Distribution of muscle activity during sleep in bruxism

10 outpatients with bruxism were investigated by polygraphic recordings during night sleep. Electromyogram, electrooculogram and electroencephalogram derivations were used to evaluate the activities of masseter muscle and the different stages of sleep. The results of the bruxist group were compared to those of an age-matched control group. The amount and the length of pressing and grinding jaw movements were correlated with the sleep period time as well as with the different sleep stages. In comparison to the control group, a significant difference of muscle activity longer than 5 s was found, but there was no difference regarding activities of 3-5 s duration. The highest level of activity was found in sleep stage two and during awakening times. No difference was seen with regard to percentages of the sleep stages.