentition. So anchor for tooth movement decreases and certain types of tooth movement are occasionally impossible in the case of the retraction of anterior incisors in posterior edentulous patient, the intrusion and protraction of third molar with incisors as anchor teeth  showing severe bone loss, the intrusion of the upper molar erupted into the mandibular edentulous space.

The use of implant makes it possible. There have been many studies about the use of implant in orthodontic treatment.

Orthosystem is newly developed endosseous orthodontic implant anchor system for palatal anchorage. It is made of titanium and consist of a screw type endosseous implant body, a cylindrical polished transmucosal neck and abutment. Clamp-caps provide attachment of square commercially available orthodontic wires to the abutment. Surgical procedure is one-stage surgery type. In severe Class II malocclusion case, after extraction of upper premolar, maximum retraction of the anterior teeth without mesial movement of molar is possible by the use of Orthosystem.

In the partially edentulous patient, the use of implant is more beneficial especially when abutment for fixed restoration is necessary. By carefully determining the proper position of the implant before orthodontic therapy, it may be used as an anchor for tooth movement, and also as an abutment for a fixed restoration following the completion of orthodontic therapy. To achieve the proper implant location, the construction of a pretreatment wax set-up is required.

After placement of the implant, generally a period of 4 to 6 months is recommended to provide new bone deposition and secondary remodeling. In other studies, however, it was reported that 3 months of healing period revealed no implant mobility or dislocation, favorable peri-implant soft tissue condition, and no marked mesial movement of the implant.

The use of implant is not familiar method yet. We, however, can achieve many benefit and satisfactory results with careful incorporation into orthodontics.

Eruption of the permanent upper canine

April 2, 1999
Dr. Youn Il Sun

Maxillary permanent cuspids are second only to the third molars in frequency of impaction, with prevalences of 1% and 2% of the population (Rayne 1969, Thilander and Jakobsson 1968, Howard 1972, Ericson and Kurol, 1986A,B). In European samples, the impacted maxillary canine has been found palatally at least two to three times more frequently than facially. Possible complications of impacted canines include resorption of the roots of adjacent teeth and cystic lesions of the follicle. The management of established canine impaction often requires surgical and orthodontic intervention if the canine is to be correctly positioned within the arch. Treatment of canine impaction, on the other hand, is complex, prolonged, and of uncertain outcome. The early detection of eruptive anomalies of the upper canine requires an understanding of its normal eruptive pattern.

The tooth germ of the maxillary canine forms high in the anterior wall of the antrum, below the floor of the orbit. It therefore has a long and tortuous eruption path to its correct position in the maxillary arch. The upper canine initially erupts with increasing mesial inclination (first rapidly and then more slowly) until a maximum point is reached, followed by gradual straightening distally. Moyers reported that at age 3 years, canine is positioned high within the maxilla, with the crown directed mesially and somewhat lingually. Posteriorly, it displaces toward the occlusal plane, straightening gradually until it appears to contact the distal aspect of the root of the lateral incisor, deviating toward a more vertical position. Fernandes, Bravo, and Canteras studied the normal eruptive pattern in terms of upper canine inclination and its relation to the lateral incisor in 1998. According to their results, "lateral movement" and "gradual straightening" of the canine would take place in a second eruptive stage, at approximately 9 years of age, whereas in a first stage, the canine would move toward the lateral incisor, increasing its mesial inclination. This straightening coincides with the age at which an important clinical sign appears, that is, palpation of the cuspid bulge in the vestibular aspect of the alveolar process. This suggests that movement takes place not only distally but also in a vestibular direction.

Considerable individual variability exists as to the degree of canine inclination at a given point in the course of eruption, therefore the capacity to predict inclination at a given age is limited. But development of the lateral incisor is a good reference for defining when a radiograph overlapping image constitutes a sign of altered canine eruption. The overlapping of the canine and lateral incisor in panoramic radiographs when the incisor has completed its development may be a sign of eruptive disorders of the canine, suggesting the adoption of preventive measures to avoid impaction; for example, extraction of the primary canine.

Normally, maxillary canines can be palpated in the labial sulcus from about 8 to 9 years of age. By viewing and by palpation, the general position and crown angulation of the canine can be assessed. However, as there is often a poor correlation between chronological age and dental age, overall dental development must be considered in the assessment. In children older than 10 years of age, an inability to palpate the canine strongly indicated a disturbance of eruption, which was then confirmed by the supplementary radiographic investigation.

Thank you very much.

References
1. Fernandez E, Bravo LA, Canteras M. Eruption of the permanent upper canine: A radiologic study. Am J Orthod 1998;113:414-20.
2. Ericson S, Kurol J. Radiographic examination of ectopically erupting maxillary canines. Am J Orthod 1987;91:483-92.
3. Ericson S, Kurol J. Incisor resorption caused by maxillary cuspids. A radiographic study. Angle Orthod 1987;57:332-46.
4. Fearne J, Lee RT. Favourable spontaneous eruption of severely displaced maxillary canines with associated follicular disturbance. Br J Orthod 1988;10:283-95.
5. Power S, Short B. An investigation into response of palatally displaced canines to the removal of deciduous canines and an assessment of factors contributing to favourable eruption. Br J Orthod 1993;20:215-23.
6. Becker A. In defense of the guidance theory of palatal canine displacement. Angle Orthod 1995;65:95-8.
7. Peck S, Peck L, Kataja M. Sense and nonsense regarding palatal canines. Angle Orthod 1995;65:99-102.
8. Peck S, Peck L, Kataja M. The palatally displaced canine as a dental anomaly of genetic origin. Angle Orthod 1994;64:249-56.
9. Harry J. The etiology of maxillary canine impactions. Am J Orthod 1983;Aug:125-32.

The use of implant for intraoral anchorage

April 9, 1999
Dr. Heung-Yuol Kim

Proffit has defined anchorage as "the resistance to unwanted tooth movement," or "the resistance to reaction forces that is provided by other teeth, or by structures outside the mouth." Orthodontic tooth movement has always been limited to action-reaction reciprocal force mechanics in the abscence of a fixed anchorage point in the mouth. Extraoral headgear, at present, is perhaps the most effective way of obtaining anchorage for orthodontic movement of teeth. A major drawback of headgear anchorage is the need for patient cooperation, which can place severe limitations on optimal results.

Gainsforth and Higley, in 1945, were unsuccessful in establishing intraoral anchorage with implant fixation using ramal screws. This early report is believed to be the first to suggest that orthodontic anchorage in basal bone may be achieved using implants. Since then, many investigators have considered a variety of materials and geometrics for endosseous implants as anchorage devices to facilitate tooth movement. Most studies have evaluated the capability of orthodontic loading forces applied from implants to implant.

In 1983, Branemark has defined osseointegration as a direct structural and functional connection between living bone and the surface of a load - carrying implant. Osseointegrated titanium implants have been repeatedly observed to be rigidly anchored on bone, so that removal is dependent on the ultimate failure strength of supporting bone, rather than separation between the implant and bone interface.

In 1984, Roberts was among the first to evaluate the effects of orthodontic-like forces on titanium implant in rabbits. One hundred grams of force using a coiled spring were applied to threaded acid-etched titanium implants placed into rabbit femora, with 19 of 20 implants remaining stable.

In 1988, Turley and associates have studied the efficacy of titanium endosseous implants as anchors for orthodontic tooth movement in dogs. They demonstrated that the stability and anchorage function of loaded (300 g) implants over time (9 to 12 weeks) may be related to implant's size and geomerty and tooth movement of 0.6 mm to 4 mm can occur with no detectable implant change in position.

More recently, in 1989, Roberts and associates placed titanium implants into dog mandibles and subjected then to loading forces of approximately 300 g. Clinical rigidity was achieved in 15 of 16 implants that remained stationary after 13 weeks of continuous loading. Microradiography studies indicated that less than 10 % of the endosseous portion of the implants were in direct contact with bone. and then in 1994, They have described a case report in which an osseointegrated titanium implant placed into the retromolar region for anchorage was used to translate two molars 10 to 12 mm mesially into an atrophic edentulous ridge.

In 1991, Higuchi and Slack have described that using the osseointegration method, a prospective study was conducted involving seven adult patients who were treated with titanium implants used as rigid anchorage units. Orthodontic forces were directed off the implants to correct a variety of malocclusions. All 14 implants placed remained stable during the course of treatment with loading forces of 150 g to 400 g. No significant complications occurred. Desirable occlusal and facial results were achieved in all cases.

In 1997, Kanomi has described that a mini-implant for orthodontic anchorage should be small enough to place in any area of alveolar bone, even apical bone. The surgical procedure should be easy enough for an orthodontist or general dentist to perform. The implant should be easily removable after orthodontic traction.

Although placement of an endosseous implant is a surgical procedure, responsibility for management of orthodontic and orthopedic problems ultimately rests with the orthodontist. The orthodontist must have a sound, basic background in the mechanical, physiologic, surgical and periodontal factors essential to consistent success.

Retention, a secondary treatment phase

April 16, 1999
Dr. Eun-Hee Kim

Orthodontists have long been aware of the fact that teeth that have been moved in or through bone by mechanical appliances have a tendency to return to their former positions. Recent studies on the assessment of long-term observations of posttreatment results have indicated that relapse occurs in most cases. Sometimes, relapse in tooth positions is noted even during the period when a patient is using the retention appliances. However, no means and effective, appropriate evidence-based practice are yet available to help predict relapse or to give objective a device about prevention of the relapse.

So, the question often asked by patients and orthodontists is, " how long should active retention with appliances be maintained?" "How do we maintain the esthetic, well-aligned results without relapse after orthodontic corrections?" "How many your orthodontic patients revisit your office to take a recall check and to retreat their relapsed conditions?" Whether patients are on long retention even permanent retention or not, a way should be found to let loose of a great majority of our retention cases. Keeping private practice patients ostensibly for six, eight, or ten years or longer does not enhance the images of the individual orthodontist and of the specialty. This is not a cradle to the grave proposition. If it were not for the grace of a substantial attrition, many orthodontic offices would be overrun with retention patients.

Then, what is the key to solve the problems? Retention, that is, the holding of teeth in ideal esthetic and functional positions is not a separate problem or phase of orthodontics but is and will continue to be a problem to be considered in diagnosis and treatment planning. The orthodontist and the patient should have the option of deciding about retention together, which may be a decision on a realistic basis between permanent retention and frequent instability. And we should consider the variable factors that can effect the relapse tendency from the beginning of the treatment.

Many early writers considered that proper occlusion was of prime importance in retention. And McCauley suggested that intercanine width and intermolar width should be maintained as originally presented to minimize retention problems. Grieve and Tweed suggested that the mandibular incisors must be kept upright and over basal bone. Rogers introduced a consideration of the necessity of establishing proper functional muscle balance. Ram S. Nanda considered the dentofacial growth in long-term retention and stability with dynamic, active retention philosophy. Kaplan stated the logic of modern retention procedures and divided the orthodontic cases to five groups according to the need of retention. In addition, good treatment should be undertaken to make a harmony with the environmental tissues and should be justified in spite of a possible loss of a percentage of correction. Patients should have a realistic view of what the odds are, even if they don't always remember what we tell them or what we write to them.

Finally, it is better that retention fee is not included in the overall treatment fee. If the impression is created that the orthodontic fee covers retention and the amount of retention is not specified, some patients will keep coming for years because the case is "unfinished". Either the contract should spell out how much retention time is included or, better still, the retention fee should be a separate fee on some appliance and per-visit basis. If the orthodontist is not making a charge for retention visits, he is giving away time that is largely non-productive.

Interproximal enamel reduction

April 23, 1999
Dr. Wang-Sik Kim

Diminishing of the mesiodistal dimensions of teeth ¡°slenderizing¡± is well-known and commonly applied treatment to achieve a better arrangement of the teeth along the dental arches. Conventional interproximal enamel reduction to solve crowding is usually limited to the mandibular incisors and involves the removal of 2-4mm of proximal enamel. In contrast, comprehensive air-rotor stripping involves a sequence of procedures designed to precisely remove interdental enamel primarily in the buccal segments. This procedure offers an alternative to extraction or expansion in case of mild to moderate crowding.

The basic principles of interproximal reduction are as follows.

1. Never reduce before appliance placement.

Space opening by enamel reduction must be avoided before the teeth have started to move because the amount of enamel to be removed cannot be precisely evaluated before treatment starts.

2. Don't reduce rotated teeth.

The best evaluation of the necessary reduction is achieved after derotation of the teeth.

3. Respect the limits of the reduction

Alexander suggests the reduction of 0.25mm on each tooth. Sheridan reduces up to 0.8mm for the lateral zones and 0.25mm for the anterior teeth. The general tendency is to consider that the maximum amount of enamel that can be removed corresponds to half of the enamel thickness

It is known that injuries to the enamel surface caused by grinding instruments can be predisposing to caries and peridontal disease. Although some people suggested an increase in caries with interproximal reduction of posterior segment, crain and sheridan did not find an increased incidence of caries 2-5 years after interproximal reduction. Also, periodontists typically dread enamel reduction for fear of a reduction of the embrasure width and creation of root proximity. But according to Kokich's study, long-term effect of root proximity on periodontal health after orthodontic treatment, it show that there is no statistically significant between proximity sites and control sites. This result indicates that teeth are not predisposed to more rapid periodontal breakdown when roots are in close proximity. However, the closer distance between the roots of interproximally reduced teeth may predispose patients with inflammation to the more rapid progression of periodontal disease.

Interproximal reduction provides a more conservative approach that allows the orthodontist greater control of the space gained and saves a more treatment time than that of extraction case because of the elimination of mechanical procedures need to close extraction sites or coordinate arches. If we selected the case adequately, interproximal reduction can reduce extraction procedures and increase stability. However, it is an irreversible procedure and should be initiated with that in mind.

Type of TMD and relationship of TMD to occlusal factor

May 21, 1999
Dr. Kwan-Mo Kim

Each structure of the masticatory system can tolerate only a certain amount of increased force created by muscle hyperactivity, when forces applied to the structures are increased beyond this critical level, breakdown of the tissues begin. This level is known as the structural tolerance. Structural tolerances are influenced by factors like anatomic form, previous trauma, and local tissue conditions. When forces of muscle hyperactivity are placed on the masticatory system, the weakest structure will show the first signs of breakdown. The potential sites o f breakdown are the muscles, the TMJ, the supportive structures of the teeth, and the teeth themselves. So muscle tenderness, pain, arthritis, periodontal disease, pulpitis could be appeared. It should now be apparent that masticatory muscle hyperactivity is responsible for various types of TMD. there are other significant factors that can contribute. Trauma, for example, may be an etiologic factor. Likewise, systemic diseases and developmental disorders may create functional disturbances and symptoms.

Now, look into the relationship of occlusal factor to TMD. The multiple factor analysis of Pullinger and colleagues has indicated that there is a relatively low association of occlusal factors in characterizing TMD. Seligman estimates that the total contribution of occlusal factors to the multifactorial characterization of TMD patients is about 10% to 20%.
The findings of current research can be summarized as follows
1. Signs and symptoms of TMD occur in healthy individuals.
2. Signs and symptoms of TMD increase with age, particularly during adolescence.
3. Orthodontic treatment performed during adolescence generally does not increase or decrease the odds of developing TMD later in life.
4. The extraction of teeth as part of orthodontic treatment plan does not increase the risk of TMD.
5. There is no elevated risk for TMD associated with any particular type of orthodontic mechanics.
6. Although a stable occlusion is a reasonable orthodontic treatment goal, not achieving an ideal occlusion does not result in TMD signs and symptoms.
7. No method of TMJ disorder prevention has been demonstrated.
8. When more severe TMD signs and symptoms are present, simple treatments can alleviate them in most patients.

Thus, according to the existing literature, the relationship of TMD to occlusion and orthodontic treatment is minor. The important question that still remains in dentistry is how this minor contribution can be identified within the population of TMD patients.

Autotransplantation of teeth

May 28, 1999
Dr. Eun-Jeong Kim

Missing teeth present a problem to the orthodontist. Orthodontic treatment may be necessary to close the existing spaces or redistribute the space available to accept a prosthesis, implant or transplant. In 1996, Priest reveals that failure rates for resin bonded bridges range from 10 per cent over 11 years to 54 per cent over 11 months. The use of osseointegrated implant is contraindicated in growing patients, too. If implants are placed in patients with residual facial growth, infra-occlusion of the implant occurs as the implant becomes ankylosed to the alveolar bone.

Autotransplantation may be defined as the transplantation of embedded, impacted or erupted teeth, from one site to another in the same individual into extraction sites or surgically prepared sockets. Clinical case reports of successful autotransplantation first appeared in the 1950s when decayed first molars replaced with transplanted immature third molars.

There are many clinical situations in which autotransplantation may have a role. Missing upper incisors by trauma was used to be replaced with premolar. Autoplantation maintains or restores alveolar bone volume and produces an aesthetic result. Premolars from one site in crowded arch may be transplanted to another site to replace developmentally absent premolars. And, autotransplantation has been used in the replacement of teeth of poor prognosis. In most cases, the tooth to be extracted is the first permanent molar. In these cases, transplantation of third molars or premolars to the first molar site may be considered.

There are several factors known to contribute to the success of transplantation. At the surgical technique of autotransplantation, a careful atraumatic surgical technique to maximally preserve a periodontal ligament is needed. Transplantation of teeth with immature roots produces high success rates. Kristerson (1985) revealed that transplants with half to three-quarter root development had the best prognosis for successful autotransplantation. Orthodontic treatment was carried out at least 6 months after transplantation. Most authors suggest teeth should be placed in the alveolus at the same occlusal level as that of the donor site. If the donor tooth has a mature root and is fully erupted, then it should be placed slightly below the occlusal level. Pulp survival is obviously an important factor for the completion of root growth. Pulpal healing decreased with increasing root maturity of transplanted tooth. Successful periodontal healing is marked by the absence of root resorption and by the presence of a lamina dura. Resorption occurs more frequently in transplanted teeth with mature root development compared to teeth with immature roots and may be detectable radiographically within 6 months of transplantation.

Several experimental and clinical studies have shown that missing teeth may be replaced successfully by autotransplantation. The combined efforts of the surgical and orthodontic team are necessary for a successful outcome.

Maxillary protraction in Cl III malocclusion

June 4, 1999
Dr. Mi-Young Seo

Patients with Class III malocclusion can have components of maxillary size deficiency, maxillary retropositioning, true mandibular excess, mandibular forward positioning, or any combination of these. Several recent studies have shown that maxillary retrusion contributed to a significant number of skeletal Class III malocclusions, either alone or in combination with mandibular protrusion. Because of deficient maxillary growth, both vertically or horizontally, the mandible might be expected to rotate forward, producing an even more prognathic appearance.

Oppenheim reported that it was impossible to move the mandible backward during the treatment of Class III malocclusion, but it is possible to bring the maxilla forward, to compensate for the mandibular overgrowth. Kambara (1977), using model casts, cephalometric radiographs, and bone markets, found that the maxillary complex can be displaced anteriorly with significant changes in the circum-maxillary sutures and the maxillary tuberosity. In histological section, he found opening of the sutures, stretching of sutural connective tissue fibers, new bone deposition along the stretched fibers, and homeostasis which maintained the sutural width.

Clinically, different types of maxillary protraction devices have been reported to be successful in the treatment of the developing class III malocclusion, and orthopedic maxillary expansion before protraction has been reported to facilitate maxillary protraction.

The correction of Class III malocclusion with palatal expansion and facemask therapy occurs by a combination of skeletal and dental movements that occur not only in the anteroposterior dimension, but also in the vertical plane of the space. The majority of Class III correction occurs by orthopedic movement, with most of the change in the maxilla. The maxilla moves forward and downward, and the posterior maxilla moves inferiorly more than the anterior maxilla. The mandible moves backward and downward. Dentoalveolar changes are mainly the linguoversion of the lower incisors and the labial inclination of the upper incisors. Overbite tends to decrease. This is accompanied by an increase in mandibular plane angle and lower facial height. The combined skeletal and dental effects contribute to the profile becoming more convex.

Patient selection is extremely important for this treatment approach. This is not indicated on longer-faced type persons with openbite tendencies, because of the bite opening effects that occur with expansion and the rotation of the maxilla during protraction. The treatment is better suited for the patient who initially presents with deep overbite, anteroposterior and vertical maxillary deficiency, and normal to mildly prognathic mandibular dimension.

The effectiveness of 3 types of dental floss for interdental plaque removal

June 11, 1999
Dr. Hee-Chang Park

Bacterial plaque plays a primary role in the aetiology of inflammatory periodontal disease. One of the primary goals of good oral hygiene is to remove dental plaque, thereby maintaining healthy gingiva. Mechanical and/or chemical plaque control is the most widely accepted preventive measure in this regard. However toothbrushing alone is still limited in its ability to remove interproximal plaque. Consequently, dental professionals routinely advise patients to use additional interdental cleansing aids. These include waxed and unwaxed dental floss, interdental woodstick, interproximal brushes and rubber tip stimulators. Dental floss has proven to be effective in interproximal plaque removal.

The objective of this clinical trial was to determine the relative effectiveness of three types dental floss, namely, waxed floss, dental tape, and Superfloss in the removal of interproximal plaque in subjects with mild gingivitis or mild periodontitis and not a periodontal patient with marked recession, wide interdental areas and deep pocketing. The relative effectiveness of waxed dental floss, dental tape and Superfloss as proximal plaque removal aids were compared in 20 subjects. Each subject used each of the three interdental aids for 1 week. The order of use was randomly selected. Interdental plaque scores were recorded at baseline, weeks 1, 2 and 3. The use of all 3 types of dental floss resulted in significant improvement in interproximal plaque scores compared to baseline scores. Improvement in plaque scores, in decreasing order were: dental tape, dental floss and Superfloss. When compared with each other, dental tape was significantly more effective than Superfloss. The difference could perhaps be attributed to the fact that tape, with a wider surface area, facilitates removal of plaque with the same vertical movement than does dental floss. There was no significant difference between dental tape and waxed dental floss or between floss and Superfloss. Regardless of the type of dental floss used, patients removed plaque more efficiently from buccal interproximal areas compared to lingual/palatal interproximal areas and from anterior teeth than posterior teeth.

Subjective responses indicated that 50% of subjected preferred dental tape, 40% waxed dental floss and only 10% preferred Superfloss. 16 out of the 20 test subjects commented that Superfloss was painful and difficult to use. This is because Superfloss is thicker than other types of floss, and is consequently more difficult to pass under the contact areas of teeth.
Interpreting the data from previous other studies with those obtained from this study, it would appear that where Superfloss can pass through interdental areas with ease, Superfloss is probably superior to floss.
Any advise that dental practitioners give to patients in regard to interdental cleansing methods must be based on patients dental characteristics.

Optimal orthodontic force for canine retraction

June 18, 1999
Dr. Hwang-sog Ryu

During canine retraction, the application of optimal force is the key to produce proper tooth movement. Orthodontic force is analyzed in two aspects of magnitude and duration. Theoretically, light continuous force produce the most efficient tooth movement. In reality, there is no appliance that exhibits absolute light continuous force. Every spring has a rate of force decay though with the new nickel-titanium materials, the decrease is amazingly small. Clinically, light continuous force thus means the force maintained at some appreciable fraction of the original from one patient visit to the next. In the Samuels' study, Ni-Ti coil spring had light continuous force and the elastic module had heavy interrupted force that started from 400 gm and declined to 0 between visit.

There is an important interaction between force magnitude and how rapidly the force decline as the tooth responds. Consider first the effect of a nearly continuous force. If this force is quite light, there will be a relatively smooth progression of tooth movement resulting from frontal resorption. If the continuous force is heavy, however, tooth movement will be delayed until undermining resorption can remove the bone necessary to allow the movement. Consider now the effect of forces that decay fairly rapidly, so that the force declines to zero after the tooth moves only a short distance. If the initial force level is heavy, the tooth will move when the undermining resorption is complete. Although the original force is heavy, after the tooth moves there is a period for regeneration and repair of the periodontal ligament before force is applied again. Heavy continuous forces are to be avoided; heavy intermittent forces, though less efficient, can be clinically acceptable. Undermining resorption requires 7 to 14 days. Experience has shown that orthodontic appliances should not be reactivated more frequently than 3-week intervals.

Now, let's investigate the force application method during canine retraction. There are two clinical strategies that would maximize anchorage within the arches. The first is to lower the stress delivered to the posterior teeth. This can be done by increasing the root surface area, either by incorporation of second molars into the anchorage unit. The decrease in stress obtained by increasing the root surface area of the posterior teeth will slow their rate of movement and allow more canine retraction. The same rationale makes extraction of second premolar teeth a logical choice in minimum anchorage cases. The second strategy for minimizing anchorage loss is to use an appliance system that can deliver relatively continuous stresses between 100 and 200 gm. This force would yield mean compressive stresses for the average cuspid root of approximately 70 to 140 gm/cm2. Excessive stress produces an increase in the rate of movement of posterior teeth without increasing retraction of anterior teeth. Appliance that have a high load-deflection rate are unable to achieve a difference in the rate of tooth movement. Low load-deflection rate mechanics, on the other hand, can maintain stresses in the desired range and maximize the difference in the rate of movement.

Appliance systems that deliver a relatively constant moment/force ratio also seem to have an advantage in that they maintain local stresses in the desired range and prevent excessive stress concentration from occurring in the apical or cervical areas of periodontal ligament. This will allow retraction to proceed at a near maximal rate while the stress on the posterior unit remains submaximal.

The currently known pathway about tooth movement

June 25, 1999
Dr. Jung-Sog Lee

Accurate and precise control of tooth movement can be optimized with the proper use of mechanics and knowledge of the subsequent tissue response. Although the art of repositioning teeth has been practiced for centuries, the exact mechanism by which orthodontic forces of tooth movement is not thoroughly understood. Tooth movement is facilitated by the remodeling of hard and soft tissues by a variety of cell types. Mechanical forces, at present the only clinical means for producing orthodontic tooth movement, are but one way to activate cells. Other chemical and physical agents are capable of stimulating bone cells to perform specific functions. The mechanism involved in the activation of cells by external stimuli has been elucidated in recent years. The important advances had led to a better understanding of the physical and biochemical interactions generated by orthodontic forces on teeth and the periodontium. It is known that bone cells ( osteoblasts and osteoclasts ) respond to orthodontic forces by proliferation and increased activity; however, the mechanisms for conversion of orthodontic forces into biologic activity are not completely understood.

There is a growing body of information that explains how various stimuli affect bone cells. The primary stimulus, or first messenger, may alter cell activity through the plasma membrane and cellular activation occurs in or through the cell membrane. It involves fluxes of ions, such as Ca2+, Mg2+ and inorganic phosphate as well as activation of the membrane-bound enzymes adenylate cyclase and guanylate cyclase. Within the membrane, these enzymes act upon their respective substrates, adenosine triphosphate (ATP) and guanosine triphosphate (GTP), to produce cyclic AMP and cyclic GMP. These latter substances, together with Ca2+, are considered to be the intracellular "second messengers" which mediate the effects of external stimuli on their target cells. All three substances serve as co-factors in enzymatic phosphorylation reactions. In support of the second-messenger pathway involvement in orthodontic tooth movement, Davidovitch and Shanfeld reported that cAMP concentrations were significantly higher in alveolar bone extracts taken from orthodontically treated cats as opposed to unstressed alveolar bone samples. Elevations in cAMP concentrations around orthodontically treated teeth may result from an increase in the number of active cells in the periodontal membrane and bone marrow. This was shown to be the case where mechanically induced bone remodeling was occurring. The experimental observations discussed above imply that cAMP may act as a chemical second-stage mediator in response to some hypothetical first-stage chemical effector present in the microenvironment. This mediator was postulated to have the ability to stimulate both bone and collagen resorption. Specifically, King and Fischlschweiger showed that extracts of tissue adjacent to orthodontically treated teeth will stimulate bone resorption in cultured fetal bones. This was interpreted as evidence for a chemical mediator of tooth movement.

Mechanical stress initiated by orthodontic forces or alveolar bone deflection induced an electrical charge polarization referred to as a piezoelectric response. In electronegative regions, bone formation occurs, whereas bone resorption predominates in electropositive areas.  Both in vitro and in vivo studies indicated that areas that have been described as predominantly osteoblastic were routinely electronegative and areas of positivity or electrical neutrality were characterized by elevated osteoclast activity. Accelerated orthodontic tooth movement resulted when exogenous electric current was administered in conjunction with orthodontic forces; furthermore, cellular activities were enhanced in the periodontal membranes in response to electrical stimulation. This suggests that the piezoelectric response propagated by bone bending incident to orthodontic forces application may be functioning as a cellular first messenger.

There are many things we can't understand. But information already available permits better comprehension of cellular events associated with orthodontic tooth movement. Moreover, this information now makes possible the development of clinical orthodontic tools which are based upon sound biologic foundations, not merely upon clinical observations.

Occlusal tooth contacts and bite force

July 1, 1999
Dr. Son Ji- Hyeong

The contact area during habitual biting can vary according to the activity of the jaw musculature. Forceful masticatory muscle activity may also induce deformations of the dento-alveolar tissues and the supporting skeleton, yielding various tooth loads despite an apparently even distribution of tooth contacts. Bite force distribution changed with biting strength and the location of occlusal contacts. Increased force in the canine region during unilateral clenching seems related to the pattern of jaw muscle co-activation and the physical properties of the craniomandibular and dental supporting tissues which induce complex deformations of the lower jaw. Orthodontists should take care to free any teeth to be moved from occlusal interferences, because occlusal contacts of inclined planes generate forces that interrupt the tooth-moving force system. We have all seen patients in whom one cuspid moves back than the other. This could be explained by an occlusal interference that interrupts the movement of one cuspid. Equilibration of placement of interocclusal plastic to eliminate the cuspid interference may be all that is necessary for the tooth to move.

