title: Masseter muscle changes following orthognathic surgery: a long-term three-dimensional computed tomography follow-up.
abstract: OBJECTIVE
  To evaluate the long-term changes of masseter muscle morphology in skeletal Class III patients with facial asymmetry following two-jaw orthognathic surgery (Le Fort I osteotomy + intraoral vertical ramus osteotomy).
  
  
  METHODS
  Using computed tomography (CT), a longitudinal study was conducted on 17 skeletal Class III patients with facial asymmetry. Measurements from the reconstructed three-dimensional (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 (CSA), orientation, thickness, and width of the masseter muscle were measured on both the deviated and nondeviated sides. The control group included 17 volunteers with skeletal and dental Class I relationships without dentofacial deformities.
  
  
  RESULTS
  At T1, there were no significant differences in CSA, thickness, or width of masseter muscle between the deviated and nondeviated sides. Masseter muscle orientation was significantly more vertical on the nondeviated side than on 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 CSA, thickness, and width (P < .01) of masseter muscle. At T3, no significant difference was noted between the study and control groups.
  
  
  CONCLUSIONS
  After surgery, the masseter muscle measurements of skeletal Class III asymmetry patients showed no significant differences compared with the control group within the 4-year follow-up period, indicating adaptation to the new skeletal environments and increased functional demand.
authors.affiliation: Department of Orthodontics, School of Dentistry, Yonsei University, Seoul, South Korea.
authors.forename: Da-Hye
authors.initials: DH
authors.lastname: Lee
authors.forename: Hyung-Seog
authors.initials: HS
authors.lastname: Yu
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D016022:Case-Control Studies; D005146:Facial Asymmetry / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008137:Longitudinal Studies; D008297:Male; D008313:Malocclusion, Angle Class III / Q000000981:diagnostic imaging / Q000601:surgery*; D008334:Mandible / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000601:surgery; D008406:Masseter Muscle / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D011378:Prognathism / Q000000981:diagnostic imaging / Q000601:surgery*; D014057:Tomography, X-Ray Computed / Q000379:methods