Aims: To determine whether an intervention reduces oromotor activity and masticatory muscle pain in myofascial temporomandibular disorder (M/TMD) patients with high levels of masticatory muscle activity associated with sleep bruxism. Methods: Fourteen women with M/TMD and prior polysomnographic evidence consistent with sleep bruxism participated in a 10-week single-group pre-test/ post-test mechanistic clinical trial. A 2-week period of baseline monitoring of individually biocalibrated electromyographic (EMG) events associated with sleep bruxism was followed by 6 weeks of EMGevent- contingent treatment via an innocuous electrical pulse to the skin overlying the temporalis muscle. Treatment was discontinued during 2-week follow-up monitoring. Each night before sleep, subjects recorded their average daily pain. Results: Mixed-model analysis of variance showed a reliable reduction of EMG events during contingent stimulation treatment periods, but frequency of EMG events returned to baseline levels during follow-up (linear term, P = .002; quadratic term, P = .001). In contrast, nightly pain reports failed to show any systematic changes during treatment (linear and quadratic trends, both P > .10). Conclusion: Spontaneous pain severity and nighttime oromotor activity vary independently over nights, even in M/TMD patients selected for relatively high levels of both characteristics. Keywords: bruxism, electromyography, orofacial pain, temporomandibular disorders