Many of the orthodontic surgery patients before the management of their problem exhibit craniomandibular functional characteristics that differ from those of a normal population. Decreased number and intensity of occlusal contacts and malocclusions reflected by frequent interferences is one of them. Furthermore, patients seeking surgery to correct mandibular prognathism have a reduced bite force and may require more chewing cycles to tritulate the food than do persons with normal occlusion. Wisth found that the number of occluding teeth was significantly greater and the number of occlusal interferences was lower in a group of patients with mandibular prognathism and treated by ramus osteotomy than in the corresponding untreated prognathic patients.

It was concluded that considerable change in bite force, which was not primarily related to jaw geometry, occurred after orthognathic surgery. There are many other factors that may influence occlusal bite force. Patients may be reluctant to bite hard after surgery, because their willingness to use the jaws vigorously can be associated with the mental attitudes and/or to comfort in the teeth, muscles, and temporomandibular joints.

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1. Kikuchi M, Korioth TW, Hannam AG. The association among occlusal contacts, clenching effort, and bite force distribution in man. J Dent Res, 1997:76(6):1316-25.

2. Athanasiou AE, Melsen B, Mavreas D, Kimmel FP. Stomatognathic functions of patients who seek orthognathic surgery to correct dentofacial deformities. Int J Adult Orthod Orthognath Surg 1989;4:239-54.

3. Ingervall B, Ridell A, Thilander B. Changes in activity of the temporal, masseter and lip muscles after surgical correction of mandibular prognathism. Int J Oral Surg 1979;8:290-300.

4. Wisth PJ. Mandibular function and dysfunction in patients with mandibular prognathism. Am J Orthod 1984;85:193-8.

5. Athanasiou AE. Morphologic and functional implications of the surgical-orthodontic management of mandibular prognathism: A comprehensive review. Am J Orthod Dentofac Orthop 1993:439-447.

The relationship between orthodontic treatment and TMJ

July 16, 1999
Dr. Ahn Jeong-Soon

The relationship between orthodontic treatment and temporomandibular joint disorders is currently an important issue in orthodontics. An important objective of orthodontic treatment is to provide an oral environment which will promote health of the periodontal tissues, neuromuscular system, and temporomandibular joints. However, orthodontic treatment has been implicated as contributing to mandibular dysfunction with the possibility of the more serious sequelae of temporomandibular joint degeneration. In most of these TMJ cases, there seems to have been some distal pressure exerted on the mandible and ultimately on the condyle. When the mandible is forced posteriorly, distal pressure is exerted on the condyles and the disks above them may be "popped" forward, allowing the condyles to be pressed directly against the very vascular, innervated retrodiskal tissue or bilaminar zone causing the pain.

Orthodontists may inadvertently exert distal pressure on the mandibular complex, which can be the beginning of a TMJ disorder. The following are examples of how orthodontic treatment may be detrimental to the TMJ and how this can be prevented. Firstly, In Class ll malocclusions with deep interlocking cusps headgear and/or Class 11 elastics are often used in an effort to get the patient into a Class I cuspal relationship. As the maxilla is moved backward, the muscles of mastication will attempt to retract the mandible when the patient closes in to maximum intercuspation. This compensating movement by the mandible can put distal pressure on the condyles and cause an anterior dislocation of the disk. To correct this problem in orthodontic treatment, a possible solution is a flat plane of acrylic, which can be bonded on the occlusal surfaces of the lower molars and premolars after the fixed appliance has been placed. There should be a reverse curve in both arch wires to prevent overeruption of the anterior segments. Secondly, Midline switch or cross elastics have a more subtle effect. As the jaw is pulled to one side, distal pressure is put on one condyle only. If this creates a TMJ problem, midline elastics should be worn only during waking hours so that muscles can help to hold the mandible forward. Thirdly, Lower headgears or reverse headgears that exert distal pressure on the chin and Class lll elastics are a very important part of orthodontic treatment, but they too can put distal pressure on the mandible. If there is a developing problem, it is better to have the patient wear lower or reverse headgear and Class III elastics only during waking hours. Finally. Retentive phase of orthodontic treatment may have caused more TMJ problems than any other orthodontic procedure. In orthodontically treated deep bite malocclusions,  As the bite deepens, it may have four possible adverse effects on a treated case. (1) It separates the upper anterior teeth. (2) It may crowd lower anterior teeth. (3) It tends to move the maxilla forward or (4) drive the mandible distally. orthodontists have retained treated cases by putting a canine-to-canine (3 to 3) fixed retainer on the lower anterior teeth. This prevents the lower anterior teeth from collapsing lingually as the bite closes. A Hawley-type retainer with a labial bow is usually placed on the upper arch to prevent the upper anterior teeth from rotating, separating, or moving forward.

In conclusion, No orthodontic procedure can be performed in isolation without considering its possible effect on the temporomandibular joint. Therefore, the following recommendations are made for diagnosis and treatment planning.
1. Etiologic factors that might cause upward and backward pressures on the mandible should be reduced as much as possible.
2. Mechanotherapy that may cause upward and backward pressures on the condyles is not recommended. Final detailed correction of dental abnormalities should always consider optimal temporomandibular health and function.
3. Retention procedures should be planned to provide a proper path of closure to minimize or prevent possible retrogressive posttreatment changes.

Distraction Osteogenesis

July 23, 1999
Dr. Jeong-Tae Kim

The process of generating new bone by stretching, which was introduced by Ilizarov and has been developed over the past 30 years, is called distraction osteogenesis. The application of distraction osteogenesis in the craniofacial skeleton was first reported by Snyder et al in 1973, who used this technique to lengthen the dog mandible. In 1992, McCarthy et al reported the first clinical cases of mandibular lengthening by gradual distraction using an extraoral device. Although this method was effective, there were still several problems. The use of extraoral transcutaneous pins in the mandible has disadvantages such as extraoral scars, facial nerve and inferior alveolar nerve injury, and infection. Block et al have suggested the advantages of an intraoral distraction device, and they also used implants for anchorage. With an intraoral device, the implants penetrate the thin oral mucosa, and the distraction appliance is near the bone. Moreover, the intraoral device is not visible and it does not cause scarring.

Lengthening of the mandible and midface has been described in several animal studies. Recently McCarthy et al described lengthening of the human mandible by distraction osteogenesis using an extraoral approach. The technique involves performing a corticotomy on the buccal and lingual aspect of the mandible, with preservation of the periosteum and the intramedullary blood supply. The distraction device is mounted on both sides of the corticotomy and a latency period of 5 to 10 days is allowed for primary callus organization. Then gradual distraction is perfomed at the rate of 1 mm per day. Slower distraction rates result in premature ossification and fusion, whereas faster rates result in fibrous tissue formation within the distraction gap. After the desired lengthening has been achieved, a period of consolidation of a few weeks is suggested before removal of the device.

Facial deformities require early treatment and the optimal time is related to the severity of the malformation. One of the most important objectives is to avoid secondary malformations of the midface resulting from growth restriction by a small mandible. Furthermore, the potential for bone-building of the hypoplastic mandible is best achieved in young children. Advancement of the anterior maxilla is often required to correct a skeletal deformity. This can be especially important for cleft palate patients for whom posterior maxillary advancement may cause speech problems. For these patient, anterior maxillary advancement can help correct their skeletal problems while limiting potential velopharyngeal compromise. Anterior maxillary advancement without distraction osteogenesis or by osteotomy alone is limited because of the restraints caused by the palatal and crestal soft tissues. These soft tissues are not acutely "stretchable" and are therefore liable to degenerate, with subsequent infection and necrosis. The use of distraction osteogenesis has the potential to solve this soft tissue problem, because slow bone lengthening is accompanied by soft tissue genesis.

Distraction osteogenesis has been shown to be an effective method of lengthening and augmenting endochondral bone. The technique has been applied effectively in the reconstruction of the membranous bones of the craniofacial skeleton, initially in the treatment of mandibular deficiency and the hypoplastic maxilla and midface. I believe we will be seeing greater and greater use of the distraction osteogenesis procedure in clinics.

Facial Esthetics in Tweed-Merrifield Philosophy

September 9, 1999
Dr. Il-Sun Youn

Evaluation of facial profiles and facial balance is a constant, continuous, lifelong study and learning process for orthodontists. Tooth movement and proper positioning of the teeth to ensure favorable facial changes and to avoid unfavorable changes should be in the orthodontist's "diagnostic" mind from the very first examination. If the face is out of proportion, and if it is within the power of the orthodontist to bring it into proportion, it should most definitely be an overriding goal of orthodontic mechanotherapy. The question becomes, "What can we as orthodontists do to either preserve or to enhance facial balance, harmony, and proportion, for each of our patients?"

The elimination of facial imbalance can be accomplished if the clinician's treatment philosophy is based on the following four concepts.
Concept 1. The mandibular incisors must be uprighted over basal bone. For most patients, uprighting of mandibular incisors is the critical ingredient necessary to achieve balance and harmony of the lower face. Angle stated that lip posture was determined directly by the position of the maxillary incisor. Tweed determined that if the maxillary incisor was to be repositioned so that lip posture could be improved, the mandibular incisor had to be uprighted.
Concept 2. The second ingredient, vertical dimension control, has a direct relationship to mechanical force systems. In order to control the vertical dimension, control of the Frankfort mandibular plane, the occlusal plane, and the palatal plane during treatment is essential.
Concept 3. Anterior Facial Height must be controlled. ANS must not be allowed to drop. A drop in ANS lengthens the lower one third of the face. Point A must move distally as the maxillary incisors are moved up and back.
Concept 4. Mandibular response should occur. If the mandibular incisors are uprighted, if the vertical dimension is controlled, and if Point A is controlled with maxillary incisor retraction and intrusion, the patient has a much greater opportunity for all important mandibular response to occur. Mandibular response is the change in the spatial relationship of the mandible to the maxilla. It is a combination of both tooth movement and growth. The attainment of these four integrally related treatment goals enhances facial balance, proportion, and harmony.

Creating a beautiful face or preserving a beautiful face is our mission as orthodontists. The face is the "art" portion of the definition of our specialty - the "art and science" of orthodontics. An understanding of facial balance and how it can be made an attainable objective is what makes orthodontics the most wonderful specialty in dentistry. The creation of a beautiful face, the elimination of facial imbalance, is our highest calling.

Implant as an Orthodontic Anchorage

September 17, 1999
Dr. Eun-Hyee Kim

Adequate anchorage control to correct a dental and/or skeletal malocclusion is a major and critical concern in treatment planning and in the design of all orthodontic appliances. When extraoral devices are employed, anchorage can be quite stable but depends on the patient£§s cooperation. All intraorally derived anchorage is unstable, necessitating appliances which can be complicated, inefficient, and often require the extraction of dental units. Because of anchorage limitations, patients may face less desirable treatment alternatives such as extraction of permanent teeth, orthognathic surgery and extraoral traction. Osseous anchorage via rigid(¡°osseointegrated¡±) bone fixtures would greatly expand the range of biomechanical possibilities.

Following the 1945 failure of Gainsforth and Higley to attain orthopedic anchorage by placing metallic screws and wires in the dog ramus, there are no reports of attempts to use endosseous implants to move teeth until the clinical case reports of Linkow about 25years later. In the last few years considerable interest has developed in endosseous implants as a source of orthodontic and facial orthopedic anchorage. A number of experiments have been reported, but none of these methods appear to have significant clinical potential. Recently a Vitallium screw was placed in the anterior maxilla of a patient as a source of anchorage to help intrude the maxillary incisors. However, because of its large size, the screw employed could not be used routinely. The present study investigates the anchorage potential of a relatively small titanium screw(3.2×8.0mm) that offers clinical promise. Titanium has a long history of biocompatibility, dating from the 1940 observation of Bothe, Beaton, and Davenport that bone has a tendency to grow into contact with it. During the 1950£§s the biocompatibility and excellent corrosion resistance of titanium were confirmed in a number of studies. In 1959 Beder and Ploger described intraoral titanium implants. There are a number of reports of endosseous oral implants that are capable of maintaining a rigid (¡°ankylosed¡±) attachment over a number of years of masticatory function. In 1984, Roberts et al. described principles for attaining rigid osseous fixation of titanium screws with an acid-etched surface.

Following an unloaded healing phase of six weeks, these endosseous implants remained rigid despite a continuously applied load. And he reported the clinical rigidity(¡°osseointegration¡±) achieved by 94 percent of the titanium implants placed in dog mandibles. All loaded implants remained rigid. Implants with¡´10 percent of the endosseous interface in direct contact with bone successfully resisted a continuous load of 3N for 13weeks. When implants are permanently placed in bone, biocompatibility is an important consideration because, even with the most inert materials, some degree of metallic corrosion and dissolution is inevitable. However, anchorage implants would probably be removed after about 1 to 3 years of treatment.

So this may not be a relevant problem in an orthodontic context. Ideal intraoral implants for orthodontic anchorage should resist push-pull, intrusive, and extrusive forces. Since all investigations thus far have evaluated only the push-pull resistance, it would be prudent to hypothetically compare their relative abilities to resist other directional forces.

There are seven major factors to make bony fixation(¡°ankylosis¡±) of the implant.
1. maintenance of vital osseous margins around the surgical defect prepared to receive the implant
2. preservation of subperiosteal osteogenic capacity
3. firm stabilization of the implant within bone
4. close adaptation of the periosteal bony margin to the implant, restricting access of the fibrous layer of the periosteum
5. avoidance of unessential radiation exposure
6. lack of immediate loading to avoid propagating stress risers(cracks) which can critically weaken adjacent bone before physiologic compensation occurs
7. an adequate, unloaded healing period(4 to 5 months in man) to allow sufficient mature, lamellar bone to adhere directly to the implant surface, as well as fill in the immature woven lattice which forms during initial healing. Also, a rigidly stabilized healing phase allows for some new secondary osteons to be propagated at or near the implant surface.

Although placement of an endosseous implant is a surgical procedure, responsibility for management of orthodontic/dentofacial orthopedic problems ultimately rests with the orthodontist. If a new entity, such as rigid endosseous abutments for orthopedic anchorage, is to develop into a reality for routine orthodontic treatment, the orthodontist must have a sound, basic background in the mechanical, physiologic, surgical, and periodontal factors essential to consistent success. In this regard, basic science is, in fact, the basis for sound clinical advance.

Root resorption after orthodontic treatment

October 1, 1999
Dr. Mi-Young Seo

Apical root resorption is a common idiopathic problem associated with orthodontic treatment and has recently received considerable attention because of medicolegal exposure. Loss of apical root material is unpredictable and, when extending into the dentin, irreversible. Individual susceptibility, hereditary predisposition, systemic, local, and anatomic factors associated with orthodontic mechanotherapy are commonly cited components.

After application of force, it can take between 10 and 35days for resorbed lacunae to appear. According to Schwartz when pressure decreases below the optimal force (20 to 26g/cm²) root resorption ceases. Repair of resorbed lacunae is seen after 35 to 70days after force application. Innermost cellular layer of the periodontal ligament supplies the protective mechanism to the root, as well as the potential for a repair. The cementoblasts, fibroblasts, osteoblasts, endothelial, and perivascular cells are included in this layer. Cemental resorbed lacunae become fully anatomically reconstructed. Deep dentinal lacunae are repaired by a thin cemental layer resulting in an irregular root shape. After both types of repair, the periodontal ligament width is usually normal. Alveolar bone and bone marrow derived cells are related to the healing of larger zones of damage that leads to ankylosis.

There is a connection between the tendency to root resorption during orthodontic treatment and these factors.
1) various dental morphologic characteristics, such as invagination, length of root, and root shapes, especially taurodontism,
2) anomalies in the dentition, particularly ectopia and agenesis
3) endodontically treated teeth and previously traumatized teeth
4) the pattern of resorption in the primary dentition
5) girls are more susceptible to root resorption during orthodontic treatment than boys.
6) one ought to be on the lookout for connections between condylar changes, root resorptions, and anterior open bites in connection with orthodontic treatment.
7) use of fixed appliances is more detrimental to the roots than use of removable appliances
8) Intrusion is probably the most detrimental to the roots involved, but tipping, torque, bodily movement, and palatal expansion can also be implicated.
9) higher degree of force causes more root resorption.
10) severity of root resorption is directly related to treatment duration.

To monitor apical root resorption associated with orthodontic treatment with fixed appliances the standard procedure is a radiographic examination after 6months of treatment. In teeth with an enhanced risk, a 3-month follow-up is recommended.

Root resorption phenomenon is unpredictable and widespread. In light of the orthodontists's liability of what is basically an unpredictable phenomenon, it is necessary that the specialty define this uncertainty and establish criteria of diagnosis, records, and informed consents to protect its members against unnecessary and unjustified litigation.

The cause of TMJ disorder

October 8, 1999
Dr. Ji-Hyeong Son

Symptoms of dysfunction and pain in the region of the joint and muscles have been grouped in a syndrome, which is characteristic for the TMJ and can be distinguished from disorders of all other synovial joints: 1) TMJ disorders occur predominantly in females and in much younger persons than comparative disorders of all other joints. 2) Radiographic signs are unusual in TMJ dysfunction. 3) Emotional stress has significant impact on the disturbed function of the TMJ and its related muscles. It is generally referred as craniomandibular pain-dysfunction.

For many years, occlusal disharmony has been considered a major factor contributing to clinical TMJ symptoms. Occlusal interferences are still considered to be of importance in causing muscular responses. Long-standing malocclusion will provoke muscular adaptation and is, therefore, not considered of etiologic significance in TMJ disorders. Recent occlusal changes, however, may induce reflex hyperactivity and muscle pain. There is a close relationship between a joint and its activating muscles. Therefore, masticatory muscle symptoms will frequently accompany TMJ disorders. Joint pain will elicit a muscular reaction tending to protect it from future damage by preventing motion. Instability of the TMJ (eg, hypermobility, internal derangement) is also likely to induce a muscular reaction tending to increase stability.

Prolonged hyperactivity may produce hypertrophy, whereas disuse may produce muscle atrophy, which is an often observed symptom in osteoarthrosis. Muscle tenderness may elicit additional responses by activating other muscle to relieve tension in the painful muscle. So, the presence of accompanying muscle symptoms fits in the proposed concept of TMJ osteoarthrosis. TMJ osteoarthrosis is probably underrated as a structural basis of craniomandibular pain dysfunction. However, muscular symptoms frequently accompany osteoarthrosis and may be important in the progression of the disorder. In most cases disc displacement appears to be an important accompanying sign of osteoarthrosis that causes a rapid progression.

Trauma, anatomic abnormalities, or loss of joint stability are frequently etiologically related to osteoarthrotic alterations. However, mechanical factors do not explain all forms of osteoarthrosis. Systemic factors, inflammatory mediators, aging, and other factors that reduce the adaptive capacity also seem to be important. It may be concluded that in many cases the initiating factor leading to TMJ osteoarthrosis is not obvious. By definition, in these cases TMJ osteoarthrosis should, therefore, be considered primary. Osteoarthrosis can be considered to be the underlying primary cause of internal derangement and craniomandibular pain and dysfunction.

Changing of arch size and form in untreated adults

October 22, 1999
Dr. Kwan-Mo Kim

Arch form and positions of the constituent teeth change during adulthood. The essence of the change is that the arches became shorter and broader. The changes are general rather than local. Finding broad-based changes of length and width suggests systemic factors controlling the age-progressive shifts observed in tooth position. Lundstr m made the important observation that these changes in arch form actually occur twice in a person, first in the deciduous dentition and analogously in the permanent dentition. On examination of the stable phase of the deciduous dentition, from about 3 to 6 years of age, arch length decreases and width increases. Lundstr m noted that, since width increases as length decreases, the degree of spacing or crowding typically remains unchanged. These same arch-shape changes occur in the permanent dentition, and they appear to develop most rapidly in the teens and twenties.

The greatest average change was in intermolar width; maxillary 6-6width increased an average of 2.7mm. But, spread across the examination interval, this is just 0.7mm per decade, or 0.07mm per year. Moreover, these changes seldom alter occlusal relationships. Skeletodental changes from adolescence to early adulthood to late adulthood are not linear and they probably are not even monotonic. Changes during early adulthood are more rapid than during older age intervals. Velocity probably follows a negative log-linear curve. Under harsher dietary condition, interproximal attrition is a resonable speculation for loss of arch length. But, in this contemporary sample, approximal wear facets were trivial even in old age, and estimates of loss of enamel thickness are insufficient to account for the observed loss of arch length. Reduction of tooth diameters due to caries is another possibility. Dental disease was minimal in health-conscious sample, so arch reduction due to loss of tooth substance can be discounted. Bite force has an anterior component because teeth are situated with their crowns tipped mesially. Occlusal forces are dissipated axially but also mesially through the proximal contacts. Stallard pointed out that, as the mandible is elevated, the lower teeth swing into occlusion on an arc, upward and forward, with a resulting upward and anterior component of motion and force. The anterior component of force acts to consolidate the tooth rows over time, resulting in diminished arch length. Reduction in arch length can occur by closing interproximal spaces, but these generally are minor after teeth are erupted into occlusion. The buccal tilt of maxillary tooth crowns ought to generate a buccal component of bite force. Murphy found highly significant expansion in arch width during adulthood, with greater increases in the more distal segments. Smith and Bailit also found significant increases in arch width with age, particularly or the more distal teeth. If the buccal teeth are drifting away from the midline, then the supporting bone ought to remodel to accommodate them. Data show that this does occur, and changes are in the predicted direction. Bj rk and Skieller showed that the palate broadens by expansion of the midline sutures, and there is greater expansion in the posterior segments. In sum, the supporting bone of the dental arches broadens with age. Finding skeletal growth during adulthood no longer is surprising, and these changes fit with what Garn has termed the "general phenomenon" of continued bone growth. The increase in incisor irregularity may be caused by occlusal and physiologic forces intrinsic throughout the tooth rows, regardless of the status of the third molar.

CONCLUSIONS
1.  Arch lengths decreased significantly with time. This appears to be a normal, predictable function of aging.
2.  Arch width increased , with little change across the canines, but appreciably more in the more distal regions of each arch.
3.  These slow, subtle changes do not appear to affect interarch relationships; incisor overbite and overjet and sagittal molar relationship remained unchanged.
4.  Forces driving these changes remain speculative, but the anterior and buccal components of occlusal force would seem to be involved.

Herbst appliance

October 29, 1999
Dr. Heung-Yeol Kim

The Herbst appliance is a fixed bite jumping device for treatment of class II malocclusion. The appliance was introduced by a German professor, Emil Herbst, in 1905. In 1979, Dr. Pancherz called attention to the possibilities of stimulating mandibular growth by means of the Herbst appliance. The Herbst appliance is effective in the treatment of class II malocclusion. The appliance must be limited to growing persons. Treatment prognosis is good with a brachyfacial growth pattern.

In the Herbst appliance, there is a bilateral telescope mechanism. Each telescope device consists of a tube, a plunger, two pivots, and two screws. The pivot for the tube is usually soldered to the maxillary permanent first molar band and the pivot for the plunger to the mandibular first premolar band. The screws prevent the telescoping parts from slipping off the pivots. During the last 15 years, the original banded design of Pancherz has been modified in various ways. For example, stainless steel crowns have been substituted for orthodontic bands on the abutment teeth. And acrylic splints have been used to carry the bite jumping mechanisms.

The action of the Herbst appliance in the treatment of class II, division 1 malocclusion with a deep overbite can be summarized as follows: Class II molar correction by increase in mandibular length, distal movement of the maxillary molars, and mesial movement of the mandibular molars. Overjet correction by increase in mandibular length and mesial movement (proclination) of the mandibular incisors. Overbite correction by intrusion (partial proclination) of the mandibular incisors and enchanced eruption of the mandibular molars. Posttreatment stability secured by stable cuspal interdigitation of the upper and lower dentition.

The Herbst appliance has several advantages when compared to removable bite jumping appliances: The appliance works all day. The cooperation from the patient is not required. The treatment time is short (6 months). By the way, the Herbst appliance has several disadvantages, including its rigidity, the need for laboratory involvement, the requirement of special bands or crowns, and the possibility of dislodgment or breakage. The hard and soft tissues would need some time for adaptation to the mandibular position. Therefore posttreatment retention with a removable functional appliance is sometimes recommended.

Consideration points for adequate activation force at using a quad-helix appliance

November 12, 1999
Dr. Hwang-Sog Ryu

The quad-helix appliance is a fixed lingual arch wire appliance that produces maxillary expansion when used in the treatment of maxillary constriction or crossbite in the primary and mixed dentitions. It is basically a W-arch type of appliance with four helical loops. The appliance is fixed to bands cemented to the first molars. Anterior and posterior helical loops are incorporated to increase the range of force application, produce more flexibility, and enhance the ability to rotate molars. The quad-helix appliance offers the advantages of excellent anchorage and retention, minimum effect on speech, continuous force delivery over time, and no adjustment responsibility for the patient. The appliance becomes particularly useful for cleft palate patients because of the continuous force delivery characteristics and the ability to use more force anteriorly than posteriorly as needed.

When activated, the quad-helix appliance produces orthopedic and orthodontic changes in the maxillary arch. There is a relative increase in the orthopedic movement component for younger persons because of a decrease with age in the resistance of the midpalatal suture. The orthopedic increase in arch width generally is considered a desirable result of maxillary expansion because it allows coordination of the upper and lower arches in an attempt to establish a stable correction in both skeletal and dentoskeletal malocclusions.

It has been recommended that quad-helix appliances be fabricated from stainless steel or Elgiloy blue arch wires with diameters of 0.038 inch or similar large sizes. Ricketts considered the design, development, and activation of these appliances. He stated that the quad-helix appliance should produce a force of 500 g to achieve an orthopedic response and advocated the use of four different sizes of preformed appliances, depending on the arch dimensions of the patient. In vitro measurements by Chaconas and Caputo have shown that activation of 8 mm produces a force of approximately 400 g for quad-helix appliances constructed from 0.038 inch diameter arch wires. An activation of 8 mm is frequently the initial expansion added to the appliance before cementation and corresponds to the average bucco-lingual width of deciduous maxillary second molars.

Urbaniak et al. investigate detailed in vitro force delivery measurements for the quad-helix appliance to determine the roles of appliance size, arch wire diameter, and alloy composition. Four different quad-helix sizes were selected for study on the basis of their clinical importance. Five appliances for each size were fabricated from 0.038-inch diameter, 0.036-inch diameter and 0.032-inch diameter Elgiloy blue and the last two diameter stainless steel (standard temper) arch wires.

As the appliances increased in size (from size 1 to 4), with the factors of wire diameter and alloy remaining constant, there was a considerable decrease in force delivery. An increase in wire diameter from 0.032 to 0.036 inch and from 0.036 to 0.038 inch, with both appliance size and wire alloy remaining constant, resulted in a considerable increase in force delivery. Alloy composition (stainless steel or Elgiloy blue) was found to have no significant effect on force delivery of the quad-helix appliance when appliances of the same size and wire diameter were compared. The nearest approximation to ideal force delivery (500 g) for 8-mm activation occurs with the combinations of appliance size and wire diameter.

In previous studies it has been found that higher force levels are required for maxillary expansion in older persons as compared with younger persons, although relatively lower force levels are generally recommended when possible. The need for increasing biomechanical force with patient age is attributed to greater resistance of the connective tissues of the midpalatal suture, the occlusion of the teeth, and the rigidity of the facial skeleton. As a child becomes older, the size of the quad-helix appliance must be increased to adapt to the increase in arch dimensions. However, the results of this investigation show that there is a considerable reduction in force when the appliance size is increased at constant wire diameter and ultimately the force may fall below the level necessary to cause sutural opening. On the basis of the present laboratory data, it is strongly recommended that to maintain adequate force levels under clinical conditions, the wire diameter for the quad-helix appliance should be increased as the arch size increases. If this principle is not followed, a higher ratio of orthodontic/orthopedic correction can be expected, particularly for older persons.

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Urbaniak JA, Brantley WA, Pruhs RJ, Zussman RL, Post AC. Effects of appliance size, arch wire diameter, and alloy composition on the in vitro force delivery of the quad-helix appliance. Am J Orthod 1988;94:311-6.

Circumferential supracrestal fibrotomy and some logic of modern retention

November 19, 1999
Dr. Byeong-Seok Lee

The major cause of rebound after orthodontic treatment is the network of elastic supracrestal gingival fibers. As teeth are moved to a new position, these fibers tend to stretch, and they remodel very slowly. If the pull of these elastic fibers could be eliminated, a major cause of relapse of previously irregular and rotated teeth should be eliminated. In fact, if the supracrestal fibers are sectioned and allowed to heal while the teeth are held in the proper position, relapse caused by gingival elasticity is greatly reduced. Surgery to section the supracrestal elastic fibers is a simple procedure that does not require referral to a periodontist. It can be carried out by either of two approaches. The first method, originally developed by Edwards, is called circumferential supracrestal fibrotomy(CSF). After infiltration with a local anesthetic, the procedure consists of inserting the sharp point of a fine blade into the gingival sulcus down to the crest of alveloar bone. Cuts are made interproximally on each side of a rotated tooth and along the labial and lingual gingiva margins unless, as is often the case, the labial or lingual gingiva is quite thin, in which case this part of the circumferential cut is omitted. No periodontal pack is necessary, and their is only minor discomfort after the procedure.

