Functional Changes after Orthognathic Surgery
Ellen Wen-Ching Ko, DDS, MS
Department of Craniofacial Orthodontics, Chang Gung Memorial Hospital
Graduate Institute of Craniofacial and Oral Science, Chang Gung University
Craniofacial Research Center, Chang Gung Memorial Hospital
Orthognathic surgery (OGS) can provide predictable changes to the jaw bones and intermaxillary occlusal relations for correcting dentofacial deformities. Outcome assessments of the treatment are not only based on aesthetic improvement and surgical stability, but also on the oral functional changes that can be assessed by patient centered reporting of long-term quality of life.
OGS causes surrounding tissue trauma and alters muscle adaptive mechanisms. Performance of masticatory function can be evaluated by range of mandibular movement, dental occlusal contact, masticatory efficiency, bite force, and surface electromyographic (sEMG) activity of the masticatory muscles. The displacement of mandibular condyles during surgery may confine and alter the behavior of mandibular motion. A study was conducted to delineate the characteristic patterns of three-dimensional mandibular movement in patients with skeletal Class III malocclusion and investigate the longitudinal changes in mandible and condylar motion subsequent to OGS. Deterioration in mandibular motion after OGS can recover totally within six months. Six months after OGS, the mandibular movement remains consistent with the amount in normal subjects.
Surface EMG of the masticatory muscles is a noninvasive tool used to analyze electrical signals that emanate during muscular contraction in the stomatognathic system during normal and abnormal conditions. The data of a consecutive series of patients with skeletal Class III malocclusion were obtained before and after OGS. sEMG of the anterior temporalis and masseter muscles were recorded. Resting tonus, maximum voluntary clench with habitual intercuspation and on cotton pads, and maximum muscle firing were evaluated. Serial sEMG data indicated a significant decrease immediately after OGS that then recovered 6 months later. A larger sagittal relapse of mandibular setback occurred in patients with greater masticatory muscle activity. Modifications in surgical design and overcorrection should be considered in patients with greater masticatory muscle activity before OGS. Early physical rehabilitative therapy is helpful for early recovery of muscle activity in masticatory muscles after OGS.