Sensory impairment and oral hygiene dependence as pragmatic risk markers for incident dementia-related functional impairment in municipal long-term care certification data from Japan: a retrospective cohort study, 2015–2025

Older adults applying for public long-term care insurance (LTCI) services in Japan undergo a standardized needs assessment that records hearing, vision, oral hygiene dependence and outings. We examined whether these routinely collected items identify people at higher risk of later dementia-related functional decline. We linked these certification assessment records from one municipality (April 2015–March 2025; 15,284 individuals) to municipal older-population statistics (July 1, 2025) and included 2,258 adults aged ≥65 years (mean age 80.5 years) rated “independent” (no recorded dementia-related functional impairment) on the LTCI dementia scale at baseline. The outcome was the first recorded rating of impairment (grade I or worse). Cox models adjusted for age, sex, physical independence and intensive medical procedures; sensitivity analyses used age as the time scale, landmark analyses at 180, 365 and 730 days, and a grade IIa-or-worse outcome. Over 6,456 person-years (median follow-up 2.0 years), 1,068 developed recorded impairment (165.4 per 1,000 person-years). Partial oral hygiene assistance (adjusted hazard ratio 1.38, 95% CI 1.13–1.68), hearing impairment (1.15, 1.01–1.31) and vision impairment (1.16, 1.01–1.32) were associated with higher hazard. The oral hygiene association persisted after excluding first-year events (1.48, 1.21–1.81) but was imprecise after excluding 2-year events. In this selected cohort, partial oral hygiene dependence and sensory impairment recorded during long-term care needs assessment were associated with later dementia-related functional impairment and may help target further assessment, although causality cannot be inferred.