ObjectiveTo test the hypothesis that periodontal disease would be associated with increased risk for dementia and mild cognitive impairment (MCI) by assessing dementia/MCI outcomes after a baseline periodontal examination.MethodsParticipants enrolled in the Atherosclerosis Risk in Communities study with a clinical periodontal examination (or edentulous participants) at visit 4 (1996–1998; mean ± SD age 63 ± 6 years, 55% female, 21% black) and adjudicated dementia outcomes through 2016 were included (n = 8,275). A subgroup of 4,559 participants had adjudicated dementia and MCI assessments at visit 5 (2011–2013). Participants received a full-mouth periodontal examination and were classified into periodontal profile classes (PPCs) based on the severity and extent of gingival inflammation and attachment loss. MCI and dementia were determined via neurocognitive testing, neurological examination and history, informant interviews, and brain MRI in a subset. Cox proportional hazards models regressed incident dementia on PPCs. Relative risk regression models were used for the composite of MCI/dementia.ResultsThe cumulative incidence and incidence density of dementia during follow-up (average 18.4 years) were 19% (n = 1,569) and 11.8 cases per 1,000 person-years. Multivariable adjusted hazard ratios for incident dementia among participants with severe PPC or edentulism (vs periodontal healthy) were 1.22 (95% confidence interval [CI] 1.01–1.47) and 1.21 (95% CI 0.99–1.48), respectively. For the combined dementia/MCI outcome, adjusted risk ratios among participants with mild/intermediate PPC, severe PPC, or edentulism (vs periodontal healthy) were 1.22 (95% CI 1.00–1.48), 1.15 (95% CI 0.88–1.51), and 1.90 (95% CI 1.40–2.58). Results were stronger among younger (≤62 years) participants (p for interaction = 0.02).ConclusionPeriodontal disease was modestly associated with incident MCI and dementia in a community-based cohort of black and white participants.