Three-Dimensional Changes of Masseter Muscle in Patients With Class III Asymmetry After Bimaxillary Orthognathic Surgery

The present study was aimed to comprehensively evaluate changes in the masseter muscle in patients with Class III facial asymmetry after bimaxillary orthognathic surgery and explore potential correlations between masseter muscle changes and facial morphology or postoperative mandibular stability. Fifty-two eligible patients with Class III facial asymmetry who underwent Le Fort I osteotomy and bilateral sagittal split osteotomy (BSSO) with or without genioplasty between January 2019 and June 2023 were included. Cone-beam computed tomography (CBCT) was collected for each patient at 3 stages: 1 week preoperatively (T0), immediately after surgery (T1), and at least 12 months postoperatively (T2). Masseter muscle changes including volume, surface area, length, and width were measured using ITK-SNAP and 3D Slicer and correlations between these changes and facial morphology, skeletal stability were further explored. The length, width, surface area, and volume of the nondeviated side (NDS) masseter muscle were greater than those of the deviated side (DS) before surgery (T0). These parameters of masseter muscle at both sides decreased significantly after surgery (T2), except the length of DS masseter increased slightly. The differences in bilateral masseter length, width, surface area were reduced significantly after surgery and NDS masseter muscle remained greater than DS masseter muscle. Changes in the NDS masseter surface area negatively correlated with FH-MP. However, no significant correlations between masseter volume changes and mandibular postoperative skeletal stability were found. Taken together, our results revealed detailed masseter muscle changes following surgical correction of Class III facial asymmetry.