Changes in the Gonial Angle Following Bimaxillary Osteotomy

Introduction: The aim of this study was to evaluate changes in the gonial angle (GA) after bilateral sagittal split ramus osteotomy (BSSRO) combined with Le Fort I osteotomy in Class II and Class III patients, and to compare the outcomes between the two groups. Materials and Methods: In this retrospective cohort study, 48 patients (21 Class II, 27 Class III) from Tehran University of Medical Sciences were included. All patients underwent bimaxillary osteotomy with rigid internal fixation using miniplates. Lateral cephalograms were used to measure the GA and occlusal plane angle (OPA) preoperatively, one day postoperatively, and 12 months postoperatively. Changes were analyzed using paired t-tests within groups and independent t-tests between groups. Pearson’s correlation was used to assess the relationship between GA and OPA changes. Results: The mean reduction in GA at 12 months was 2.81° (±2.89°) in Class II and 3.81° (±2.60°) in Class III patients. The mean relapse (increase) in GA from the first postoperative day to 12 months was 1.57° (±1.60°) in Class II and 2.00° (±1.41°) in Class III patients. No statistically significant difference was found between the two groups for the magnitude of GA change or relapse (p > 0.05). Furthermore, no significant correlation was found between the amount of GA change and OPA change within either group (p > 0.05). Conclusion: Bimaxillary osteotomy with rigid fixation resulted in a significant reduction of the gonial angle in both Class II and Class III patients. Although the magnitude of change and relapse was numerically greater in Class III patients, the difference was not statistically significant. The occlusal plane angle changed in a similar direction but was not strongly correlated with the gonial angle change.