Chemical Changes and Surface Morphology of Acid-Etching of Human Enamel Treated with Topical Fluoride Agents in vitro

Abstract

The fluoride (F) uptake by, and the appearance of polished human enamel which was exposed to topical F agents directly or via an artificial membrane was studied in vitro. The topical F agents used included Duraphat® varnish, Gelution® APF gel and an experimental alginate-based formula (EF), which were applied for 5 min. In addition, Duraphat was applied for 24 h and the uptake of F by sound enamel treated for 5 min with EF was tested. The uptake of F was assessed by three successive layers sampled from experimental and control enamel using the acid-etch technique. All topical F agents increased the F concentrations in almost all depths of the membrane-uncovered enamel and to a level significantly higher than in the control group. The F uptake by membrane-covered enamel was mostly confined to the first depth of 2.5 μm. Application of Duraphat for 24 h significantly increased the F concentration compared with 5 min of treatment (p < 0.01). Polished enamel acquired more F (40%) and dissolved in acid at a higher rate (45%) than sound enamel. There is no correlation between the F contents in the agents and enamel F uptake. After relating the data to the F contents in the applied agents, a strong correlation was found between F released by the dialysis system and F uptake by enamel. SEM examination revealed remnants of the applied agents on the enamel surface which were not removed by brief washing and the acid-etch procedures.