Outcome of a National Education Program on Supervised Daily Toothbrushing and Biannual Fluoride Varnish Application on Dental Caries in Chilean Preschool Children: An Ecological Cohort Study

Introduction: Dental caries in childhood remains a major global public health issue. In response to persistently high caries levels among children, Chile implemented a national programme (Sembrando Sonrisas) including daily supervised toothbrushing and biannual fluoride varnish applications in nurseries. This study aimed to examine the association between these interventions and caries experience in preschool children, and to assess related socioeconomic inequalities. Methods: We analysed aggregated municipality-level data (n = 346) on dental caries outcomes in 5-year-olds, coverage of fluoride varnish applications, delivery of toothbrushing materials (toothbrushes and 1,000 ppm fluoride toothpaste), exposure to community water fluoridation (CWF), rurality, and socioeconomic deprivation. The primary outcome was the caries experience of children covered by the programme since its national rollout in 2015. Univariate and multivariate weighted linear regression models assessed associations between programme interventions and caries experience, adjusting for deprivation and CWF. Socioeconomic inequalities in caries experience were evaluated using the Slope Index of Inequality (SII) and Relative Index of Inequality (RII). The distribution of programme delivery across socioeconomic deciles was assessed using weighted regression models. Results: Data on 309,360 5-year-olds were included. Complete delivery of toothbrushing materials was associated with lower caries experience (50.1% vs. 55.0%), a 4.9% difference (95% CI: 2.5%, 7.2%) after adjustment. CWF exposure was associated with a 7.5% lower caries experience (95% CI: 4.2%, 10.9%). The combination of both interventions showed the lowest caries levels, with a 13.4% difference compared to areas with neither intervention (95% CI: 7.5%, 19.3%). Fluoride varnish application was not significantly associated with caries experience. Delivery of interventions was equitable across socioeconomic groups. However, caries experience was significantly higher in the most deprived municipalities (SII = 14.7%, 95% CI: 11.7%, 17.7%; RII = 0.283, p < 0.001). Conclusion: Lower caries experience was associated with supervised daily toothbrushing and CWF exposure, but not with fluoride varnish application. Despite equitable programme coverage, substantial socioeconomic inequalities persist. As this ecological study cannot establish causality, further research is needed to evaluate long-term trends and the role of broader determinants in improving child oral health.