Before-after (1998 and 2008) trend analyses on regional clustering of clinical dentist-to-population ratio in all 1,976 municipalities of Japan

Purpose: The main purpose of this study was to obtain geographic clustering information in order to identify shortages (“cold spots”) and surpluses (“hot spots”) of dentists in all municipalities of Japan. Methods: Pretreatment steps were conducted to recover the lost comparability between pre-1998 and post-2008 data due to the large-scale merging of municipalities (42.1% reduction) in the Heisei era. Moran’s I, LISA and spatial multiple regression analyses with AIC were performed to verify regional clustering. Dependent variables of the regression analyses were the clinical dentist-to-population ratio in 2008 (Model 1) and the difference between 1998 and 2008 (Model 2). Results: The R was 0.8379 (p<0.0001) for Model 1 and 0.5832 (p<0.0001) for Model 2. The initial dentist-to-population ratio in 1998 showed the highest significance in both models. However, the coefficient of Model 2 was negative, which was exactly the opposite of that of Model 1. Furthermore, indices relating to urbanization and hospital dentist-to-population ratio in 1998 were also highly significant (p<0.01) after adjustment for confounding factors. HighHigh clustered municipalities are located in most urbanized areas, whereas Low-Low clustered municipalities are located in remote areas far from urbanized areas. This study revealed that factors which attract dental clinics are urbanization and hospitals with dental care capabilities. Conclusion: Clinical dentist-topopulation ratios have improved only in municipalities in urbanized areas in the past ten years. On the contrary, accessibility of dental treatment has not improved in remote/isolated areas. Introduction This study was conducted as part of a series of studies on the supply and demand of dentists in Japan funded by the Health Labour Sciences Research Grant [1] by the Ministry of Health, Labour and Welfare (MHLW) in fiscal 2009 and 2010. Both the shortage of dentists in rural, isolated areas and the excessive concentration of Before-after (1998 and 2008) trend analyses on regional clustering of clinical dentist-to-population ratio in all 1,976 municipalities of Japan Toru Takiguchi, Hitoshi Aoyama, Kakuhiro Fukai, Tatsuo Yamamoto, and Yuichi Ando 1 Department of Health Informatics, Niigata University of Health and Welfare, Niigata, Japan 2 Tochigi Prefectural Medical and Social Welfare College, Utsunomiya, Japan 3 Fukai Institute of Health Science, Misato, Japan 4 Division of Sociological Approach in Dentistry, Department of Dental Sociology, Kanagawa Dental College, Yokosuka, Japan 5 Department of Health Promotion, National Institute of Public Health, Wako, Japan