Inhibitory Effects of Zinc Ions on Enamel Demineralisation Kinetics in vitro

Abstract

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 <smlcap>M</smlcap> 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.

Effect of phytate and zinc ions on fluoride toothpaste efficacy using an in situ caries model

“…Furthermore, like phytate, zinc may offer its own protection against demineralisation. Data from in vitro and in situ studies support this proposition [19,20]. Overall, the effect of zinc on caries development is proposed to be neutral [6,21].…”

Validation of a Real-Time ISE Methodology to Quantify the Influence of Inhibitors of Demineralization Kinetics in vitro Using a Hydroxyapatite Model System

“…The inhibitory effects of F -and of Zn 2+ on enamel demineralization in vitro have been studied previously using SMR [Mohammed et al, 2014[Mohammed et al, , 2015. The results showed a log-linear relationship between mean percentage reduction in the rate of enamel mineral loss (PRML enamel ) with increasing F -concentration, and with Zn 2+ concentration [Mohammed et al, 2014[Mohammed et al, , 2015.…”

“…The results showed a log-linear relationship between mean percentage reduction in the rate of enamel mineral loss (PRML enamel ) with increasing F -concentration, and with Zn 2+ concentration [Mohammed et al, 2014[Mohammed et al, , 2015. In this study, we investigated the use of Ca 2+ ISEs for real-time monitoring of calcium loss of hydroxyapatite (HAP) discs in order to validate the technique, by comparison with the previously reported dose-response studies of cariostatic inhibition.…”

“…The varnished discs were then allocated into 16 groups (n = 3) of either increasing [Zn 2+ ] or increasing [F -] as previously described [Mohammed et al, 2014[Mohammed et al, , 2015.…”

“…A 0.1 M acetic acid demineralizing solution buffered to pH 4.0 using KOH was prepared, as used previously [Mohammed et al, 2014[Mohammed et al, , 2015.…”