OBJECTIVETo evaluate the morphological change of masseter after the mandibular angle osteotomy.

METHODSComputerized 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.

RESULTSAfter 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.

CONCLUSIONSThe masseter atrophy happens spontaneously after mandibular angle osteotomy, especially at the region of mandibular angle. It should be considered during surgical design.