Evaluation of mandibular positional changes after orthognathic surgery in skeletal class II and class III surgery-first approach patients.

PURPOSE: The aim of this study was to predict and compare postoperative changes of mandibular position between mandibular setback and advancement surgery in a surgery-first approach (SFA). MATERIALS AND METHODS: The study population included patients who underwent mandibular setback or advancement surgery using bilateral sagittal split ramus osteotomy, those were divided into two groups: mandibular setback and advancement surgery. Surgical and postoperative mandibular positional changes were evaluated by lateral cephalograms and CTs taken within 2 months before surgery (T0), 1 week after surgery (T1), and after the debonding procedure (T2). The postoperative mandibular positional changes were predicted from the increase in vertical dimension (VD) in surgical occlusion and the counterclockwise rotation to the preoperative VD on the lateral cephalograms and CT at T1. Furthermore, resultant measurement on postoperative mandibular positional changes was performed. Finally, we compared the prediction with actual positional changes of the mandible after the debonding procedure. RESULTS: Nine SFA patients with mandibular setback surgery and six with advancement surgery were evaluated and significant mandibular changes from T0 to T1 and from T1 to T2 were observed. Negative correlation between horizontal surgical changes and postoperative horizontal changes was present in both groups. The difference between the predicted and actual amount of postoperative mandibular movement was significant in the mandibular advancement surgery group. CONCLUSION: Postoperative mandibular relapse appeared much larger in the mandibular advancement surgery group than in the setback group. Therefore, it is more important to consider the postoperative mandibular position change in mandibular advancement surgery in SFA.

Effect of Bone Buttressing at the Vertical Osteotomy Site on Postoperative Stability After Mandibular Setback Surgery.

ABSTRACT: This study aimed to assess the effect of bone buttressing at the vertical osteotomy site on postoperative stability after mandibular setback surgery and determine factors contributing to postoperative relapse. This retrospective study was conducted on patients who received mandibular setback surgery using bilateral sagittal split ramus osteotomy. Patients were divided into two groups: group I, intimate bony contact, and group II, bony gap of 2 mm or more. Using lateral cephalograms taken before surgery, 1 week after surgery, and 6 months after surgery, surgical changes, and postoperative relapse were compared between 2 groups. To assess associations between postoperative relapse and other variables, Pearson correlation analysis and multiple linear regression analysis were performed. Twenty-eight patients were evaluated (17 in group I and 11 in group II). Mean relapse was greater in group II (1.8 mm) than in group I (1.2 mm), although there were no significant differences between 2 groups (P = 0.203). Postoperative relapse was significantly associated with intraoperative clockwise rotation of the proximal segment (P < 0.001) and the amount of mandibular setback (P = 0.038). Bony gap was only correlated with postoperative counterclockwise rotation of the proximal segment (P = 0.014). In the regression analysis, intraoperative clockwise rotation of the proximal segment significantly predicted postoperative relapse (P < 0.001, R2 = 0.388). The absence of bone buttressing at the vertical osteotomy site may not significantly affect postoperative stability after mandibular setback surgery, and it is important to minimize intraoperative clockwise rotation of the proximal segment for better postoperative stability.