Abstract
The mechanistic action of fluoride on inhibition of enamel demineralization was investigated using <sup>19</sup>F magic angle spinning nuclear magnetic resonance (MAS-NMR). The aim of this study was to monitor the fluoride-mineral phase formed on the enamel as a function of the concentration of fluoride ions [F<sup>-</sup>] in the demineralizing medium. The secondary aim was to investigate fluorapatite formation on enamel in the mechanism of fluoride anti-caries efficacy. Enamel blocks were immersed into demineralization solutions of 0.1 <smlcap>M</smlcap> acetic acid (pH 4) with increasing concentrations of fluoride up to 2,262 ppm. At and below 45 ppm [F<sup>-</sup>] in the solution, <sup>19</sup>F MAS-NMR showed fluoride-substituted apatite formation, and above 45 ppm, calcium fluoride (CaF<sub>2</sub>) formed in increasing proportions. Further increases in [F<sup>-</sup>] caused no further reduction in demineralization, but increased the proportion of CaF<sub>2</sub> formed. Additionally, the combined effect of strontium and fluoride on enamel demineralization was also investigated using <sup>19</sup>F MAS-NMR. The presence of 43 ppm [Sr<sup>2+</sup>] in addition to 45 ppm [F<sup>-</sup>] increases the fraction of fluoride-substituted apatite, but delays formation of CaF<sub>2</sub> when compared to the demineralization of enamel in fluoride-only solution.
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