Un alternative method is to make an incision in the center of each gingival papilla, sparing the margin but separating the papilla from just below the margin to 1 to 2 mm below the height of the bone buccally and lingually. This modification is said to reduced the possibility that height of the gigival attatchment will be reduced after the surgery, but their is little if any risk of gingival recession with the circumferential supracrestal fibrotomy unless cuts are made across thin labial or lingual tissues. From the point of view of improved stability after orthodontic treatment, the surgical procedures appear to be equivalent. Neither the CSF nor the papilla-dividing procedure should be done until malaligned teeth have been corrected and held in their new position for several months, so this surgery is always done toward the end of the finishing phase of treatment. It is important that the teeth continue to be held in good alignment while gingival healing occurs. This means that either the surgery should be done a few weeks before removal of final orthodontic appliance or, if it is performed at the same time the appliance is removed, a retainer must be inserted almost immediately. It is easier to do the CSF procedure after the orthodontic appliances have been removed, although it can be carried out with appliances in place. An advantage of the papilla - dividing procedure may be that it is easier to performed with the orthodontic appliance still in place. The only problem with placing a retainer immediately after the surgery is that it may be difficult to keep the retainer from contacting soft tissue in a sore area.
Next, I would like to introduce some logic of modern retention from journal review.
Cases are divided into following groups,
1. There are very few cases requiring minimum or no retaining appliances and these would include:

a. Blocked out canines in Class I extraction cases with no incisor crowding
b. Class I anterior and/or posterior crossbites with very steep cusps and no anterior crowding
c. Class II cases slightly overtreated with headgear to restrict maxillary growth with sufficient arch length indicated by mandibular anterior spacing and absolutely no mandibular incisor rotations
d. The above-described cases should be seen on a scheduled basis during the posttreatment adolescent period to check possible spacing or unfavorable growth changes or TMJ symptoms.

2. Routine cases, extraction or nonextraction, should have retaining appliances fixed or removable.

a. At least until the destiny of the third molar teeth is determined [or]
b. Until the growth process has slowed in late teens and early twenties [and]
c. Afterward at the option of the patient

3. Cases that will need indefinite retention

a. Class II, Division 2 Angle deepbite cases
b. Arch expansion treatment for esthetic demands
c. Patients with uncontrolled muscular or tongue habits
d. Again the orthodontist should be most emphatic about this need.

4. Cases that require operative procedures with indefinite retention

a. Treatment limitations such as tooth size discrepancies (that is, larger maxillary teeth) may result in increased overbite or super Class I.
b. Reversely, larger mandibular teeth will result in end-to-end incisor relationships, maxillary spacing, or buccal end-on occlusion.
c. Stripping or reproximation of oversized teeth and esthetic bonding of malshaped or undersized teeth may help resolve this problem.
d. A very vertical incisal relationship, which for any reason cannot be corrected, will lead to deepening overbite unless retained.
e. The patient should be informed.

5. Cases requiring special construction and/or renewal of removable retaining appliances or acrylic on the labial bows

a. Posttreatment adolescent palatal changes
b. Late mandibular growth spurt and Tweed type C growers
c. To maintain torque and overbite correction

Implant maintenance

November 26, 1999
Dr. Yong-Seung Lee

Although implant techniques and materials have been developed which are capable of a high degree of clinical success, the ultimate long-term success of implants is dependent upon the efforts of both the patient and dentist in maintaining the health of the peri-implant tissues. Prevention of peri-implant disease should be a prime motivating factor for patient and therapist involvement in a regular maintenance program. Optimal peri-implant health depends largely on: 1) inhibition of plaque formation 2) prevention of early plaque attachment 3) elimination of existing plaque 4) interference with succession from non-pathogenic to pathogenic plaque.

It is critical that the surface of the implant not be subjected to any manipulation that would render it less biologically compatible or more plaque retentive. Ultrasonic or hand scaling with metallic instruments is absolutely contraindicated with implants. The titanium oxide coating of titanium implants enhances biocompatibility and is readily removed by metal instruments. Hydroxyapatite coatings can easily be separated from the metallic substrate by a scaling action. Unfavorable intermetallic reactions from scaling can contaminate the implant surface and create surface scratches resulting in corrosion and facilitating plaque retention. Only instruments made of plastic or the same metal should be in contact with the implant. Until recently, there were no instruments available to debride the subgingival area at implants. Plastic curettes in the shape of Gracey curettes are now marketed, although reports of their clinical efficacy have not been published. An antimicrobial rinse and hand or motorized toothbrushes produced minimal alteration in surface appearance from originally machined implants. An effective means of soft tissue maintenance around the dental implant might be the use of a topical mouthwash containing commercially available compounds such as phenolic agents (Listerine, Warner-Lambert Co., Morris Plains, NJ.), plant alkaloids (Viadent, Viadent, Inc., Fort Collins, CO), or chlorhexidine gluconate (Peridex, Procter & Gamble Co., Cincinnati, OH). Most dentists placing implants use the ADA-approved chlorhexidine gluconate because of its demonstrated binding action to soft and hard tissues in the oral cavity. It has also demonstrated close to a 100% bacterial kill in a 0.12% concentration, up to 5 hours after a 30-second mouthrinse. The recent study (J Periodontol 1998;69:857-864) showed that the air powder-water spray with Sodium hydrocarbonate solution is the most effective method for removing plaque from titanium implant surface without damaging the surface of the implant. Hydroxyapatite-titanium implants were severely abraded by ultrasonic and air-powder polishing instruments. Overall, the rubber cup with polishing paste appeared to be the least abrasive professionally applied modality. Ethylene oxide or disinfectant solutions should not be used for sterilization of metallic implant components because they alter the surface chemistry of metallic implants. Steam sterilization is the only method currently recommended. But information on specific home-care procedures for implant patients is meager. The standard soft, polished bristle toothbrush is the first line of prevention in accessible area. The end-tufted brush can be very useful in areas with complex contours. Superfloss between abutments with floss threaders is very effective. The interdental brush is also helpful, but the patient must be advised to use the type with a nylon coated core wire. Gauze strips for the underside of broad pontics or soft nylon mesh for narrower subpontic areas are recommended. A rotary uni-tufted brush (Rotadent ) can be particularly effective in posterior lingual areas. It is advisable to dip the hand or motorized brush head in the antimicrobial solution with subsequent application to the implant head and neck. Some patients use floss or shoestring dipped into the antimicrobial for care around the implant "neck". All of these procedures should be used daily and at the soft tissue / implant interface.

Prediction of Mandibular Growth Rotation

December 3, 1999
Dr. Eun-Jeong Kim

In Orthodontics, knowledge of mandibular growth is highly beneficial in diagnosis and treatment planning and is critical in the development of balanced dentofacial structures. Various parameters have been used to predict mandibular growth with varying success.

Bjork with his implant studies, described multiple structural signs seen in extreme types of mandibular rotators. Backward mandibular rotation is associated with a pronounced apposition below the symphysis with more overall concavity of the lower mandibular border. An inclination of the symphysis with proclination is an indicator of a backward rotating mandible. Jarabak predicted the direction of mandibular growth from a facial polygon, including the saddle angle, articular angle, gonial angle. With sums of these three angles greater than  396°, posterior mandibular growth patterns were predicted while less than 396°was associated with anterior mandibular growth. Also, a ratio of posterior to anterior facial height of 56% to 62% indicated a posterior growth pattern, whereas a ratio of 65% to 80% indicated an anterior growth tendency. Singer et al. suggested that the clinical presence of a deep mandibular antegonial notch is indicative of a diminished mandibular growth potential and a vertically directed mandibular growth pattern. Huggare stated that there was a significant correlation between horizontal growth of the mandible and the initial height of the atlas dorsal arch. The treated subjects with forward mandibular rotation demonstrated a significantly higher pretreatment atlas dorsal arch than the subject with either no rotation or a backward mandibular rotation. Aki et al stated symphysis morphology was found to be associated with the direction of mandibular growth, especially in male subjects with symphysis ratio having the strongest relationship. A mandible with an anterior growth direction was associated with a small height, large depth, small ratio, and large angle of the symphysis.,

Although many cephalometric measurements have been used, it has been shown that it is still very difficult to accurately predict the direction of mandibular growth. Baumrind et al. conducted a study with five clinicians, who were considered experts, and attempted to predict the direction of mandibular growth and hence concluded that prediction of the direction of mandibular growth by lateral cephalometrics was poor. Lee et al. studied the reliability of the Skieller et al. prediction methods. Although Skieller's four variables accounted for 86% of the variability in change in the direction of mandibular growth (mandibular inclination, intermolar angle, shape of the lower border of the mandible, and inclination of the symphysis), it accounted for only 8% in Lee's study.

In closing, we express our belief that clinically useful individualized prediction of craniofacial development are not yet possible. For the near future at least orthodontists must continue to rely more on clinical observations made during treatment than upon predictions made using pretreatment records.

Implant and Cost Effectiveness

December 10, 1999
Dr. Seong-Ho Han

Dental implants were developed as an alternative mean of support for conventional dentures. When commercially implants were first introduced to dentistry, the focus in practice and in the literature was on osseointegration. And so the main criteria for clinical success seems to be survival. As experience has increased, implants are becoming a more complete process. Recently, Implants have been used more effectively as fixed prostheses for restoration of single or multiple tooth missing. In addition to factors to satisfy objectives of prosthesis (such as esthetics, phonetics, mastication, comfort), clinician must also consider the time and cost required not only to fabricate implants, but also to maintain implants after placement. Therefore, effectiveness of dental implants is widely studied, especially in terms of their safety and efficacy in decision making of patients and dentist.

Recently, a few article have been reported regarding the cost of dental implants as compared to the cost of conventional treatment. Van der Wijk et al¹⁾ reported that four possible treatment alternatives were included in his design for edentulous patients; 1) transmandibular implants using 5-fixture, 2) permucosal implants as bar attachment, 3) preprosthetic surgery using vestibuloplasty and deepening of the floor of mouth, 4) conventional therapy. The cost components were divided according to the dentist's labor, practice expenses such as material, hospital, overhead costs. The results suggested that the costs of conventional denture at first year were more favorable three times than overdenture permucosal implants, seven times than fixed implants of transmandibular implants, and three times than preprosthetic surgery. Also, Lewis'²⁾ reported similar results by using similar methods in edentulous patients like Van der wijk's. Walton et al³⁾ reported four designs; 1) single fixture, 2) multiple implants of two or more, 3) bar and clip attachment, and 4) individual ball attachment. The costs of prosthesis were divided as dentists, laboratory, materials. The highest mean costs were associated with removable bar type, while the lowest costs were incurred by single-tooth fixed restorations. Regardless of the type of prosthesis, clinical fee constituted between 56 - 62 % of the total fee; laboratory cost were between 20 - 25 % of total fee, and material component cost made up from 15 % to 24 % of entire cost. The removable bar and clip attachment necessitated a longer time than any other type of prosthesis, while the single unit fixed restoration required the least amount of time. While the clinical fees per hour for multiple-unit fixed prosthesis and bar/clip overdenture were similar, they were substantially higher than the fees for single tooth and individual attachment. MacEntee⁴⁾ compared three designs of implant prosthesis over 12-years; 1) conventional denture, 2) removable implant prosthesis, and 3) fixed implant prosthesis. He reported that conventional denture were more favorable five times than removable implant prosthesis, ten times than fixed implant prosthesis.

But, the cost is not all, as mentioned in beginning. The choice of dental implant depends on several factors such as implant type, patient's economic, oral, physical, and psychological condition etc. In conclusion, if we consider in only cost aspect for patient, we will choose cemented type, one stage type, unsubmerged type, removable type, non-hydroxyapatite type.

Glass Ionomer Cement

December 16, 1999
Dr. Hee-Chang Park

Glass ionomer cements are being used more frequently as bonding agents in orthodontics. Glass ionomer (polyalkenoate) cements were invented in 1972 by Wilson and Kent. They have the favorable properties of the silicate cements (insolubility, hardness, the ability to release fluoride) and the adhesive properties of polycarboxylate cements. Glass ionomer cements have also been shown to adhere to base metal alloys and to plastics.

Glass ionomer cements, frequently have been used for the direct bonding of orthodontic brackets and cementation of orthodontic bands. The problem of caries lesions during and after orthodontic treatment is well known. In the absence of fluoride the caries process underneath an orthodontic band is fast and caries can develop cavities within 4 weeks. The frequency of mutans streptococci has also been reported to increase during orthodontic treatment. Fluoride reduce or prevent enamel decalcification and give rise to an increase of fluoride uptake in plaque. Svanberg et al. reported significantly lower viable counts of mutans streptococci on glass ionomer cement than on amalgam, while Hallgren compared frequency of counts of mutans streptococci on composite and glass ionomer cement, with the significantly lowest counts for the glass ionomer cement. The mechanism for the lesion inhibition of fluoride released from the glass ionomer is not clearly established. A possible explanation is that fluoride adsorbs onto the enamel and stabilizes the crystals. Fluoride is also generally acknowledged to increase the initial rate of remineralization. Below pH 4.5, fluoride will have a limited effect, since the liquid phasewill be undersaturated with fluorapatite.

It is known that glass ionomer cements are bound to enamel through calcium bridges, hydrogen bonds, or other Van der Waals forces; however the major important bonding mechanism is a ¡°phosphate substitution¡±. In this way, glass ionomer cements provide a stronger bond strength and are not as easily leached out as conventional cements. Fluoride released from glass ionomer cements had cariostatic properties. The use of glass ionomer cement for cementation of bands in orthodontic therapy has shown 75% fewer band failures than zinc-phosphate cement (White, 1986). However, orthodontic bands should be checked regularly, since fluoride released from the cement may inhibit lesion development incompletely under loose bands or in areas where the cement is missing. The use of glass ionomer cement for bonding for brackets, however, is significantly weaker than with composite. So far, different opinions have been presented concerning the possibility of using glass ionomer cement for bracket bonding as well as to how the enamel surface should be treated prior to bonding. Etching of the enamel did not increase the bond strength, which was found by Kullman (1986), and Cook and Youngson (1988), though in a different experimental set up, and the combination etching-polyacrylic acid also did not improve the adhesion. The enamel structure therefore seems to be less important. The water-hardening materials were in general found to have higher bond strength than conventional ones. Evans and Oliver (1991) also stated that increasing the powder liquid ratio in general creates a higher bonding strength. The choice of glass ionomer cement for orthodontic use should be a water-hardening glass ionomer cement and the use of different surface treatments can be restricted to the
recommendations of the manufacturer.

The properties of glass ionomer cements make them attractive for conventional bands and directly bonded brackets. Unfortunately, glass ionomer cements exhibit a prolonged setting reaction and a late gain of strength, and they are sensitive initially to moisture contamination and later to dehydration. The powder-liquid ratio is crucial in maximizing the physical properties and the proper setting of the cement. The most common cause of failure of the glass ionomer cement is incorrect proportioning and mixing. Glass ionomer cements should not be contaminated by moisture for 10 to 60 minutes after mixing and should be protected from dehydration for at least 24 hours. During the initial setting stage, moisture contamination will cause the matrix to become chalky and porous and will result in a loss of surface hardness. During the second phase, the matrix is susceptible to desiccation. The fast initial set of the light-cured glass ionomer enables them to be less susceptible to dehydration. The adhesive bond strength of the light-cured glass ionomer to enamel was greater than that of the chemically cured glass ionomer to enamel.

Enamel loss occurs during acid etching in the orthodontic bonding process. Debonding brackets and cleaning of composite resin residue cause scratches and facets in the enamel that promote plaque and stain formation. Unlike the resin filling-materials, glass ionomer cement negates the need for acid etching, thus preserving the integrity of the enamel prism and further protects the adjacent enamel by acting as a reservoir of fluoride ions to minimize the incidence of enamel decalcification. Glass ionomer cements can adhere to unetched enamel by physicochemical means, therefore reducing the need for mechanical retention and facilitating debonding.

Distraction Osteogenesis in the Maxilla

December 24, 1999
Dr. Hyun Kim

Distracton osteogenesis is a technique for bone lengthening which was introduced by Ilizarov at 1989. In order to the long bone lengthening, extrabony device with the turning screw is fixed to the bone surface and rigidly hold the bony segments. After placement of the distraction device, a corticotomy is performed and distraction is delayed 7 days to allow for revascularization of the wound and inflammation to subside. The optimum rate of distraction for long bone is 1 mm per day, and bone is formed within the gap due to the tension-stress effect. Usually about 6 weeks after the completion of distraction, bony union can be found. Slower distraction rates result in premature ossification and fusion, whereas faster rates result in fibrous tissue formation within the distraction gap.

Distraction osteogenesis is rapidly becoming an alternative technique to treat craniofacial dysplasias. In the oral and maxillofacial region, mandibular lengthening by this technique was performed experimentally in dogs by Snyder et al, about 27 years ago. And many other investigators reported experimental studies and clinical reports on mandibular lengthening by distraction osteogenesis with extraoral device. At 1994, Block and Brister showed the possibility of maxillary advancement in dog by distraction osteogenesis, using an intraoral device supported by the teeth.

Advancement of the anterior maxilla is often required to correct a skeletal deformity especially in cleft lip & palate patients. Maxilla advancement with LeFort I osteotomy is a common method used to correct the profile and occlusion of maxillary hypoplasia patients. But, it has some limitations. Advancement amount is limited because of the restraints caused by the palatal and crestal soft tissue, and can aggravate the speech problems in the cleft patients. This surgical procedure requires a rigid internal fixation hardware for stabilization of the repositioned maxilla. Moreover, long-term study of cleft lip & palate patients treated with maxilla advancement surgery reported the increased relapse tendency. Otherwise, the use of distraction osteogenesis in maxillary advancement needs no screw fixation and bone graft. It can provide significant movement with better stability also. So several studies about distraction of maxilla have been performed with various aspects.

At 1995, distraction osteogenesis study to advance the anterior maxilla of the dog using a totally tooth supported distraction device was performed by Block et al, and resulted in greater tooth movement than skeletal movement. So they concluded that perhaps the use of endosseous implants or other bone anchors may be necessary to provide skeletal fixation and hence achieve more equal and predictable bone and tooth movement in the maxilla.

At 1997, Yamamoto et al reported the study about the distraction osteogenesis in maxilla of the dogs, using an osseointegrated implant and intraoral device. After extraction of the premolar and molar teeth, four titanium implants were installed in the maxillary alveolar bone. Three months later, device setting and osteotomy was performed and, at the rate of 1 mm per day, screw was turned to obtain a 10 mm elongation. At 2 weeks after completion of distraction, fibrous connective tissue was evident in the distraction gap, and by 8 weeks, the matured regenerated new bone was visible. And no bone resorption was observed around the fixtures, even after stabilization period.

Recently, case reports that treated the cleft maxillary hypoplasia patients with a rigid external distraction device have been presented. Figueroa & Polley reported that 14 cleft patients who treated using the rigid external distraction device showed dramatic improvement in facial, skeletal, and dental relations with minimal modality.

Distraction osteogenesis can be applied at an earlier age than traditional orthognathic surgery because the technique is relatively simple and bone grafts are not required for augmentation of hypoplastic craniofacial skeleton. In this technique, the surgeon and the orthodontists have become collaborators in a process that gradually alters the magnitude and direction of craniofacial growth.

Etching Time and Bond Strength

December 31, 1999
Dr. Jung-Suck Lee

Bonding of orthodontic brackets as well as different types of retainers and space maintainers to enamel surfaces has developed rapidly in recent years. In order to improve hygiene, there has been a tendency to Use minimal contact areas for their retention. Composite resin has been used in orthodontics for more than 20 years since its first application. The accepted mechanism of bonding involves etching of the enamel surface. The direct bonding of orthodontic attachments to acid-etched enamel is an accepted clinical procedure. The concept of etching enamel surfaces with orthophosphoric acid (H3PO4) was first introduced by Buonocore in 1955. He reported that the bond strength of acrylic restorative resins to enamel was significantly increased when the enamel surface was etched with phosphoric acid. Silverstone suggested that etching of enamel with phosphoric acid results in a superficial etched zone and subsurface qualitative and quantitative porous zones. The enamel from the superficial etched zone is permanently lost but the subsurface porous zones remineralize in the oral environment. The curing dental resin flows into the porous zones and establishes a mechanical bond to etched enamel. The depth of etch or the amount of surface enamel lost during the etching procedure is dependent on the type of acid used, the acid concentration, the duration of etching, and the chemical composition of enamel. Silverstone found that phosphoric acid in concentrations between 20% and 50%, when applied to the enamel for 60 seconds, created the most retentive conditions. However, he did not study shorter etching periods. In a recent study no apparent difference was found between 15 and 120 seconds of etching with 37 percent phosphoric acid solution. This suggests that a shorter etching time might be acceptable. Nordenvall et al. conducted serial studies of different etching times on deciduous and young and old permanent teeth and found on young permanent teeth that 15 seconds of etching created a more retentive condition than 60 seconds. They used the degree of surface irregularities as an indicator for the quality of mechanical retention. Therefore it did not indicate the absolute bond strength. Barkmeier et al. found neither qualitative differences in the enamel surface structure nor differences in bond strength after etching for 15 or 60 seconds with a 50% phosphoric acid. However, the study did not use wide ranges of etching time or count the percentages of the bond failure interface distributions. Wang et al. compared the tensile bond strengths for 15-, 30-, 60-, 90-, or 120-second etching times with 37% phosphoric acid on the buccal surfaces of young permanent teeth. Bond failure locations on tooth surfaces and bracket bases were examined by scanning electron microscope and calculated with mapping of energy dispersive x-ray spectrometry to analyze the distributive percentages. The results of bond strength are as follows. There were no statistical differences among etching times of 15, 30, 60, or 90 seconds. However, etching for 120 seconds gave significantly less bond strength than others. The conditioning of the enamel surface with phosphoric acid causes loss of enamel surface contour. Furthermore, there may be a possibility that etched enamel is predisposed to the development of initial caries resulting in discolorations such as white spots. Even after removal of the brackets, the histologically changed tooth structure may be more susceptible to decalcification processes. Only a few investigators have published experimental results about the actual amount of bulk enamel loss that etching produces. In his studies Gwinnett applied different types of acid on enamel surfaces for a period of 2 minutes. He found that 50 percent phosphoric acid produced a bulk enamel loss in excess of 5 microns but always less than 25 microns.

Silverstone investigated the effect of etching durations of different types of etching solutions at various concentrations. His results show less loss of tissue with increasing acid concentrations, whereas the first minute's etching caused the greatest effect. A possible explanation of the differences in enamel solubility may be the biologic variation in structure and composition of the various enamel samples investigated. Moreover, the fluoride concentration of the enamel at the surface plays an important role in the reduction of enamel solubility and, consequently, in the loss of bulk enamel due to etching. High fluoride concentrations (>50 ppm) slow down the dissolution of bulk enamel in phosphoric acid. It has been shown that plaque readily accumulates on or adjacent to bonded attachments. The caries risk and enamel decalcification can be greatly reduced by good oral hygiene and the application of topical fluorides or the use of fluoride-containing dentifrices during orthodontic treatment. Other methods of topical fluoride application before orthodontic therapy have been suggested to increase the resistance of enamel to decalcification. These procedures include the application of topical fluorides to the enamel surfaces before acid etching, the incorporation of fluorides in the etching solutions, and the topical application of fluorides to the etched enamel surfaces before bonding.

Although variations occurred in the types of etching patterns produced by the various phosphoric acid solutions, the irregularities and porosities on the enamel surfaces should provide adequate mechanical retention of the resin to the etched enamel surfaces.

The Role of Folic Acid in Prevention of Cleft Lip and Palate

January 7, 2000
Dr. Jin-Hyoung Cho

In practice, we, as orthodontists, have met many cleft patients. If our children are born with cleft, what can we do for them? In most cases, they will experience long period therapy that is consist of lip and palate surgery, orthodontic therapy, psycho-, speech therapy, orthognathic surgery. It is enough to make our heart break, so we try to find out prenatal diagnoses of cleft lip and palate by screening obstetrical ultrasound and high resolution obstetrical ultrasound done for these reasons. Moreover Jensen et al. have previously reported an increase in cleft lip and palate incidence in recent years.

How can we prevent these anomalies?
Recently I read interesting article associated with preventing oral clefting, so I will introduce it to you.

It had been suspected for many years that a mother's periconceptional diet may have a role in the causation of birth defects. In 1991, a multi-centre recurrence study produced good evidence to recommend folic acid supplements to prevent neural tube defects in mothers who previously had an affected pregnancy.
Not surprisingly, since facial mesenchyme is derived from neural crest, it was postulated that periconceptional folic acid supplementation may reduce the occurrence of offspring with orofacial clefts. Naturally occurring folates are found widely in foodstuffs, especially in liver, yeast extract, legumes, and fresh greenleafed vegetables. Folic acid is a commercially available compound used for supplementation or food fortification. It does not occur naturally in living tissues, but is readily converted in vivo into the biologically active folates.

In combination with specific enzymes, folates act as co-enzymes in the transfer of one-carbon units in many biochemical reactions involving amino acid matabolism. Folates are essential in the synthesis of purines and pyrimidines, which are components of DNA and RNA required in the regulation of gene expression and cell differentiation.
Certain anti-folate drugs have been shown to be teratogenic and the use of valproate drugs during pregnancy, for the treatment of epilepsy, has been associated with a 5- to 20-fold increase in the incidence of neural tube defects. The most carefully controlled studies involve animal models, where an increased risk of oral clefting in animals given folate deficient diets or anti-folate drugs has been observed. In humans, drugs which interfere with folate metabolism, for example, phenytoin, are known to have teratogenic effects. Low blood folate levels were associated with spontaneous abortion and developmental abnormalities of the foetus.

There appears to be an association between maternal smoking and clefting. Khoury et al. found that mothers who smoked were 1.6-2 times more likely to have offspring with isolated oral clefts. Smokers are also known to have significantly lower folate status than non-smokers, but it is not known if the decreased folate levels in smokers is due to decreased folate intake or increased folate requirement. Clearly, there is potential to rectify folate levels in mothers who persist in smoking during pregnancy.

Current recommendations to prevent neural tube defects, advise all women planning to conceive a child to supplement their diet with 0.4 mg folic acid from preconception to the twelfth week of pregnancy. Women with a previously affected prognancy should take 4 mg folic acid daily. The protective effect for periconceptional folic acid on oral clefting has not been proved conclusively. However, studies have found significant protective effects and the above guidelines should be adhered to.

In addition, the national health system in many advanced nation covers all expenses of hospital treatment, speech therapy, orthodontic and prosthodontic treatment, accommodations, and transportation for the patient and the parents. In my country, many cleft patients make a living with a hope by this social security prepared as soon as possible.

Orthodontic Office Design

January 21, 2000
Dr. Jeong-Soon Ahn

All practicing dentists must at sometime grapple with the matter of office design. New graduates usually spend many hours deciding on an office layout to meet their expected needs. A modern orthodontic office may be broken down into six areas according to function 1) treatment area, including records room and tooth brushing area, 2) reception room, 3) laboratory, darkroom, supply storage, 4) consultation room, 5) receptionist's office, including business area, 6) rest room. In a well-designed office the treatment area should comprise about 45% of the total office. It should include an record room designed to contain all x-ray equipment, the study models and x-ray record folders of all current patients, and a chair for record impression taking and examinations at minimum. A patient tooth brushing alcove or preventive dentistry niche at the edge of the treatment area should be provided  this serves not only for each patient's preappointment oral hygiene but also for patient education in general. The reception room should occupy approximately 15% of the total square footage making it the second largest component of a functional, efficient office. The laboratory, darkroom, and supply storage areas, collectively, should involve 12% of the total office area. The consultation room and private office area should occupy approximately 10% of the total square footage. Case presentations and examination reports to parents are conducted in the consultation room. A separate consultation area, apart from the rest of the office, is ideal. Often, it is best located near the receptionist area, since the receptionist will generally be responsible for greeting new patients and directing them to the consultation area. Entrance directly from the waiting room to the consultation room might be desirable, but not necessary. An exit from it should be convenient to the appointment desk for reappointment. If the records room or exam room is adjacent to the consultation room, parents can wait in the consultation room while records are taken in the adjoining room. The receptionist's office including secretarial and business areas encompasses 9%. The rest rooms, both public and private, should consume approximately 3% of the available space. Lately more orthodontists are designing children's areas as part of their internal marketing. Patients' younger brothers and sisters are potential patients themselves, and it makes sense to make them feel comfortable in our office. It is another subtle way to show patients and their families that you care about their individual needs.

When patient enter the our office, To create a sensation of openness, comfortable and relaxed feeling, in general, any room will feel and appear larger with windows. Blend objects from one side of the window to the other plants, similar wood patterns, same carpeting to create a feeling of space. Wall of dark or busy colors make objects or walls come forward, contracting space. Light, monochromatic color schemes make a room feel larger. Avoid paneling in small areas, especially dark stained paneling on all four walls. Using the same color or wallpaper throughout makes a space seem larger. Consider armless sofas and chairs in cramped quarters. Select thinline styles with reflective surfaces. Avoid bulky, overstuffed upholstered furniture. Use glass-top tables in areas where high maintenance is not a problem. Avoid clutter. Keep lines plain and simple throughout. Too low a ceiling creates a cramped feeling in a small room. Pitch to a ceiling helps, if planned in advance. A floating ceiling effect can be applied even to a small area, and is decorative. Mirrors in good taste and with proper planning can expand a ceiling. Glass panels or a complete glass wall between rooms create a feeling of space, and can be functional for visual communication. A full glass door with thin metal frame opens up a room. A door with a wider wooden framework can do the same and has a warmer appearance. A long, vertical panel of glass within the door can be stylish and functional. Finally, Color has also an important role in hospitals. Orthodontists should also pay attention to the color needs of patients. Busy adult patients want a relaxed feeling, while younger patients should be stimulated into action. Cool colors can make a room seem larger, warm colors have the opposite effect. Floor color should be mostly uniform throughout an office so that a series of spaces can be tied together effectively. This increases the apparent size of each room and forms a good visual platform for the rest of the decor. The lighting should not be harsh, but rather generalized in nature.

Today, all dentists must consider factors such as work simplification, traffic flow, applied psychology, and the utilization of auxiliary personnel when planning an office.

Usefulness of mini-implant as an anchorage in orthodontic treatment

January 28, 2000
Dr. Sang-Yeol Lee

Implant-based anchorage in orthodontics is increasingly obtaining significance. In recent study, histological analysis of the implant-bone interface was performed following the retrieval of implant which were subjected to prolonged oblique orthodontic loading. And several results of histomorphometric study indicated that all the implants serving for orthodontic anchorage were well integrated into the bone despite the prolonged application of the orthodontic loading. Hence, it may be concluded that small-size, one-part transmucosal implants with a self-tapping thread seemed provide adequate anchorage for orthodontic therapy. Furthermore, the successful integration and the subsequent oblique loading of these orthodontic implants provide evidence that continuous forces in the order of magnitude of 2-6 N are compatible with the maintenance of osseointegration. Osseointegrated titanium implants have been used successfully to replace missing teeth, but their use for orthodontic anchorage has been limited by space. Conventional dental implants can only be placed in retromolar or edentulous areas. Another limitation has been the direction of force application: a dental implant is placed on the alveolar ridge and is too large for horizontal orthodontic traction. Furthermore, dental implant are troublesome for patients because of the severity of the surgery, the discomfort of initial healing, and the difficulty of oral hygiene. The problems related to anchorage are far from solved, and, especially in partially edentulous patients or where the need for tooth displacement represents an inconsistent configuration (eg, all teeth have to be moved in the same direction), introduction of the extradental intraoral anchorage system has been welcomed. Three types have been introduced: the osseointegrated implant, the on plant, and the use of wires directly from the zygomatic arch. However these types of anchorage have their limitations and drawbacks. For implants the costs, especially when the implant can not be used as part of the post-treatment reconstruction, can be considered an important factor. The delay of the loading for several months is another drawback that may be of importance in severely degenerated cases. The intervention necessary for removal of the unusable implants has further prevented many clinicians from using implants for anchorage only. The onplant suffers from the same disadvantages as the implants with respect to cost and delay but seems to be considerably easier to remove following treatment. One drawback, however, is that the location of the onplant seems to be limited by the morphology of the osseointegrating surface. Zygoma wires are also limited by location, but they have the advantage of immediate load.

With this information a new type of intraoral extradental anchorage, a mini-implant(screw), is suggested. A mini-implant for orthodontic anchorage should be small enough to place in any area of alveolar bone, even apical bone. The surgical procedure should be easy enough for an orthodontist or general dentists to perform and minor enough for rapid healing. The implant should be easily removable after orthodontic traction. Conventional dental implants are 3.5-5.5 mm in diameter and 11-21 mm long. The mini-implant is only 1.2 mm in diameter and 6 mm long, making it much more useful in orthodontic applications. Besides intrusion, mini-implant could be used for horizontal traction if placed on the alveolar ridge. The screw is small enough to be inserted between the mesial and distal roots of a molar for molar intrusion, or, if placed in the palate, could provide anchorage for molar distalization. Another possible application is distraction osteogenesis, with the implant placed intraorally instead of extraorally. Oral hygiene is easier to maintain with the ligature wire tied to an attached hook rather than directly to the screw head. Care should be taken to prevent postoperative infection from inflammation of the peri-abutment mucosa. However, the mini-implant is too small to cause irreversible damage, and can be removed any time either the orthodontist or the patient desires. Bone healing after removal should be uneventful.

Chincap in Class III patients

February 11, 2000
Dr. Wang-Sik Kim

Chincap therapy to correct mandibular prognathism has been used clinically for over a century. This therapy attempts to retard or redirect the growth of the mandible to obtain a better anteroposterior relationship between the two jaws.

Many studies have showed that Chincap decreased in the prechondroblastic layer of the condylar cartilage that led to a decrease of bone formation at the condyle. Similar growth retardation was reported by Matsui and Noguchi. These findings seem to demonstrate retardation of vertical growth of the ramal height as reported by Graber and Suzuki. Thilander, however, insisted that little effect on skeletal components with chincap force. She found a slight posterior shift of the mandible, suggesting a condylar response to the mechanical stimuli.

There are two factors contribute to a decrease of mandibular body length. Increase of the mandibular body length is generally achieved by the bone apposition at the posterior border of the ramus along with bone resorption at the anterior border of the ramus. This mechanism requires the mandibular body to displace forward to increase or maintain a normal pharyngeal airway and deglutitional function. Because the chincap force restricts such forward displacement of the mandibular body, the remodeling pattern of the posterior border of the ramus is most likely suspected. Thus, growth inhibition may take place in this region when such restriction is maintained for a long period. In some cases the thickness of mandibular symphysis is decreased during chincap therapy. Therefore, the remodeling of the chin morphology at the pogonion area may contribute to a decrease of body length to some extent. Thus, the mandible may respond to the force in the area where the force is applied either directly or indirectly.

During chincap therapy, there are many cephalometric changes. Mandibular ramal length (Ar-Go), mandibular body length (Go-Pg), and total mandibular length (Ar-Pg) showed a percent decrease of between 60% and 68% from the non-treatment Class III patients. The horizontal and vertical components of pogonion (Pg) change were used to indicate mandibular directional changes. During treatment, pogonion showed a 43% decrease in downward displacement from the control. The posttreatment effects showed just the opposite. There was a 60% increase in downward displacement of pogonion. The anterior facial height measurement (N-Me) was highly significant for effects associated with active therapy. Compared with the nontreatment Class III, there was a 39% decrease in anterior facial height related to chincap therapy. The changes in the dentition showed interesting results. In general, there was a retardation of the eruption of the mandibular dentition. The molars were displaced anteriorly 50% further than the controls during treatment and 90% further following active therapy. The incisors were displaced anteriorly 26% during treatment but showed a posterior displacement of 10% following treatment relative to the Class III control sample. Sugawara and Mitani studied long term effects of chincap therapy on skeletal profile in mandibular prognathism. In this study, they used 63 Japanese girls and divided into 3 groups according to their ages when chincap therapy was started; 7, 9, 11years old. The final skeletal profile of each group show no significant difference between the anteroposterior positions of the mandible when compared with those of the control sample. However, there is a statistical difference between the vertical position of the mandibles of patients who began treatment at age 7 and the mandibles of the control groups. Pearson and Heckman reported that the chincap could control dentoalveolar growth and reduce lower facial height. It may indicate that the mandibular position is more alterable vertically than anteroposteriorly, and such effects could exist for a longer period in the face.

From the standpoint of long-term results, we should not overestimate the effects of a chincap appliance to correct skeletal facial profiles. Also, it is important that a chincap should be applied within limitations on the basis of proper diagnosis and treatment objectives.

Incisor Position

March 9, 2000
Dr. Sung-Ho Han

Of concern to patients and practitioners at the completion of active orthodontic treatment is the degree of anticipated stability. The positions of maxillary and mandibular incisors have long been recognized as useful guides in the diagnosis and treatment of malocclusion. Correct incisor position is generally acknowledged to be the key to successful orthodontic treatment. Also, stable incisor positions are considered to influence the stability of orthodontic results. Especially, mandibular incisor position is of critical importance during orthodontic diagnosis and treatment. Because posttreatment maxillary incisor position is determined by mandibular incisor position, the clinicians must have an analysis. Tweed gave the speciality guidelines for mandibular incisor position. He stated that the mandibular incisors should make angle from 85°to 95°with the mandibular plane if the mandibular plane to Frankfort Horizontal plane angle is in the 22°to 29°range.

Steiner's ideal values for his measurements include an ANB angle of 2°, maxillary incisors at 22°and 4 mm to NA line, mandibular incisors at 25°and 4 mm to NB line, and interincisal angle of 131°. He suggested that the individual position of the mandibular incisors is dependent on the individual ANB angle and prominence of the bony chin, following the Holdaway ratio.
Ricketts et al. focused on the A-Po line. And their norms are based on the mandibular incisors at 1 mm(±2 mm) and 22°(±4°) relative to this plane. Also, he favored an interincisal angle of 125° in brachyfacial types, increasing to 135° in dolichofacial types.

Mills analysed the lower incisor position using a cephalometric SNI angle(I = tip of lower incisor). Hasund was essentially changed Steiner's analysis. He introduced the 'floating norm' concept by modifying ideal incisor position to take account of the skeletal anterior-posterior discrepancy and chin prominence as guiding variables. Holdway derived his soft tissue analysis. He concluded that a single hard tissue measurement is inappropriate.

In spite of the widespread use of lower incisor positioning formula in treatment planning, there are few evaluations of the clinical effectiveness of the these methods. Tweed mentioned that application of the Tweed triangle is successful for majority of his treated cases, but except minority worsening of facial esthetics. He has attributed this to the inappropriateness of the 65°goal in patients exhibiting certain growth patterns. And so this principle is later modified by Tweed to consider vertical skeletal discrepancy; If FMA is above 30°, the desired FMIA is 65°. If FMA is 22°to 28°, the desired FMIA is 68°. If FMA is below 20°, IMPA should not increase 98°. But Holdaway felt that failure to take into account soft tissue morphology is responsible. Anderson et al evaluated 70 cases treated to the Tweed philosophy. He found that the lower incisors had been moved lingually with respect to N-Po line 2-3 mm. No significant change was evident in reevaluation 10 years out of retention.

Using the 'chevron' diagrams from Steiner's analysis is largely unchallenged with respect to incisor positioning. Servoss has attempted to discount the origin of acceptable compromises.

Williams evaluated Ricketts A-Po line. He felt that A-Po line is the key to lower incisor positioning in achieving lip balance and stability. But he suggested that lower incisor to A-Po line is less important that the crown position. Shulhof et al. concluded that the maxilla is important when determining the incisor position, and that A-Po line is a useful reference line in respect of stability and lip harmony.

Lindquist observed that application of Tweed, Steiner, Ricketts methods arrived at different incisor prognosis. He concluded that linear measurements are more successful than angular measurements, no method or formula is ideal.

Mill's concluded that lower incisor position is not changed as a result of treatment. This concept has been supported by Hixon and further emphasized by Riedel. But Schulof has rejected this theory on the basis of result achieved by Ricketts. Brenchley has shown cases where the incisors were moved by treatment towards the A-Po line only to relapse later, but he pointed out that skeletal and soft tissue morphology is extreme, and growth is unfavorable in each case.

In conclusion, the position of the lower incisor is of importance in treatment planning. Tweed triangle, Shevron's diagrams from Steiner's analysis, A-Po line from Ricketts are widely used as a determining method of incisor position. But various limitations are clear; most rely heavily on various cephalometric points, lines, and planes which are they subject to variation and errors in identification. Also growth and the response to treatment are still not completely predictable and further limit the value of prognosis.

Reducing Radiation Exposure in Orthodontic Patients

March 17, 2000
Dr. Il-Sun Yun

High quality radiographs are essential in the successful treatment of orthodontic patients. The goal of high-quality films should not compromise the need for minimal radiation exposure to the patient. Unfortunately, there is no absolute amount of radiation that can be administered to a patient with the assurance that there will be no damaging effect.

The essential point is not whether a risk exists but rather its quantification. Many orthodontic patients are adolescents or young adults and consequently have an increased statistical risk from radiation due to rapid growth of organs and organ systems. The thyroid, with its anatomically superior position in children, is especially sensitive to radiation. Children also experience a longer duration for the effects of radiation to become apparent. This is critical because the latency period for radiogenic cancer is 20 to 35 years or more.

Radiation protection concepts that involve the setting of maximum permissible doses for occupational exposure and dose limits for population exposure seem inappropriate. The National Council on Radiation Protection and the International Commission of Radiation Protection have made recommendations that are summarized by the principle of ALARA (as low as reasonably achievable). When applied to patients the ALARA concept means that diagnostic radiographs should be exposed using every available dose-reducing means consistent with good diagnostic quality. Because dental radiography is only one part of any patient's lifetime radiation experience, including background radiation, it is essential to limit its contribution. We have no idea how much diagnostic radiation a person will require in his/her lifetime.

So I am going to describe many available techniques that have been presented in the literature to limit exposure while satisfying diagnostic criteria.

1. Screen / Film Combinations

Exposure of film emulsion to light from fluorescent or intensifying screens started in 1896 shortly after the discovery of x rays. The screens emit either a blue or green visible light image when irradiated by x-ray energy. The cephalometric radiography's latent image is therefore produced primarily by light from the two screens, rather than by the x-ray photons themselves.
Currently there are two groups of intensifying screens used in extraoral radiographic procedures. Screens coated with calcium tungstate, which emit light from the blue portion of the visible light spectrum when energized by x-ray photons. The relative film speed is 200. The other is coated with gadolinium and lanthanum, which emit green light and are known as rare earth screens. This film speed is 400.

2. Shielding and Collimation

Optimal radiation hygiene requires that the field size be limited to only those areas that yield diagnostic information. On the basic level, patients should always be draped properly with a lead apron before any radiographic procedure.
The basic function of collimation is to regulate the size and shape of the x-ray beam to those areas of diagnostic interest. L'Abbe and Tan described a method for reducing the irradiated area of a patient by 77% using a properly collimated beam for lateral cephalometric radiographs. Hirschmann and associates found a 55% reduction in field size with a similar collimating device.

3. Quality Control

Because of the greater speed and therefore sensitivity to light of rare earth films, a darkroom must be absolutely light tight and use the proper safelight that is matched to the film. The film should be tested under darkroom conditions. Distance, bulb size, and exposure time are just as important, even with the correct filter, because most emulsions have only reduced sensitivity to light outside their useful exposure range. Under the ideal circumstances, a safelight is only safe for a certain period of time.
The techniques and procedures described are valuable methods for reducing radiation exposure in orthodontic patients. We have the responsibility to maintain high radiographic standards, to minimize radiation to our patients, and to expand our efforts in educating the public on the health benefits of these low-risk procedures.
I would like to appreciate your listening.

Patient Cooperation

March 24, 2000
Dr. Eun-Jeong Kim

A cooperative patient is an essential of successful orthodontic treatment. The literature on co-operation also refers to compliance and adherence. Patients are more likely to co-operate with orthodontic treatment, if they are satisfied with the way in which their orthodontist communicates with them and if the orthodontist decreases their anxiety. Co-operation has been examined in terms of patient's keeping their appointments, wearing their elastics, headgear or functional appliances, keeping their teeth clean and refraining from chewing substances which will distort their archwires or de-bond their brackets.

In 1997, Ma Mphil represented eight important factors that should improve patient cooperation.
1) Being polite, friendly and making the patient feel welcome.
2) Having calm, confident manner.
3) Giving information about the problem, the proposed treatment plan and the procedure you are going to perform.
4) Not using jargon
Sometimes, it is hard to recognize when you are using jargon, particularly when you have become very familiar with the terminology.
5) Paying attention to what the parent and child says.
6) Reassuring the child that you will do everything to prevent pain.
7) Express concern about the child's well being.
8) Do not criticise the child's tooth brushing or oral hygiene.

Reward charts can be used in many situations e.g. to help a child stop sucking their thumb, to encourage a child to wear a functional appliance or headgear and to improve oral hygiene. To follow are some basic guidelines, in which encouraging a child to wearing their functional appliance is used.
1) Establish a baseline chart
In 1993. Cureton et al have shown that children who were given a headgear calender complied better than children who were not.
2) Set the reward at an achievable level.
3) Decide on rewards.
4) Giving a child their own individual package will make them feel important.

To promote and measure compliance with extraoral traction, timing headgear was developed by the Aledyne Corporation, first for cervical -pull and later for high-pull headgear. Northcutt claimed that headgear wear increased from 35-50 hours per week too more than 100 hours per week after he introduced this timer.

When a patient is co-operating poorly, the first step is to examine whether you can improve the way in which you are communicating with the child and their parents. You could also give the child a chart to record their use of their appliance or you could follow the above guidelines and set up a reward system. If these steps are followed, you should be faced less frequently with the need to abandon orthodontic treatment.

Clinical Consideration About Root Resorption During Orthodontic Treatment

March 31, 2000
Dr. Yeun-Soo Lee

All permanent teeth may show microscopic amounts of root resorption that are clinically insignificant and radiographically undetected. Root resorption of permanent teeth is a probable consequence of orthodontic treatment and active tooth movement. The incidence of reported root resorption during orthodontic treatment varies widely among investigators. Usually, extensive resorption does not affect the functional capacity or the effective life of the tooth. Most studies agree that the root resorption process ceases once the active treatment is terminated

Root resorption of the deciduous dentition is a normal, essential, and physiologic process. Permanent teeth have the potential to clinically undergo significant external root resorption when affected by several stimuli. This resorptive potential varies in persons and between different teeth in the same person. This throws doubt on the role of systemic factors as a primary cause of root resorption during orthodontic treatment. Tooth structure, alveolar bone structure at various locations, and types of movement may explain these variations. The extent of treatment duration and mechanical factors definitely influence root resorption. In most root resorption studies, it is not possible to compare the results and conclusions because of their different methods. Further research in this field is necessary to advance the service of the specialty.

Many studies indicate the unpredictability and widespread incidence of the root resorption. The question of whether there is an optimal force to move teeth without resorption or whether root resorption may be predictable remain unanswered.

Therefore, the following is clinically considered during orthodontic treatment.
1. The patient or his parents must be informed that apical root shortening may be a consequence of orthodontic treatment
2. Since it is impossible to predict the onset of root resorption, periodic control radiographs are indicated
3. Orthodontic treatment should begin as early as possible since there is less root resorption in developing roots and young patients show better muscular adaptation to occlusal changes. Adults have poorer adaptive ability and need more rigid and longer lasting mechanical forces.
4. The orthodontic force should be intermittent and light.
5. When root resorption is detected during active treatment, final goals must be reassessed.
6. Habits should be stopped, since it was shown that root resorption is more severe in such orthodontic patients.
7. All types of tooth movement can cause root resorption. It seems that intrusion is the most detrimental.
8. Occlusal traumatism is potentially detrimental to the roots, and it is suggested to finish treatment with a correct occlusion.
9. Orthopedic effect in the early treatment phase has less destructive potential on the roots compared with the dentoalveolar effect at a later treatment phase.
10. In choosing treatment appliances, the risk of root resorption should be weighed against appliance efficiency and individual treatment objectives.
11. Treatment time should be as short as possible.
12. Traumatized teeth should be treated cautiously since they are more prone to root resorption during orthodontic treatment.
13. If root resorption continues after appliance removal or during retention, sequential root canal therapy with calcium hydroxide is advisable. Gutta-percha filling is the definitive therapy only after root resorption ceases.

References
1. Brezniak N, Wasserstein A. Root resorption after orthodontic treatment: Part 1.
Literature review. Am J Orthod Dentofacial Orthop 1993;103:62-66
2. Brezniak N, Wasserstein A. Root resorption after orthodontic treatment: Part 2.
Literature review. Am J Orthod Dentofacial Orthop 1993;103:138-146
3. Acar A, Canyurek U, Kocaaga M, Ererdi N. Continuous vs. discontinuous force application and root resorption. Angle Orthod 1999;69:159-164

Anterior Open Bite Treatment With Magnets

April 7, 2000
Dr. Jae-Nam Kim

The difficulties, which arise during treatment of anterior open bites, have challenged many orthodontists. Treatment of this malocclusion has been based on one of the following principles: extrusion of the anterior teeth, which is often unsatisfactory due to a poor aesthetic result: and intrusion of the posterior teeth, resulting in auto-rotation of the mandible anteriorly. One of the treatment methods that have been used for intrusion of the posterior teeth has been the posterior bite block, where the intrusive forces are generated by the masticatory muscles.

In 1986, Dellinger, who achieved intrusion of the posterior teeth by means of repelling magnets, described a new method in the literature. In 1988, Woods & Nanda saw little difference between the results of these "active" appliances and "passive" biteblocks without magnets in growing baboons and questioned whether the intrusive effects are due to the magnets incorporated in the appliance systems or whether the changes are due solely to the increased vertical dimension caused by the acrylic blocks themselves. They concluded that since similar responses were produced with both magnetic and nonmagnetic bite blocks, it would appear that the altered maxillary displacement, changes in mandibular shape, and depression of buccal teeth could be attributed as much to the muscular response to the artificially-increased vertical dimension as to the presence of the repelling magnets.

Von Fraunhofer and Bonds questioned the use of magnets for clinical use because of their rapid decrease in force with separation as well as their cost. In 1990, Stavros Kiliaridis et al. reported that the effect of using repelling magnets for treatment of anterior open bite and to compare them with the use of acrylic posterior bite-blocks. They have found that the use of repelling magents in the treatment of the anterior open bite produced a quick response in the dental and skeletal vertical relation in the growing individuals. However, transverse problems, unilateral cross bite were observed. Using a less powerful magnet system of decreasing the treatment time could possibly diminish this side effect. Furthermore, a guiding flange in the palatal side of the upper splint might counterbalance the lateral forces. Non-active acrylic posterior bite-blocks also showed improvement in the dental and skeletal vertical relation, but it was neither so rapid nor so extensive. Nevertheless, no transverse problems were noticed. Both appliances caused an intrusion of the posterior teeth, with intrusive forces generated by the masticatory muscles.

The repelling magnets, however, transferred continuous forces to the posterior teeth, varying in magnitude according to the distance between the magnets; the closer the magnets, the higher the force, while the biteblock appliance transferred intermittent forces to the teeth only when it was in contact with them.

In 1996, Noar et al. have shown that the forces produced by magnets are affected severely by their relative position and that the force levels fall dramatically with increasing separation, particularly if the magnets are not aligned optimally. The jaw is constantly in motion and capable of movement in three planes of space, such that the magnets will rarely be in perfect alignment

We have described that magnet has various problems such as high cost, difficulties in manufacturing, weakness of force during its use. It, however, has benefits that it can shorten the time for whole treatment and also treat severe open bite. If the side effect of magnet are abolished or at least, minimized with many studies, it would be successfully employed for patients in growing stage whom have open bite. On the other hand, we recommend POBB and chincap, which are used in this orthodontic department as a method for the treatment of growing patients with anterior open bite. Thank you.

Effects of the Twin - Block Appliance

April 21, 2000
Dr. Young-Ah Yun

Functional appliance therapy has become an popular method of correcting Cl.¥± malocclusion with appliance such as the bionator, the FR-2, Herbst appliance, Bass appliance and the twin block appliance. William J. Clark developed the twin block for use in the correction of Cl.¥± malocclusions.

Treatment effect of twin block may be listed as follows.

1. Significant decreases in overbite and overjet.
The overjet was reduced by combination of maxillary incisor retroclination, mandibular incisor proclination and forward movement of mandible.
2.Increase in mandibular length with an anterior movement of pogonion and point B.
Approximately two thirds of the overall length increase could be attributed to an increase in ramus height and the remaining one third was the result of an increase in the mandibular body length.
3. No significant restriction of maxillary growth and the least forward movement of point A.
4. A reduction in ANB.
It was largely the result of an increase in SNB.
5. A significant increase in lower anterior facial height.
6. The twin block appliance produced significant dentoalveolar change
  1) Retroclination and extrusion of the maxillary incisor.
  2) Distal movement and no extrusion of the upper molars
  3) Proclination of the lower incisor.
  4) Lower molar extrusion
7. Significant soft tissue changes occured.
  1) Upper lip position remained stable but lower lip protrusion and lower lip length increased
  2) Soft tissue lower and total face height increased significantly
8. A definitive muscle response of anterior temporalis and masseter muscles was observed.
It is indicating neuromuscular adaptations to the altered posture of the mandible.

Thus, Cl¥± correction can be achieved with twin block appliance. Twin block appliance produces both skeletal and dentoalveolar effect. Further modifications to the twin block appliance might attempt to minimize dentoalveolar tipping and to maximize skeletal change by including the use of headgear.

Forced Eruption and Implant Site Development : Soft Tissue
Response

May 12, 2000
Dr. Kwon-Hee Jeong

The increased use of implants in orthodontics has stimulated interest in augmenting bone in patients who have deficient alveolar ridges that preclude ideal implant placement. A nonsurgical procedure for increasing the amount of available bone for implant site development & fixture placement is orthodontic extrusion or forced eruption.

Implant site development guided by forced eruption enhances two specific areas: the hard tissue component & the soft tissue component. Both of the areas are essential to the success of an implant restoration. The volume of the osseous structure must allow for implant placement in an ideal situation for the restoration, whereas the anatomic topography of the soft tissue must mimic that of the adjacent soft tissue architecture. The initial effect of orthodontic tooth movement on the gingiva has been studied.

Reitan demonstrated that eruptive tooth movement resulted in a stretching of the gingival & periodontal fibers, which produced a coronal shift of bone & gingiva. Elongation of the tooth in its alveolus causes a stretching of the gingival & periodontal ligament fibers. This results in a coronal shift of the bone at the base of the defect as the tooth moves occlusally. Kokich has demonstrated the relationship between tooth position & gingival esthetics, delineating when tooth movement or periodontal surgery is most appropriate to improve anterior dental esthetics. In the past, less emphasis has been placed on the anatomic changes occurring with the soft tissue when a periodontal compromised tooth is moved coronally by orthodontic means. The purpose of this article is to describe in greater detail the clinical alterations in the soft tissue architecture of the periodontium demonstrated during eruptive tooth movement of periodontally compromised teeth.

In periodontal disease, the deepening of the gingival sulcus occurs as a result of apical migration of the junctional epithelium. Pocket formation initially starts as an inflammatory change in the connective tissue wall of the gingival sulcus caused by bacterial plaque. The cellular & fluid inflammatory exudate causes degeneration of the surrounding tissue, including the gingival fibers. In association with the inflammation, as the pocket depth is increased, the coronal portion of the junctional epithelium detaches from the tooth surface so that the sulcus bottom shifts apically and the oral sulcular epithelium occupies a gradually increasing portion of the sulcular lining. When a periodontally compromised tooth is moved during orthodontic extrusion, changes may be observed in the surrounding gingiva. The teeth with deep gingival pocket move coronally for a considerable distance before the gingival margin follows.

Concurrently the pocket depth is reduced, and an immature appearing tissue "the red patch" appears coronal to the original gingival margin. It is recognized that the increase in the soft tissue component is directly due to an eversion of the pocket lining. Specifically, the appearance of the "red patch" that is sulcular epithelium, has peeled off the tooth surface directly, because of an eversion of the pocket lining. Initially, this epithelium lacks a keratinous covering of the oral epithelium & is only a few cells thick. It is anticipated that the sulcular epithelium, when peeled off the tooth surface, would be bright red, because it is so thin and, for the same reason, would lie below the general level of the gingiva.

In summation the reduction in soft tissue pocket depth occur as a result of coronal displacement of the attached fiber bundles below the epithelial attachment, causing a substantial portion of the pocket wall to become eversion. The direct relationship was identified with a mean pocket depth reduction of 5.32mm accompanied with a coronal-apical distance of the "red patch" at 4.5mm.

This directly explains the leveling of the soft tissue defect & coronal positioning of the new gingival margin. The enhanced anatomic topography and increased volume of soft tissue develop the emergence profile for the restoration. Subsequently the osseous support allows for improvement of the three-dimensional configuration of the soft tissue.

Forced eruption and implant site development is a nonsurgical technique for improving the three-dimensional topography of the implant recipient site before extraction. Therefore the concept of a periodontally compromised tooth moving coronally by orthodontic means, and the clinical alterations in the soft tissue architecture reveal a red patch appearance in the wake of orthodontic extrusion.

<Reference: Am J Orthod Dentofac Orthop 1997;112:596-606>

Considerations With Palatallw Impacted Canine

May 19, 2000
Dr. Chang-Hun Park

Many orthodontic patients exhibit teeth that have not penetrated the oral mucosa or will not erupt. Certain teeth demonstrate eruption that has been delayed significantly beyond the time when normal dental eruption for a particular patient should have occurred. Clinical orthodontists that have treated cases involving unerupted teeth have been faced all the problems of devitalization, re-exposure or re-uncovering of the tooth, ankylosis, external root resorption, and injury to adjacent teeth when an unerupted tooth has been surgically uncovered from the wrong side ridge. The marginal bone loss, gingival recession, and sensitivity problems that are seen once the roots are exposed for an individual are complications that invariably result in prolonged treatment time, esthetic deformities, and, in many cases, loss of teeth. Most of these problems: re-exposure, gingival recession, and bone loss can be prevented. Proper management of the periodontal tissues is critical in preventing loss of attachment. When the teeth are uncovered, it is not recommended to use electrosurgery or lasers-techniques that have attracted a lot of attention recently: these instruments are used strictly to remove the overlying tissue. Excision of the surrounding tissue on the unerupted tooth leaves inadequate keratinized tissue.

