Predictability of jaw muscle pains from surface electromyograms.

In seven (88%) of eight healthy subjects, weak to moderate pains were elicited in the masseter muscles through the isometric contractions of maximum voluntary teeth clenching. Integrated surface electromyograms of the right and left masseter muscles were used to quantify the absolute and relative contractile activities of the two muscles. The risk (relative probability) of inducing pain onset in the single masseter muscle generating the larger amount of isometric activity was 2.5 times the risk of eliciting pain onset in the single masseter muscle generating the lesser amount of isometric activity. However, as an aid in the diagnosis of pain onset, the method of masseteric surface electromyography had a false diagnostic ratio of 0.67.