The role of tooth-grinding in the maintenance of myofascial face pain: A test of alternate models

Objective. While mechanisms of myofascial face pain are poorly understood, bruxism has been implicated in the maintenance of this painful disorder. This study evaluates whether evidence of one aspect of bruxism, tooth-grinding, is positively associated with pain severity, as predicted by a psychophysiological model, or negatively associated, as predicted by an adaptation model of face pain. Patients. Participants were 51 women who met Research Diagnostic Criteria for the myofascial subtype of temporomandibular disorder. Outcome Measures. Tooth-grinding was quantified by changes in microwear features of the molar teeth over 2 weeks. Palpated pain severity was quantified on an 11-point scale in response to palpation of the skin overlying the masseter and temporalis muscles bilaterally. Other measures included validated scales of spontaneous pain severity, stress, distress, and psychological symptoms. Association was quantified as Pearson correlation coefficients. Results. Data showed an inverse correlation (r = -0.37, P < 0.05) between palpated pain severity and the index of tooth wear, supporting the adaptation model. This correlation provided a weighted average of a strong effect (r = -0.80, P < 0.01) seen in those women reporting pain only the right side of their face with an effect that approximated zero in those reporting bilateral pain. Tooth wear measures were negatively associated with ratings of pain severity only over the right masseter. Discussion. While these data do not address the role of clenching, they cast serious doubt on the theory that myofascial face pain is maintained by tooth-grinding.