Relationship between status of dentition and incident functional disability in an elderly Japanese population: prospective cohort study of the Tsurugaya project

Purpose: The purpose of this study was to examine whether the status of dentition is associated with incident functional disability in elderly people. Methods: This prospective cohort study targeted community-dwelling Japanese adults of age ≥70 years (n = 838). Participants were classified into the following four groups in accordance with Miyachi's Triangular Classification, which represents the status of dentition on the basis of numbers of remaining teeth and occlusal supports: Zone A, ≥10 occlusal supports; Zone B, 5–9 occlusal supports; Zone D, ≤4 occlusal supports and ≥11 remaining teeth and Zone C, ≤10 remaining teeth. Incident functional disability was defined by the first certification of long-term care insurance in Japan. Data regarding age, sex, body mass index, medical history, smoking, alcohol consumption, education, depressive symptoms, cognitive impairment, social support, history of fall, and subjective masticatory ability were collected. Results: During follow-up for 5185 person-years, 305 participants experienced functional disability. Considering the follow-up data of ≥3 years from baseline, participants in Zones C (hazard ratio [HR], 1.98; 95 % confidence interval [CI], 1.26–3.11) and D (HR, 2.50; 95 %CI, 1.54–4.05) were found to be more likely to develop functional disability than those in Zone A (p for trend = 0.002). Conclusions: Status of dentition was associated with incident functional disability in an elderly Japanese population. The findings of this study suggest that maintenance of remaining teeth and retention of occlusal supports contribute to the prevention of functional disability.