Method to Measure the Rate of Release From Fluoride Varnishes

Objectives: Fluoride varnishes (FV) are effective in the treatment and prevention of dental caries, despite only receiving FDA approval for hypersensitivity. However, this effectiveness is dependent on the release of fluoride from the product. The objectives of this study were to 1) determine the pattern of fluoride release from four FVs and 2) evaluate a novel method to measure release.
Methods: Custom holders with wells (Grainger, 4DAT4) were filled with approximately 20-mg NaF varnish. Wells (n=10) were submerged into 3-mL of pre-warmed artificial saliva (AS)(36°C), placed into an environmental chamber, and stirred (150-RPM). Duraphat, MI Varnish, Prevident, and Vanish were tested at 10, 20, 30, 45, 60, 120, 240-min, and suspended wells containing the varnish were moved into fresh, pre-warmed vials of AS for each time point. The remaining saliva was capped, frozen (-20°C), and analyzed using a fluoride ion selective electrode (Accumet XL250) following standard curve generation. The novel method was developed by the University of Michigan School of Dentistry (UM) and performed in parallel at UM and the ADA Science Institute.
Results: One-way analysis of variance (ANOVA) with post hoc Tukey-Kramer tests were used to compare mean fluoride release of each brand at each time point. Between the two labs, the method produced an ICC of 0.9875 (F-test p<0.0001) among the tested products. At 10-min, a statistically significant higher fluoride release (p<0.001; µg F/mg varnish) was observed from MI Varnish (196.1) compared to Prevident (99.9) and Duraphat (83.5), followed by Vanish (43.5). A similar pattern was observed for all other time points.
Conclusions: The novel methodology is reliable and reproducible. However, clinical studies are required to determine the optimal amount and rate of release for efficacy. All FV tested released fluoride within the expected range of efficacy, albeit in differing rates.