Supplementary Material for: Inhibitory Effects of Zinc Ions on Enamel Demineralisation Kinetics in vitro

2015-11-04T00:00:00Z (GMT) by Mohammed N.R. Lynch R.J.M. Anderson P.
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 (Zn<sup>2+</sup>) in the literature. Therefore the aim was to measure the effects of zinc ion concentration ([Zn<sup>2+</sup>]) 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 [Zn<sup>2+</sup>] (0.1-3,565 ppm) in the acidic solutions were measured on the rate of enamel demineralisation. This study demonstrated that Zn<sup>2+</sup> even at low concentrations significantly reduces enamel demineralisation. There was a log-linear relationship between the mean percentage reduction in demineralisation and increasing [Zn<sup>2+</sup>] 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 Zn<sup>2+</sup> to reduce the rate of enamel demineralisation under real-time in vitro acid conditions simulating dental caries. The results suggest that Zn<sup>2+</sup> in the oral fluids could protect against enamel demineralisation during an acidic challenge. The log-linear relationship between [Zn<sup>2+</sup>] and demineralisation suggests that the reduction in enamel dissolution is limited by the saturation of surface sites on the enamel surface.