Orthodontic Treatment of Class III Malocclusion

Often referred to as mandibular prognathism, the Class III phenotype can be a result of mandibular prognathism, maxillary hypoplasia (also termed maxillary retrognathism), or a combination of the two. These terms reflect the anatomical heterogeneity of Class III, as either or both jaws may be affected in sagittal length, or in position relative to each other. Familial aggregation studies suggest that familial environmental factors and/or heredity can play a substantial role in the etiology of Class III phenotype. This is supported by the findings that prevalence and anatomical characteristics of Class III malocclusions vary largely according to ethnic background, and may represent the effects of cultural differences at least to some degree. Current genetic inheritance patterns proposed for the Class III malocclusion include autosomal-recessive, autosomaldominant, autosomal-dominant with incomplete penetrance, and a polygenic threshold model. Studies will be presented showing that the familial distribution of mandibular prognathism could be explained by the presence of a dominant major gene with an autosomal Mendelian mode of transmission that is affected by other genes and environmental factors leading to incomplete penetrance and variable expressivity. Finally, findings from both genetic linkage and association analyses in humans will be presented implicating variation in chromosomal locations with the Class III phenotype, including 1p35, 1p36. 4p16.1, 6q25, 12q13, 14q24.3-31.2 and 19p13.2 in Asian populations; and 1p22.1, 3q26.2, 7p22, 11q22, 12q13.13, and 12q23 in families from South American; and 12q24.11 in primarily a Caucasian sample residing in the United States.

The relationship between body height increments and facial growth is well documented in the literature. Correlations are also found between body height and mandibular growth because both lower extremities and mandible are long bones with epiphyseal cartilage. The growth characteristics are similar for the mandible and long bones. On the average, body height tends to be greater in Class III than in Class I individuals. Furthermore, Class III individuals mature slower than Class I individuals during puberty. This may mean the growth period is much longer in Class III subjects, but that still needs to be substantiated. However, studies show there is no significant difference in facial growth increments between Class III and Class I subjects during the pubertal growth period. This means there is already differences in facial growth pattern between Class III and Class I subjects before the pubertal growth spurt. It is also important to note that patients with acromegaly also exhibited abnormal growth. This chapter suggested a few reasons why the occlusion tends to be unstable in Class III patients after treatment. In Class I subjects, stability can be explained by skeletal and dental compensation; cranial base growth compensates occlusal changes. However, the growth of the posterior cranial base is smaller in Class III individuals during puberty so that mandibular growth more directly affects the occlusion. Other factors in occlusal stability occur after treatment. The prediction of mandibular growth potential is possible using hand-wrist X-rays after the pubertal growth spurt. Clinically, there are limitations of orthopedic treatment with chincup and/or maxillary protraction appliance. These appliances may inhibit or at least mask mandibular growth. However, if there is excess mandibular growth after removal of the orthopedic appliance(s), Class III malocclusion may reoccur. The risk of orthodontic and orthopedic treatment can be minimized by a better understanding of the characteristics of facial growth in Class III patients.

Early orthopedic treatment of skeletal malocclusions continues to challenge clinicians and the efficacy of mandibular growth modification by orthopedic appliances has long been a debate without conclusion. Several growth theories support the mandibular condyle as a growth site rather than a primary growth center. The response of cartilages and chondrocytes to mechanical stimulation is still considered a major parameter for controlling the growth of mandible. This chapter summarizes results of laboratory and clinical studies related to orthopedic interventions, focused on mandibular prognathism. The clinical problems with chincup therapy are discussed at the cellular level and with animal models. Based on the results from animal model studies, the magnitude and direction of the mechanical stress is analyzed relative to loading cells. Differentiating chondrocytes appear to be the effectors of the cellular physiologic and the pathologic reactions to mechanical stress. The possible mechanotransduction pathways in differentiating chondrocytes are discussed relative to cellextracelluler matrix (ECM) adhesion and ion channels. A combined signal transduction mechanism is proposed for integrin based cell-ECM adhesion, This mechanism, acting through a mitogen activated protein kinase (MAPK) pathway mediated by ion channels, is discussed as a possible mechanism for regulating mandibular growth. The promotion of endochondral bone formation in the mandibular condylar cartilage is proposed as an important example of this basic mechanism. Further horizons for craniofacial research in orthodontics and mechanobiology are proposed.

