Inhibition of erosive dissolution by sodium fluoride: evidence for a dose-response

The aim of this study was to investigate the protective effects of sodium fluoride solutions and commercial mouthrinses on hydroxyapatite (HA) dissolution in citric acid in vitro, with and without a salivary pellicle.

A rapid-throughput HA solubility-reduction model was employed in which HA dissolution was quantified using ion chromatography. Two HA substrates were selected, a high-resolution powder and 80 μm diameter beads, and studied in the presence and absence of a salivary pellicle (pooled human saliva, 2 h). Immediately prior to acid exposure, substrates were exposed to one of a number of pre-treatments that included aqueous fluoride (F(-)) solutions and commercially available mouthrinses with F(-) concentrations of 0-450 μg/g (as NaF). Dissolution reduction was calculated relative to a deionised water negative control.

For aqueous solutions and mouthrinses, a fluoride dose-response was observed with a plateau around 100 μg/g F(-) for both HA substrates, with or without pellicle. Concentrations as low as 10 μg/g F(-) significantly reduced HA dissolution. The HA substrate had little impact on the fluoride dose-response, and the fluoride was equally effective in the presence of a pellicle as in its absence.

Fluoride significantly reduced HA dissolution at concentrations of 10 μg/g and higher. A fluoride dose-response was seen at low concentrations. This study illustrates the use of a powerful rapid-throughput HA solubility-reduction model for investigating HA dissolution in citric acid in the presence of dissolution inhibitors.

A single exposure to fluoride solutions with fluoride concentrations and exposure time representative of brushing or rinsing with mainstream oral care products was shown to significantly inhibit HA dissolution under conditions relevant to dental erosion. A similar efficacy was observed in the presence and absence of salivary pellicle.