Periodontitis, Tooth Loss, and Risk of Cognitive Impairment and Dementia: A Systematic Review With Meta-Analysis.

AIM: To systematically review and meta-analyze cohort studies evaluating associations of gingival inflammation, periodontitis, and tooth loss with cognitive decline and incident mild cognitive impairment or dementia. METHODS: PROSPERO-registered searches of MEDLINE, Embase, Scopus, Web of Science, and the Cochrane Library identified cohort studies from inception through October 10, 2025, with a PubMed update on June 24, 2026. Random-effects meta-analyses pooled adjusted hazard ratios (HRs) for dementia/MCI; cognitive function outcomes were summarized qualitatively. Risk of bias (RoB) was assessed using the Newcastle-Ottawa Scale. RESULTS: Fifty-nine studies met inclusion criteria; 28 contributed to dementia/MCI meta-analyses. Severe periodontitis (HR: 1.16; 95% CI: 1.06-1.27; I2 = 0%; Q-test p = 0.49), periodontitis of unspecified severity (HR: 1.45; 95% CI: 1.21-1.73; I2 = 98%; Q-test p < 0.001), edentulism (HR: 1.26; 95% CI: 1.19-1.33), and low tooth count (HR: 1.27; 95% CI: 1.14-1.42; I2 = 94%; Q-test p < 0.001) were associated with elevated dementia/MCI risk. RoB was low in 31 studies (53%), moderate in 25 (42%), and high in 3 (5%); inadequate confounder adjustment was common. Meta-regression showed stronger estimates for ICD-code periodontitis definitions (fold change (FC) = 1.44 95% CI: 1.04-2.01), older cohorts (FC per year = 1.02 95% CI: 1.00, 1.05), and weaker estimates with lower RoB (FC per NOS star = 0.81 95% CI: 0.73-0.92). Follow-up duration, cohort age, and RoB were not associated with tooth-count estimates. CONCLUSION: Periodontitis and tooth loss are associated with modestly higher dementia/MCI risk and poorer cognitive function, but heterogeneity, residual confounding, and bias temper causal interpretation. Longitudinal studies with rigorous baseline cognition assessment and intervention studies are needed.