Social Economic Inequality of Oral Health among U.S. Residents from 1999 to 2023 and International Comparison: A Multilevel Analysis Based on NHANES and WHO Oral Health Data

ObjectiveTo investigate socioeconomic inequalities in oral health across global and national contexts, to quantify income related gradients in oral health among United States adults, and to elucidate the mechanisms through which socioeconomic status (SES) shapes oral health, with a focus on access to dental care and the potential role of state Medicaid policies. DesignMulti level observational study combining macro level global and national comparisons with micro level individual data and meso level state policy analysis. SettingUnited States nationally representative surveys and publicly available international data. ParticipantsAdults aged 20 years and older in the National Health and Nutrition Examination Survey (NHANES) 1999-2023 (pooled cross sectional samples), and state level adult populations from the Behavioral Risk Factor Surveillance System (BRFSS) 2011-20XX. Main outcome measuresIndividual outcomes were the Decayed Missing Filled Teeth index (DMFT) and self rated oral health (good versus fair or poor). State level outcomes were the prevalence of past year dental visits, any permanent tooth loss, and complete edentulism among adults aged 65 years and older. SES was measured by the poverty income ratio (PIR) and education. Mediators included annual dental visits, unmet dental need, and health behaviours. State policy variables included indicators of Medicaid expansion and adult Medicaid dental benefit generosity. ResultsIn NHANES, higher PIR and higher education were independently associated with lower DMFT and higher odds of self rated good oral health across all age groups. PIR coefficients for DMFT were approximately -0.25 (20-44 years), -0.79 (45-64 years), and -1.07 (65 years and older), while the corresponding odds ratios for self rated good oral health were about 1.48, 1.46, and 1.33. Predicted probabilities of self rated good oral health increased monotonically from PIR quartile 1 to quartile 4 in every age group. Income related concentration indices indicated that caries and tooth loss were concentrated among low income adults (CI for DMFT about -0.105), whereas good oral health was concentrated among higher income adults (CI about 0.094). The Slope Index of Inequality suggested that moving from the lowest to highest income rank was associated with an average reduction of about 2.48 affected teeth, and the Relative Index of Inequality indicated approximately eight fold higher odds of reporting good oral health in the highest versus lowest income ranks. Oaxaca Blinder decomposition showed that adults in the highest income quartile had on average 1.31 fewer affected teeth than those in the lowest quartile; about one quarter of this gap was explained by observed variables, with access to dental care (annual visits and unmet need) accounting for roughly two thirds of the explained component. In state level difference in differences models with state and year fixed effects and state clustered standard errors, Medicaid expansion and adult dental benefit generosity were not associated with large, statistically significant changes in aggregate dental visit rates, any tooth loss, or edentulism among older adults. ConclusionsMarked socioeconomic inequalities in oral health persist among United States adults, particularly in midlife, and are strongly linked to differences in access to dental care and socially patterned behaviours. State level Medicaid expansion and adult dental benefit policies, as measured here, did not produce large detectable changes in aggregate tooth loss outcomes, consistent with the highly cumulative nature of these endpoints and the dilution of effects in whole state populations. Expanding dental coverage remains necessary to reduce financial barriers and unmet need, but is unlikely to eliminate oral health inequalities without broader policies that address underlying income and education inequalities and other social determinants of health. These findings have implications for the integration of oral health into universal health coverage agendas in the United States, China, and other countries.