The mouth‐opening muscular performance in adults with and without temporomandibular disorders: A systematic review

Background: The mouth-opening muscular performance in patients with temporomandibular disorders (TMDs) is unclear. Understanding the impairments of this muscle group within specific TMDs is important to develop proper management strategies. Objectives: Characterize the mouth-opening muscular performance in adults with and without TMDs. Methods: PubMed, EMBASE, CINAHL, Scopus, Web of Science and Cochrane databases were searched from inception to 12 November 2020. Bibliographies were searched for additional articles, including grey literature. Case-control, cross-sectional and interventional studies reporting mouth-opening muscular strength and/or endurance were included. Risk of bias was assessed by the SIGN checklist for case-control studies and by the NIH quality assessment tool for cross-sectional studies. Results were pooled with a random-effects model. Confidence in cumulative evidence was determined by means of the GRADE guidelines. Results: Fourteen studies were included; most were rated as having a moderate risk of bias. Only three studies assessed patients with TMDs and the other eleven assessed healthy adults. Significant sex differences in muscular performance were found for healthy adults in the review (strength deficit for females versus males). There was a significant reduction in maximal mouth opening performance (strength and endurance) in the three studies that assessed patients with temporomandibular disorders. Conclusion: Sex plays a significant role in maximal mouth opening strength. There is a lack of reliable data on the normal mouth-opening strength and endurance of healthy adults as well as for patients with TMDs. Implications: Lack of reliable TMDs patient data and comparable healthy adult data highlights future direction for research