No abstract

These results have a significant implication on the understanding of the fundamental chemistry of zinc in toothpastes and demonstrate its therapeutic potential in preventing tooth mineral loss.

The mechanistic action of fluoride on inhibition of enamel demineralization was investigated using ¹⁹F 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^-] 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 M acetic acid (pH 4) with increasing concentrations of fluoride up to 2,262 ppm. At and below 45 ppm [F^-] in the solution, ¹⁹F MAS-NMR showed fluoride-substituted apatite formation, and above 45 ppm, calcium fluoride (CaF₂) formed in increasing proportions. Further increases in [F^-] caused no further reduction in demineralization, but increased the proportion of CaF₂ formed. Additionally, the combined effect of strontium and fluoride on enamel demineralization was also investigated using ¹⁹F MAS-NMR. The presence of 43 ppm [Sr²⁺] in addition to 45 ppm [F^-] increases the fraction of fluoride-substituted apatite, but delays formation of CaF₂ when compared to the demineralization of enamel in fluoride-only solution.

Metal ions including zinc have the ability to influence enamel demineralisation. However, there is a paucity of data regarding reductions in demineralisation effected by zinc ions (Zn²⁺) in the literature. Therefore the aim was to measure the effects of zinc ion concentration ([Zn²⁺]) on the real-time in vitro demineralisation of enamel, during exposure to caries-simulating conditions, using scanning microradiography (SMR). Human enamel blocks were fixed in SMR environmental cells, through which acidic solutions (0.1 M acetic acid, pH 4.0) were circulated for periods of 50 h. SMR was used to quantitatively measure continuous mineral mass loss. Subsequently, the effects of sequentially increasing [Zn²⁺] (0.1-3,565 ppm) in the acidic solutions were measured on the rate of enamel demineralisation. This study demonstrated that Zn²⁺ even at low concentrations significantly reduces enamel demineralisation. There was a log-linear relationship between the mean percentage reduction in demineralisation and increasing [Zn²⁺] up to 3,565 ppm, i.e. the change in the overall percentage reduction in demineralisation was greater at lower concentrations than at higher concentrations, with 60% reduction at 36 ppm increasing to 90% at 3,565 ppm. In conclusion, SMR demonstrated the ability of Zn²⁺ to reduce the rate of enamel demineralisation under real-time in vitro acid conditions simulating dental caries. The results suggest that Zn²⁺ in the oral fluids could protect against enamel demineralisation during an acidic challenge. The log-linear relationship between [Zn²⁺] and demineralisation suggests that the reduction in enamel dissolution is limited by the saturation of surface sites on the enamel surface.