Trends in Socioeconomic Inequalities of Dental Caries Experience Among 12-Year-Olds in Chile: an Ecological Cohort Study

Introduction Socioeconomic inequalities in childhood dental caries remain a major public health concern, even in countries with declining overall prevalence. Chile provides a unique setting to examine these inequalities nationally and assess the potential mitigating role of systemic fluoride delivery programmes. Methods This ecological cohort study analysed 1,261,690 dental examinations of 12-year-olds across 325 Chilean municipalities from 2009 to 2023, representing 99.8% of eligible national records. Caries prevalence was modelled against area socioeconomic deprivation (IDSE deciles), adjusting for rurality and systemic fluoride delivery programmes, and weighting for number of total examinations by municipality/year. Inequality metrics included Absolute Rate Difference (ARD), Slope Index of Inequality (SII), and Relative Index of Inequality (RII). Results A strong and persistent socioeconomic gradient was observed: adolescents in the most deprived municipalities had a 17 percentage-point higher caries prevalence than those in the least deprived (β = -0.17, 95% CI: -0.20, -0.14). This gradient followed a dose-response pattern and was confirmed by summary measures (ARD = 0.151; RRR = 1.234). Temporal analysis revealed peak inequality pre-pandemic (SII = 0.17, 95% CI: -0.20, -0.14), followed by a steady decline post-2018, reaching non-significant levels by 2023 (SII = 0.04, 95% CI: -0.15, 0.06). Fluoridation programmes modestly attenuated the deprivation gradient by 24% (β = -0.13), though they explained limited variance (ΔR² = 0.04). Conclusion Socioeconomic inequalities in dental caries among Chilean adolescents remain substantial, despite national declines in prevalence. While systemic fluoridation contributes to modest reductions in inequality, structural determinants are the primary drivers of persistent inequalities.