The Reciprocal Risk Relationship of Dental Caries with NAFLD and Liver Fibrosis: Combined Evidence from the NHANES Study and Mendelian Randomization Analysis.

PURPOSE: To explore the relationship between dental caries and non-alcoholic fatty liver disease (NAFLD) and its advanced stage of liver fibrosis, and to confirm causality by employing a bidirectional two-sample Mendelian Randomization (MR) analysis to confirm causality. MATERIALS AND METHODS: 6650 participants of the National Health and Nutrition Examination Survey (NHANES), 2017-2020 were included. Two multivariable logistic regression models were used to evaluate the relationship between untreated dental caries (UDC) and liver conditions of NAFLD and fibrosis, with adjustments for demographics, lifestyle, and medical history. Furthermore, two-sample MR was performed with caries as exposure and NAFLD with NAFLD-related conditions as outcome, and vice versa for bidirectional causality validation. RESULTS: In observational research, UDC was notably associated with NAFLD (OR [odds ratio]: 1.40, 95% CI [confidence interval]: 1.06-1.86) and significant fibrosis (SF) (OR: 1.29, 95% CI: 1.03-1.62). NAFLD and SF were statistically significantly associated with UDC (OR: 1.40, 95% CI: 1.08-1.83; OR: 1.62, 95% CI: 1.26-2.08). In the MR analysis, caries posed a statistically non-significant risk for liver conditions. In contrast, liver conditions non-significantly protected against caries (NAFLD: OR: 0.99, 95% CI: 0.98-1.01; fibrosis: OR: 0.99, 95% CI: 0.99-1.00; cirrhosis: OR: 0.99, 95% CI: 0.99-1.00; fibrosis/cirrhosis: OR: 1.00, 95% CI: 0.98-1.02). CONCLUSION: Observational studies suggested a statistically significant association between UDC and liver conditions of NAFLD and fibrosis. However, MR suggested a statistically non-significant causal relationship between caries and liver conditions; in contrast, liver conditions had a non-significant protective effect on caries.