Inequality in the distribution of dental caries among Iranian schoolchildren: evidence from a low-middle income country

This study aimed to quantify socioeconomic inequalities in different dental caries indices among Iranian primary schoolchildren and to identify the factors contributing to these inequalities in primary dentition. This cross-sectional study was conducted between April 10 and May 8, 2024, among 7-years old schoolchildren in Isfahan, Iran. Participants were recruited using a multi-stage cluster random sampling method. Information regarding demographic, socioeconomic, and psychological characteristics of parents, oral health and dietary behaviors of their child was assessed using validated questionnaires and the families’ socio-economic status (SES) was determined through a reliable self-administered questionnaire, which included questions on assets, wealth, education level, and occupation. Based on the ICDAS II classification, clinical examinations of the children were performed on-site at the schools. To examine the association between SES and various dental indicators quantile regression models at the 2nd, 4th, 6th, and 8th deciles were used. Socioeconomic-related inequality in dental health outcomes was also assessed using the Concentration Index (CI). 417 schoolchildren were examined. Quantile regression across the caries severity spectrum revealed that untreated cavitated decay (d₃–₆) exhibited a consistently negative and statistically significant SES gradient across all percentiles, with unadjusted βs ranging from − 1.25 (SE = 0.40, p < 0.01) at the 80th percentile to − 1.00 (SE = 0.21, p < 0.001) at the 20th percentile; adjusted effects remained significant at central percentiles. Early-stage lesions (d₁–₂) showed a modest positive association with SES only at the 40th percentile (adjusted β = 0.30, SE = 0.14, p < 0.05). Conversely, filled surfaces (f) exhibited a strong pro-rich gradient, with unadjusted β peaking at the 60th percentile (2.14, SE = 0.38, p < 0.001) and falling to zero at the 20th percentile; adjusted βs were significant from the 80th percentile (1.95, SE = 0.40, p < 0.001) through the 40th percentile (0.51, SE = 0.24, p < 0.05). The CI for d 3–6 was − 0.14 (SE = 0.022, p < 0.001), indicating that untreated dental decay in teeth was disproportionately concentrated among those from lower socioeconomic backgrounds. The filled teeth (f) and sound teeth indices showed significant pro-rich inequality, with CIs of + 0.16 (SE = 0.03, p < 0.001) and + 0.07 (SE = 0.01, p < 0.001), respectively. The findings of our study highlight a distinct social gradient in oral health, with dental health disadvantages burdening the lower SES groups and treatment-related advantages favoring wealthier populations.