Insoluble NaF in Duraphat® may prolong fluoride reactivity of varnish retained on dental surfaces.

There is no consensus about the clinical recommendation of the time that Duraphat® varnish should be maintained on enamel surfaces without suffering mechanical disturbance by the patient. Considering the importance of calcium fluoride (CaF2)-like reservoirs on the anticaries effect of professional fluoride application, an in vitro study was designed to test the reactivity of Duraphat® varnish with enamel forming these reservoirs as a function of time. Since most fluoride in Duraphat® varnish is insoluble to react and form products on enamel, the relative contribution of the varnish soluble and insoluble fluoride fractions to the reactivity was also evaluated. For this, whole-varnish, containing soluble and insoluble fluoride (total fluoride concentration of 23699 ± 384 µg F/g), or centrifuged varnish, containing only soluble fluoride (fluoride concentration of 258 ± 97 µg F/g), were applied in a standardized manner on enamel slabs (n=8/varnish group/time), which were immersed in continuously renewed artificial saliva for up to 36 h. CaF2-like reservoirs formed on enamel by varnish application were extracted using 1 M KOH and fluoride concentration was measured with ion specific electrode. The results were expressed as µg F/cm(2) of enamel area. Whole varnish formed significantly higher fluoride concentration on enamel than centrifuged varnish, reaching maximum concentration at 24 h (22.0 ± 4.5 µg F/cm(2)). Centrifuged varnish reached maximum concentration at 6 h (3.20 ± 0.81 µg F/cm(2)). In conclusion, a longer varnish retention time than the usually recommended could improve the anticaries effect of Duraphat® varnish, allowing that NaF particles, initially insoluble in the varnish matrix, prolong the reactivity with enamel.