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 (CaF 2 )-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. CaF 2 -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/cm² 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/cm²). Centrifuged varnish reached maximum concentration at 6 h (3.20±0.81 µg F/ cm²). 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.

Introduction: There is a possibility of intracanal medication remain in the root canal even after its removal prior to obturation. The present study aims to evaluate under scanning electron microscopy the persistence of residues in the root canal from calcium hydroxide medications prepared with different vehicles. Methods: Thirtysix bovine incisors had their crowns removed, the root canals prepared and were assigned randomly to six different experimental groups, according to the intracanal medication used. Group I (control) received no intracanal medication, whereas root canals of Group II were filled with P.A. calcium hydroxide. Group III received a mixture of Ca(OH) 2 and saline solution, in Group IV glycerin was used as vehicle, and Groups V and VI received Ca(OH) 2 mixed with propylene glycol or polyethylene glycol 400, respectively. After one week, medication was removed, roots were split and the canals observed under the scanning electron microscope. Representative photomicrographs of the apical third of each experimental group were observed and analyzed quantitatively by means of a grid, with results expressed in percentage of canal walls covered by debris. Results: Statistical analysis (one-way ANOVA and Tukey's post hoc test, α=0.05) revealed significant differences between groups, indicating higher amounts of Ca(OH) 2 residues in the canals where propylene glycol or polyethylene glycol were used as vehicles. The dentinal walls of the canals that received pure P.A. calcium hydroxide or its association to glycerin presented amounts of debris similar to the control group. Conclusions: Ca(OH) 2 P.A. based medications or its association to glycerin allows an easier removal from the root canal.