Objective To evaluate the dynamic morphologic changes in the masseter muscle after mandibular angle sagittal split osteotomy (MASO).
Methods Computed tomographic (CT) examinations were performed on 130 patients treated with MASO before surgery and at 3, 6, 12, and 18 months after surgery. These CT images were stored and a 3-dimensional reconstruction was made for calculating the volume of masseter muscle using Mimics 10.01 software. The cross-sectional area of masseter muscle was evaluated preoperatively and postoperatively using 3-dimensional CT images observed from 3 selected slice levels, which paralleled the Frankfurt horizontal plane.
Results Following treatment, the reduction of the volume and cross-sectional area of masseter muscle were calculated. The volume of the masseter muscle was reduced by 28.18%, 39.58%, 33.37%, and 31.18% at 3, 6, 12, and 18 months postoperatively, respectively. The cross-sectional area of 3 slices were reduced, but the sectional area of the lower slice had the sharpest decline, with reductions of 79.27%, 84.39%, 84.02%, and 83.57% at 3, 6, 12, and 18 months postoperatively, respectively.
Conclusions The results showed that the masseter muscle undergoes significant atrophy after mandibular osteotomy, and these changes could be considered as a guide for the design and simulation of MASO before surgery.