Class III malocclusion and anterior crossbite are common clinical problems, especially in patients of Asian ancestry. Management of the developing Class III malocclusion continues to challenge practicing clinicians. This chapter focuses on the treatment of Class III malocclusions in growing patients. The question arises as to what type of Class III malocclusion will benefit from early treatment; when is a good time to start an early phase of orthodontic or orthopedic treatment; how successful are these treatments long-term; and do we have evidence in the literature to support early treatment? Protraction facemask is used in the treatment of Class III malocclusions with maxillary deficiencies. The question is whether side effects such as proclination of maxillary incisors and loss of arch length can be resolved using a bone anchored protraction device. These questions will be addressed and illustrated with clinical cases.

Class III malocclusion has been treated in the past using several different approaches. In growing patients, appliances such as the chin cup and facemask, with or without palatal expansion, have been used for orthopedic correction. Whereas the chin cup has been used to restrain or change the direction of mandibular growth, the facemask has been used to protract the maxilla. The traditional approach of facemask treatment with expansion involves using the maxillary dentition as an anchorage unit. This invariably results in an increase in the vertical dimension of occlusion, due to the buccal tipping and extrusion of the maxillary dentition as well as an increase in incisor inclination, due to the forward movement of maxillary dentition. In Class III high angle cases, both the transverse and anterior movements can cause tipping of the dentition which tends to open the bite; thus, controlling the vertical dimension is of utmost importance during the treatment phase. The aim of this chapter is to introduce a novel approach, using a combination of micro-implants with a rapid palatal expander, and a facemask. This approach skeletally expands and protracts the maxilla, leading to an almost negligible change in vertical dimension, an elimination of adverse dental movements, and a significantly positive change in the patient’s facial profile.

It has been reported that mandibular growth that was retarded and/or redirected during growth modification therapy could not be maintained during the retention period. However, research is necessary to substantiate these findings. During the last 15 years, the authors have studied the morphology, growth, function and treatment effects in Class III malocclusion. For patients with Class III malocclusion, the growth of the mandible is already 3 mm larger than its Class I counterpart by 4-5 years of age. It is also generally accepted that skeletal Class III malocclusions worsen with age, with 3 to 4 mm (or 0.5-1.0mm/year) greater increase in mandibular length compared to Class I mandibles in both genders, during the growth period. Facemask therapy is currently an accepted approach to treatment of Class III malocclusion with maxillary deficiency in young patients. On the other hand, two years of chin cup application showed a more effective orthopedic treatment and a diminished skeletal relapse at the post-retention period. Previous publications by the authors have compared the growth, TMJ response and treatment strategies with reverse headgear or chin cap compared to untreated subjects. In the current article, a systematic review was conducted to provide an evidence-base for the following orthodontic questions: Are there differences in mandibular growth between Class III and normal individuals? If so, what is its magnitude and is it clinically relevant? How is mandibular growth changed following orthopedic treatment in Class III malocclusion? Are these changes stable?

Anterior crossbite in the permanent dentition may be due to abnormal inclination of the maxillary and mandibular incisors, occlusal interferences, or skeletal discrepancies of the maxilla and/or mandible. Traditionally Class III patients are treated with lower premolar extraction. When extractions are performed only in the mandibular arch, special attention should be paid to the torque of the lower incisors to prevent excessive lingual tipping. Gingival recession may occur with excessive retraction of the lower incisors to close extraction space(s). The use of a self-ligating bracket system may have advantages for treating crossbite associated with both Class III and Class I malocclusions. The play between the main arch wire and the bracket slot provides mechanical freedom to facilitate tooth movement. Clinical cases are presented to demonstrate this technique for correcting Class III and Class I malocclusions with anterior crossbite.

