Electromyographic screening of myogenous and arthrogenous TMJ dysfunction patients.

Sixty patients, clinically examined for TMJ dysfunction, were also electromyographically screened. The TMJ dysfunction pain in forty patients was evaluated to be mainly of a myogenous origin and in fourteen patients of a mainly arthrogenous origin. Due to lack of findings in the clinical examination six patients were not to be classified into either of the two groups. They were excluded from the EMG study. For the EMG examination the patients were asked to clench for 30 s in the intercuspal position at 50% of the maximum EMG activity of the masseter muscles. Surface electromyograms of the right and the left masseter and anterior part of the temporalis muscles were monitored. The amplitude of the EMG signal, the duration of the silent period and the changes in the frequency composition of the signal during the 30 s contraction were analysed. Statistically significant differences between the two patient groups were found in EMG amplitude and in silent period duration. However, the difference in silent period duration was due to the dependency of the silent period on the activation level of the muscle. No statistically significant difference in silent period was found when this dependency was corrected for in the data. The EMG parameters related to muscular fatigue phenomena did not show any difference between the two groups. The difference in EMG amplitude and consequently the difference in silent period duration support the clinically made distinction into mainly a myogenous or mainly an arthrogenous origin of TMJ dysfunction pain.