Large dental follicles frequently occur, especially on maxillary canines in 9- or 10-year-old individuals, before the teeth have erupted out of the palate. When these enlarged dental follicles are resorbing hard tooth structure in the arch, they must be uncovered. Even though they may not have more than 50% root formation at that point, the canine should be uncovered and a bonded attachment placed. The canine should be moved in contact with the palatal mucosa, the attachment taken off, and the root allowed to develop on the canine.

With the maxillary palatally positioned canines, which occur 3 times more frequently, the problem is different with labial impaction. The palate is all masticatory mucosa, therefore a graft is not placed on the teeth. These teeth uncovered by reflecting the palatal tissue, by placing a window, and then by replacing the tissue over the palate. A periodontal dressing is placed for 7 to 10 days before being removed, at which time a bonded attachment is placed, and tooth movement is started.

A major orthodontic principle that applies to palatal canines is the use of a sufficient-sized basal arch (at least a 0.018 or a rectangular stainless steel base arch). The base arch must be large enough to prevent deflection of teeth in the maxillary arch into the opposing occlusion each time the patient closes his or her mouth. The devitalization of lateral incisors often occurs because a very flexible, multistranded base arch or light nitinol base arch has been used so that when the palatally impacted tooth is activated over a long period of time it deflected teeth into opposing occlusion, and lateralis can be devitalized by occlusal trauma. Palatally impacted teeth as well must be constantly evaluated for bleeding around the crown or for active bleeding around the tooth. If there is excessive bleeding, the patient should be treated for scaling and curettage. Otherwise, there is a small chance of loss of attachment on a palatally impacted tooth. Any tooth that has been surgically uncovered should always be checked at each visit for excessive mobility. In many instances the dental follicle can grow aggressively around the erupting tooth that has been uncovered and can displace or detach the graft from the crown on labial impaction, and it can cause bone loss around the entire tooth as the tooth is moved into the arch. When excessive mobility is observed, a x-ray examination should be made to evaluate the presence of osteoid tissue and to ensure that the periodontal attachment is following the tooth as it is being guided into the arch.

Funcitional Unilateral Posterior Crossbite

June 2, 2000
Dr. Mi-Young Seo

Unilateral posterior crossbite is one of the most frequently occurring malocclusions in the deciduous and mixed dentitions. Moyers attributes the etiology of crossbite to dental, muscular, and osseous reasons. Schroder found that crossbite often resulted from different degree of maxillary contraction leading to bilateral or unilateral crossbite. In the early stages, such crossbites are associated with a lateral functional shift of the mandible in approximately 80% of cases.

Children with functional unilateral posterior crossbite are characterized by:
1. An asymmetric pretreatment condylar position with the noncrossbite side condyle in an anterior and inferior position in the glenoid fossa.
2. An asymmetric pretreatment molar and canine relationship with a more Class II relationship on the crossbite side and a less Class II relationship on the noncrossbite side, concomitant with a midline deviation toward the crossbite side.
3. Establishment of more symmetric occlusal and condylar relationship after maxillary expansion through elimination of the crossbite and shift.
4. Establishment of more symmetry through posterior and superior movement of the noncrossbite side condyle and only minimal anterior and inferior movement of the crossbite side condyle.
5. A small amount of autonomous mandibular intermolar expansion concomitant with the maxillary expansion.

Early treatment is advocated in this malocclusion for these reasons.
1. It rarely corrects spontaneously.
2. Occlusal disturbance characteristics of this type of crossbite increase risk of temporomandibular disorders.
3. If not corrected the crossbite may give rise to asymmetric growth and development due to lateral displacement of the mandible and asymmetric muscle function.

Various correction methods have been used from simple selective grinding to complicated palatal expansion depending on case situation. Rigorous grinding of cusps of deciduous teeth is discouraged since it disturbs the growth and development of the masticatory system. Grinding can be a choice of treatment if the initial value of maxillary / mandibular width difference is more than 3.3 mm in the canine region. Orthodontic appliances including fixed and removable were suggested in the literature. Fixed appliances were preferred by clinicians in a young child age because of compliance by the patient. Expansion appliances such as rapid palatal expander and lingual arch were considered effective procedures for posterior crossbite correction. Hermanson et al. concluded that quad-helix (fixed) appliance was preferable to removable plates in expansion effect, number of visits and total cost of treatment for the treatement of unilateral posterior crossbite.

Early orthodontic treatment of functional unilateral posterior crossbite was successful in most of the subjects, both in the short and long term. The aim of an early orthodontic treatment is to create conditions for normal growth and development by eliminating the lateral forced bite.

The Surgical Techniques For Labially Impacted Maxillary Canine

June 9, 2000
Dr. Kwan-Mo Kim

Various surgical techniques have been described for exposing impacted teeth before orthodontic tooth movement. Frequently these techniques are designed for a specific method of attachment. Wire ligation or direct bonding were used for attachment.

The wire ligation method of attachment to impacted teeth was associated with clinically significant loss of attachment, ankylosis, and root resorption. The direct-bond attachment did not have any clinically significant loss of attachment, any occurrence of ankylosis or root resorption. In the present, usually direct bonding is used for traction of the impacted canine.

¡´ Surgical techniques ¡µ

(1) exposure of the entire labial aspect of the anatomic crown with total excision of all keratinized tissue (the window approach)  (2) a technique which exposes only 4 to 5 mm of the most superficial portion of the labial aspect of the cusp tip while maintaining 2 to 3 mm of keratinized tissue and  (3) tunnel traction.

First technique
Howe and others described that periodontal problems, such as recession, lack of attached gingiva, and persistent inflammation were associated with the window technique in which all keratinized tissue was removed.
Window approach indicates that statistically significant loss of attachment, recession and gingival inflammation occur on maxillary canines after surgical exposure.

Second technique
A criticism of the surgical procedure used the 2nd surgical technique may be that postsurgical overgrowth of soft tissue from the wound edges rapidly occurs when only 4 to 5 mm of crown, instead of the entire crown, is exposed. In addition, if a direct bond is placed at the time of surgery, the plaque that accumulates can lead to gingival hyperplasia and overgrowth of the exposed area more quickly than when the exposed area is larger. To overcome these liabilities, it is necessary to have the patient initiate plaque removal as soon as possible after surgery to prevent gingival hyperplasia. Also, the clinician should not place the direct bond until the tissues have healed and effective plaque control is established.

Third technique
A full thickness flap was raised to expose the cortical plate, and the deciduous canine was removed. Cortical bone was removed to provide access to the crown, and the follicular socket was eliminated. A low speed bur was inserted into the seat of the deciduous tooth's root to drill a perforation into the bone under careful cooling, to reach the crown of the impacted canine. The perforation and the deciduous socket formed a tunnel that was used for the traction. A handmade wire chain of rings approximately 1.5 mm in diameter was prepared with 0.011-inch ligature wire. The chain was passed through the osseous tunnel and fixed as closely as possible to the cusp of the impacted canine by means of an attaching device, which, depending on the case, was either a bonded button, a bonded bracket base with a soldered ring on it, or an anatomically contoured fine mesh. The force of 150 gm was applied with a dynamometer to test the bonding. The flap was then repositioned and sutured in its original seat. The chain passed through the bone tunnel and emerged from the socket of the deciduous tooth. One week after surgery, the sutures were removed and the traction phase began. A force of approximately 100 gm was applied while care was taken to maintain the chain at the center of the socket. The elastic traction was directed to the center of the alveolar ridge.
During the orthodontic traction phase, the eruption of the impacted tooth was guided through the tunnel, between the internal and external cortical plates. The cusp of the impacted canine thus emerged at the center of the alveolar process, replacing the deciduous canine in an area surrounded by keratinized gingiva.

Deep infraosseous canines associated with persistent deciduous teeth may be successfully and safely treated by repositioned flap and tunnel traction toward the center of the alveolar ridge. Physiologic attachment levels without gingival recession and adequate amounts of gingiva may be obtained and maintained on the treated teeth. No gingival augmentation procedure is required and the natural appearance of the tissues may be preserved.

Mandibular Lengthening By Distraction Osteogenesis Using Osseointegrated Implants And An Intraoral Device

June 16, 2000
Dr. Ji-Hyun Min

The conventional method of elongating the mandible usually involved some form of splitting osteotomy or direct bone grafting. Recently, there has been interest in the use of distraction osteogenesis for the mandible. Successful animal studies and clinical reports have demonstrated its usefulness in mandibular reconstruction.

The application of distraction osteogenesis for mandibular lengthening, as with bone lengthening in tubular bones, has been used experimentally and clinically. The mandible differs from tubular bones in its origin, structure, and function.

What is the mode of ossification during distraction osteogenesis? New bone was formed predominantly by intramembranous ossification with fibrocartilage islands observed in some elongated sites. Those were not only in the central radiolucent area, but also between the proximal segment and newly formed bone. This cartilagenous formation may be the result of the instability of bone segments, the influence of distraction rate, or other reasons. If the elongated mandible underwent endochondral ossification, distraction osteogenesis in the canine mandible was successfully performed.

The use of transcutaneous pins in the maxillofacial area has numerous disadvantages, such as extraoral scars, possible facial nerve and inferior alveolar nerve injury, pin loosening, and infection. The thicker the soft tissue a pin penetrates the more the risk of the infection.
The region of the mandibular angle has thick soft tissue because of the masseter muscle, the parotid gland and the buccal fat. Moreover, the farther the distraction device is from the bone, the more easily the pin bend. Repeated force on the long pins can lead to pin loosening.
The transcutaneous pins used for distraction osteogenesis also can cause facial scars.
Then, there are the facial nerve and inferior alveolar nerves in the pathway of the pins, and injury to these nerves can occur during pin installation. Finally, the daily life of the patient is affected because the extraoral device is conspicuous. With an intraoral device, the implants penetrate the thin oral mucosa, and the distraction appliance is near the bone. Moreover, the intraoral device is not visible and it does not cause scarring.

An intraoral device using osseointegrated dental implants can be used for distraction osteogenesis in the maxillofacial skeleton. Experimental and clinical reports have advocated the potential usefulness of the endosseous implants as a source of orthodontic anchorage.

The titanium implants used for rigid anchorage of the distraction device remained stable against the continuous mechanical force used during the course of mandibular lengthening. Osseointegrated implants can perform three roles: anchorage of the distraction device, anchorage of retainer, and anchorage of the final prosthesis.

Other possible advantages of the this apparatus include the following:
1) Patients can have a normal social life during the course of treatment:
2) The implants can be used for anchorage of a retainer to prevent relapse and:
3) The technique of distraction osteogenesis can be performed repeatedly using the implants.

In situations involving congenital deformities such as hemifacial microsomia, the use of osseointegrated implants could provide the possibility for long-term retention against relapse and the chance of repeated distraction without skin scars.

Reference
1) Sawaki Y, Ohkubo H, et al. J Oral Maxillofac Surg 1996:54(5):594-600
2) Sawaki Y, Ohkubo H, et al. Int J Oral Maxillofac Implants 1996:11(3):186-93

Orthopedic Appliance of Class III Malocclusion

June 23, 2000
Dr. Young-Sung Lee

If a maxillary deficiency is diagnosed, the treatment options for non-growing patients are limited to orthognathic surgery and dental camouflage. However, younger individuals can be treated by growth modification with functional appliances or protraction headgear.

Although maxillary expander-facemask appliances and reverse headgear can achieve excellent orthopedic effects, they demand special patient compliance because they are worn extraorally, and are not as esthetic or comfortable as intraoral appliances. Proper oral hygiene can also be difficult to maintain, since mandibular growth lasts longer than maxillary growth, and thus can prolong the use of fixed appliances.

Proffit believes the optimal age for maxillary protraction is about age 6-7. Other authors recommend such treatment before age 10, or at least one to two years before the pubertal growth spurt. But because only a few permanent teeth have erupted at this young age, adequate anchorage for a maxillary protraction appliance can be problematic.

Dr. Chun et. al. introduced a new appliance for treatment of growing Class III patients: the Tandem Traction Bow Appliance. The TTBA is more esthetic and comfortable than conventional devices because it is worn intraorally. It is removable, making it easy for the patient to maintain oral hygiene, and allowing treatment to be suspended or restarted whenever the clinician deems necessary, without bonding or debonding.

In clinical trials of the TTBA, structural superimposition according to Bj rk showed anteroinferior movement of the maxilla, posteroinferior repositioning of the mandible, and protraction of the maxillary dentition. Therefore, they concluded that the TTBA has a similar treatment effect to that of an expander-facemask combination.

The TTBA comprises an upper splint, a lower splint, and a traction bow. Its design allows the patient to open the mouth freely. The upper splint, which can serve the same function as a rapid maxillary expander, covers the palatal and occlusal surfaces of the maxillary teeth. A portion of the buccal surfaces are also covered, providing adequate retention to overcome the maxillary protraction force of as much as 400-500g per side. During active treatment, the labial bow is embedded in the acrylic; it is uncovered and used to retain the incisors when the TTBA is reassembled as a monoblock retainer.

The lower splint covers the buccal and lingual surfaces of the mandibular teeth to reinforce retention. Because the patient wears the TTBA while sleeping, retention is critical, and reduction of interdental resin must be avoided except in cases of severe undercuts. The splint should be relined whenever retention is inadequate.

The maxillary hooks should be placed distal to the deciduous or permanent canines, so that the elastic force passes through the center of resistance of the maxilla(at about 20o to the occlusal plane). The mandibular tubes should be located as posteriorly as possible.

In the deciduous and mixed dentition, the applied force should be 300-500g for orthopedic effect; in the early permanent dentition, it should be 150-300g for orthodontic effect, avoiding undue stress on the TMJ. The patient is asked to wear the TTBA 12-14 hours a day for orthodontic effect.

After the crossbite is overcorrected, the two splints are fused into a monoblock and used as a retainer. The TTBA can be modified for use with bonded fixed appliances if necessary. While the treatment effect of the TTBA is similar to that of a facemask, the TTBA is much more convenient for both clinician and patient.

Etiology and Prevention of Downward Rotation of Maxilla Following RPE

June 30, 2000
Dr. Hyun Kim

Rapid palatal expansion has long been a commonly used means of correcting maxillary transverse deficiency. It is recognized as a very successful orthopedic therapy in growing patients. However, the transverse force delivered during RPE have been shown to create undesirable orthodontic and orthopedic side effects in patients. As midpalatal suture opening is processed, the mandible autorotates in a backward and downward direction. This movement is an obviously undesirable characteristic for many dental and skeletal types of patients. For example, the patients with a Class II dentition, long face, and open bite pattern could ill afford the extrusive characteristics of rapid palatal expansion.

A downward movement of the maxillary arch following rapid palatal expansion is due to the location of the center of resistance of the maxilla. In 1970, Wertz not only recorded data from his clinical study but used dried skulls to supplement his work concerning skeletal changes. He demonstrated that the center of resistance of the maxilla was close to the frontomaxillary suture, and observed a lateral buccal tipping of the two alveolar shelves of the maxilla, leading therefore to a pyramidal opening of the midpalatal suture, the apex being in the nasal cavity. In 1965, Isaacson and Zimring showed that because of the resistance of the midpalatal suture and circummaxillary articulations to the expansion forces, microfractures within the buccal cortical plate were generated before the breakage of the suture. This causes buccal tipping and extrusion of the lingual cusps of the maxillary posterior teeth. Therefore it may be beneficial to try to counteract the iatrogenic orthodontic and orthopedic side effects during RPE therapy.

Downward and anterior displacement of the maxilla often associated with the banded rapid palatal expansion appliance may be negated or minimized with the more versatile bonded appliance. Bonded rapid palatal expansion appliances were designed to cover the maxillary posterior occlusal-buccal segments so that the appliance not only serves as an expansion device but intrudes on the freeway space through its vertical thickness. And, the bonded rapid palatal expansion appliance would increase rigidity by limiting unwanted tipping and rotation of teeth due to the increased surface of acrylic bonded to the teeth.

A high-pull headgear or a vertical pull chincap may be used, coincident with RPE, to reduce vertical dimension in the posterior region and significantly improve dental and skeletal open bite. In 1974, Thompson used high-pull headgear combined with RPE in his monkey experiment. The results showed that the downward displacement of the maxilla could be reduced. However, the use of a high-pull headgear to control buccolingual tipping seems to be much less effective when compared with the use of a vertical-pull chincap. Because the point of force application of headgear is located at the buccal to the center of resistance of molar, it will produce a moment that will tip the maxillary posterior teeth even more buccally.

The use of a vertical-pull chincap delivers a more ideal force system. During and immediately after RPE, chincap delivers an intrusive force at the lingual cusps of the maxillary posterior teeth and offers potential control of both the extrusive and buccal tipping side effects created by RPE. Favorable results seem to be achieved when the chincap is worn 12 to 16 hours a day with a force level of 250 gm per side.

If you plan to use the RPE in Class II patient with long face and open bite, use the bonded RPE or use the vertical-pull chincap or high-pull headgear together with the RPE. You can achieve the satisfactory treatment results. Thank you.

Clinical Application of the Jasper Jumper

July 7, 2000
Dr. Jeong-Soon Ahn

A common strategy in the treatment of Class II division 1 malocclusion in growing patients is a two-step approach. In the first phase of treatment, the sagittal jaw relationship is normalized. The Class II malocclusion is transformed to a Class I malocclusion. In the second phase of treatment, adjustment of tooth position is performed, normally with a fixed appliance. The correction of the sagittal jaw relationship can be achieved in several ways. Removable appliances such as activator leave the orthodontist totally dependent on the patient, and bonded functional appliances present hygiene and cleanup problems. But, The Jasper Jumper is a relatively new auxiliary capable of producing rapid change in occlusal relationships. It is a flexible fixed appliance that delivers light, continuous force. By anchoring the device intraorally, the need for patient cooperation is reduced substantially.

This appliance produces both sagittal and intrusive forces, as does the Herbst bite jumping mechanism, but affords the patient much more freedom of mandibular movement. The system is composed of two parts, the force module and the anchor units. The force module, analogous to the tube and plunger parts of the Herbst bite jumping mechanism, is flexible. The force module is constructed of a stainless steel coil or spring that is attached at both ends to stainless steel endcaps, in which holes have been drilled in the flanges to accommodate the anchoring unit. When the force module is straight, it remains passive. As the teeth come into occlusion, the spring of the force module is curved axially as the muscles of mastication elevate the mandible, producing a range of forces from 1 to 16 ounces. The most common method of attachment of the force module to the dental arches in the permanent dentition is through the use of previously placed fixed orthodontic appliances. When the jumper mechanism is used to correct a Class II malocclusion, the force module is attached posteriorly to the maxillary arch by a ball pin that is placed through the distal attachment of the force module and then extends anteriorly through the face-bow tube on the upper first molar band. The ball pin is anchored in position by having the clinician place a return bend in the ball pin at its mesial end. Anteriorly, the module is anchored to the lower arch wire. Bayonet bends are placed distal to the mandibular canines and small Lexan beads are slipped over the arch wire to provide an anterior stop. The most important aspect of the clinical management of this appliance system is the preparation of lower anchorage and the control of mandibular mesial tooth movement. Alignment of the upper and lower anterior teeth during the initial phases of orthodontic treatment must be completed. Full-sized arch wires should be inserted into the brackets in both arches before the placement of the force modules. The arch wires should be tied or cinched back posteriorly to increase anchorage, including second molars whenever possible. In addition, the clinician can place posterior tip-back bends in the mandibular arch wire to enhance anchorage. Directions of force generated by the modules bilaterally include sagittal as well as intrusive and expansive forces. The sagittal forces will distalize the posterior anchor unit and also will apply an anterior force to the mandible and mandibular dentition. In addition, an intrusive force is produced in the maxillary posterior region as well as the mandibular anterior region.

Finally, This flexible force module system differs from the Herbst bite jumping mechanism in a number of significant areas. First, the amount of force applied by the modules is more easily controlled by the clinician. The flexibility of the force module has been shown to increase patient comfort because greater lateral and sagittal movements are possible. In addition, the force module curves away from the dental arches in its activated position, thus making mastication and oral hygiene procedures easier to perform than with the Herbst appliance. Another advantage is that it can be added to existing appliances virtually at any point after arch preparation. The modules can be used as a primary method of treatment or can be added at a later time after alternative treatments have proven unsuccessful. There is no need to remove the entire fixed appliance setup before the force modules are placed, nor is there additional laboratory cost or lost time during treatment if the fabrication of lower lingual or transpalatal arches is not required.

In conclusion, this appliance system provides the opportunity of minimizing patient cooperation in the correction of sagittal discrepancies. If proper anchorage preparation is achieved and force values are kept within physiologic limits, successful treatment outcomes can be attained.

Efforts to reduce enamel demineralization around bonded brackets

July 14, 2000
Dr. Hwang-Sog Ryu

Enamel demineralization has been greatly reduced by the use of directly bonded orthodontic attachments. However, enamel demineralization adjacent to bonded attachments still occurs. Plaque more readily accumulates on resin materials than on enamel. There is a significant increase in plaque on the gingival side of bonded brackets.

Orthodontists have long recognized this problem and had attempted to reduce enamel demineralization. Zachrisson recommended several methods to prevent demineralization of tooth surfaces: use efficient hygiene instruction and supervision, apply fluoride, and use various coating techniques.

Topical fluoride has been used extensively around orthodontic brackets. The topical fluoride programs includes fluoride prophylaxis pastes, solutions, gels, mouth rines, and dentifrices. Apart from topical fluoride therapy during orthodontic treatment, several methods have been suggested to increase the resistance of the enamel to decalcification. These procedures are the application of topical fluorides to the enamel surfaces prior to etching, the incorporation of fluorides in the etching solutions, and the topical application of fluorides to the etched enamel surfaces before bonding.

Some investigators found that light-cured pit and fissure sealants placed on the labial surface adjacent to bonded orthodontic brackets were 80% effective in preventing demineralization in vitro and required no patient compliance. Todd et al showed that the teeth treated with Duraflor floride varnish exhibited 50% less demineralization than the control teeth.

All of above are effective in reducing enamel demineralization during orthodontic treatment. However, the basic effort of orthodontists should be performed during bonding procedure.

It has been suggested that etching of enamel surfaces with phosphoric acid before placement of the orthodontic attachments may predispose the uncovered etched enamel to caries. It was shown that plaque accumulated readily on bonded orthodontic attachments, on the resin surfaces adjacent to the attachments, and at the junction of the bonding resin and the etched enamel surfaces. All etched surfaces should be covered with a mix of enamel bond resins.

The use of acid etching and bonding in orthodontics differs from their use in preventive and operative dentistry, where they are designed to be used as an adhesive system to permanently retain pit and fissure sealants and restorations. In orthodontics, the bonding of attachments to tooth surfaces is of a temporary nature in so far as the attachments are removed at the conclusion of the active treatment period.

Pus et al showed that the soft unfilled resin was removed with a hand scaler whereas the filled composite resin required the use of a rotary instrument to achieve a surface clinically clean in appearance. So orthodontists had better cover the remaining etched surface with unfilled resin than with filled resin. That is a basic effort.
Thank you.

References

Zachrisson BU. Cause and prevention of injuries to teeth and supporting structures during orthodontic treatment. Am J Orthod 1976;69:285-300.

Bryant S, Retief DH, Bradley EL, Denys FR. The effect of topical fluoride treatment on enamel fluoride uptake and the tensile bond strength of an orthodontic bonding resin. Am J Orthod 1985;87:294-302.

Todd MA, Staley RN, Kanellis MJ, Donly KJ, Wefel JS. Effect of a fluoride varnish on demineralization adjacent to orthodontic brackets. Am J Orthod 1999;116:159-67.

Pus MD, and Way DC. Enamel loss due to orthodontic bonding with filled and unfilled resins using various clean-up techniques. Am J Orthod 1980;77:269-83.

Condylar Displacement and Temporomandibular Joint Dysfunction Following Bilateral Sagittal Split Osteotomy

July 28, 2000
Dr. Eun-Hee Ko

Mandibular advancement surgery has been associated with many complications. Relapse, hypomobility, and temporomandibular joint dysfunction have all been reported following bilateral sagittal split osteotomy with advancement. Particularly, there is concern that if condylar position is changed, when rigid fixation is used with surgery, there will be an increase in temporomandibular joint symptoms.

Posterior displacement of the condyle is thought to be an etiologic factor in the development of internal derangement of the temporomandibular joint. Condylar resorption has been demonstrated following bilateral sagittal split osteotomy, leading to late postsurgical instability. A comprehensive insight into this problem remains elusive, although compression of the condyle against the articular fossa has been considered the most frequent and likely cause. Experimental investigations in adult monkeys in which extensive posterior condylar displacement was produced showed remodeling, adaptation, and extensive degenerative changes in the joint structures.

Some authors have suggested that as the mandible is set back the condylar width will decrease and, conversely, as the mandible is advanced the width will increase. Widely divergent rami and large surgical movements will result in larger changes in intercondylar width and angle. But, Clinical changes in intercondylar angle and intercondylar width do not conform to a simple geometric model. A geometric model of mandibular advancement also implies that larger advancements should result in larger changes in intercondylar angle and intercondylar width. However, no correlation between the percent change in either of these measurements and the magnitude of advancement was noted.

Precision screw osteosynthesis of bilateral sagittal split osteotomy does not significantly change intercondylar angle or intercondylar width from preoperative values when compared with postoperative measurements. Clinical studies have demonstrated that irrespective of whether the condyle is displaced more using one method of fixation over another, no greater incidence of temporomandibular joint dysfunction has been found following bilateral sagittal split osteotomy with rigid internal fixation. This might indicate that the remodeling changes noted in the temporomandibular joint are adaptive in nature. Moreover several articles have reported no change in temporomandibular joint symptoms as a result of condylar displacement after ramus osteotomies. Even though changes were noted, they were not significant increase in temporomandibular joint symptoms occurred during the same time frame indicates that the changes in condylar position were not clinically significant. It appears that these changes were within the adaptive range of patients, As no increase in the incidence of temporomandibular joint symptoms occur.

It is necessary to consider the deformity preoperatively, because the deformity itself and the direction of mandibular advancement appear very important when the temporomandibular joint function is concerned.

It would have been beneficial if the change of the condylar fragment in the sagittal plane had been measured together with the change of intercondylar angle and intercondylar width. Upward rotational movement of this fragment results in a change of relation between condyle, disc, and eminence, which certainly has influence on the temporomandibular joint function.

Maxillary Expansion

August 4, 2000
Dr. Hee-Chang Park

Angell reported rapid maxillary expansion procedure in 1860, and since then it has gone through periods of popularity and decline. Aetiological causes of buccolingual discrepancies can be either genetic or environmental. Harvold et al(1972) stated that upper arch narrowness was generally due to abnormal functions.

Removable expansion plates are not recommended if significant skeletal changes are required. For these appliances to be effective, they must be used in the deciduous or early mixed dentition and must have sufficient retention to be stable during the expansion phase. The advocates of the tissue-borne fixed appliance believe that it causes a more parallel expansion force on the two maxillary halves and that the force is more evenly distributed on the teeth and the alveolar process.

Several authors have recommended different types of maxillary expansion appliances by changing the rate of expansion and form of the appliance. With maxillary expansion treatment, the aim is to achieve minimal dental and maximum skeletal effect. Advocates of rapid expansion (1 to 4 weeks) believe that it results in minimum tipping and maximum skeletal displacement. The rate of rapid maxillary expansion is 0.2 to 0.5mm per day and can result in an increase in intermolar width of up to 10mm. Skeletal changes are approximately 50% at the total change. However, clinical and histological studies have shown that relapse, microtrauma of the TMJ, microfractures at the mid-palatal suture and especially external root resorption are observed in rapid maxillary expansion treatment. Advocate of slower expansion (2 to 6 months) believe that it produces less tissue resistance in the circummaxillary structures and better bone formation in the intermaxillary suture, and that both factors help minimize postexpansion relapse.

Slow expanders like the quad helix and W-spring can transmit forces ranging between several ounces and two pounds. They can separate the maxillae, particularly in the deciduous and mixed dentitions. The rate of separation varies between 0.4 and 1.1mm per week and can result in an increase in intermolar width of up to 8mm. Skeletal changes are estimated to be 16% to 30% of the total change and vary with age.

Hicks observed that the amount of relapse is related to the method of retention after expansion. With no retention, the relapse can amount to 45% as compared with 10% to 23% with fixed retention and 22% to 25% with removable retention. Krebs found that after fixed retention was discontinued, there was a substantial reduction in dental arch width. This tendency continued for up to 5 years.

Bell concluded that slow expansion is less disruptive to the sutural systems. Slow expansion that maintains tissue integrity apparently needs 1 to 3 months of retention, which is significantly shorter than the 3 to 6 months recommended for rapid expansion.

One should over expand the molars 2 to 4mm beyond the required distance to allow for the expected postfixation relapse. The magnitude of maxillary expansion would vary between individuals and according to the severity of the malocclusion, but 10 to 12mm should be considered as the upper limit of RME correction. For discrepancies of this magnitude, clinicians must consider a combined orthodontic-surgical approach in order to provide a more stable result.

Mandibular advancement surgery has been associated with many complications. Relapse, hypomobility, and temporomandibular joint dysfunction have all been reported following bilateral sagittal split osteotomy with advancement. Particularly, there is concern that if condylar position is changed, when rigid fixation is used with surgery, there will be an increase in temporomandibular joint symptoms.

