Masseter muscle changes following orthognathic surgery : a long-term three-dimensional computed tomography follow-up

Abstract

The aim of this study was to evaluate the long-term changes of masseter muscle morphology in skeletal Class III patients with facial asymmetry following 2-jaw orthognathic surgery (Le Fort I osteotomy + Intraoral vertical ramus osteotomy).Using computed tomography (CT), a longitudinal study was conducted on 17 skeletal Class III patients with facial asymmetry. Measurements from the reconstructed 3D CT images were compared from T1 (before surgery), T2 (1 year after surgery), and T3 (4 years after surgery). The maximum cross-sectional area, orientation, thickness, and width of masseter muscle were measured on both the deviated and non-deviated sides. The control group included 17 volunteers with skeletal and dental Class I relationships without dentofacial deformities. At T1, there were no significant differences of masseter muscle measurements (cross-sectional area, thickness, or width of masseter muscle) between the deviated and non-deviated sides. Masseter muscle orientation was significantly more vertical on the non-deviated side than the deviated side at T1 (P < .01), no significant bilateral differences were noted at T2 and T3. At T1, masseter muscle measurements were significantly lower than controls (P< .01). During T1-T3, a significant increase was noted in cross-sectional area, thickness, and width (P < .01) of masseter muscle. At T3, no significant difference was noted between the study group and control group. After surgery, the masseter muscle measurements of skeletal Class III asymmetry patients showed no significant differences compare to control group within the 4-year follow-up period, indicating adaptation to the new skeletal environments and increased functional demand.