Background Social inequalities in oral health exist in various countries. In Japan, a country with universal healthcare insurance policy, people can receive medical and dental care and pay only 10-30% of the total cost of treatment. Additionally, very poor Japanese can receive care without any charge, by the benefit of public assistance. These policies are considered to affect oral health inequalities. Objectives This study examined the association between using a dental prosthesis and household income among older Japanese people. Methods Self-administered questionnaires were mailed to subjects as part of the Japan Gerontological Evaluation Study (JAGES) project in 2010. Of the 8576 people aged 65 years or more living in Iwanuma, Japan, 5058 responded. We used 4001 respondents with no missing values. We stratified into two groups by having 20 teeth or not. Then, cross-tabulation, univariate logistic regression, and multivariate logistic regression were conducted for these two groups. The covariates are sex, age, education, and size of household. Results Of the all respondents included in the analyses, poorer respondents tended to have lower proportions with 20 or more teeth, and 54.6% respondents used dental prostheses. In the respondents with 19 or fewer teeth, higher-income group tended to show significantly higher dental prosthesis use. But the poorest income group showed high prevalence of dental prosthesis use as same as highest income group. Multiple logistic regression among respondents with 19 or fewer teeth showed that after adjustment for sex, age, education, and size of household, compared with the respondents with annual incomes of US$ <5000, those with incomes of US$5000-9999 and US$10 000-14 999 had significantly lower odds ratios for using a dental prosthesis (OR = 0.48 [95% CI = 0.28-0.83], 0.56 [95% CI = 0.33-0.95], respectively). The other respondents did not show significant differences. Conclusions Although universal healthcare insurance covered dental prostheses, a social gradient in dental prosthesis use was still observed. Low-income respondents tended to not use dental prosthesis, but the poorest respondents showed dental prosthesis utilization as high as the highest income group.
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