Income, access to care and adult oral health inequalities in the United States: a multilevel analysis of national surveys and Medicaid policies

BackgroundSocioeconomic status (SES) strongly shapes oral health, yet the magnitude of these gradients, their pathways and the influence of US Medicaid policies remain uncertain. We quantified SES gradients in adult oral health, examined potential mechanisms and assessed whether state Medicaid expansion and adult dental benefit generosity were associated with aggregate oral health indicators. MethodsWe analysed adults aged [≥]20 years in NHANES 1999-2019 and state adult populations in BRFSS 2011-2025, supplemented with international oral health and Medicaid policy data. Individual outcomes were DMFT and self-rated oral health (good vs fair/poor). State-level outcomes were past-year dental visit rates, any permanent tooth loss and complete edentulism among adults [≥]65 years. SES measures included poverty-income ratio (PIR) and education; mediators included annual dental visits, unmet dental need and sleep duration. Analytic methods comprised survey-weighted regression, concentration and slope indices of inequality, Oaxaca-Blinder decomposition and state-level difference-in-differences models with state and year fixed effects and state-clustered standard errors. ResultsHigher PIR and education were independently associated with lower DMFT and higher odds of good self-rated oral health in all age groups. PIR coefficients for DMFT were {approx}-0.25 (ages 20-44), -0.79 (45-64) and -1.07 ([≥] 65); corresponding odds ratios for good oral health were {approx}1.48, 1.46 and 1.33. Predicted probabilities of good oral health increased monotonically across PIR quartiles. Concentration indices indicated that DMFT burden was concentrated among low-income adults (CI {approx} -0.105), whereas good oral health was concentrated among high-income adults (CI {approx} 0.094). The Slope Index suggested that moving from the lowest to highest income rank corresponded to {approx}2.48 fewer affected teeth; the Relative Index indicated {approx}eight-fold higher odds of reporting good oral health. Oaxaca-Blinder decomposition showed a Q4-Q1 DMFT gap of 1.31 teeth, with roughly one quarter explained by observed variables, mainly differences in dental access. State-level difference-in-differences models did not identify large, precisely estimated changes in dental visit rates, tooth loss or edentulism associated with Medicaid expansion or adult dental benefit generosity. ConclusionMarked SES-related oral health inequalities persist among US adults, particularly in midlife, and are strongly linked to differential dental access and socially patterned behaviours. Medicaid expansion and adult dental benefit generosity, as implemented, did not produce substantial detectable shifts in state-level oral health indicators. Reducing inequalities will require improved financial protection for dental care and broader action on income, education and other social determinants of health.