Background: No studies have examined the associations between the numbers of teeth and sleep disturbance. Therefore, we examined the associations between the number of teeth and sleep duration in older people, considering the evidence linking fewer teeth and sleep apnoea through changes in jaw position. Methods: For this study we used information from a sample of 23,444 cohort participants, randomly selected from the Japan Gerontological Evaluation Study 2010 (N = 169,215). The outcome variable was self-reported sleep duration (h/day), and the explanatory variable was self-reported number of teeth (0, 1–9, 10–19, ≥20). We treated age, sex, body mass index, educational attainment, annual equalized household income, depressive symptoms, physical activity, activities of daily living, presence of diabetes, and smoking status as covariates. Multinomial logistic regression was used among the 20,548 eligible participants with all necessary information. Results: The mean age was 73.7 (standard deviation = 6.13) years. Most participants (28.1%) reported sleep duration of 7 h, while a small proportion of the participants reported short (≤4 h, 2.7%) or long (≥10 h, 4.7%) sleep duration. The proportion of edentulous participants was 14.7%. Taking the 7-h sleep duration as the reference category, edentulous participants (relative risk ratio (RRR) = 1.43, 95% confidence interval (CI) = 1.07–1.90) or one to nine teeth (RRR = 1.29, 95% CI = 1.02–1.63) had a significantly higher relative risk ratio for short sleep, independent of covariates. Furthermore, they had a higher relative risk ratio for long sleep duration (RRR = 1.75, 95% CI = 1.40–2.19; RRR = 1.48, 95% CI = 1.21–1.81, respectively). Conclusions: Compared to people with 20 or more teeth, older adults with fewer than 10 teeth have higher risks for short and long sleep durations.
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