Posterior displacement of the condyle is thought to be an etiologic factor in the development of internal derangement of the temporomandibular joint. Condylar resorption has been demonstrated following bilateral sagittal split osteotomy, leading to late postsurgical instability. A comprehensive insight into this problem remains elusive, although compression of the condyle against the articular fossa has been considered the most frequent and likely cause. Experimental investigations in adult monkeys in which extensive posterior condylar displacement was produced showed remodeling, adaptation, and extensive degenerative changes in the joint structures.

Some authors have suggested that as the mandible is set back the condylar width will decrease and, conversely, as the mandible is advanced the width will increase. Widely divergent rami and large surgical movements will result in larger changes in intercondylar width and angle. But, Clinical changes in intercondylar angle and intercondylar width do not conform to a simple geometric model. A geometric model of mandibular advancement also implies that larger advancements should result in larger changes in intercondylar angle and intercondylar width. However, no correlation between the percent change in either of these measurements and the magnitude of advancement was noted.

Precision screw osteosynthesis of bilateral sagittal split osteotomy does not significantly change intercondylar angle or intercondylar width from preoperative values when compared with postoperative measurements. Clinical studies have demonstrated that irrespective of whether the condyle is displaced more using one method of fixation over another, no greater incidence of temporomandibular joint dysfunction has been found following bilateral sagittal split osteotomy with rigid internal fixation. This might indicate that the remodeling changes noted in the temporomandibular joint are adaptive in nature. Moreover several articles have reported no change in temporomandibular joint symptoms as a result of condylar displacement after ramus osteotomies. Even though changes were noted, they were not significant increase in temporomandibular joint symptoms occurred during the same time frame indicates that the changes in condylar position were not clinically significant. It appears that these changes were within the adaptive range of patients, As no increase in the incidence of temporomandibular joint symptoms occur.

It is necessary to consider the deformity preoperatively, because the deformity itself and the direction of mandibular advancement appear very important when the temporomandibular joint function is concerned.

It would have been beneficial if the change of the condylar fragment in the sagittal plane had been measured together with the change of intercondylar angle and intercondylar width. Upward rotational movement of this fragment results in a change of relation between condyle, disc, and eminence, which certainly has influence on the temporomandibular joint function.

Airway Analysis

September 4, 2000
Dr. Chang-Hun Park

 One of the most controversial areas in orthodontic diagnosis and treatment planning today is the relationship between upper airway obstruction and craniofacial growth. Conflicting opinions exist concerning this interrelationship. For the purpose of this analysis, two measurements are used to examine the possibility of an airway impairment.

 Upper pharynx  The upper pharyngeal width is measured from a point on the posterior outline of the soft palate to the closest point on the posterior pharyngeal wall. This measurement is taken on the anterior half of the soft palate outline, because the area immediately adjacent to the posterior opening of the nose is critical in determining upper airway patency. It must  be noted, however, that the headfilm outline of the nasopharynx is only a two-dimensional representation of a three-dimensional structure, and thus cephalogram cannot be used as a primary diagnostic tool for airway evaluation.

 If a patient is swallowing when the radiograph is taken, the soft palate takes on the appearance of an inverted "V", as the tensor and levator veli palatini muscles pull the palate upward and backward during closure. This configuration of the soft palate suggests only limited usefulness of the upper pharyngeal measurement.

 Warren(1987) has reported that 40 §± of nasopharyngeal airway must be present in order for nasal breathing to occur without an oral component. Because the average nasopharynx is approximately 15-20§® in width, a width of 2 §® or less in the upper pharyngeal measurement may be used as an indicator of possible airway impairment ( in contrast to 5§® or less stated in the McNamara[1984] article in the American Journal of Orthodontics.) A more accurate diagnosis can be made only by an otorhinolaryngologist during a clinical examination or more accurately by a measurement oral and nasal airflow. The upper airway increases with age (McNamara, 1984) and, for adult of both sexes, average 17.4 §®.

 Lower Pharynx  Lower pharyngeal width is measured from the intersection of the posterior border of the tongue and the inferior border of the mandible to the closest point on the posterior pharyngeal wall. The average value for this measurement is 11-14 §®, independent of age (McNamara, 1984). In contrast to the upper pharynx, a smaller-than-average value for the lower pharynx is not remarkable. It is rare to see an obstruction of the lower pharyngeal area because of the position of the tongue against the pharynx; however, a lower pharyngeal width of greater than 18 §® suggests a possible anterior positioning of the tongue, either as a result of habitual posture or due to an enlargement of the tonsils. Determination of tongue position is important in the diagnosis of certain clinical condition, such as mandibular prognathism, dentoalveolar anterior crossbite, or bialveolar dental protrusion. These clinical conditions are thought to be associated with a forward tongue position and/or enlarged tonsils; however, studies of this relationship have not been published.

Obstructive Sleep Apnea (OSA)

September 15, 2000
Dr. Gue-Hyeong Lee

OSA is a complex syndrome characterized by recurrent upper airway obstructive during sleep. Patients complain of a range of symptoms, particularly excessive daytime sleepiness, and may develop physical complications that include systemic hypertension, right heart failure, and cardiac arrhythmia.

The patency of the upper airway is a result of many interrelated anatomic and physiologic factors. During inspiration, a negative intrapharyngeal pressure develops but airway collapse is prevented by the action of the pharyngeal adductor and dilator muscles. These muscles are activated rhythmically during daytime respiration but in common with other skeletal muscles, they become hypotonic during sleep, and airway stability becomes dependent upon pharyngeal size and pharyngeal tissue compliance.

OSA patients have adenotonsilar hypertrophy or macroglossia. Airway size is also affected by craniofacial morphology as reflected in the airway narrowing and sleep apnea observed in patients with significant retrognathia. OSA patients showed a posteriorly positioned maxilla and mandible, a steep occlusal plane, overerupted maxillary and mandibular teeth, proclined incisors, a steep mandibular plane, a large gonial angle, high upper and lower facial heights, and an anterior open bite in association with a long tongue and a posteriorly placed pharyngeal wall.

The technique of Computed Tomography scanning and supine lateral cephalometry are most commonly used to visualize the pharynx. Also pharynx has been visualized with other several techniques including upper airway magnetic resonance imaging, fluoroscopy, nasopharyngoscopy, acoustic reflection study. Diagnosis of OSA is confirmed by a single night of polysonographic monitoring documented by EEG, EOG, and EMG.

The treatment of OSA depends on the severity of symptoms, the magnitude of clinical complications and the etiology of the upper airway obstruction. Simple measures such as weight reduction, avoidance of alcohol and relief of nasal obstruction are indicated in the majority of patients. Nasal continuous positive airway pressure(CPAP) is a very effective form of treatment for OSA. Uvulopalatopharyngoplasty(UPPP), which enlarges the upper airway by removing excessive distal palatal tissue, was proposed as a surgical treatment for OSA. and two maxillomandibular procedures, inferior sagittal osteotomy with hyoid myotomy and maxillomandibular and hyoid advancement have been proposed for the another surgical treatment method of OSA.

The development of intraoral appliances represents an new approach to the management of OSA such as Mandibular Repositioning Appliance, Tongue Retaining Device, Nocturnal Airway Patency Appliance, Equalizer. These appliances are designed to produce a downward and forward repositioning of the mandible and superior and forward repositioning of the tongue which result in an enlarged upper airway.

Bone Grafting

September 22, 2000
Dr. Seong-Ho Han

To create new living bone in a deficient site is a process carefully studied since the early 1900s. In spite of extensive efforts to create and promote graft substitues in modern times, the standard remains autogenous bone as compared with all other materials. Autogenous grafts are transferred from one body site to another in the same individual. The advantage of autogenous grafts is attributed to their mechanism of healing. It allows for rapid incorporation and functional adaptability once healed. Proper handling of the graft insures a two-phase healing process. The first or Phase¥° is characterized by osteogenesis. Live osteoblasts in transplantation proliferate and lay down an immature osteoid matrix. The amount of phase I bone formation is directly proportional to cellular density of osteoblasts in the transplant. Therefore, packed marrow cells produce the greatest quantity of phase I bone, and this process is exclusive to the healing of autogenous grafts.

Phase II graft healing is a slower process. Normally, it begins several weeks after graft placement and may continue for up to 2 years. The initial response in phase II healing is osteoclastic resorption of the unorganized osteoid matrix created in phase I healing. Coupled to this resorptive process by promoter proteins is the induction of pleuripotent mesenchymal stem cells to become osteoblasts. This process is known as osteoinduction. The most extensively studied of these promoter sustances is a high-molecular-weight protein called bone morphogenic protein (BMP) or osteogenin. These proteins are secreted by osteoclasts but are also found in small concentrations in all natural bone. In autogenous bone, the highest concentrations are found in dense intramembranous bone of the chin, ramus, and calvaria. Allografts, such as human demineralized freeze-dried bone (DMFDB), also contain these BMPs. The inductive potential of demineralized cadaver bone is minimal due to low concentrations of this protein after processing. Research comparing autogenous bone grafts to DMFDB questions the potential of DMFDB to induce bone formation at all. Osteoblasts are induced by promoter substances or present in the graft defect margins. They complete the phase II response by a process known as osteoconduction or creeping substitution. This is a slow process requiring oxygen from a healthy vascular bed and complete graft immobility. The new matrix of phase II bone once complete is well organized with live haversian systems and is capable of responding to functional loads by remodeling.

The time required for graft maturation varies, but, in general, most autogenous grafts with good blood supply are capable of withstanding loads on 6 months. Grafts or grafts in low oxygen tension areas such as the sinus may require 9 to 12 months before maturation is complete. Many dead bone particles can be found in some demineralized bone grafts as long as 2 years after their placement and may be the reason for their high percentage of resorption. Large, mostly cortical autogenous block grafts may also require longer healing periods. Because the osteocytes in their lacunae do not survive transplantation and larger segments of the graft heal primarily by osteoinduction and osteoconduction. It should be noted that allogeneic grafts (DMFDB), xenografts (bovine hydroxyapatite), and alloplats (nonanimal bone substitutes) are all nonviable materials and can generate new bone only by osteoconduction. The quantity and quality of the resultant bone matrix vary between materials; however, tissue bed health, blood supply, and immobility of the graft are essential to the final graft quality for all materials. Autogenous grafts using osteogenesis as well as osteoinduction and osteoconduction should produce the greatest quality and quantity of new bone formation after maturation. Materials other than autogenous bone still have good merit in given clinical situations and always possess the advantage of no donor site risks or morbidity. These factors must be compared with the final desired outcome. Non-autogenous grafts work favorably in limited size defects adjacent to implants or small defects. Several alloplastic materials work well when used as expanders to mix with autogenous grafts. The advantage of alloplastics supports the graft matrix during the osteoclastic resorption phase of autogenous graft healing.

Care of Bonded Retainers

October 6, 2000
Dr. Jae-Nam Kim

Flossing bonded lingual retainers

Flossing is simple! If someone hasn't been shown how easy it is to floss, they won't try it. Over the years we've heard of SuperflossR, floss threaders, and all kinds of extra tools, but it's so easy to use the same floss as usual - just think of how shoes are shined...look at the drawing again. This method is a snap for routine canine to canine lingual retainers which are used in virtually every case.

Method one - "as easy as one, two!"

The floss is snapped between two teeth as usual, then the end is snapped between the next two teeth before pulling so it wraps around one entire tooth proximal-lingual-proximal. Now just shine! That's all there is to it.

Patients are shown how to floss at the time retainers are bonded, and given a written handout to take home for enforcement of the message that bonded retainers must be flossed. We have also sent these instructions to hygienists at our referring offices, so they are aware of our efforts. Flexible spiral wire retainers which are bonded to several adjacent teeth can be 90% flossed using this method, but the next method is best for them.

Method two - for excellent brushers and flossers only

The second good way to floss is to thread the floss under the wire. This is more difficult for most people, and they will do better with SuperflossR (the end of the floss is stiff to facilitate pushing it between tooth and papilla) or a threader, but every additional requirement lessens the chances that patients will cooperate.

Failures

Almost all failures of bonded retainers occurr within a few days of a prophylaxis, presumably by overzealous scaling (operator trauma). The orthodontic team can lessen this by carefully contouring adhesive so hygienists aren't compelled to pick. A few occur within a few days of placement (salivary contamination?).

Both problems are preventable. A newsletter similar to this article can be sent to our referrers, so they understand the philosophy and care of such retainers. An antisialogogue may be used when bonding to avoid salivary contamination (Atropine 15mg child, 30mg adult).

Bonded retainers are superior in comfort, fit, and esthetics, but they do require proper flossing and professional monitoring by the entire dental team; orthodontist, family dentist, dental assistants, and hygienists.

Failing Oral Implant

October 6, 2000
Dr. Ji-Hyun Min

Osseointegration has been described as the direct anchorage of an implant by the formation of bony tissue around the implant without the growth of fibrous tissue at the bone-implant interface. A biologic failure can be defined as the inadequacy of the host to establish or to maintain osseointegration. The inability to establish osseointegration can be regarded as an early failure, whereas the inability to maintain the achieved osseointegration, under functional conditions, may be considered a late loss.

Clinically, lack of osseointegration is generally characterized by implant mobility. Therefore, in principle, a mobile implant is a failed implant. However, the failure process may be slow and gradual. An implant that is progressively losing its bone anchorage, but is still clinically stable can be defined as "failing". If properly recognized and treated, a "failing" implant might be saved. A biologic complication may indicate an increased risk for failure, which can be of temporary significance or amenable to treatment.

In general, problems limited to the soft tissue compartment and not involving the supporting bone are thus defined as "biologic complication". If the supporting bone is involved and the implant is still stable, the implant is "failing". The implant is failed if mobile. Most likely, implant complications and failures have a multifactorial background. Three major etiologic factors, which in some instances, may overlap, have been suggested; infection, impaired healing, and overload. Peri-implantitis has been referred to as "Inflammatory reactions with loss of supporting bone in the tissue surrounding a functioning implant. Fistulations and hyperplastic mucositis are often found in conjunction with loose prosthetic components. Fistula formations and abscesses can occasionally be seen in relation to dense food particles trapped in the peri-implant crevice. Hyperplastic mucositis seems to be more common under overdentures, possibly as a result of a shift in the composition of the microflora, but it has also been observed in relation to treatment with dilantin sodium, an anti-convulsive agent.

Failures related to implant healing are generally discovered in conjunction with second operation for connecting the abutment in 2-stage systems. The magnitude of the surgical trauma, micromotion, and some local as well as systemic characteristics of the host are believed to play a major role. Failures that occur between abutment connection and delivery of the prosthesis, possibly caused by premature or unfavorable loading conditions or induced by the prosthetic procedures, may, in many instances, be considered to have an "overload" etiology. After prosthesis placement, the patient should be enrolled in a custom-designed maintenance program.

Soft tissue conditions, prosthesis stability, and occlusion should always be inspected and, at regular follow up intervals, intraoral radiographs should be taken. The treatment strategy for complications and failing implants is influenced by identification of the possible etiologic factors. When a diagnosis is established and possible etiologic factors identified (superficial infection, denture-induced mucosal perforation. deep infection involving supporting bone, etc) the causative agent should be eliminated and treatment attempted as soon as possible. Therefore, patients should be advised to report immediately any adverse symptoms such as pain, sensitivity on pressure, swelling, pus, mobility of the implant components, etc. In particular, the therapy of infected failing implants should be immediate, aggressive, and combined (prolonged systemic or local antibiotics and surgical debridement). Antibiotic administration alone is unlikely to be successful because of the difficulties in eradicating bacterial colonies from surfaces of biomaterials. If no improvement occurs, removal of the implant is indicated.

References:

1. Esposito M et al. Differential diagnosis and treatment strategies for biologic complications and failing oral implants. Int J Oral Maxillofac Implants 1999;14;473-490.

2. Esposito M et al. Biological factors contributing to failures of osseointegrated oral implants (II) Etiopathogenesis Eur J Oral Surg 1988;106;721-764.

Glass Ionomer Cements

October 13, 2000
Dr. Il-Sun Yoon

The glass ionomer cements were introduced in 1972, primarily as luting agents and as direct restorative material with their unique property of being able to chemically bond with both enamel and dentin. These cements are also recognized for their ability to bond with some metals, and they have another unique property of being able to release fluoride ions. These qualities prompted some investigators to evaluate their use in orthodontics. The retention of bands cemented with glass ionomer cements is reported to be superior to those cemented with zinc phosphate cements. Similarly, decalcification under these bands cemented with glass ionomer cements is reported to be considerably less.

Although the present bonding systems with the acid-etch technique may be adequate for routine clinical use, the clinicians are becoming increasingly aware of a few drawbacks of these materials. These include loss of enamel during etching and debonding, difficulty in debonding, and decalcification around the brackets. In these regards, the glass ionomer cements are said to be superior, as etching is not required, debonding is easier, and fluoride ion release helps to prevent decalcification. However, it is still not very clear whether the presently available glass ionomer cements have adequate bond strength to withstand occlusal and orthodontic forces when used for bonding brackets.

In 1986, White described a method of bonding orthodontic brackets to the enamel surfaces of teeth, with a glass ionomer cement. However, he warned of the necessity for drying the teeth with cotton rolls and isolating the newly bonded brackets from mouth moisture during the early stage of glass ionomer setting. He also stated that the glass ionomers used in his evaluation were not as strong as "other conventional" bonding cements. He was obviously referring to composite resins. The article stressed the need to avoid early saliva contamination and to use only very light arch wires immediately after the bonding procedure, because the material did not achieve full strength for at least 24 hours.

Cook in 1990 compared the in vivo bond strength of a glass ionomer cement, Ketac (ESPE Premier Denbol Products, Norristown, Pa.), with a composite resin bonding agent. The results of his evaluation indicated that the bond strength of the glass ionomer was not nearly as good as that of the composite resin. Cook stated that thorough drying of the teeth before glass ionomer use was not necessary, but that cotton rolls should be used to isolate the field of operation.

Fajen et al. in 1990 evaluated the bond strength of three glass ionomer cements against a composite resin in vitro, and like Cook, found the bond strength of the glass ionomers to be "significantly less." Rezk-Lega et al. also conducted an in vitro study of glass ionomers versus composite resin bonding agents. Their results were similar to those previously indicated. Compton et al. compared the bond strength of glass ionomer cements in 1992, emphatically stating that they must not be contaminated by moisture during the bonding procedures. In addition, they suggested "conditioning" the tooth bond sites with a weak acid to enhance the cohesive strength.

Fricker, in 1994, worked with Fuji II LC glass ionomer cement (GC Corp., Kyoto, Japan) and found the same rate of success bonding brackets to enamel surfaces as he did with composite cements. He did mention however that a dentine conditioner was utilized for ten seconds, then rinsed, followed by lightly drying the tooth surfaces before bonding the brackets with the glass ionomer cement.

In vitro bond strength studies have shown that the bracket bond strength of composite resins are significantly higher than those of the glass ionomers. However, White has estimated that there were no more bracket failures with glass ionomers than with composite resins. If adherence to the enamel alone is the main requisite in orthodontic bonding, then composite resins alone should be used for bonding. However, glass ionomer cements possess a number of advantageous properties over composite resins that may outweigh its relatively inferior bond strength.

Four Basic Methods of Surgical Treatment of Cyst

October 27, 2000
Dr. Kweon-Heui Jeong

Cysts of the jaws are treated by one of four basic methods: enucleation, marsupialization, a staged combination of the two procedures, and enucleation with curettage.

Enucleation

Enucleation is the process by which the total removal of a cystic lesion is achieved. By definition, it means the "shelling-out" of the entire cystic lesion without rupture. Enucleation is the treatment of the choice for removal of cysts of the jaws and should be employed in any cyst of the jaw that can be safely removed without unduly sacrificing adjacent structures. The main advantage is that pathologic examination of the entire cyst can be undertaken. Another advantage is that the initial excisional biopsy (enucleation) has also appropriately treated the lesion. The patient does not have to care for a marsupialization cavity with constant irrigations. Once the mucoperiosteal access flap has healed, the patient is no longer bothered by the cyst cavity. The main disadvantage is that normal tissue may be jeopardized, jaw fracture could occur, teeth devitalization could result, associated impacted teeth that one may wish to save could be removed, and so on.

Marsupialization

Marsupialization, decompression, and the Partsch operation all refer to creating a surgical window in the wall of the cyst; evacuating the contents of the cyst; and maintaining continuity between the cyst and the oral cavity, maxillary sinus, or nasal cavity. The only portion of the cyst that is removed is the piece removed to produce the window. The remaining cyst lining is left in situ. This process decreases intracystic pressure and promotes shrinkage of the cyst and bone fill. The following factors should be considered before deciding whether a cyst should be removed by marsupialization
1. Amount of tissue injury. Proximity of a cyst to vital structures can mean unnecessary sacrifice of tissue if enucleation is employed
2. Surgical access. If access to all portions of the cyst is difficult, portions of the cyst wall may be left behind, which could result in recurrence. Marsupialization should be considered.
3. Assistance in eruption of teeth. If an unerupted tooth that is needed in the dental arch is involved with the cyst (that is, a dentigerous cyst), marsupialization may allow its continued eruption into the oral cavity.
4. Extent of surgery. In an unhealthy or debilitated patient marsupialization is a reasonable alternative to enucleation, because it is simple and may be less stressful for patients.
5 Size of cyst. In very large cysts, there is a risk of jaw fracture during enucleation. It may be better to marsupialize the cyst and defer enucleation until after considerable bone fill has occurred.

The main advantage is simple procedure to perform. It may also spare vital structures from damage should immediate enucleation be attempted.
The major disadvantage is that pathologic tissue is left in situ without thorough histologic examination. Although the tissue taken in the window can be submitted for pathologic examination, there is a possibility of a more aggressive lesion in the residual tissue. Another disadvantage is that the patient is inconvenienced in several respects. The cystic cavity must be kept clean to prevent infection, because the cavity frequently traps food debris. In most instances this means that the patient must irrigate the cavity several times every day with a syringe. This may continue for several months, depending on the size of the cystic and the rate of bone fill.

Marsupialization followed by enucleation

Marsupialization is frequently followed by enucleation later date. Rapid Initial healing is obtained after marsupialization, but the size of the cavity may not decrease appreciably past a certain point. The objectives of marsupialization procedure have been accomplished at this time, and secondary enucleation may be undertaken without injury to adjacent structures. This combined approach reduces morbidity and accelerates complete healing of defect.

Enucleation with curettage

Enucleation with curettage means that after enucleation, a curette or bur is used to remove 1 to 2 mm of the bone around the entire periphery of the cystic cavity. Its purpose is to remove any remaining epithelial cells that may be present in the periphery of the cyst wall or bony cavity. These cells could proliferate into recurrence of cyst. But curettage is more destructive to adjacent bone and other tissues. Curettage must always be performed with great care in order to avoid these hazards.

Reference
1. Larry J. Peterson: Contemporary Oral and Maxillofacial Surgery, C,V. Mosby Co.,St Louis, 1988, pp498-509.
2. Clauser C, Zuccati G, Barone R, Villano A: Case Report : Simplified surgical ortho -dontic treatment of a dentigerous cyst, J Clinical Ortho, 1994:28:103-6.
3. Sain D, Hollis WA, Togyre AR. Correction of a superiorly displaced impacted canine due to a large dentigerous cyst. Am J Ortho 1992:102:270-6.
4. Archer, W.H.: Oral and Maxillofacial Surgery, 5th ed., W.B. Saunder Co., Phila -delphia,1975, pp524-705.

Distraction Osteogenesis

November 17, 2000
Dr. Mi-Young Seo

Maxillomandibular hypoplasia, facial asymmetry, and congenital micrognathia are relatively common abnormalities of the craniofacial complex. Numerous surgical procedures have been advocated to correct the facial deformity in the patients with hemifacial microsomia, including chondrocostal grafts, mandibular osteotomies combined with bone grafts, and maxillary osteotomies done at early age or after permanent dentition is completed.

Despite the fact that conventional orthognathic surgery and craniofacial reconstruction have experienced wide spread success, several limitations are associated with these treatment modalities. One of these limitations is the inability of the muscles to be acutely stretched without the inherent risk of relapse. Moreover, many of the congenital deformities require such large musculoskeletal movements that the soft tissues simply will not accommodate the change, leading to compromised function and esthetics unless additional soft tissue procedures are performed. In addition, modern surgical intervention only permits acute changes in the spatial arrangement of bones with limited possibilities for new bone growth. It does not allow complete bone sculpting, that is, changing the shape and form of the bones to maximize the three-dimensional structural, functional, and esthetic needs of the patient.

Recently, a number of experimental and clinical investigations have demonstrated that gradual mechanical traction of bone segments at an osteotomy site created in the craniofacial region can generate new bone parallel to the direction of traction. This phenomenon, known as distraction osteogenesis, opens up new possibilities in the correction of craniofacial deformities by orthodontists and maxillofacial surgeons. Specifically, the process is initiated when incremental tractions is applied to the reparative callus that joins the divided bone segments and continues as long as this tissue is stretched. The traction generates tension within the callus and stimulates new bone formation parallel to the vector of distraction. Importantly, distraction forces applied to bone also create tension in the surrounding soft tissues, initiating a sequence of adaptive changes termed distraction histogenesis. Under the influence of tensional stresses produced by gradual distraction, active histogenesis occurs in different tissues, including: skin, fascia, blood vessels, nerves, muscle, ligament, cartilage, and periosteum. These adaptive changes in the soft tissues may allow larger skeletal movements while minimizing the potential relapse seen in acute orthopedic corrections.

Based on recent dog experiments, it is clear that the regenerate tissue begins to mineralize within the first 2 weeks of distraction, and remodeling begins shortly thereafter. Because orthodontic tooth movement is based on mechanically mediated bone remodeling, there is no reason to believe that tooth movement could not be initiated within the first month of consolidation.

The use of slow incremental traction has allowed up to 20 mm of mandibular lengthening with no associated pain. Because these conditions are typically treated by a team approach, a thorough understanding of the evolution and future development of osteodistraction is of paramount importance to the orthodontist.

Considerations in Selecting a Digital Camera for Orthodontic Records

November 24, 2000
Dr. Eun-Jeong Kim

The cost for digital cameras has dramatically decreased in recent months makes digital records in the orthodontic office a practical reality. Specifically, our needs include the ability to take excellent facial images and then conveniently switch the camera and its accessories to intraoral capability. This involves the lighting source(s), lens change, focusing method, image preview, and image capture. Other considerations in choosing the right digital camera include resolution, power source, portability, and ease of use.

1. Resolution
Camera resolution is the factor that produces a sharp or not so sharp image. Although many argue that better resolution is always desired, such may not be the case as there will be a downside to better resolution. The stored file will be larger, it may take longer to download, upload, and print, and the camera may cost more as a result of the higher resolution. Before deciding that higher resolution is better, one should first determine one's requirements.

2. Lens focal length
Lens focal length needs to be correct to avoid a photographic effect called perspective distortion, especially for facial images. A short focal length lens will elongate the nose in a frontal picture; a long focal length lens will have the reverse effect. The effective focal length of the human optical system is equivalent to a 90mm lens, which is why a portrait is typically taken with a lens of this length. Taking the facial images with a lens approximating 90mm is important if perspective distortion is to be avoided.

3. Lighting source(s)
If adequate lighting for intraoral images is desired, typically the camera will need an onboard flash lighting source associated with the macro or close-up lens. Flash position relative to the lens is important for perfect intraoral lighting, as any flash mounted on top or on the side of the lens will by definition create a shadow on the opposite side of the image. A top mounted flash used for a facial photograph will cast a shadow below the nose and chin of the lateral facial image. This is usually eliminated with a slave back lighting system.

4. Lens change
For most digital cameras, the lens focal length will have to be changed between taking intraoral and facial pictures. Sometimes an electronic "zoom" button on the camera accomplishes this with a digital focal length switch. Other cameras use a swinging gate, snap on, or screw on lenses.

5. "Through the lens " viewing
Historically, 35mm cameras found the subject through a viewfinder, a viewing device located in the camera body, above the lens. This worked nicely for subjects taken at distance, but when the camera to subject becomes close, the lens is seeing something different than the viewfinder- a phenomenon called parallax. The 35mm reflex camera solved this problem with the invention of " through the lens viewing by placing the view finder directly above the lens then directing the viewing path through two mirrors located at 45°to each other and the lens. When the shutter is depressed, the lower mirror elevates before the shutter opens thus exposing the film to the precise image seen by the lens.
Digital cameras typically come with a viewfinder, which will not work for close-up intraoral images. Typically, an LCD (liquid crystal display) is added to the camera so it electronically sees just what the lens is viewing. High-end digital cameras combine a single lens reflex body with a digital back.

6. Image preview and capture
The camera's ability to view the image about to be taken, then "freezing" it for inspection before saving it is a nice feature if one wants to conveniently take high-quality pictures.

7. Power source
AC is generally not acceptable as it limits portability. A rechargeable battery is best, and no rechargeable A cells with a short life will be most inconvenient when they need replacement in the middle of taking a series of images.

Long-Term Effects of Chincap Therapy and TMJ Morphologic Adaptation

November 24, 2000
Dr. Young-Ah Youn

Chincap therapy has been the usual technique for the treatment of growing patients with true, mild skeletal class ¥² malocclusion. For the last 20 years, a number of clinical and experimental studies have been reported that chincap force has several orthopedic effects such as redirection of mandibular growth, backward repositioning of the mandible, retardation of mandibular growth, and the remodeling of the mandible. These effects may induce permanent skeletal changes and can alter the prognathic skeletal profile, particularly when applied at early ages.

