Effect of Stannous Fluoride and Dilute Hydrofluoric Acid on Early Enamel Erosion over Time in vivo

Recent experimental in vivo studies have shown that aqueous solutions of stannous fluoride (SnF2) and hydrofluoric acid (HF) can reduce enamel solubility after 5 min. The aim of this study was to evaluate the longer-term protective effect of SnF2 (0.78%, pH 2.9) and HF (0.2%, pH 2.0) (both ∼0.1 mol/l F) using the same experimental model. Labial surfaces of healthy anterior teeth (all four surfaces when possible, otherwise a pair of surfaces) in 103 subjects (n = 399 teeth) were exposed to citric acid (0.01 mol/l, pH 2.7). The acid was applied using a peristaltic pump (5 ml, 6 ml/min) and was collected in coded test tubes (etch I). The test solutions were then applied to the same surfaces of the teeth (1 min, 6 ml/min). After either 1, 7, 14 or 28 days, citric acid was again applied to the same surfaces and subsequently collected (etch II). Enamel solubility was examined by assessment of calcium concentration in etch I and etch II solutions using atom absorption spectroscopy. Median values were calculated for all time periods and statistical analysis was carried out using the Wilcoxon signed-ranks test. Results showed that HF reduced enamel solubility by 54 and 36% after 1 and 7 days, respectively. After 14 and 28 days, there was no longer any effect. SnF2 showed no protective effect after the first day. Given these results, repeated application of HF and especially SnF2 may be necessary to improve the protective effect of these fluorides, and this requires further testing.