Electromyographic studies of craniomandibular disorders: a review of the literature.

Craniomandibular disorders have been investigated from many points of view, structurally and functionally. To evaluate the behaviour of the masticatory muscles, electromyography (EMG) has been widely used and the studies have emanated from many different paradigms. The purpose of this paper is to review articles in which EMG has been used to study symptomatic subjects. Findings from sleep studies and basic laboratory studies seem to support the hypothesis of a correlation between masticatory muscle hyperactivity and symptoms. Experimentally induced stress studies consistently show an increased activity in symptomatic subjects. Investigations of motor pauses, the often lengthened silent period, are summarized and discussed. Several different treatment strategies, particularly splints and biofeedback, have been evaluated using EMG, indicating a normalization, but controlled outcome studies are sparse. The use of EMG has thus substantially increased our knowledge of dysfunction of the masticatory system.