“CaF₂” Extraction From Enamel Treated With Fluoride Gel or Varnish

Objectives: Acidulated fluoride gel and varnish form “CaF₂” reservoirs on enamel/dentine based on fast (gel, all soluble fluoride) or slow (varnish, mostly insoluble fluoride) chemical reactions. “CaF₂” products are considered responsible for the anticaries effect of professional fluoride application and their concentration have been estimated based on their alkali solubility, using a 24h-extraction in 1M KOH (Caslavska et al., 1975). However, the time needed for “CaF₂” extraction in alkali has not been tested in details. Also, the solubility of these products in alkali may not represent their solubility in the oral cavity (i.e. saliva). Therefore, the aim of this study was to evaluate the effect of alkali extraction time, 6 or 24 h, on the concentration of “CaF₂” from enamel slabs treated with fluoride gel or varnish. Also, the solubility of these reservoirs in artificial saliva during 6 and 24 h was evaluated.
Methods: Bovine enamel slabs (4x4mm) were randomly divided into 4 treatment-groups: untreated (negative control); neutral fluoride gel (4-min), acidulated phosphate fluoride gel (4-min) or fluoride varnish (24-h under continuous artificial saliva flow). Slabs were immersed in 1M KOH or artificial saliva for either 6-h or 24-h under agitation. Fluoride in both extracts was determined using a specific fluoride electrode.
Results: ANOVA showed that all groups differed from each other (from lowest to highest, control=0.17±0.05; neutral gel=12.1±2.8; varnish=19.5±1.6; acidulated gel=54.5±14.1 µg F/cm², for extraction in KOH for 24h, n=5, p<0.05), irrespective of time or extraction solution (p>0.05). There was no effect of time on the amount of “CaF₂” extracted (p>0.05). Saliva extracted about 40% of the fluoride amount extracted by KOH, irrespective of the fluoride treatment or time (p>0.05).
Conclusions: The results suggest that “CaF₂” reservoirs formed by fluoride gel or varnish can be estimated using 6-h extraction in KOH and that this extraction mirrors the potential fluoride release to oral fluids.