Industry sponsorship in trials on fluoride varnish or gels for caries prevention

Fluoride is effective for caries prevention, but trials on fluoride varnish or gels are often industry-sponsored. We assessed trial design and findings in sponsored and nonsponsored trials on fluoride varnish and fluoride gels for caries prevention.

Data on trials included in the most recent Cochrane Reviews on fluoride varnish and fluoride gels were extracted. Sample sizes/age/dentition, year/country of publication, follow-up, test and control, risk of bias and spin (claims of a beneficial effect that were not supported by reported data) were assessed. Studies were categorized as certainly, possibly and not sponsored, and statistically compared. Inverse-generic meta-analysis and multivariable weighted least-squares meta-regression were used to assess impact of sponsorship status on effect estimates.

Based on 19 nonsponsored, 14 possibly sponsored and 11 certainly sponsored trials, sponsored studies were published significantly earlier, always had >1 test group, and had significantly lower risk of spin. Caries-preventive effects were higher in earlier trials, without indication for sponsorship bias in trials published until 1990 (there were no sponsored trials afterwards). If assessing the overall body of evidence and accounting for confounders, the caries-preventive effect was significantly associated with year of publication (β: -0.06, 95% CI: -0.10/-0.02), but not sponsorship status.

Industry-sponsorship bias had limited impact on the overall evidence.