Are jaw range of motion, muscle function and proprioception impaired in adults with persistent temporomandibular disorders? A systematic review and meta-analysis

Background: The nature of certain musculoskeletal impairments associated with temporomandibular disorders (TMD) is unclear. Understanding impairments within TMD subgroups is important to guide management. Objectives: Characterise local musculoskeletal impairments in adults with persistent TMD. Methods: PubMed, EMBASE, CINAHL, Scopus, Web of Science and Cochrane databases were searched from inception to 12 January 2020. Bibliographies were searched for additional articles, including grey literature. Case-control and interventional studies reporting temporomandibular range of motion (ROM), muscle function (MF) or proprioception in TMD and control groups were included. Risk of bias was assessed using SIGN checklist for case-control studies. Results were pooled using random-effects model. Confidence in cumulative evidence was determined using American Academy of Neurology guidelines. Results: Sixty-six studies were included, most rated moderate risk of bias. Twelve primary outcomes were assessed, with partial scope for meta-analysis. Significant reductions were found for active maximal mouth opening (P <.00001, MD=−4.65 mm), protrusion (P <.0001, MD=−0.76 mm) and maximum bite force (P <.00001) in TMD versus controls. Subgroup analysis scope was limited. Reduced AMMO was found in myogenic TMD subgroups versus controls (P =.001, MD= −3.28 mm). Few studies measured proprioception, with high methodological variability. Confidence in cumulative evidence ranged from high to very low. Conclusion: ROM and bite force impairments accompany TMD. Insufficient data were available to investigate impairments within TMD subgroups. Implications: Several musculoskeletal impairments have been identified, which may guide clinical management of TMD. Lack of subgroup data, and data for proprioception and MF, highlights future direction for research. PROSPERO: CRD42020150734.