DesignA two year placebo-controlled, double-blind, randomised control trial in 1-4-year-old children.InterventionChildren were recruited from low income families in Rio de Janeiro, Brazil, with access to a fluoridated public water supply. Both groups received oral hygiene instruction along with provision of toothbrushes and 1450ppm F- toothpaste. The control group had a placebo fluoride varnish applied every six months. The intervention group had 22,600ppm F- varnish applied every six months. Clinical examinations for the presence of caries were conducted at baseline and at each subsequent six monthly visit.Outcome measureThe primary outcome was the proportion of children in each group that went on to clinically develop any new carious surfaces using the ICDAS criteria. The number of new carious surfaces was assessed as a secondary outcome, both at the enamel and dentine level. The study also reported on the safety and acceptability of the varnish.ResultsTwo hundred children participated in the trial, 91% were followed up at two years and adherence to the six-monthly applications was 84% in the intervention and 85% in control groups. The results did not show a significant difference for the development of new lesions between the two groups. In the fluoride varnish group 36% had developed new dentinal lesions compared to 47% in the placebo group, a difference of -10.8% (95% CI -24.9 to 3.3, p = 0.14). In relation to caries increment, at the enamel level, this was a mean of 2.0 teeth in the fluoride varnish group and 2.8 teeth in the placebo group, a difference of -0.8 (95% CI -2.0 to 0.4, p = 0.19). At the dentine level, caries increment was a mean of 1.8 teeth in the fluoride varnish group and 2.5 in the placebo group, a difference of -0.7 (95% CI -1.9 to 0.4, p = 0.23). Two minor complaints related to taste and appearance of the varnish were recorded and no safety events were reported.ConclusionsWhilst no significant difference was found, the authors note that this does not indicate ineffectiveness of fluoride varnish. Re-assessment of the power calculation following study completion demonstrated that a significantly larger sample size would have been indicated, preventing the drawing of any direct conclusions from the results of this study. The use of fluoride varnish amongst this group appears to be safe and overall well tolerated.