Changes of masseter muscles after mandibular angle ostectomy in rhesus monkeys

Mandibular angle ostectomy is a common procedure for the correction of a prominent mandibular angle in Asia. However, the alterations of masseter muscles following resection of the mandibular angle are not well known. In this study, 12 adult rhesus monkeys were used to investigate the effects of mandibular angle ostectomy on the masseter muscle. Mandibular angle ostectomy was performed on one side of the mandible and the other side remained intact and was used as normal control. Four animals were randomly killed at 12, 24, and 48 weeks postoperatively, respectively. The morphologic, histologic, and electromyographic examinations were used to compare the differences of masseter muscle between the ostectomized and normal sides. On the ostectomized side the electromyographic activity, cross sectional area, mass, thickness, and length of the masseter muscle were all decreased, despite a trend to recover with time. Histologic examination showed that the muscular reattachment on the ostectomized side resembled normal muscle attachment eventually. The results showed that secondary atrophic changes would occur in the masseter muscle after mandibular angle resection. This study may be helpful for predicting the final cosmetic outcomes of mandibular angle ostectomy.