Causal Relationship Between Autoimmune Arthritis and Temporomandibular Disorders

Accumulating evidence has indicated a close interrelation between autoimmune arthritis (AA) and temporomandibular disorders (TMD), but the causality is still unclear. The study aimed to explore the causal inference between AA and TMD using a bidirectional Mendelian randomization analysis.

Online genome-wide association study data on rheumatoid arthritis (RA), ankylosing spondylitis (AS), psoriatic arthritis, and TMD were obtained from the FinnGen and IEU databases. Causality was using the inverse variance-weighted method as the primary analysis and supplemented by other methods. Sensitivity analyses, including heterogeneity tests, horizontal pleiotropy tests, and leave-one-out methods, were conducted to investigate the stability and reliability of the results.

The inverse variance-weighted test indicated that several AA types could causally increase the TMD risk, including overall RA (odds ratio [OR] = 1.348, 95% confidence interval [CI] = 1.1232-1.618, P = .001), subtype nRA (OR = 1.118, 95% CI = 1.044-1.197, P = .001), and AS (OR = 1.060, 95% CI = 1.024-1.097, P = .001). Moreover, the causal association of the above combinations has been proven to be stable and reliable using sensitivity and other tests.

These findings suggest that RA and AS might be causally associated with an increased risk of TMD. However, more studies are needed to check the causal effects of AA on TMD and analyse the potential mechanisms further.