There are many ways of using temporary anchorage devices (TADs) to treat patients with severe Class III malocclusions. The mini-plate is one example but a surgical flap is required to place and remove the device. Miniscrews placed in the retromolar pad enjoy the advantage of being placed in dense cortical place, but it is difficult to use them to apply direct force to retract the whole lower arch. The inter-radicular mini-screw is easy to place, but the amount of whole lower arch distalization is very limited. In this article, the author will discuss the use of miniscrews placed in the buccal shelf to correct severe Class III malocclusions. As long as the patient has an orthognathic, or at least acceptable profile, most severe Class III malocclusions can be treated by this method. Buccal shelf mini-screws are placed outside the alveolar process, so extensive lower arch distalization is possible. The thick cortical plate of high density bone in the buccal shelf area offers very good skeletal anchorage for retracting the mandibular arch and/or intruding lower molar to correct an anterior openbite. When treatment is complete, the miniscrews can be removed easily, even without local anesthetic. In this chapter, the anatomic considerations, materials and size of the screws, and the clinical application will be discussed and illustrated with case reports.

The Class III facial asymmetry, mandibular deviation and its related surgical orthodontic treatment will be discussed in this chapter. The number of orthodontic patients with a diverted bite and/or facial asymmetry has been increasing recently. Diagnosis and treatment for Class III patients with facial asymmetry and/or mandibular deviation tend to be more complex than those without asymmetric mandible are. Orthodontists have to discriminate between asymmetric problems of dental nature as opposed to skeletal origin. For instance, the amount of dentoalveolar compensation in the molar region should be part of the diagnosis. Management of the developing Class III malocclusion with mandibular deviation is important since malocclusion tends to deteriorate with growth. On the other hand, skeletal Class III patients are frequently accompanied by facial asymmetry or midline deviations and some eventually need surgical orthodontic treatment. In this chapter, the authors will review the literatures on prevalence of orthodontic asymmetries, possible changes in Class III mandibular deviation with age, morphological features of Class III mandibular deviation, including three-dimensional evaluation and perception of facial asymmetry. In addition, Class III facial asymmetry cases treated with orthognathic surgery will be introduced. Since twojaw surgery has been recently indicated, more often than before for better outcomes, surgical orthodontic cases corrected with one-jaw or two-jaw surgery will be discussed. Postoperative changes of the frontal facial appearances in skeletal Class III patients with deviation will be compared between one-jaw and two-jaw surgeries as well as postoperative stability of Class III cases with facial asymmetry that surgically treated.

Young Class III patients with deficient maxilla can be treated with maxillary orthopedic appliances such as the facemask. Patients with an over-developed mandible require orthodontics, in combination with orthognathic surgery to correct the underlying skeletal and dental discrepancy, after growth is completed. For Class III patients, craniofacial morphology varies among different racial groups and it is important to understand the cephalometric characteristics of these different ethnic groups. For example, in Northeast Asian countries such as Korea and Japan, there are more Class III patients with mandibular excess rather than maxillary deficiency, compared to the Caucasian populations. In treatment planning for orthognathic surgery, 3-dimensional analysis using CBCT provides more detailed information than a conventional 2-dimensional cephalogram. Also, for orthognathic surgery patients, laser scanning may show 3-dimenisonal information on soft tissue as well as hard tissue changes. Therefore, soft tissue changes in facial profile as well as mid-facial area can be quantitatively calculated. The best orthognathic surgery cases result from a close interaction with the oral surgeon and a well planned pre-surgical orthodontic phase. This can simplify the orthognathic surgical plan and result in good long-term stability. In this chapter, 3-dimensional analysis of the hard and soft tissue will be introduced for both pre- and post-surgical consideration of Class III patients treated by combined orthodontics/orthognathic surgery.

