Evaluation of Postoperative Mandibular Positional Changes After Mandibular Setback Surgery in a Surgery-First Approach: Isolated Mandibular Surgery Versus Bimaxillary Surgery

Abstract

The aim of this study was to compare postoperative positional changes in the mandible after isolated mandibular surgery (IMS) or bimaxillary surgery (BMS) in a surgery-first approach (SFA). The authors designed and implemented a retrospective cohort study composed of patients who underwent mandibular setback surgery using the SFA. Surgical and postoperative changes were evaluated using lateral cephalograms taken 1month before surgery (T0), 1week after surgery (T1), and immediately after debonding of orthodontic appliances (T2; 16.6±8.7months after surgery). To predict postoperative mandibular positional changes from the increase in vertical dimension (VD) in surgical occlusion, the mandible was rotated counterclockwise to the preoperative VD on the lateral cephalogram at T1, and resultant mandibular positional changes were measured. To evaluate actual postoperative mandibular positional changes between each time point and compare them between the 2groups, independent t test, paired t test, and repeated-measures analysis of variance were performed. Thirty patients were evaluated (16 in IMS group and 14 in BMS group). The 2 groups showed significant time-course mandibular positional changes from T0 to T1 and from T1 to T2 within each group (point B, P<.001), although no statistically significant differences were observed between groups. There was no statistically relevant difference between groups in the predicted and actual postoperative rotational movements. In addition to the mandibular forward movement that resulted from postoperative mandibular counterclockwise rotation, additional horizontal relapse occurred. The present findings suggest that the mandible exhibits notable postoperative forward movement during postoperative orthodontic treatment, regardless of the extent of the orthognathic surgery in the SFA, and it is necessary to consider mandibular forward movement from the VD increase in surgical occlusion and additional relapse during the treatment planning stage.