Effect of Fluoride and Salivary Flow Rate on Enamel Erosion

The effects of low concentrations of fluoride (~1 mg/L F) on the enhancement of enamel remineralization and thus prevention of caries have been the rational basis of water fluoridation for many years.  The inhibition of enamel erosion is also an important factor in the long term retention of healthy enamel.  Dental erosion is defined as the chemical removal of tooth surface mineral without microbiological aide.  F concentration and salivary flow rate are considered to be primary factors that mitigate erosion progression.  Purpose:  Determine the effects of low concentrations of F (≤1.0 mg/L F) on enamel erosion at two flow rates.  Method:  the continuous flow mouth model (Carey et al, JDR, 2004) was used with 0, 0.5, or 1.0 mg/L F as NaF included within the saliva-like solution (SLS) at flow rate of 0.25 or 0.5 mL/min.  Enamel slices (n³3 for each condition) with all cut edges protected by epoxy were exposed to three 1-hour demineralization challenges daily, with the SLS flowing across the samples throughout the interim cycles for a period of two weeks.  The enamel slices were evaluated for erosion by comparing before and after x-ray microradiographs.  Results:  at 0.25 mL/min the amount of erosion (µm) was: F₀ = 12±4; F_0.5 = 3±1; F_1.0 = 0.7±1; whereas at 0.5 mL/min the amount of erosion was: F₀ = 7±1; F_0.5 = 6±1; F_1.0 = 0±1.  At 0.5 mL/min the amount of erosion was less than at 0.25 mL/min at F₀ and F_1.0 concentrations (p≤0.01). Conclusions: at each flow rate there was a dose-like response to the amount of F present in the bathing solution on the amount of erosion.  The protection of enamel surface was generally greater at the higher flow rate at a given F concentration. Supported by NIH Grant R01DE14707, ADAF and NIST.