Class III malocclusion results from skeletal disharmony and unfavorable incisor inclination. Early use of intraoral appliances in Class III malocclusion would improve the inclination of retroclined upper incisors and proclined lower incisors. Intraoral appliances used in the upper dental arch include the posterior bite plate containing an anterior spring and the Yanagisawa Class III (YC3) Shield. When using the posterior bite plate, the upper anterior teeth are pushed forward by the force of the spring. The YC3 Shield, developed by M. Yanagisawa, results in forward movement of the upper anterior teeth by tongue pressure. Intraoral appliances used for the lower arch are the inclined bite plate and 2x4 utility archwire. The upper anterior teeth are protracted by the inclined plane of the bite plate, and the lower anterior teeth are retracted by the force of a 2x4 utility archwire. Since the early use of intraoral appliances only improves the inclination and position of the anterior teeth, they are usually used in combination with extraoral protractors in treating early Class III malocclusion. Bone-anchored maxillary protraction (BAMP) was recently developed by H.J. DeClerck and coworkers. BAMP works as an extraoral protractor and provides orthopedic correction. It consists of Class III elastics and two pairs of temporary anchorage devices (TADs). BAMP is a novel intraoral treatment modality for growing patients with Class III malocclusion.

Class III treatment can be divided into two categories: Orthopedic treatment for developing Class III malocclusions in growing patients and camouflage/surgical treatment for non-growing Class III patients. Recently, several articles have described on the use of temporary anchorage devices (TADs) for protracting the maxilla in developing Class III patients [1, 2]. The application of TADs can maximize the skeletal response of maxillary protraction and minimize the side effects such as dentoalveolar protrusion. TADs can be placed in the inter-proximal alveolar bone, with attachment to a tooth-born protraction device, or can be used directly in the form of a mini-plate for maxillary protraction. In adult patients, Class III malocclusion either is camouflaged by orthodontic tooth movement or is treated in combination with orthognathic surgery. The use of TADs has narrowed the gap between the two types of treatment modalities because it has expanded the range of orthodontic camouflage treatment. In camouflage treatment, a Class III relationship is usually corrected via differential tooth movement of the upper and lower dentition with premolar extraction. In non-extraction treatment, the anterior movement of the upper dentition and/or posterior movement of the lower dentition can be used to correct the Class III relationship. In this chapter, the authors will focus on the anchorage consideration in treatment of Class III malocclusion with extraction of the lower premolars and nonextraction with distalization of the lower dentition. In addition, an adult cleft palate case is presented in which maxillary expansion was reinforced by the use of TADs. The application of TADs for decompensation in Class III surgery cases is also discussed.

Lingual Orthodontics is believed to require long treatment time and the results are usually unsatisfactory. However, Lingual Orthodontics has a lot of advantages that are not seen with Labial Orthodontics. In this chapter, the author will illustrate with cases that Lingual Orthodontics can be very effective in treating Class III cases due to the ease in tipping back mandibular molars. In addition, the author will demonstrate that tooth movement in Lingual Orthodontics is quite different from Labial Orthodontics. Quite often, cases that require orthognathic surgery with Labial Orthodontics may be done non-surgically if Lingual Orthodontics is used.

Class III malocclusion and midfacial retrusion are major problems in patients with cleft lip and palate (CLP) because maxillary growth is compromised by postsurgical scar contraction. As well as dental problems, these patients also suffer from multiple functional problems, such as suckling, swallowing, speech, and hearing problems. Successful management of patients with CLP requires a multidisciplinary approach. In contrast to conventional Class III treatment, treating cleft palate patients requires attention to multiple functional problems during orthodontic treatment. CLP patients often have multiple, complex problems that require coordinated and comprehensive treatment. Although major progress had been made towards the effective treatment of dentofacial complications, the diversity of approaches to cleft treatment remains great. Furthermore, there is insufficient clinical data about cleft palate treatment to establish an evidence-base for treatment of CLP. A European intercenter comparative study of treatment outcomes in CLP patients provided a methodology for comparing practices, highlighted the potential for wider collaboration including opportunities to promote clinical trials, and encouraged intercenter comparisons. In this chapter, the authors will discuss the problems of cleft palate patients and the implications for their orthodontic and orthognathic management. The findings obtained from recent intercenter comparative studies will also be presented.