[The characteristics of masticatory muscle activity in bruxers].

OBJECTIVE: To evaluate the effects of bruxism on masticatory muscle electromyographic (EMG) activity. METHODS: Twenty-four bruxers and sixteen asymptomatic control subjects were included through questionnaire and clinical examination. EMG activity was recorded by placing surface electrodes on bilateral anterior temporalis (TA), masseters (MM), anterior digastrics (DA) and sternocleidomastoid (SCM) muscles. EMG activities at rest, during maximal voluntary clenching in intercuspal position and swallowing were recorded by means of Bio PAK system. RESULTS: EMG activities of TA and MM at rest were significantly higher in bruxism group than in control group (P<0.05). When subjects clenched their teeth in intercuspal position, the activities of TA and MM were much lower in bruxism group than in control one (P<0.05). EMG activity during swallowing was no significant difference between the two groups. The asymmetry index of bilateral TA and MM in bruxism group was a little higher than the control group, but there was no significant difference between the two groups (P>0.05). CONCLUSION: Masticatory muscle dysfunction of bruxers is mainly represented as higher potential in postural position and lower potential during maximal voluntary clenching in intercuspal position of anterior temporalis and masseters.