Three-Dimensional Analysis of Lip Asymmetry and Occlusal Cant Change After Two-Jaw Surgery

Abstract

Lip asymmetry greatly influences patient satisfaction after 2-jaw surgery. The purpose of the present study was to identify the influence of skeletal changes on lip cant correction in 2-jaw surgery for mandibular prognathism with asymmetry. The present retrospective cohort study included consecutive skeletal Class III patients who had undergone Le Fort I and sagittal split ramus osteotomy with preoperative and 6-month postoperative cone-beam tomography scans available. The primary predictor variables were the postoperative hard tissue changes (canine cant, first molar cant, transverse change at menton [Me] after surgery, and changes postoperatively from preoperatively). The primary outcome variable was the change in the soft tissue lip cant. The secondary outcome variables were the changes in various landmarks representing perioral asymmetry, including center of cupid's bow, lower lip vermilion, and subnasale. Other variables included subject age and gender. Descriptive statistics and regression and correlation analyses were used to investigate the important predictors influencing lip cant change. A total of 58 patients (33 males; average age, 21.7years) were included in the present study. The demographic variables of the asymmetry group (Me deviation >4mm) were not different from those of the control group. Postoperative changes in Me deviation correlated significantly with the changes in the transverse position of the subnasale, upper lip, and horizontal and vertical differences in the mouth corner position (P<.01 for all) but not with the maxillary occlusal cant change. Linear regression analysis showed lip cant correction was associated with changes in Me deviation (P<.001) and molar cant change (P=.032), but not with canine cant change. Maxillary occlusal cant correction itself cannot fully account for changes in lip cant. The transverse Me change-rather than maxillary cant correction-had the greatest influence on lip cant. These results suggest that correction of chin deviation must be addressed in lip cant correction for facial asymmetry.