A qualitative and quantitative investigation into the effect of fluoride formulations on enamel erosion and erosion-abrasion in vitro

Objectives: To investigate the effect of a single application of highly concentrated SnF2 and NaF solutions and a NaF/CaF2 varnish on human enamel subjected to hydrochloric acid erosion and tooth brush abrasion. Methods: Forty enamel samples were prepared from human third molars and NaF (9500 ppm, pH 8.0), SnF2 (9500 ppm, pH 2.6) solutions; Bifluorid10 (R) varnish (42,500 ppm, NaF 5%, CaF2 5%) and deionized water (control) was applied to the enamel. Following this three, six and nine cycles of erosion [1 cycle = erosion (0.01 M HCl, pH 2.2, 2 min) + artificial saliva (1 h, pH 7.0)] and erosion-abrasion [1 cycle = erosion (0.01 M HCl, pH 2.2, 2 min) + artificial saliva (1 h, pH 7.0) + abrasion ( 120 linear strokes in artificial saliva from Tepe medium soft brushes 200 g loading)] were carried out. The fluoride treated enamel was analysed using Knoop microhardness, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Results: For erosion alone, there was significantly less microhardness reduction in the Bifluorid10 (R) group after three and six cycles of erosion (P < 0.05), however no other groups showed statistically different hardness (P > 0.05). The EDS analysis showed that only the Bifluorid10 (R) group had any detectable fluorine following erosion and erosion-abrasion (0.1 wt.% and 0.2 wt.% fluorine respectively). The surface fluorine was found to have been removed after erosion and erosion-abrasion for all other surface treatments. Although precipitates were observed after application of the surface treatments, following erosion-abrasion, no visible surface effects from any fluoride preparation remained. Conclusions: Enamel surface precipitates from application NaF, SnF2 solutions appear to not be able to provide protection against gastric erosion and tooth brush abrasion. The NaF/CaF2 varnish provided limited protection against erosion but the role for such varnishes in gastric erosion and tooth brush abrasion remains uncertain. (C) 2011 Elsevier Ltd. All rights reserved.