Caries incidence in permanent first molars after discontinuation of a school-based chlorhexidine-thymol varnish program

– Objectives: To determine whether the cessation for 3 years of a 24-month program of chlorhexidine-thymol varnish applications would affect caries incidence in the first permanent molars of a population of schoolchildren of middle and lower-middle socioeconomic level. Methods: Two groups of 6–7-year-old schoolchildren, randomized by school-class, were followed up in a clinical trial. One group received applications of chlorhexidine-thymol varnish every 3 months and the other group acted as controls. The program ended after 24 months and its effects were evaluated. Three years later, 55.5% of the schoolchildren were re-examined and the caries increments were documented. Results: At the end of the 24-month program, the treated children had significantly fewer decayed and filled surfaces in permanent molars (lower DFS index) versus the controls. At 3 years after the discontinuation of the program, this difference had disappeared; there were no differences in the incidence of decayed, missing and filled surfaces (DMFS) index in permanent molars between the treated children and the controls. Conclusion: The cessation for 3 years of a 3-month program of chlorhexidine-thymol varnish applications resulted in a nonsignificant increase in the prevalence of dental caries in the permanent first molar.