Does mandibular osteotomy affect gonial angle in patients with class III deformity? Vertical ramus osteotomy versus sagittal split osteotomy

The mandibular angle represents an important part of facial aesthetics. Mandibular osteotomy can affect the gonial angle. The aim of this study was to compare the effects of sagittal split osteotomy (SSO) and intraoral vertical ramus osteotomy (IVRO) on the gonial angle. This retrospective cohort study assessed subjects with mandibular prognathism who underwent SSO (group 1) or IVRO (group 2). Lateral cephalograms obtained before and 1 year after the osteotomies were analyzed. In this study, age, sex, the change in occlusal plane (OP) and mandibular plane (MP) angles, and the amount of mandibular setback were considered as variable factors, while the type of surgery (SSO or IVRO) was considered the predictive factor. Fifty-six subjects were studied: 26 in group 1 and 30 in group 2. The changes in MP angle and OP angle were not significantly different between the groups (P > 0.05). The change in gonial angle was 6.07 ± 4.46° in group 1 and 7.33 ± 5.73° in group 2; assessment of the data did not demonstrate a significant difference between the two groups studied (P = 0.53). Mandibular osteotomy (SSO or IVRO) may change the gonial angle, but a significant difference between SSO and IVRO was not detected.