Abstract
The aim of this study was to evaluate the recovery process of masticatory muscle activity after orthognathic surgery. The subjects were 5 adult female patients with mandibular prognathism who had received orthodontic treatment at the Department of Orthodontics of Showa University Dental Hospital before undergoing mandibular osteotomy at the Department of Oral Surgery of Showa University Dental Hospital. Surface electromyography was performed just prior to surgery, and 1 month, 3 months and 6 months postoperatively. Bilateral recordings were made from the masseter muscles and from the anterior and posterior temporal muscles during maximal clenching. The results were as follows : (1) One month postoperatively, all of the muscles showed markedly lower levels of activity than before surgery. However, the 3 month and 6 month examinations showed a tendency for gradual recovery of muscle function. (2) Six months after surgery, the degree of recovery varied, with the muscle function in some patients not recovering to preoperative levels. (3) Two of the patients showed distinct asymmetries of muscle activity in the preoperative recordings. In these cases, the asymmetries persisted 6 months after surgery. Our findings indicate that the recovery of muscle function in patients with mandibular prognathism who have undergone sagittal split ramus osteotomy varies between patients, and is likely to continue for longer than 6 months in most cases
