Fluoride varnishes (Duraphat): A meta‐analysis

– In the present article we analyze a series of studies designed to detect the caries preventive effect of Duraphat by means of meta‐analysis. Meta‐analysis is a collection of statistical methods designed to investigate and to summarize a series of investigations. It may be a valuable tool to complement traditional narrative reviews. During the last years meta‐analysis has attracted increasing interest in sociology, psychology and medicine. In order to find previous studies concerned with the clinical effects of Duraphat we applied a systematic literature search. Papers were included independent of results when they fulfilled a checklist of well defined methodological selection criteria. In order to aggregate the results of the Duraphat‐studies we used different complementary statistical approaches: Firstly, the so‐called file drawer problem is considered. This may help to get a better insight into the problem of underreporting non‐significant results or publication bias. It was found to be very unlikely that underreporting of non‐significant results could reverse the conclusion into an overall null‐result. After that, the in homogeneity between studies is investigated. The overall variation of caries reduction R is separated into two components: A between study component of variance and a variance pertaining to the individual studies (random effects model). It was found that the overall variation is dominated by the between studies variation and not by the sampling variation. Due to the pronounced variation between studies the confidence interval of the overall effect size (R = 0.38) is quite large (95%‐Cl: 0.19–0.57). The heterogeneity of our studies naturally suggested exploring possible sources thereof by investigating the dependence of caries reduction on variables characterizing the studies. It was found that caries reduction is negatively correlated with study duration. This finding provided a study‐duration‐adjusted effect of caries reduction.