Income-related inequalities in preventive and curative dental care use among working-age Japanese adults in urban areas: a cross-sectional study

BACKGROUND Preventive dental care use remains relatively low in Japan, especially among working-age adults. Universal health insurance in Japan covers curative dental care with an out-of-pocket payment limit, though its coverage of preventive dental care is limited. The aim of this study was to test the hypothesis that income inequality in dental care use is found in preventive, but not curative dental care among working-age Japanese adults. METHODS A cross-sectional survey was conducted using a computer-assisted, self-administered format for community residents aged 25-50 years. In all, 4357 residents agreed to participate and complete the questionnaire (valid response rate: 31.3%). Preventive dental care use was measured according to whether the participant had visited a dentist or a dental hygienist during the past year for dental scaling or fluoride or orthodontic treatments. Curative dental care use was assessed by dental visits for other reasons. The main explanatory variable was equivalent household income. Logistic regression analyses with linear trend tests were conducted to determine whether there were significant income-related gradients with curative or preventive dental care use. RESULTS Among the respondents, 40.0% of men and 41.5% of women had used curative dental care in the past year; 24.1% of men and 34.1% of women had used preventive care. We found no significant income-related gradients of curative dental care among either men or women (p = 0.234 and p = 0.270, respectively). Significant income-related gradients of preventive care were observed among both men and women (p < 0.001 and p = 0.003, respectively). Among women, however, income-related differences were no longer significant (p = 0.126) after adjusting for education and other covariates. Compared with men with the lowest income, the highest-income group had a 1.79-fold significantly higher probability for using preventive dental care. CONCLUSIONS The prevalence of preventive dental care use was lower than that of curative care. The results showed income-related inequality in preventive dental care use among men, though there were no significant income-related gradients of curative dental care use among either men or women. Educational attainment had a positive association with preventive dental care use only among women.