The effect of psychological stress on masticatory muscle electromyography—a scoping review

Temporomandibular disorders (TMDs) are the second most common reason for orofacial pain with myalgia being the most prevalent diagnosis. Overuse of the masticatory muscles and the presence of stress are both risk factors for myalgia. The extent to which these risk factors interact remains unclear, including whether psychological stress contributes to increased masticatory muscle activity. The purpose of this scoping review was to identify, examine, and map the available literature exploring the relationship between psychological stress and masticatory muscle electromyography (EMG). Pre-clinical and clinical studies that studied adults with or without TMD who were exposed to psychological stress and had masticatory muscle electromyography recordings were included. The electronic databases CINAHL, EMBASE, Medline, and PsycINFO were searched in March 2025. Using a pre-defined data extraction sheet, basic study information and specific results regarding the research question were extracted. These were analysed and the results were described based on the type of study (pre-clinical vs. clinical), as well as the type of stress (experimental vs. clinical). Following screening, 38 studies (published between 1971 and 2025) were included: 29 clinical experimental studies, 3 cross-sectional studies and 6 pre-clinical studies. All pre-clinical and cross-sectional studies demonstrated that psychological stress increased masticatory muscle EMG. Among the clinical studies, 25 of the 29 studies reported that psychological stress increased masticatory muscle EMG. Psychological stress consistently increased masticatory muscle EMG in both human and animal models, although some caution is warranted given the paucity of manipulation checks in the included studies. Putative biological mechanisms are discussed herein. A trend towards greater EMG amplitude in response to stress in patients with TMD compared to healthy controls was demonstrated. Given the high prevalence of psychological stress in Western populations, these findings argue that the presence of psychological stress should be consistently evaluated when assessing patients with TMD.