Utilization of third molars in the orthodontic treatment of skeletal class III subjects with severe lateral deviation: case report

This clinical report discusses the importance and use of third molars in the adult patient by presenting a case in which their use during orthodontic treatment allowed occlusal improvement. SUBJECT AND TREATMENT PLAN: The patient was a Japanese adolescent boy who had a skeletal Class III malocclusion with severe lateral deviation of the mandible, significant loss of posterior occlusal vertical dimension, due to premature loss of the maxillary and mandibular left first molars, and furthermore, both first molars had advanced carious lesions that had resulted in reduced crown heights and bilateral chewing surfaces. The mandible had shifted to the left, with a bilateral chewing pattern and a lack of posterior vertical alveolar height, which in turn had produced an abnormal occlusal plane and curve of Spee. The maxillary arch was expanded, the maxilla was moved downward and forward, and the mandible was moved slightly backward and rotated open to increase posterior vertical alveolar and crown height. The reconstruction of a functional occlusal plane was achieved by uprighting the posterior teeth to correct asymmetric posterior vertical alveolar and crown height, using a full multibracket system incorporating four third molars and closing the space from the missing first molars and extraction of the questionable first molars.

A normal overbite and overjet and adequate posterior support and anterior guidance were established, achieving a better intercuspation of the posterior teeth. A favorable perioral environment was created, with widened tongue space to produce an adequate airway. A well-balanced lip profile and almost symmetric face were achieved using the four wisdom teeth without extraction of the four premolars. Subsequent mandibular growth, with development of posterior vertical alveolar height and temporomandibular joint adaptation, has resulted in an almost symmetric posterior vertical height and joint structure between right and left sides. These factors have contributed to the occlusal stability maintained for more than 5 years.

In the growing patient, with missing and/or early advanced caries of the first molars, it may be more beneficial to plan occlusal improvement through extraction of the questionable first molar rather than premolar extraction. This method of treatment can equalize posterior vertical dimension and does not restrict tongue space. In addition, this treatment method addresses the clinician's concern about postorthopedic relapse due to tongue habits and eruption of the third molars.