CHANGES IN ELECTRIC-ACTIVITY OF MASSETER AND TEMPORAL MUSCLES AFTER MANDIBULAR SAGITTAL SPLIT OSTEOTOMY

The functioning of the masseter and anterior temporal muscles was asse ssed by electromyography in 18 patients before orthognathic surgery an d 6 weeks, 3 months, 1 year, and 2 years afterwards. Electromyogram (E MG) recordings were made during maximal bite in intercuspal position a nd chewing. The mean electric activity in the masseter and anterior te mporal muscles decreased markedly 6 weeks after surgery but increased clearly for 1 year in both functions. Only a slight further increase w as observed at a 2-year follow-up during chewing, but not during maxim al bite in intercuspidation. The mean changes in electric activity inc reased more clearly in patients with hyperplastic mandible than in pat ients with hypoplastic mandible and in those with long shift of the ma ndible. The same finding was also more visible in men and older patien ts than in women and younger patients.