Psychophysiological definitions of clenching.

This study tested the hypothesis that individuals show considerable variability in EMG activity produced by the masticatory muscles when they are instructed to clench than when they are instructed to make minimal or maximal contact. Twenty individuals without temporomandibular disorder (TMD) pain participated in a biofeedback-training task to establish a relaxed baseline. They were instructed to clench their teeth according to their personal definition of the term, while EMG data were collected. This process was repeated two more times, followed by similar instructions to make minimal and maximal contact between the teeth. Results showed that individual subjects were very consistent in their behavioral definition of clenching and that the subjects taken as a whole showed markedly greater variability. The precise behavioral meaning of clenching varies across individuals. The failure to account for these individual differences may explain in part reported discrepancies on the role of parafunctions in TMD.