Investigation of bidirectional causal association between temporomandibular disorders and five mental disorders

This study utilized two-sample Mendelian randomization (TSMR) to investigate the bidirectional causal associations between temporomandibular disorders (TMD) and five mental disorders.

Single-nucleotide polymorphisms (SNPs) linked to TMD were extracted from the Genome-Wide Association Studies (GWAS) database. The SNPs selected as instrumental variables (IVs) were required to have strong associations with the exposure phenotype and to meet the assumptions of Mendelian randomization (MR) analysis. The primary method employed for TSMR analysis was the Inverse Variance-Weighted (IVW) method. Additionally, the Weighted Median, Weighted Mode, and MR Egger methods were used as secondary approaches to ensure the reliability and credibility of the results. Furthermore, heterogeneity, pleiotropy, and sensitivity tests were conducted to ensure the accuracy and robustness of the findings. After MR analysis, we performed reverse analysis to explore the bidirectional association between TMD and five mental disorders.

Our study provided evidence of a positive correlation between TMD and both anxiety (P = 5.94 × 10^-15, OR = 1.5253, 95 % CI = 1.3719-1.6959) and depression (P = 3.79 × 10^-12, OR = 1.4243, 95 % CI = 1.2890-1.5738). In the reverse TSMR analysis, a positive association was found between anxiety and TMD (P = 0.0126, OR = 1.0664, 95 % CI = 1.0139-1.1217). However, no causal relationship was found between TMD and depression, insomnia, bipolar disorder, or schizophrenia (P > 0.05).

These evidences indicated a bidirectional relationship between TMD and anxiety, and TMD may also contribute to the development of depression.