Occlusal plane rotation and orthodontic decompensation: influence on the outcome of surgical correction of class III malocclusion

Purpose The aim of this retrospective multicenter study is to evaluate the influence of surgical manipulation of the upper occlusal plane (UOP) and orthodontic decompensation on the outcome of class III orthognathic surgery. Methods Incisor inclinations, occlusal plane inclination as well as skeletal and soft tissue changes were assessed in lateral cephalograms of 85 class III patients who had previously undergone orthognathic surgery. Fourteen linear and eight angular measurements were performed on each radiograph at the beginning of treatment (T0), before surgery (T1) and at the end of treatment (T2) using imaging software. After measurement of variables, Mann-Whitney U-test, repeated-measures analysis of variance (ANOVA) with Bonferroni multiple comparison test, and Spearman's correlation analysis were performed. Results A statistically significant improvement was observed in both sagittal skeletal and soft tissue measurements (p < 0.05). Surgical change in UOP was significantly correlated with changes in overbite, upper lip strain and soft tissue B-point change in the sagittal direction (p < 0.05). Overjet change was significantly correlated with changes in the soft tissue and all sagittal skeletal parameters except for SNA. Changes in the incisor inclinations was significantly correlated with changes in the sagittal skeletal parameters and lower facial height. Significant differences were also observed between the groups with induced clockwise or counterclockwise rotation of the mandible in terms of IMPA (long axis of LI to mandibular plane), overbite, upper lip strain and position of soft tissue B-point (p < 0.05). Conclusion Sufficient dental decompensation is crucial for controlling the sagittal as well as the vertical relationship during surgery. Counterclockwise rotation provides an increase in sagittal projection of the mandibular body at the soft tissue B-point.