Combined Effect of Toothbrushing and Interdental Cleaning on the Risk of Dementia

Purpose: Systemic inflammation contributes to dementia risk by promoting amyloid beta production and enhancing brain neurotoxicity. While oral hygiene is key in managing inflammation, few studies have assessed the combined effect of toothbrushing frequency and interdental cleaning on dementia risk. This study examined the association between oral hygiene behaviors and dementia onset among older Korean adults. Materials and Methods: A retrospective cohort study followed participants for 11 years using data from the National Health Insurance Service–National Health Information Database. Kaplan–Meier estimates computed cumulative incidence probabilities, and differences between oral hygiene groups were evaluated using the log-rank test. Cox proportional hazards models were applied to evaluate the impact of oral hygiene behaviors on dementia incidence, estimating the hazard ratio (HR) and 95% confidence interval (CI). Results: Higher frequency of toothbrushing and interdental cleaning device use were each significantly associated with reduced dementia risk [“≥3 times toothbrushing daily,” adjusted HR (aHR)=0.85; “always using interdental cleaning devices,” aHR=0.89], though no clear linear dose-response pattern was observed. Combined frequent toothbrushing and interdental cleaning showed a further risk reduction [“≥2 times toothbrushing with interdental cleaning (always or sometimes),” aHR=0.75], regardless of dementia type. Professional dental cleaning within 1 year (aHR=0.88) and always brushing before sleep (aHR=0.82) were also associated with lower risk. Conclusion: Proper oral hygiene practices, especially toothbrushing combined with interdental cleaning, were associated with a lower risk of dementia.