Morphological Changes of the Mandibular Angle After Orthognathic Surgery with Class III Deformity in East Asia

The aims of this study were to analyze the morphological changes of the mandibular angle after orthognathic surgery for mandibular setback and investigate related factors. This retrospective study included patients from January 2017 to December 2021 diagnosed with skeletal class III deformity who underwent BSSRO (Group I) or bimaxillary surgery (Group II). Preoperative (T0), within 1 month postoperatively (T1), and 6 months postoperatively (T2) CT scans were collected from 61 patients to three-dimensionally analyze the proximal segment displacement, the linear and angular changes of the mandibular angle. The gonion points moved posteriorly and laterally (P < 0.001), while the inferior movement was not significant (P = 1.000, P = 0.274). The intergonial width increased by 3.32 ± 1.87 mm and 2.34 ± 1.77 mm as revealed by T2 CTs, respectively, in Group I and Group II. Mandibular angle decreased in both groups and by 1.41 ± 2.95° in Group I and 1.37 ± 3.41° in Group II. The increase in intergonial width between T1 and T0 was negatively correlated with the preoperative mandibular angle (P = 0.003) and positively correlated with the transverse outward movement of the proximal segment (P < 0.001). After surgery, the intergonial width increased and the inferior and posterior border of the proximal segment flared outward. The changes in intergonial width and mandibular angle were mainly related to the rotation of the proximal segment, which has a certain impact on the aesthetics of the lower face. Therefore, controlling the position of the proximal segment is of vital importance to lessen the changes in the mandibular angle area.Level of Evidence III. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .