Effect of a combination of fluoride dentifrice and varnish on enamel surface rehardening and fluoride uptake in vitro

The purpose of this study was to evaluate the effect of combining fluoride dentifrice (FD) and varnish (FV) on in vitro enamel surface rehardening and on fluoride uptake under a pH-cycling regimen. Seventy-eight bovine enamel blocks with early lesions were used and 52 were divided into four treatment groups: (a) placebo non-fluoridated dentifrice (PD); (b); FD (1100 p.p.m. F as NaF); (c); FV (Duraphat) + PD; and (d) FV + FD. The FV was applied to enamel blocks of groups FV + PD and FV + FD before the pH-cycling regimen, and all of them were submitted to dentifrice during cycling. Surface enamel microhardness was determined on the dental blocks before and after demineralization, and after the pH-cycling regimen. The percentage of surface microhardness recovery (%SMHR) was calculated. Fluoride in the blocks was also determined, after removing three layers of enamel. The highest values of percentage SMHR were observed for the FD group. The greatest fluoride uptake was found in the FD and FV + FD groups, but the difference between them was not statistically significant. It was found that the frequent use of fluoride dentifrice resulted in greater benefit in enamel surface rehardening, with a similar effect on fluoride uptake, when compared with its combination with a single fluoride varnish application.