Are temporomandibular joint disorders associated with facial asymmetry? a systematic review and meta-analysis.

OBJECTIVE To assess scientific evidence of the association between temporomandibular joint (TMJ) disorders and facial asymmetry (FA). METHODS A systematic review was performed in accordance with the PRISMA checklist. A search strategy was developed in electronic databases including MEDLINE, Scopus, Web of Science, Virtual Health Library and Cochrane Library until January 2020. Eligibility criteria included observational studies that investigated the occurrence of FA among patients with and without signs and symptoms of TMJ disorders. Risk of bias of individual studies was analyzed after study selection and data collection processes according to Fowkes and Fulton guidelines. Four meta-analyses (MA) were performed to evaluate the association between TMJ disorders and linear/angular menton deviation, subgrouping the studies into unilateral and bilateral cases. The evidence was certainty-tested using the GRADE approach. RESULTS The search retrieved 2371 studies, 31 of which were eligible for full text reading. Seven cross-sectional clinical studies met the eligibility criteria and were included in the qualitative synthesis, comprising a total of 621 subjects (345 with TMJ disease and 276 in control group), four of which, were classified as being methodologically sound. Five studies were eligible for quantitative synthesis. Linear and angular menton deviation were greater in individuals with unilateral TMJ disorders than controls (MD = 2.41 [0.33, 4.50] p=0.02; I2 =86% and MD = 2.68 [0.99, 4.38] p=0.002; I2 =0%, respectively). CONCLUSIONS Despite the low certainty in evidence, the present study indicated that unilateral TMJ disorders are associated to FA. However, longitudinal studies with greater certainty of evidence should be conducted to achieve a stronger estimate of this association.