Although they represent significant improvement in younger children, the changes in skeletal profile are not maintained for a long period in most cases. This suggests that profiles have a tendency to return to their original shapes which may have been predetermined morphogenetically. It has been speculated that some catch-up mandibular growth or repositioning may occur during or after the pubertal growth period. Therefore by the Sugawara et. al. it is desirable that the chincap therapy should be continued until the mandibular growth is complete.

The final skeletal profile shows no significant difference between the anteroposterior position of the mandible but vertical position of the mandibles shows significant difference after chincap therapy. Pearson, Heckman and Hiorse et. al. reported that the chincap could control dentoalveolar growth and reduce lower facial height. Wendel and Nanda also reported that the mandible exhibited less downward displacement relative to the cranial base as a result of chincap therapy. These findings may indicate that the mandibular position is more alterable vertically than anteroposteriorly and such effects could exist for a longer period in the face.

After chincap therapy, a significant change in the TMJ was observed in the eminence to FH plane angle, condyle head angle, height of condyle, height of fossa, width of fossa and superior and anterior condyle space. Chincap stress emanated through the mandibular body, the angle, and retromolar triangle of the mandible, radiating in a posterosuperior fashion and concentrating at the neck of the condyle. By chincap application, bone resorption on the roof of the fossa and posterior surface of the condyle and bone deposition on the posterior border of the ramus, ant surface of the condyle.

Summarizing, the fossa was deepened and widened, mandibular heads were bent forward and elongated and the clearance between the condyles and fossa was narrowed.

Altered Passive Eruption

December 1, 2000
Dr. Hyun Kim

With the increased emphasis on facial esthetics, both patients and dentists are developing a greater awareness of the impact of the gingiva on the beauty of the smile. In recent years, more attention has been given to the problem of excessive gingival display.

Common causes of short clinical crowns include coronal destruction resulting from traumatic injury, caries, or incisal attrition, as well as a coronally situated gingival complex resulting from tissue hypertrophy or a phenomenon known as altered passive eruption. And one of the most commonly overlooked etiologies of the short clinical crown is altered passive eruption.

Passive eruption is the apical shift of the dentogingival junction and it can be divided into four stages. Stage 1. The epithelial attachment or junctional epithelium rests on the enamel surface. Stage 2. The epithelial attachment rests on the enamel as well as the cementum. Stage 3. The epithelial attachment rests entirely on the cementum. Stage 4. Inflammation causes the epithelial attachment to migrate apically. When passive eruption does not progress past stage 1 or 2, it is referred to as altered or delayed passive eruption.
Occurrence of altered passive eruption is unpredictable, but the incidence in the general population is about 12 percent.

When altered passive eruption is presented, there are several problems. It has been postulated by Prichard that an incisally located gingival margin has diminished protection from the trauma of oral function, leading to accelerated gingival pathosis. Because the gingival margin is on the convex facial surface of the enamel, it is not protected from the excursion of food during mastication.
Restoration of teeth with altered passive eruption poses both functional and esthetic challenges for the dentist. And Restorations and orthodontic appliances placed in or near the sulcus may cause an exaggerated inflammatory response.

When altered passive eruption is diagnosed, the age of the patient should be considered. Normal passive eruption may continue throughout the teen-age years. Gingiva may be present on the crown of the tooth in adolescents because the dentogingival unit has not fully receded to its final position. The anterior teeth typically undergo passive eruption in the early teen years. Passive eruption of the posterior dentition may continue into the 20s. Therefore, a diagnosis of altered passive eruption cannot be made until one is sure that passive eruption should be complete.

The first step in the diagnostic process is to observe the patient both in repose and smiling a natural smile. If there is an excessive display of gingiva during smile, further diagnostic data are required. Then, the length and activity of the maxillary lip must be evaluated. If the gummy smile is due solely to inadequate lip length or hyperactivity, no treatment is generally indicated. It is important to discuss this limitation with the patient.
Next, the dentist should attempt to gently locate the cementoenamel junction using an explorer subgingivally. There may be no other signs of disease such as bleeding upon probing, suppuration, inflammation or radiographic bone loss. If CEJ is located in a normal position in the gingival sulcus, then the patient probably does not have altered passive eruption. In this case, the short teeth are probably due to incisal wear or a variation of normal dental anatomy. When the CEJ is not detectable in the sulcus, a diagnosis of altered passive eruption may be made, and crestal bone sounding is performed. Because it is usually determined that the CEJ is approximately at the base of the sulcus in altered passive eruption, the measurement can be used to determine the relationship between the CEJ and the alveolar crest. Nature requires approximately 2 mm for both epithelial and connective tissue attachment between the CEJ and alveolar crest. Therefore, a determination can now be made regarding whether a gingivectomy and/or gingival flap with osseous resection is indicated.

Altered passive eruption is characterized by excessive gingiva and sometimes hard tissue covering the clinical and anatomic crown. Altered passive eruption may be localized or generalized and may exist in conjunction with periodontal disease. This entity should be given consideration when undertaking restorative dentistry, orthodontics and cosmetic alterations. Correct diagnosis of this consideration and proper therapy will result in improved dental care and esthetic results for the patient.

Osseointegrated Implants as Orthodontic Anchorage

December 7, 2000
Dr. Yeoun-Soo Lee

In recent years the demand for orthodontic treatment in adults has increased significantly, mainly due to the fact that patients today are more aware of their dental health situation and require the result to be an aesthetic improvement. Furthermore, Thilander (1979, 1992) is more aware of the problems of occlusion and tooth alignment in the total treatment planning. Some obvious differences exist between the orthodontic treatment of adults and that of children, due to basic biological concepts, as well as biomechanical principles of force and anchorage.

Anchorage control is the most important determinant for successful orthodontic treatment. Each tooth has its own anchorage potential, which is among others dependent on the length and the surface of its periodontal ligament, its biomechanical characteristics, and the density of the alveolar bone. Occlusion, masticatory activity, craniofacial morphology and oral habits influence this biological anchorage.

In some patients, the orthodontic treatment may be difficult or even impossible to perform as in partially edentulous jaws. To overcome such problems, the use of osseointegrated implants has been discussed, since experimental studies of Roberts et al (1984, 1989), Smalley et al (1988), Turley et al (1988), and Linder-Aronson et al (1990) have shown that implants, loaded with orthodontic forces, remained stable (ankylosed anchorage). According to study on osseointegrated oral implants of Adell et al (1990), remarkable success rates both in full and partial edentulism has been shown. Thilander et al (1992) reported that osseointegrated oral implants act as ankylosed teeth. Roberts et al (1989) reported that the intimate bone-to-implant apposition prevents any movement during orthodontic force applications and this allows tooth movements, which are very difficult or even impossible if they are to be carried out based on conventional dental anchorage. Jan Odmam's study (1994) showed that osseointegrated implants resisted displacement forces in all planes and functioned well as orthodontic anchorage units. Consequently, it was possible to perform tooth movements by means of the osseointegrated support without reciprocal action. After the orthodontic treatment, the implants also served as abutments for permanent prosthetic reconstructions of missing teeth. Furthermore, there was no adverse increase in the loss of marginal bone support at the fixtures used for orthodontic anchorage. Implants proved to be very useful aids in orthodontic treatment, especially in cases with a large number of missing teeth, which could not have been treated without implant anchorage.

Special care must be taken with the use of endosseous implants in growing patients. Like ankylosed teeth, implants will end up in infra-occlusion when compared with the neighboring erupting teeth. Endosseous implant insertion before the end of the growth of the jaws and/or rapid tooth eruption is therefore looked upon with reluctance. Hand wrist X-rays give an indication of the overall growth of a patient whether there is still much growth to be expected or not. Also Spear et al (1997) reported that superimposition of two headplates taken at an interval of 6 months gave more detail on growth of the jaws.

There was no difference in the orthodontic treatment procedures carried out in these patients, compared to adult conventional orthodontics. Odmam's study showed that the only technical problem experienced was loosening of brackets on fixture crowns in some patients.

Obstructive Sleep Apnea Subtypes

December 22, 2000
Dr. Hee-Chang Park

Obstructive sleep apnea occurs because of recurrent occlusion of the upper airway during sleep. Upper airway collapse during sleep is a result of interrelated structural and functional factors.

The majority of patients with OSA are obese; however, some patients with OSA are not obese. OSA patients with and without obesity are likely to have a different pathogenesis. The characteristics of the two distinct groups segregated by the cluster analysis, the patients with high Apnea Index and low Body Mass Index ratio had proclined mandibular incisors, retruded mandibles, and a skeletal open bite tendency. The other patients with low Apnea Index and high Body Mass Index ratio had inferior hyoid bones and large soft palates. The high Apnea Index/low Body Mass Index ratio patients were characterized by skeletal deformities, and the low Apnea Index/High Body Mass Index ratio patients were characterized by soft tissue abnormalities.

In the patients with a high Apnea Index and a low Body Mass Index ratio, a high Apnea Index was related to a large skeletal anterior discrepancy, a steep mandibular plane, and an inferoanterior position of the hyoid bone. In the patients with a low Apnea Index and high Body Mass Index ratio, severe OSA was related to a large tongue and a small upper airway.

The hyoid bone serves an important respiratory function. In the present study, an inferior- and anterior-positioned hyoid bone was strongly associated with a severe OSA in the high Apnea Index/low Body Mass Index ratio group. In comparison, the low Apnea Index/high Body Mass Index ratio group revealed an inferior-positioned hyoid bone. In patients with high Apnea Index and low Body Mass Index ratio, the hyoid bone may migrate inferiorly and anteriorly to maintain airway patency as the Apnea Index increase. In contrast, patients with low Apnea Index and high Body Mass Index ratio tended to have a large tongue and soft palate, and a small upper airway which may be related to obesity. In compensation for these soft tissue abnormalities of the upper airway, the hyoid bone may migrate and reach an anatomic limitation. Consequently, mean differences were determined, but statistically significant correlations between Apnea Index and hyoid bone variables could not be found.

With regard to the contribution of obesity to the pathogenesis of OSA, more fat was present in the regions of pharynx in the patients with OSA. In low Apnea Index/high Body Mass Index ratio patients who are obese, a large tongue and/or a large soft palate possibly related to obesity may result a small upper airway and consequently contribute to the development of OSA. On the contrary, in high Apnea Index/low Body Mass Index ratio patients who are moderately obese, skeletal abnormalities may be more important etiologic factors in OSA.

These two groups may represent different disease entities. The high Apnea Index/low Body Mass Index group could respond well to the procedures that advance the mandible forward. In contrast, weight reduction and/or uvulopalatopharyngoplasty may better contribute to the improvement of OSA symptoms for the low Apnea Index/high Body Mass Index group.

Bonding to Porcelain

December 29, 2000
Dr. Jeong-Soon Ahn

As a result of increased education and communication, the field of orthodontics has recently expanded to include a greater number of adult treatment procedures. With this increased demand for adult orthodontic treatment, a problem that frequently arises is the placement of appliances on teeth restored with porcelain and fixed-gold prostheses. Although bands can be placed on single porcelain or gold crowns, this is not possible on the abutment teeth of fixed bridges. The past decade has seen many advances in the direct bonding of orthodontic attachments to natural teeth. Recent progress in materials and techniques suggest that direct bonding of orthodontic attachments to surfaces other than enamel may now also be possible.

Conventional acid etching is ineffective in preparing porcelain surfaces for mechanical retention of orthodontic attachments. Roughening the porcelain surface with burs or green stones, adding a porcelain primer, and using a highly-filled adhesive have been shown to add progressively to bond strengths with glazed porcelain. These bond strengths can reach values such that the porcelain surface can be damaged by machines during debonding. Although recent laboratory studies have indicated that surface roughening with burs or stones and silane treatment can produce clinically acceptable bond strengths, the practitioners continue to find unacceptably high failure rates. The continuously increasing load applied to bonded brackets in vitro is not the same as the force application that occurs clinically. Outside of traumatic incidents, brackets that loosen in the mouth probably do so as a result of repeated stress producing microcracks that propagate until bond failure occurs. Furthermore, a few authors have claimed that silane application does not make a significant contribution to a chemical bond. Therefore orthodontists should investigate the possibility of etching porcelain with hydrofluoric(HF) or other acids, a technique introduced in the early 1980s to increase the microretention of porcelain laminate veneers. The most commonly used porcelain etchant is 9.6% HF acid in gel form, applied for two to four minutes. The etchant creates microporosities on the porcelain surface that achieve a mechanical interlock with the composite resin. The etched porcelain will have a frosted appearance similar to that of etched enamel. A silane bonding agent such as Ormco Porcelain Primer, Scotchprime, or Clearfil Porcelain Bond is then painted onto the porcelain surface and allowed to dry. This coupling agent alters the surface so that chemical and mechanical bonding are possible. Application of a 1.23% acidulated phosphate fluoride (APF) gel for 10 minutes may provide equivalent bond strength to 9.6% HF acid applied for four minutes. If a 4% APF gel (containing 1.43% HF acid) is used, the etching time is reduced to a more clinically acceptable two minutes. Therefore, when maximum bond strength to porcelain is desired, etching with an HF or APF gel is recommended.

Etching of glazed porcelain produces less prominent micromechanical patterns than etching of porcelain roughened by aluminum oxide sandblasting. Intraoral sandblasting is preferable to grinding with a green stone, which can produce microcracks. However, clinicians may be reluctant to roughen a porcelain surface and destroy the glaze on a maxillary incisor porcelain crown or laminate veneer unless the roughened surface can be repolished. The contour, color, and reflective quality of the porcelain may not be restorable if extensive defects are created in debonding. Although there is some difference of opinion, it appears possible to restore the original finish with graded Shofu Ceramiste polishing points or porcelain polishing wheels, followed by application of diamond polishing paste.

Conclusionally, for optimal bonding of orthodontic brackets to porcelain surfaces, we recommend the following procedure:

1. Deglaze the porcelain surface by sandblasting with 50-micron aluminum oxide for two to four seconds.
2. Etch the porcelain with 9.6 % HF acid gel for two minutes.
3. Apply two or three coats of a silane porcelain primer.
4. Bond the brackets with a highly filled bisGMA resin such as Concise.

We feel if these procedure were understood, perhaps we will experience a greater success rate in bonding to porcelain.

Topical Fluoride in Orthodontic Bonding

January 5, 2001
Dr. Eun-Hee Ko

Use of a post-etch fluoride treatment in association with bracket bonding has been proposed as a preventive measure. Topical fluoride applications fill in the interprismatic spaces produced by etching and thus reduce the bonding capacity of adhesives. Ideally, this would cause minimal interference with the application and subsequent adhesive strength of the resin bond, while providing maximal fluoride uptake for protection against the initiation of carious lesions.

Several investigations have shown that topical treatment with either neutral or acidified NaF preparations results in fluoride incorporation into intact enamel. Other investigators have found that acid-etching the enamel before fluoride application increases fluoride uptake.

Increased depth of etch and decreased fluoride mass upon successive etchings corroborate previously published work demonstrating that successive acid etches remove an increasingly greater mass of enamel. Etches of fluoride-treated specimens, was not as deep as its respective etch on the control specimens. This suggests higher levels of incorporated fluoride in the treatment specimens that topical fluoride treatment of enamel produces a more acid-resistant outer layer. Increased fluoride mass in enamel plays an important role in decreased enamel solubility.

The large variability in etch depth and fluoride mass seen in specimens may be explained by the systemic fluoride history of the teeth. Although the precise history of each tooth was not known, it is possible that some of the teeth were from individuals who used fluoridated drinking water as children, and some from individuals who did not. The amount of fluoride actually incorporated into enamel as Ca5(PO4)3F, in comparison with the amount of fluoride persisting on the surface as CaF2, remains unknown. However, we believe that there was little CaF2 remaining on the fluoride-treated surfaces. This conclusion is based on the low fluoride levels found with the application of 4% NaF in dH2O, a treatment which is likely to produce large amounts of CaF2.

Further, the thorough rinsing and storage in distilled water would have removed much of any CaF2 that might have formed. Finally, there were no clear visual differences, as viewed by SEM, in the surfaces of fluoride-treated and control tooth halves. Acidified NaF is more readily incorporated into enamel than is neutral NaF.

Assuming that the practitioner wants to use a topical fluoride treatment to increase enamel fluoride levels, the next question is when it should be applied in relation to the bonding procedure. It could be applied either immediately after acid etching but before resin placement, or after the entire bonding procedure has been completed.

Studies using SEM to examine the effect of various topical fluoride treatments on acid-etched enamel surfaces have demonstrated the formation of a globular reaction product (possibly CaF2) on the etched surface following topical fluoride treatment. This reaction product could cause a reduction in resin bond strength.

However, studies in which bond strength has been measured indicate that some topical fluoride treatments (eg. acidified NaF, stannous fluoride, and basic phosphate fluoride) did not cause significantly lower bond strength.

Thorough rinsing following topical fluoride application may be important to remove residual fluoride products that could interfere with bond strength. The best time to apply a topical fluoride treatment during the orthodontic bracket bonding procedure remains an open question.

In general, topical application of acidified NaF appears to be more effective than neutral NaF treatments.

Orthodontic Space Consolidation for Implant Prostheses

January 12, 2001
Dr. Jeung-Suk Lee

The concept of osseointegration was developed and the term was coined by Dr. Per-Ingvar Branemark, Professor at The Institute for Applied Biotechnology, University of Goteborg, Sweden. He discovered a direct, strong bone anchorage of a titanium chamber he was using while studying microcirculation in bone repair mechanisms. The titanium chamber was surgically inserted into the tibia of a rabbit. From additional information gathered in this study, he found titanium was the best material for artificial root replacement. Direct bone anchorage has been shown to be very strong. A force of over 100 kilograms was applied to dislodge an implant but instead, a fracture of the implant site was necessary for implant removal.

Diagnostic study casts are used to evaluate location and number of fixtures. The areas for fixture placement and remaining dentition should be checked carefully. If two fixtures will be placed, a minimum 17.0 mm of space is necessary between remaining teeth; if three fixtures will be placed, a minimum of 24.0 mm space is necessary to insure safe fixture placement.

Bone Height - The minimum height of available bone for endosteal implants is in part related to the density of bone. The more dense bone may accommodate a shorter implant, and the least dense weaker bone requires a longer implant. The mandibular first premolar region may present reduced height of available bone compared with the anterior region, because of the anterior loop of the mandibular canal (when present) as it passes below the foramen and proceeds superiorly, then distally, before its exit through the mental foramen. The original anterior maxillary available bone height is less than the mandibular available bone height. The opposing landmarks limit the available bone height more in the posterior regions. The available bone height is first estimated by radiographic evaluation in the edentulous ideal and optional regions where implant abutments are required for the intended prosthesis. A panoramic radiograph is still the most common method used for this purpose.

Bone Width - Once adequate height is available for implants, the primary criterion affecting long-term survival of endosteal implants is the width of available bone. Root form implants of 4.0 mm crestal diameter usually require more than 5.0 mm of bone width to ensure sufficient bone thickness and blood supply around the implant for predictable survival. These dimensions provide more than 0.5 mm bone on each side of the implant at the crest. Because the bone usually widens apically, this minimum dimension rapidly increases.

Bone Length - The mesiodistal length of available bone in an edentulous area is often limited by adjacent teeth or implants. The length of available bone necessary for endosteal implant survival depends on the width of bone. For bone more than 5 mm wide, a minimum mesiodistal length of 7 mm is usually sufficient for each implant. A width of bone less than 5 mm requires a 3.2 mm implant with compromises such as less surface area and greater crestal concentration of stress. In the narrower ridge, it is often indicated to place two or more implants of smaller diameter when possible, in order to achieve sufficient implant-bone surface area to compensate for the deficiency in width of the implant.

In 1994 the number of implants used in the United States averaged fewer than two per patient. This is a consequence of most implant treatments including the single tooth implant, small span fixed partial dentures connecting implant and teeth, and two implant overdentures. Single tooth implants are now the most common implant procedure performed in the United States. One of the most common sites for a single tooth implant is in the maxillary anterior arch. The mesiodistal width of most Division A implant designs(>4.0 mm) require at least 6 mm of bone between the roots of the maxillary central incisor and canine to accommodate for the implant dimension, surgical error, hard and soft tissue health, interdental papilla, proper contour, and daily care. Yet, often less than 5 mm of bone is available between these adjacent teeth. Convergent roots of the adjacent natural teeth further compromise the implant placement.
As a result, smaller diameter implants may need to be selected which satisfy the mesiodistal and height requirements but often compromise the facial crown contour, requiring the creation of an overcontoured facial emergence profile, which has long-term maintenance limitations. The potential damage to adjacent roots caused by angulation and proximity is an obvious limitation of the procedure and should be carefully considered and reviewed with the patient.

Parafunctional Activities of the Masticatory Muscles

February 2, 2001
Dr. Hwang-Sog Ryu

Activities of the masticatory muscles can be divided into two basic types: functional, which include chewing, speaking and swallowing, and parafunctional, which include clenching or grinding of the teeth and various oral habits. Parafunctional activity can be subdivided into two general types: that which occurs through the day (diurnal) and that which occurs at night (nocturnal).

Parafunctional activity during the day consists of clenching, grinding, and many oral habits that are often performed without the individual even being aware of them. It is not uncommon during daily activities for individuals to place their teeth together and apply force. This type of diurnal activity may be seen in someone who is concentrating on a task or performing a strenuous physical chore. The masseter muscle contracts periodically in a manner that is totally irrelevant to the task at hand. The clinician must recognize that most parafunctional activities occur on a subconscious level. In other words, individuals are often not even aware of their clenching or cheek-biting habits. It is therefore difficult to question the patient and expect a reliable response. This is especially true of nocturnal parafunctional activity.

The exact mechanism activating muscle hyperactivity has yet to be clearly described. Many factors, including emotional stress, may affect the level of activity. The influence of these factors, however, may vary greatly not only between patients but also between the types of parafunctional activities. They can be either diurnal or nocturnal. The characteristics and controlling factors of each are likely to be different. Diurnal activity may be more closely related to an altered occlusal condition or to increased levels of emotional stress, or both. Since diurnal activity can usually be brought to the patient's attention, it is often managed well with patient education, relaxation, and biofeedback techniques.

Patient education should begin with informing the patient that the teeth should only contact during chewing, speaking, and swallowing. During all other times the jaw should be positioned with the teeth apart. Most patients are quite unaware of their tooth contacts, and making them aware is the first step in controlling excessive tooth contacts during in controlling excessive tooth contacts during unnecessary times. Once the patient becomes aware of tooth contacts, he or she should be asked to make a conscious effort to keep the teeth apart during all waking moments.

Nocturnal bruxism, however, seems to be different. It appears to be influenced less by tooth contacts and more by emotional stress levels and sleep patterns. Because of these differences, nocturnal bruxism responds poorly to patient education, relaxation biofeedback techniques, and occlusal alterations. It can in many cases be effectively reduced with occlusal appliance therapy. The mechanism by which occlusal appliances reduce bruxism is not clear.

Since diurnal and nocturnal parafunctional activities appear to be different in character and origin, it is important that they be identified and separated. Often this differentiation can be made through a careful history regarding the timing of symptoms. Identifying the type of parafunctional activity present allows for more effective treatment selection.

References

Okeson JP. Management of temporomandibular disorders and occlusion. Mosby-Year Book, St Louis 1998:161-70.

Kleinberg I. Bruxism: aetiology, clinical signs and symptoms. Aust Prosthodont J 1994;8:9-17.

Pierce CJ, Gale EN. A comparison of different treatments for nocturnal bruxism. J Dent Res 1988;67:597-601.

Is The Mandibular Third Molar A Risk Factor For Mandibular Angle Fracture?

Ma'aita J, Alwrikat A.
Oral Surg Oral Med Oral Pathol
2000;89:143-6.

March 9, 2001
Dr. Hyun Kim

Orthodontists are frequently making recommendations for removal of third molars. We may base the decision on the lack of sufficient space for eruption, potential for pericoronitis, possible effects of third molars on orthodontic results or compromised bone support for the second molars. What about the effect of third molars on the strength of the mandible and the susceptibility to the fracture?

The literature has mixed conclusion on this relationship. A new study of Jordan by Dr. Ma'aita provided additional informations regarding the risk of mandibular fracture in patients with third molars. This report appears on the February 2000 issue of Oral Surg Oral Med Oral Pathol.

The author retrieved patient records on radiographs for 685 consecutive mandibular fractures occurring between 1993 and 1998 in a group of military hospitals in Jordan. Seventy patients had incomplete records, and could not be included, which left the study group of 615. The panoramic radiographs were used to determine the presence of third molars. If third molars were present, they were further classified as to the angulation and depth of impaction. The mechanism of injury was recorded and the age and sex of the patient noted. The mean age of the fracture patient was 33 years.

Not surprisingly, males made up really 80 percent of the fracture group. The most frequent cause of the fracture was motor vehicle accident which made up almost 60 percent, followed by falls, fights, sports injuries and others. Almost 70 percent of study group had third molars present. Analysis of the data revealed that the patients with third molars present were more than two times more likely to have angle fracture, compared to those without third molars. The risk of angle fracture was found to be related to the severity of impaction as well, that is the patients with distoangular, vertical, or horizontal impaction were in the greater risk for angle fracture.

This data supports the theory that the presence of unerupted third molar in angle region of the mandible interrupts a trabecular bone pattern thereby creating a relative weakness.  What this study doesn't tell us is whether removal of the third molars can help prevent fracture due to the trauma or whether the fracture may just occur in a different place.  If you like to see more details of this study, the entire article, entitled "Is The Mandibular Third Molar A Risk Factor For Mandibular Angle Fracture?" is found in the February 2000 issue of Oral Surg Oral Med Oral Pathol.

Long-Term Follow-Up of Clinical Symptoms in TMD Patients Who Underwent Occlusal Reconstruction by Orthodontic Treatment.

Imai T, Okamoto T. et al.
Eur J Orthod 2000;22:61-67.

March 16, 2001
Dr. Kweon-Heui Jeong

People who have undergone splint treatment for internal derangement of the temporomandibular joint may undergo subsequent orthodontic treatment to stabilize the occlusion. Are these patients at risk of having the symptoms return during orthodontics?
Some practitioners advocated continuing use of splint therapy during orthodontic treatment, another discontinued the splint when beginning treatment.

A group, led by Dr. Tohru Imai from Hokkaido University in Japan, recently published the findings of the study that compared groups treated orthodontically after initial splint therapy. All patients in the study were diagnosed to having internal derangement of the TMJ and has splint therapy initially.

The first group of 18 patients then underwent orthodontic treatment with fixed appliances in conjunction with continuous use of splints. The second group of 27 patients underwent fixed orthodontic treatment without the further use of splints. The third group of 13 patients did not receive any orthodontic treatment, only the splint therapy.

This was a retrospective study and the authors indicated those patients in the first group that did receive splint therapy along with orthodontic treatment received continuous splint treatment, because they had a changed mandibular positions or had recurring symptoms. This indicates the study groups may have a difference at the beginning of orthodontic treatment so that comparisons after treatment may not be the results at the different treatment method employed.

The results in this investigation show that both groups undergoing orthodontic treatment had an improvement of symptoms during the orthodontic treatment periods. About 80% of all patients had pain on movement before any treatment. This decreased to about 40% after initial splint therapy and decreased further to less than 10% at the end of orthodontic treatment. One year after the completion of orthodontic treatment, the number with some pain on movement increased slightly to about 20%. That was about the same as the control group who had splint treatment only. There was no difference noted between those patients who had orthodontic treatment with splints and those who had orthodontic treatment without.

The authors also looked at the type of malocclusion found in treatment groups. They found about 40% had anterior openbites and 12% had posterior crossbites. This is a greater than the prevalence of this type of malocclusions in the general population and may indicate susceptibility of this patients to TMD problems.

This study does give us some comfort and the returning of TMD symptoms during or after orthodontic treatment is very low. Again the authors did not find any difference between a group with continued splint's use during fixed appliance treatment and a group that had no splint during orthodontic treatment.

More details on this study can be found in the February 2000 EJO in an article entitled "Long-term follow-up of clinical symptoms in TMD patients who underwent occlusal reconstruction by orthodontic treatment."

A Xenon Arc Light-Curing Unit for Bonding and Bleaching

Cacciafesta V. Sfondrini MF. Sfondrini G
J Clin Orthod 2000;34:94-96.

March 23, 2001
Dr. Ji-Hyun Min

How would you like to bond orthodontic brackets with only 2 seconds of light curing time. This is the promise offered by a new Xenon Arc Curing Light described in the February 2000 issue of the Journal of Clinical Orthodontics. Dentistry first began using light-cured composite materials more than 30 years ago.

These first systems used the initiator that was sensitive to the wavelength of ultraviolet light. These early light-cured systems required extended curing times and some concern about the long term safety of using the ultraviolet light. Visible light curing was introduced in about 1980. The composites and need system used camphoroquinone as initiator that is sensitive to light in the range of 470 nanometers, a wavelength which is within the visible light range. These newer systems also require less curing time and had a greater depths of cure than the ultraviolet light counterparts. This is the type of composite system that is widely used in orthodontics today.

In the early 1990's, Argon lasers were introduced. They could greatly reduced the curing time. These have not been widely used in orthodonics due to the high cost of the lasers and concerns about the safety of the laser light.

Most recently, the Plasma Arc Curing System has been introduced for use in Dentistry. This Xenon Arc Light is filtered to provide the intense light focuses on the 470 nanometer wavelength to activate the camphoroquinone initiator. The authors referenced literature showing that the Xenon Light System provides the same strength 24 hours after curing has the standard visible light or argon laser. The claim is made that this new curing light can cure composite through enamel so that curing from the lingual is possible when bonding brackets.

