A new classification of mandibular asymmetry and evaluation of surgical-orthodontic treatment outcomes in Class III malocclusion

Abstract

Introduction: Facial asymmetry is a common manifestation in patients with Class III malocclusion. The aims of this study were to classify mandibular asymmetry in Class III patients and to evaluate treatment outcomes according to different characteristics of asymmetry.

Materials and methods: Three dimensional cone-beam CT images of 38 patients were analyzed for menton deviation and discrepancies between bilateral structures of mandibular ramus and body. The patients were classified into 3 groups. Groups 1 and 2 exhibited a larger distance of ramus to midsagittal plane on menton-deviated side. In group 1, menton deviation was greater than ramus asymmetry and the condition was reversed for group 2. Group 3 had menton deviation contralateral to the side with larger transverse ramus distance. The features of asymmetry were delineated and the outcomes after surgical-orthodontic treatment were analyzed.

Results: Group 1 exhibited a roll rotation of mandibular structures. Mandibular deviation of group 2 patients was more of a horizontal shift nature rather than rotation. Group 3 patients displayed a yaw rotation of mandible to the side with lesser growth in body and ramus. After treatment, menton deviation and body asymmetry were significantly improved in all 3 groups, but the effect of therapy on ramus asymmetry was less predictable, especially for group 3.

Conclusions: The classification system is simple and clinically useful and could form a base for future studies on facial asymmetry.

Keywords: Bilateral sagittal split osteotomy; Class III malocclusion; Mandibular asymmetry; Menton deviation; Ramus asymmetry.