Regional Disparity in Dental Care Utilization in Japan: Ecological Study Using the National Database of Health Insurance Claims

Background: We examined regional disparities in dental care utilization and their associations with dental care utilization and socioeconomic factors in Japan. Methods: Using the Fourth NBD Open Data Japan, a database for the universal healthcare insurance claims, we conducted an ecological study by analyzing 216 million pieces of aggregated data from April 2017 to March 2018. We used nine indicators to represent dental care utilization: outpatient visits, outreach services, cavity fillings, pulpectomies, dental calculus removals, periodontal surgeries, tooth extractions, dental bridges, and dentures. Standardized claim ratios (SCRs) for these indicators were calculated for Japan’s 47 prefectures, each of which was divided into three groups based on socioeconomic factors (i.e., average income per capita and the proportion of university enrollments). Kruskal-Wallis tests were performed among the three groups to examine the associations between the supply-adjusted nine indicators and the socioeconomic factors. Findings: The ratios between the maximum and minimum SCRs were 1·4 for outpatient visits, 19·3 for outreach services, and 17·6 for periodontal surgeries. Income level was negatively associated with dental bridges and dentures. Educational level was positively associated with outreach services and dental calculus removals, and negatively associated with pulpectomies, tooth extractions, dental bridges, and dentures. Interpretation: In Japan, regional disparities in dental care utilization exist for periodontal care and outreach services but are smaller for urgent and substantial dental care. Educational level appears to be a more important determining factor than income level in dental care utilization. Funding Statement: This work was supported in part by a Health and Labour Sciences Research Grant (Multidisciplinary research project on measures against lifestyle-related diseases such as cardiovascular diseases and diabetes mellitus) “Research study aimed at the development of new evaluation indices and new evaluation methods for the preservation of dental and oral health: Health service research aimed at reducing health disparities in Japan” received by the principal investigator, Nanako Tamiya (Grant number: H31-19FA1001). Declaration of Interests: Takahiro Mori: His appointment as an associate professor at the University of Tsukuba was sponsored by JMDC Inc. in the financial year 2018 (i.e., April 2018 – March 2019), by SMS CO., LTD. in the financial year 2019 (i.e., April 2019 – March 2020), and by FAST DOCTOR CO., LTD in the financial year 2020 (i.e., April 2020 – present). JMDC Inc., SMS CO., LTD, and FAST DOCTOR CO., LTD did not play any role in the conception, design, conduct, or reporting of this study. Sakata Nobuo: His appointment as an associate professor at the University of Tsukuba was sponsored by JMDC Inc. in the financial year 2020 (i.e., April 2020 – present). JMDC Inc. did not play any role in the conception, design, conduct, or reporting of this study. The other authors declare they have no competing interests. Ethics Approval Statement: This study was approved by the University of Tsukuba Medical Ethics Committee (date of approval: December 17, 2019; approval number: 1446).