Determining the In Vitro Anticaries Efficacy of Fluoride Varnishes

Objectives: To investigate the in vitro anticaries efficacy of fluoride varnishes (FV) by determining their ability to reharden and to deliver fluoride to an early caries lesion when applied directly or in close vicinity to the lesion.

Methods: Eighty bovine enamel specimens were demineralized (24h, 0.05M lactic acid, 0.2% Carbopol C907, 50% saturated with respect to hydroxyapatite, pH 5.0). Specimens were allocated to five treatment groups (n=16) based on Knoop surface microhardness (KHN). FV (n=5) was applied (10±2mg per lesion) to eight specimens per FV group; the remaining eight specimens received no FV. Specimens were paired again and placed into containers (one per FV). Artificial saliva (1.45mM CaCl₂×2H₂O; 5.4mM KH₂PO₄; 14.9mM KCl; 28.4mM NaCl; 2.2g/l mucin, pH 7.0) was added (27h at 37°C). Subsequently, FV was removed using chloroform. Specimens were exposed to fresh artificial saliva again (67h at 37°C). KHN was measured and differences to baseline values calculated. Enamel fluoride uptake (EFU) was determined using the acid etch technique. Data were analyzed using two-way ANOVA.

Results: Two-way ANOVA highlighted significant interactions between ΔKHN+EFU vs. application (p<0.001). Means are shown in the table below:

¹different letters indicate differences between groups (p<0.05); capital letters for direct, small letters for indirect application;

²italics highlight differences (p<0.05) in application within FV

Conclusions: Bearing in mind the limitations of laboratory studies, the predicted anticaries efficacy of FV depends not only on the type of FV but also on the application mode.