Association between Dental Diseases and Oral Hygiene Care and the Risk of Dementia: A Retrospective Cohort Study

Objectives: To investigate the associations of dental diseases and oral hygiene care with the risk of dementia. Design: Retrospective longitudinal cohort study. Setting and Participants: We conducted a population-based study of individuals in the Korean National Health Insurance System. A total of 2,555,618 participants who underwent cardiovascular and dental screenings in 2008 were included. Methods: Dental diseases including periodontal diseases, dental caries, and tooth loss were assessed by dentists. Information on oral hygiene care, including professional dental cleaning and the frequency of tooth brushing, was collected using a self-administered questionnaire. Study outcomes were all-cause dementia, Alzheimer's disease (AD), and vascular dementia (VaD). Results: Periodontal diseases [adjusted hazard ratio (aHR) 1.07, 95% CI 1.04-1.09], dental caries (aHR 1.03, 95% CI 1.00-1.05), and 8-14 missing teeth (aHR 1.07, 95% CI 1.02-1.12) were associated with an increased risk of all-cause dementia. In contrast, either professional dental cleaning or frequent tooth brushing were associated with decreased risks of all-cause dementia (aHR 0.91, 95% CI 0.89-0.93 each; aHR 0.83, 95% CI 0.80-0.86 for both). The increased risks by dental diseases were reduced by oral hygiene care: periodontal diseases with professional dental cleaning (aHR 0.94, 95% CI 0.91-0.98) or tooth brushing ≥2 times/day (aHR 0.97, 95% CI 0.94-1.00) and 1 to 7 missing teeth with professional dental cleaning (aHR 0.94, 95% CI 0.89-0.98) or tooth brushing ≥2 times/day (aHR 0.92, 95% CI 0.89-0.95). Consistent results were noted for AD and VaD and in various subgroup analyses. Conclusion and Implications: Periodontal disease, dental caries, and a high number of missing teeth were independently associated with a higher risk of dementia. Conversely, improved oral hygiene care, such as professional dental cleaning and frequent tooth brushing, may modify the risk of dementia associated with dental diseases.