ABSTRACT
<p><b>OBJECTIVE</b>To evaluate the morphological change of masseter after the mandibular angle osteotomy.</p><p><b>METHODS</b>Computerized tomography (CT) examination was performed on 120 patients treated by mandibular angle osteotomy before operation and at 3, 6, 12 months after operation, respectively. The pre- and postoperative masseter muscle thickness and cross-sectional area were evaluated using 3D CT images observed from 3 selected slice planes, which were paralleled with Frankfurt horizontal plane. These CT images were stored and three-dimensional reconstruction were made for calculation of masseter muscle volume through software.</p><p><b>RESULTS</b>After operation, the reduction of the masseter muscle volume and cross-sectional area was seen. The volume of the masseter at 3, 6, 12 months postoperatively decreased to 82.02%, 77.00% and 80.43% (P < 0.05). The cross-sectional area at 3, 6,12 months postoperatively decreased to 85.81%, 78.86% and 81.56% at A plane, 80.94%, 75.03% and 77.04% at B plane, and reached to 13.46%, 11.48% and 13.89% at C plane (P < 0.05, P < 0.05, P < 0.01). The masseter thickness after operation was significantly different from that before operation during the follow-up period, but not at 12 months after operation at A plane.</p><p><b>CONCLUSIONS</b>The masseter atrophy happens spontaneously after mandibular angle osteotomy, especially at the region of mandibular angle. It should be considered during surgical design.</p>