An orthodontic bonding technique is described by the authors that is conventional in everyway, except that it requires only 2 seconds of curing time per tooth with the Xenon Arc Light. If you are bonding 20 teeth, you could save 20-30 seconds per tooth decadely into a time savings about to 10 minutes. Unfortunately, this report is purely descriptive in nature and is not investigative. It leads a little like an advertisement for the manufacturer. The authors are currently conducting a clinical investigation looking at the retention of brackets bonded with this securing light. The Xenon Arc Curing Light has the potential to help improved clinical efficiency in bonding orthodontic brackets.

It apparently can also be used to bleach teeth, although the technique to do so is not described in this report. To read this article for yourself, see a Xenon Arc Light-Curing Unit for Bonding and Bleaching, in the February 2000 issue of the Journal of Clinical Orthodontics.

A Retrospective Study of Unerupted Maxillary Incisors Associated With Supernumerary Teeth.

Mason C, Azam N. et al.
Br J Oral Maxillofac Surg 2000;38:62-65.

March 30, 2001
Dr. Chang-Heun Park

Imagine the clinical situation. Wherein 9-year old is referred to your office due to the fact that maxillary left central incisor has not yet erupted. Your clinical evaluation shows all other dental development is normal for the middle maxillary dentition. If panoramic x-ray is taken and shows the presence of the supernumerary tooth associated with the unerupted incisor, the root of the unerupted incisor is between one-half and two-thirds formed. What is the proper course of an action to allow the eruption of the left central incisor? Should the supernumerary tooth and the retained primary tooth be removed? Should the unerupted tooth be exposed? Should you plan to proceed with uncovering and bonding of unerupted tooth and apply orthodontic traction? All these are possible to approach to this problem.

Do we have any evidence as to which approach is best? An article in the February 2000 issue of the British journal of oral and maxillofacial surgery gives the some insight into the particular problem. 100 patients were identified retrospectively for this study that had unerupted maxillary incisor associated with supernumerary teeth. The records all reviewed and radiograph used to classify the degree of the root formation of the unerupted incisor. Notations were made regarding the need for additional surgical procedure later to facilitate eruption. Here is the outer bound. The mean age in these patients was 9-years and 3 months. Males predominated 2 to 1. The 100 patients had total of 127 unerupted incisors. The supernumerary tooth was palatal to the unerupted incisors at 99 of 100 cases. Here is the important part. The teeth were classified immature at the any unerupted incisor that had 2/3 of the root formation. Teeth that had more than 2/3 root formation were classified as mature. Most of the immature teeth in this study were treated by the removal of supernumerary tooth and retained primary tooth. Of this group, nearly 3/4 of these teeth were erupted spontaneously afterwards. Of the 16 mature teeth treated with this conservative approach of removal of supernumerary and retained primary teeth, more than 60% were required additional later surgery for the uncover. One other interesting factor of this study, average time for eruption of permanent incisor was 11month after the removal of supernumerary tooth. Now, if we think again about the clinical situation involving the 9-year old with supernumerary tooth and unerupted left central incisor, we have a good idea how to proceed. Based on the evidence in this study, we would recommend the removal of the supernumerary tooth and retained primary tooth. But not to any further uncover since the root development was last until 2/3. Further more, we can tell the patient and parents that it will likely near a year before they can expect the permanent tooth to erupt. But there is 75% chance. It will do so on and its on. Further detail about this study from the Eastman dental institute in London can be found any article in retrospective study of unerupted maxillary incisor associated with supernumerary teeth which appears for the February 2000 issue of the British journal of the oral and maxillo facial surgery.

Three-Dimensional Analysis of the child cleft face

Duffy S. Noar J. et al.
Cleft Palate Craniofacial Journal 2000;37:137-144.

April 6, 2001
Dr. Gye-Hyeong Lee

We are known that cleft lip and palate deformities have a significant effect on the shape and position of the teeth, alveolus, palate and nose. How far this effect of cleft extend on the developing phase of the child. Do they effects on the mouth and nose do they extend further into the face.

Previously this is very difficult question to the answer because analysis was limited to measurement taken directly from faces all from facial molls. Modern technology has provided better tools for investigation involving facial shape and contours. Dr. Duffy & Kally in the England used such a tools in a recent study reported in a Cleft Palate Craniofacial Journal. Let me first describe this new tools for looking at faces.

It is a laser scanning technique that project the thin laser line on the contour of face and then recorded with video camera. Scanning this line across the whole faces and putting all the images line together can construct complete three dimensional contour map of the face. The effluence used this study takes about ten second to scan on the face. But newer scanner is now available that reduced this time under one second.

Now let's look at how the authors used this laser scanning tool used this particular study. They recorded 39 volunteers from cleft population between 8-11 years old that had not any bone grafting surgery. This cleft patients were subdivided into bilateral complete cleft lip and palate, unilateral complete cleft lip and palate, unilateral cleft lip and alveolus, and cleft palate alone. They also recruited 25 unaffected subjects with no obvious skeletal discrepancy acts as controls. This control patients were also 8-11 years old. All patients underwent facial scanning procedure that I described.

The authors took scan two ways. They may measurement between the found landmarks to look at such things nasal base width, mouth width and so on. They also produced average scan based on the mathematical average scan each group. This average scan could then be superimpose to visualized differences contours and shape beyond linear measurement. The computer image processing also allowed the investigator to compare all unilateral cleft as they were left side cleft. The right side cleft were mirror image by the computer to produce left side cleft result. The result of this study show some expected and some surprising result. That nasobase width of cleft patient with wider and mouth narrower. They were significant nasal asymmetry in most cleft subjects. The differences from control subject were greatest in the bilateral cleft group. The surprising thing to me was that differences on the face extend well beyond oral and nasal region. The cleft patient had narrower interocclular width and narrower face over all. the contour on the mandibular width stingily different cleft group as well. The difference seen bilateral cleft side may be due to related developmental disturbance or could be due to secondary effect of ungrowth early cleft surgery. The study could not tell us each.

I believed that we will be seeing more reported on treatment of facts outcome using the facial scanning technology. To see more details this technology and study I discussed reported march 2000 issue of Cleft Palate Craniofacial Journal and article entitled Three-Dimensional Analysis of the Child Cleft Face.

Laboratory and clinical evaluation of a self etching primer

Miller RA

J Clin Orthod 2001;35:42-45

March 8, 2002

Dr. Young Mi Jeon

If your office is anything like mine, there is never we showed as of salesman stopping in ready to sell the next great advancement in bonding systems. The most recent, seems to be the introduction of the self etching primers. These are known as sixth generation adhesives. I'm glad I don't have to recite the previous five. The advance in this newest generation is the combining of the etchant in the primer. In other words, the chemists have grafted the primer molecule onto the phosphoric acid molecule with the idea being that the hydrogen ions will be given out first acid etchant, thereby leaving the primer molecule alone as the byproduct. This eliminates many steps on the process and presumably the chances for errors as well. It sounds feeling, but does it work for bonding orthodontic brackets?

In the January two thousand and one issue of the Journal of Clinical Orthodontics, Dr. Robert Miller published report entitled ¡°Laboratory and clinical evaluation of a self etching primer¡±. I was disappointed one I found out the laboratory part of this investigation was data provided by the manufacturer rather than independent testing. The laboratory data shows that the strength of the self etching primer should be at least as great as a traditional etching-priming bonding procedure. So with the laboratory data supported it is the time to demonstrate the clinical usefulness of the self etching primer.

Dr. Miller conducted the study, which place brackets on teeth using either the self etching primer or a conventional etching-priming technique. The self etching primer technique consisted of pumicing the teeth, swirling the self etching primer on each enamel surface for two to five seconds, thinning the primer with the burst of air, than placing brackets with conventional light cured resin.

In this study, the author use the ESPE Prompt L-Pop self etching primer, which is identical to the Unitek Transbond Plus. In the clinical test, 464 brackets were bonded with the conventional etching-priming technique and 514 brackets with the self etching primer. The author didn't specify how many patients the brackets were place than but my math tells me about 25 patients per group, The bracket failures were recorded for six months, and the two techniques were compared. The bracket retention rate was about 99 percents for both techniques. In other words, the self etching primer was just as effective in bonding orthodontic brackets as conventional technique. The retention rate of 99 percent is quite high, and makes me wonder whether this study was done unconsecutive patients or select group with ideal characteristics.

It seems clear that the self etching primer has great promise, elimination of the rinsing and drying step has the potential to reduce the chance for error in the bonding process. I look forward to a little more vigorous investigation of self etching primers, so I can decide whether the added cost is worth possible gains and efficiency. In the meantime, if you want further information about this sixth generation bonding agent now, you can refer the Dr. Miller's article in the January two thousand one issue of the Journal of Clinical Orthodontics.

The radiographic localization of impacted maxillary canines:

a comparison of methods

Mason C, Papadakou A, Roberts GJ

Eur J Orthod 2001;23:25-34

 March 15, 2002

Dr. Jeong Soon Ahn

Last month in these tape serise I reviewed the new experimental technique for three-dimensional imaging in localization of objects within the craniofacial region. Part of that study involved a localization test which indicated dentists were only correct 15 percent of the time when judging whether the mandibular canal was buccal or lingual to a tooth root. Are we any better when judging the buccal or lingual position of an impacted maxillary canine? Carol Mason and Colleagues from Eastman Dental Institute in London, recently published a paper entitled ¡°The radiographic localization of impacted maxillary canines: a comparison of methods¡±. This paper appears in the February, 2001 issue of the European Journal of Orthodontics and examines the questions of how accurately we can locate an impacted maxillary canine from commonly taken x-ray films.

The authors identify one hundred cases that had at least 1 impacted maxillary canine. In addition, these patients also had panoramic x-ray and a maxillary occlusal x-ray available, and had undergone surgery to verify the actual position of the impacted tooth. The canine location was determined by two radiographic methods using a panel of six practitioners. The practitioners varied in specialty training and experience.

The first radiographic technique was the parallax or image shift technique. This used vertical tube shift between a panoramic film and an maxillary occlusal film to localize the impacted tooth. The magnification technique was used with panoramic film only as the second technique for localization. The magnification technique uses the greater horizontal magnification of palatally placed objects to determine location. Well, how good were these two techniques and how did they compare to one another? Overall, there was no statistically significant difference between the two techniques. Both techniques located the palatal canines correctly almost 90 percent of the time. The buccal canines however were different story. The parallax, image shift technique located the buccal canines correctly almost half the time, but the image magnification technique was only rarely successful. Based on these results, the authors recommend initially using the panoramic film for location. If the palatal position cannot be confirm from the panoramic film, then additional views should be taken for localization. The overall success rate for localization was only about 75 percent when palatal and buccal impactions were combined. This indicates a place for new technology in localization of impacted maxillary canines. I think we can say that radiographic localization of impacted canines is some what better than the previous study of locating the mandibular canal, but we are still far from perfect.

To read more about this specific study, refer to the February, 2001 issue of the European Journal of Orthodontics.

Long-term hard and soft tissue relapse rate after genioplasty

Talebzadeh N, Porgel MA

Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91:153-6

March 22, 2002

  Lee Seong Chool

Occasionally I have a class II patient with skeletal mandibular deficiency, that can be treated very nice dental result with orthodontic treatment only. The esthetic outcome is not optimal though because of the convex profile and chin deficiency. An ideal solution may be to consider advancement genioplasty. When I suggested this option to such a patient, they may ask whether such a procedure stable long term. Much of data on genioplasty is from studies of patients also had mandibular advancement procedure.

Recently, Dr. Talebzadeh and colleagues from university of California at San Francisco conducted a study to determine if advancement genioplasty is stable when done alone and to see how the stability compares to genioplasty done in conjunction with mandibular advancement surgery. The study is recently published in the journal, Oral surgery Oral medicine and Oral pathology in February 2001 issue.

The title of the article is "Long term hard and soft tissue relapse rate after genioplasty". The authors collected 20 patients when underwent genioplasty. 11 of these patients had genioplasty alone and 9 had genioplasty along with mandibular advancement surgery. Lateral cephalometric X-rays were taken before surgery, immediately after surgery and 12 month after surgery.

The X-rays were traced and measured for both hard and soft tissue movements. The average advancement of the chin was just under 10 mm for the group of genioplasty alone and almost 15 mm for the genioplasty with mandibular advancement. The average hard tissue relapse was less then 1 mm when measured at 12 month. There is no difference in the relapse rate between those patients with genioplasty alone and those with concurrent mandibular surgery.

In addition there is no difference in the relapse rate a genioplasty greater than 7 mm compared to those less than 7 mm. The soft tissue advancement was approximately 90 % of the hard tissue advancement right after surgery. 1 year later although the hard tissue was stable, the soft tissue was only about 75 % of the hard tissue change. This likely indicates soft tissue remodeling takes place following surgery.

This study supports the long-term stability of genioplasty procedure done with or without mandibular advancement surgery. The average relapse of hard tissue was very small and the other look at the raw data indicates significant variability. The significance of this study is limited by small sample size.

However I think when put in context of all the data we have this suggest that we can be comfortable in offering genioplasty procedures to our patients with confidence of they will have good long-term stability. For more details of this study refer to February, 2001 issue of the triple 'O'.

Surgical and Orthodontic Management of Palatally Impacted Canines

David P. Mathews PROD 13-4(1), August 2001

March 29, 2002

Dr. kwang Taek Ko

Palatally impacted canines can be classified as either simple or complex. The majority of palatally impacted canines fall in the simple category. These canines are usually not very deeply imbedded in the palatal bone and the incisal edge is located near the CEJ of the adjacent lateral and central incisor. Often times, these teeth can be palpated in the palate and a small bump can be seen which helps in the diagnosis of their location.

The complex palatal impaction is deeply imbedded within the palatal bone and is positioned very high apically near the middle to apical third of the adjacent roots of the central and lateral incisor. There is usually no bump in the palatal tissue indicating the location of the tooth. The best way to ascertain the exact location of the tooth is by taking appropriate periapical radiographs from two different angles and using the buccal object rule, which will precisely allow the surgeon to know whether the tooth is on the labial, palatal or midalveolar position. A panoramic radiograph will not give this information.

The timing of the surgical uncovery is different for the simple and complex palatal impactions. I prefer to uncover the simple palatal impactions at least 6 months prior to the orthodontist initiating treatment. Our experience has found that these teeth will erupt on their own after they have been uncovered and it will greatly simplify the orthodontic positioning of the teeth, with less trauma on the canine, and less trauma on the adjacent dentition.

On the other hand, the complex palatal impaction should be surgically uncovered only after appropriate appliances are in place, and space is being opened for positioning of the canine. Because of the deep location of the complex palatal impaction, it is imperative that a bracket and chain be attached to the tooth and orthodontic movement be initiated within a few weeks after the uncovering. Otherwise, the tissue will grow over these deeply imbedded teeth.

Surgical uncovering of the palatal impaction is different depending on whether it is a simple or complex impaction. The simple palatal impaction is by far the most common impaction encountered. To uncover a simple palatal impaction, a palatal flap is reflected usually from the second bicuspid up to the central incisor. Often times the tooth has a shell of bone completely covering it. This bone can be removed very easily with a curette or with small round burs?

Curetting the sack around the tooth will help delineate the periphery of the clinical crown. It is very important that complete bone removal be accomplished around the clinical crown of the tooth. However, do not expose the cementoenamal junction. Once complete bone removal is accomplished, the palatal flap is repositioned and the tooth can be palpated through the flap. A small scalloping incision is made over the tooth, so that when the flap is ultimately sutured the tooth can be seen through the fenestration in the flap. I will often take a photograph, either a slide or a polaroid photograph of the tooth for the orthodontist so they can see the exact orientation of the tooth. This will be helpful for the orthodontist. If the deciduous canine is present, it is extracted at the time of the surgery. The flap is sutured and a dressing can be placed on the clinical crown of the tooth to prevent any tissue overgrowth.

If the tooth is moderately imbedded in the palate, then there is some concern that the tissue may grow over it. Then a bracket can be bonded to the tooth, which will aid in retention of the dressing. The patient is seen in one week, and the dressing is removed. If it appears that the tissue is not going to grow over the tooth, then no replacement of the dressing is necessary. If there is some concern that the tissue may granulate over the tooth, then the dressing will be placed for one more week. Following the removal of the dressing the patient is instructed in brushing the visible portion of the tooth in keeping it plaque free. Usually the margins of the scalloped flap will be healed within 4 weeks, and the tooth will already have begun to erupt.

Our experience has shown that when simple palatal impacted teeth are uncovered before orthodontic treatment, they will erupt considerably. And most interestingly, tend to erupt distally and move away from the adjacent central and lateral incisors. When the orthodontist initiates treatment, these teeth are very easy to move into the edentulous site with minimal trauma on the anchorage teeth. Most importantly, there is no trauma on the adjacent teeth, since the canine has already erupted and moved away from the root of the central and lateral.

The complex palatal impaction should be uncovered after appliances are on the teeth, and the appropriate space is being opened for the canine. Fortunately, the complex palatal impaction occurs infrequently, because these teeth are very difficult to surgically uncover, keep uncovered, and orthodontically move into the appropriate position. An extensive palatal flap is needed to uncover these teeth. Oftentimes, the flap will need to go from the first molar around to the opposite central incisor crossing the midline. Since these teeth are deeply imbedded with in the palatal bone, they can be very difficult to find and bone removal is necessary, as stated previously. This needs to be done very slowly and judiciously, so the enamel of the tooth is not marred and the root surface is not exposed.

Once the appropriate bone removal is accomplished, the area is isolated with hemostatic agents, the tooth is etched, a bonding agent is placed on it, and then a bracket is bonded on the tooth. I like to verify the security of the bracket by getting a hold of it with the hemostat when trying to dislodge the bracket. This will also verify that the tooth is mobile and not ankylosis. A photograph is taken of the exact location and orientation of the tooth, which will assist the orthodontist in the appropriate mechanics for tooth movement. The palatal flap is repositioned and a fenestration is made through the flap exposing the bracket on the tooth. A gold chain is ligated to the bracket and the other end is ligated to the bracket on the lateral incisor or bicuspid adjacent to the edentulous area. The orthodontist can initiate tooth movement within a few weeks. Usually, with the complex palatal impaction, it is necessary for the orthodontist to fabricate a lingual arch, soldered to the maxillary first molar bands. A spring can solder to the mid portion of the palatal arch which will allow eruption in a posterior direction. This will avoid damage to the adjacent root surfaces of the central and lateral incisor. Once the tooth is erupted into the palate, and away from the central and lateral incisor, it can then be walked into the edentulous area with the appropriate elastics and other orthodontic means.

With proper diagnosis, proper surgical uncovering, and proper orthodontic mechanics, a palatally impacted canine can be orthodontically positioned in the ideal location. In my experience of uncovering these teeth, over a twenty-five year period of time, I have never found a palatally impacted canine in an adolescent to be ankylosed. As patients approach 35 years of age and older, there is a greater likelihood that a palatally impacted canines could become ankylosed. However, in adolescents, we have never found and ankylosed palatally impacted tooth. Most of the palatally impacted canines that are claimed to be ankylosed, are usually ones that were improperly uncovered and appropriate bone removal was not accomplished so that the tooth could not be orthodontically erupted.

The other problem is improper orthodontic mechanics. If the tooth is pre-uncovered it will erupt on its own to a point where it will be very easy to move. On the other hand, if the tooth is more deeply imbedded in the bone, it is important for the orthodontist to realize that the tooth has to be erupted into the palate first and then moved into the site. If the orthodontist simply attaches a wire or elastic to the teeth and makes a direct pull to the edentulous area, the tooth will be very very slow to move, and may not move at all. The reason being that the coronal portion will not resorb bone and if you are pulling the crown into the bone the process is going to be very slow or may not occur at all. So the direction of the mechanics is important in erupting these teeth, and of course the surgeon has to create the appropriate bone removal so that they can be erupted out of the bone. The pre-orthodontic uncovery technique has really facilitated movement of the palatally impacted canines by allowing these teeth to erupt on their own in the palate and away from the central and lateral incisor.

We found that, not only is the orthodontic movement easier, it puts less trauma on the adjacent teeth so there is less possibility for root resorption on the anchorage teeth. We also found that the bone around the lateral incisor is normal, and the bone around the impacted tooth is normal following the completion of orthodontic treatment because there is no trauma to the adjacent site. The other important factor for retention of these teeth is that the orthodontist appropriately finishes the case with a root torque. Often times, these teeth have been pulled out of the palate and have improper root alignment and the orthodontist needs to make the appropriate root torque to finish the case, which will enhance the post-treatment retention of the tooth.

I hope that you have found this information to be helpful in dealing with the simple and complex palatally impacted canines.

Orthodontic In Vivo Bond Strength: Comparison with In Vitro Results

Pickett KL, Sadowsky PL, et al

Angle Orthod 2001;71:141-148

April 12, 2002

Dr. Hye Young Ryu

Let me ask you a couple of questions about your bonding technique. First of all, what type of bonding material do you use to secure brackets to teeth? I think today, most orthodontist use some sort of light-cure bonding material in order to enhanced strength of the bond bracket. Question number 2. Why did you select that particular bonding material? Today there's many many products available on the market to bond bracket to teeth. So, why were you using the current product, if selected? I'm sure the answer that question was very significantly among clinicians.

Some of simply use what works? Others several recieve recommendations from colleagues about certain products and still others may have seen products demonstrated at regional or national meeting. You know probably the best way the select the bonding material is to read literature. We're all interested keeping brackets on the teeth or another words, to avoid debonding during orthodontics. So What depending upon the bond strength? All products are tested in the laboratory. It is possible to find out the in vitro or laboratory bond strength of any product in use today in orthodontics, but what is that values mean? Does the laboratory testing of bonding bracket really relate to its clinical use? Other bond strength reported in the literature, actually related to bonding strength, that exist intraorally. I've often wonder about those questions. I found the answers in the articles, published in April, 2001 issue of the Angle Orthodontist.

The title of that article is¡°Orthodontic In Vivo Bond Strength: Comparison with In Vitro Results¡±. This study was coauthers by Kevin. Pickett and Lioneal Sandowsky, from the department of orthodontics at the University of Alabama in Birmingham. Studies in the past have evaluated in vivo and in vitro bond strength, but different types of debonding mechanisms were used. The significants of this particular study is the same type of debonding tool was used in both situations. Even more importantly the debonding tool was compared to the standard universal instron testing machine, Which is reported in most in vitro or laboratory studies. Let me explain what I mean. In the laboratory, when brackets are placed on extracted teeth and debonded, a standard machine called a universal Instron testing apparatus is typically used to measure the amount of force takes to debracket a tooth. But this type of machine, can't be used intraorally. So accurate comparison of intraoral and laboratory debonding strength is not possible. In this study, the researcher develop the tool and used this tool both intraorally and extraorally. Photographs of the instrument are printed in the article. Distinct of this paper is that the researchers then compare this apparatus to the Instrun testing machine in the laboratory. But also use the same debonding device on patient that had undergone orthodontic treatment.

For the laboratory test, 60 extracted premolars were used, they were etched and brackets were bonded using a light cure composite. Then the brackets were debonded and in 30 of the brackets and Instron testing machine was used debracket and the other 30, and intraoral debonding device was applied. The amount of force necessary to debond bracket was comparable. In other words, the force necessary to debond using the Instron was 12 MPa, and for the intraoral debonding device it was 11 MPa. So that was only a small difference between these two in vitro or laboratory approaches. Then 8 patients who near the end of the orthodontic treatment had the premolar brackets debonded with this intraoral testing device. These patients who had the bracket in placed for nearly 2 years. None of these brackets had accidently become debonded during orthodontics. The intraoral testing devices was then used to debracket these teeth and the force was recorded. What do you think this researchers found? Do you think the force, necessary to debond bracket intraorally, was the same as the in vitro or laboratory test? Not even close. That average force necessary to debond brackets intraorally was about 5 MPs. This is less than half the force necessary to debond bracket in the laboratory, and this was using the same device. So what's my point? Well I guess my point is don't believe the laboratory test entirely. In this study, the amount of force necessary to debond bracket in the lab was over twices much as that necessary intraorally. I believe that manufacturers should give us accurate information.

But we, clinician ready need to have connections reading little to know is the in vivo or intraoral debond strength of the materials that we use. Only in that way can be actually and adequately choose the proper bonding material. Hopely in the future, these the debonding tools or something like it would be used to test other bonding materials and have a better idea of the true bond strength of whatever material briefly using intraorally. If you interested in reading this article, you find it in the April 2001 issue of the Angle Orthodontist.

Long-term stability of dental arch form in normal occlusion from 13 to 31 years of age

Henrikson J, Persson M, Thilander B

Eur J Orthod 2001;23:51-61

 April 19, 2002

Dr. Seon Mi Kim

 As orthodontists, we attempt to create the ideal arch form for an individual patient at age 13, and then expect it to remain stable from that time forward. We may indicate the patients that with the proper maintenance and use of retainers, our treatment results can be stable long-term. Some orthodontists also believe that treating patients to a single universal arch form is indicated, and strive to obtain that arch form in all patients.

 We may be able to make some judgement on these beliefs if we were able to look at the arch form of a group of untreated class I patients at age 13 and then follow these patients into adulthood to look at arch form changes might occur. This is exactly what a group of researchers from Sweden recently did when they published their paper; Long-term Stability of Dental Arch Form in Normal Occlusion from 13 to 31 Years of Age. This paper was published in the February 2001 issue of the European Journal of Orthodontics.

 These researchers found a group of 30 individuals that had dental casts from age 13 and were available for follow-up at age 31. All of these individuals had Class I normal occlusion at age 13. The dental casts from age 13 and age 31 were subjected to a standardized photographic technique and digitized for arch form analysis and measurements. The arch forms were quantified using conic sections to allow comparison.

 Did the researchers find evidence for a single universal arch form in this population? The answer is NO. There were significant variation in arch form at age 13 and even greater arch form variation at age 31. If this much variation was noted in rather homogeneous Scandinavian sample, imagine the variation that is likely to be found in the more diverse population.

 Did the arch form remain stable for individuals from age 13 to 31? The answer is again NO. The mandibular arch form tended to become more rounded with age and both the upper and lower intercanine widths were reduced. One interesting finding was that  the lower intermolar width increased in the males and decreased slightly in the females.

 Did the arch form changes that were noticed correlate with increase in incisor irregularly? The answer in this case is YES. The lower arch form became more rounded and shortened in depth, and these changes were correlated with an increase in lower incisor crowding.

 This is only a small amount of the information that is available in this paper. There is additional information about specific arch form changes and about the variation and arch form that was discovered. This additional information is available in the article published in the February 2001 issue of the European Journal of Orthodontics.

 Based on the information that I've reviewed with you, I think it is safe to say that searching for universal arch form that is right for all people is unrealistic. We also should consider the changes in arch form over time that were discovered when we determine strategies for long-term orthodontic stability.

Integrating Esthetic Dentistry and Space Closure in Patients with Missing Maxillary Lateral Incisors

Rosa M, Zachrisson BU

J Clin Orthod 2001;35:221-234

                                                                     May 10, 2002

                                                                Dr. Hang Ik Jang

Now that we have predictable and esthetic dental implant restorations available. is canine substitution treatment no longer popular option for missing maxillary lateral incisors? Can't esthetics of canine substitution treatment be improved by combining orthodontic treatment with techniques of contemporary esthetic dentistry? Dr. Rosa & Dr. Zachrisson recently published the paper in the April 2001 issue of the Journal of Clinical Orthodontics that emphasizes the positive aspects of canine substitution treatment and demonstrates how the esthetics can be improved to make the result virtually indistinguishable from a natural dentition.

The article is entitled, "Integrating esthetic dentistry and space closure in patients with missing maxillary lateral incisors." To get the most value from this article, you must see the clinical photographs included, but I will try to summarize for you how the authors deal with the common esthetic problems associated with canine substitution treatment.

The crown shape problem is handled by a combination of enamel recontouring and esthetic build-up with hybrid composites or porcelain veneers. It is suggested that the canine in the lateral position elapse slightly convex on the facial surface due to the thin enamel and risk of dentin exposure if recontouring is too aggressive.

The gingival alignment difficulties often result in gingival contours too high on the canines in the lateral position and too low on the premolar in the canine position. This can be corrected by extruding the canine in the lateral position and recontouring the crown along with intruding the premolar to raise the gingival contour and an building up the crown with composite or porcelain veneer.

The problematic yellow color of some canines can be corrected prior to composite build-up with modern vital bleaching procedures. The inadequate crown torque of the canine in the lateral position can be corrected by proper orthodontic positioning focusing on increasing the lingual root torque of this tooth. The combination of this techniques leaves some impressive treatment results as demonstrated in the photographs included in the article. The authors emphasize that this approach to treatment allows completion of treatment in the adolescent dentition, where implant treatment may require interim tooth replacement until facial growth is complete. Other advantages may be improved gingival health and lower cost as compared to implant treatment.

I was very impressed with this article. I do a fairy number of canine substitution treatment and I am anxious to include some of these ideas to improve the esthetic results. The authors also address solutions to the functional problems involved with the canine substitution, but I don't have time to review them here.

Look up this article in the April 2001 Journal of Clinical Orthodontics and I believe that you too will be impressed with the esthetics with cases that I presented and it may change your belief that canine substitution is a second best esthetic option for the treatment of missing maxillary lateral incisors.