Nonlinear Association between Density of Dental Clinics and Dental Visits among Older Japanese

Objectives: Correcting clinic maldistribution is key to universal health care. The imbalance in dental clinic supply, characterized by both oversupply and undersupply, remains underexplored, and few studies link geographic distribution with patient utilization patterns. This study examined the association between the density of dental clinics and dental visits among the older Japanese population. Method: This repeated cross-sectional study used data from 3 waves (2016, 2019, and 2022) of the Japan Gerontological Evaluation Study targeting functionally independent older adults aged ≥65 y. The dependent variables were dental visits for prevention and treatment. The independent variables were the density of dental clinics based on habitable areas, measured as both categorical and continuous variables. Covariates included age, sex, marital status, equivalent household income, and educational status. Multilevel Poisson regression analysis was conducted to calculate the prevalence ratios (PRs) and 95% confidence intervals (CIs) of preventive and treatment dental visits according to the density of dental clinics. Results: A total of 48,088 participants were included (mean age: 73.9 y, 50.7% of men). Living in an area with the lowest density of dental clinics (0.0000–0.0199 clinics/km 2 ) was significantly associated with lower preventive visits (PR = 0.70; 95% CI, 0.57–0.85) and lower treatment visits (PR = 0.78; 95% CI, 0.68–0.91) compared with the highest density category (≥5.00 clinics/km 2 ). Similar associations were observed up to the density of 0.400 to 0.599 clinics/km 2 . However, at 0.600 clinics/km 2 or more, there was no increase in dental visits, suggesting an oversupply of dental clinics. Conclusions: Living in an area with fewer than 0.600 clinics/km 2 was significantly associated with lower dental visits, particularly for preventive care. On the other hand, no increase in dental visits was observed at 0.600 clinics/km 2 or more. This study emphasizes the importance of equitable clinic distribution in sustaining access to dental care. Knowledge Transfer Statement: This study suggests that the density of dental clinics is associated with the frequency of dental visits. Additionally, a ceiling effect was observed in this effect, suggesting the possibility of an oversupply of dental clinics. This study provides valuable guidance for researchers and policymakers in assessing dental health systems and addressing the uneven distribution of dental clinics to improve oral health.