Enamel Fluoride Update From 2.5 and 5.0% NaF-varnish

Objectives: Enamel fluoride uptake (EFU) is a quantity that the U.S.-FDA requires for all F-releasing varnish products. In the past it was reported that all the available F-binding sites on hydroxyapatite (HAp) discs were saturated with an experimental 2.5%NaF-varnish. Our hypothesis is that a 2.5% NaF varnish will saturate all available enamel F-binding sites.
Methods: Thirty-six enamel slabs from caries-free teeth were divided into 3 groups: blank, 2.5% NaF and 5.0% NaF. Baseline F-concentration ([F]) was determined for each sample by 1 mol/L HClO₄ extraction. The groups of samples were painted with varnish containing either 0, 2.5 or 5.0 % NaF and soaked for 3 hours in DI-H₂O. F was extracted 3-times from each sample by HClO₄ extraction. EFU was calculated as the sum of the extractions minus the baseline [F]. [F] was normalized by the surface area.
Results: The figure shows the results of these analyses. The mean ± standard deviation for the Blank, 2.5% NaF and 5.0% NaF were (n=12/group): (0.0122±0.042; 0.020±0.010; and 0.033±0.019) ppmF/mm², respectively. All groups were significantly different at p≤0.05 (ANOVA and ranked comparison).
Conclusions: The hypothesis is not supported as the EFU from the 5.0% NaF varnish was significantly greater than that from the 2.5%NaFvarnish. The difference between these results for enamel and those previously reported for HAp needs further investigation.