A cluster-randomized controlled trial: fluoride varnish in school children.

We conducted a school-based parallel cluster randomized controlled trial with 36-month follow-up of children aged 7 to 8 years. Primary schools were randomly assigned to 2 groups: 3 applications of fluoride varnish (22,600 ppm) each year or no intervention. The primary outcome was DFS increment in the first permanent molars, with the hypothesis that 9 applications of varnish over 3 years would result in a lower increment in the test group. Follow-up measurements were recorded by examiners blind to the allocation. Ninety-five schools were randomized to the test and 95 to the reference groups; 1473 (test) and 1494 (reference) children participated in the trial. An intention-to-treat analysis was carried out with random effects models. The DFS increment was 0.65 (SD 2.15) in the test and 0.67 (SD 2.10) in the reference groups, respectively. There was no statistically significant difference between the groups. We were unable to demonstrate an effect for fluoride varnish when it was used as a public health intervention to prevent caries in the first permanent molar teeth (Inter-national Standard Randomized Controlled Trial Registration: ISRCTN: #72589426).