Masticatory muscle function in patients treated for condylar fractures of the mandible.

The activity of the temporal and masseter muscles and of the upper lip was examined by electromyography in five adults and in five children who had sustained uni- and bilateral fractures of the mandibular condyle. Electromyographic recordings were done in the postural position of the mandible, during maximal bite in the intercuspal and retruded mandibular positions, during chewing and swallowing of peanuts and during swallowing of water. In the children, who were examined on three occasions after the trauma, a reduced muscle activity was found shortly after the trauma, but it had normalized at follow-up examination 1 year after the injury. The adults, who were examined 4-6 years after the trauma, had, in general, normal muscle function. In subjects with a unilateral fracture, no difference in muscle activity was found between the two sides. An enlarged distance between the retruded and intercuspal positions of the mandible did not, in these subjects, seem to influence the muscle activity during the functions studied.