Stress-evoked muscle activity in women with and without chronic myofascial face pain.

BACKGROUND: Amplified muscle activity in reaction to daily life stressors might explain chronic pain in temporomandibular disorder (TMD). OBJECTIVES: To assess whether patients with myofascial TMD pain (MFP) react to standardised stressors with greater masticatory muscle activity than demographically matched controls. METHODS: A total of 124 female MFP patients and 46 demographically matched and pain-free controls rated distress while performing a series of standardised stress-reactivity tasks (viz., cold pressor test, mental arithmetic test, speech stressor test and reaction time/startle response test) as well as a vanilla baseline control task. Blood pressure was measured before and after each task, and electromyographic (EMG) activity was continuously recorded over the jaw-closing muscles and several non-masticatory muscles during each task. Linear mixed model analyses were used to test the hypothesis that case status, stress-reactivity task and muscle recording site influenced EMG activity. RESULTS: Stress induction was successful, as evidenced by distress ratings and blood pressure measurements that were significantly elevated during performance of the stress tasks. Participants reported that some of the tasks were stressful in a way that resembled stressors experienced in their daily lives. Elevated muscle activity could be confirmed only for the reaction time/startle response task, where mean EMG activity was elevated more in cases than in controls, specifically in the jaw-closing muscles. CONCLUSION: These data could not provide clear support for the theory that psychological stressors produce a differential increase in masticatory muscle activity in MFP patients than pain-free controls.