Dose-Response Effects of Zinc and Fluoride on Caries Lesion Remineralization

Abstract

The present mechanistic in vitro study aimed to investigate dose-response effects of zinc and fluoride on caries lesion remineralization and subsequent protection from demineralization. Artificial caries lesions were created using a methylcellulose acid gel system. Lesions were remineralized for 2 weeks using citrate-containing artificial saliva which was supplemented with zinc (0–153 µmol/l) and fluoride (1.1 or 52.6 µmol/l) in a 7 × 2 factorial design. Lesions were also remineralized in the absence of zinc and citrate, but in the presence of fluoride. After remineralization, all lesions were demineralized for 1 day under identical conditions. Changes in mineral distribution characteristics of caries lesions after remineralization and secondary demineralization were studied using transverse microradiography. At 1.1 µmol/l fluoride, zinc exhibited detrimental effects on remineralization in a dose-response manner and mainly by preventing remineralization near the lesion surface. At 52.6 µmol/l fluoride, zinc retarded remineralization only at the highest concentration tested. Zinc enhanced overall remineralization at 3.8–15.3 µmol/l. At 76.5 and less so at 153 µmol/l, zinc showed extensive remineralization of deeper parts within the lesions at the expense of remineralization near the surface. Citrate did not interfere with remineralization at 1.1 µmol/l fluoride, but enhanced remineralization at 52.6 µmol/l fluoride. Lesions exhibiting preferential remineralization in deeper parts showed higher mineral loss after secondary demineralization, suggesting the formation of more soluble mineral phases during remineralization. In summary, zinc and fluoride showed synergistic effects in enhancing lesion remineralization, however only at elevated fluoride concentrations.

Effects of zinc fluoride on inhibiting dentin demineralization and collagen degradation <i>in vitro</i>: A comparison of various topical fluoride agents

“…The rationale behind using ZnF 2 was that Zn compounds, such as ZnCl2 and zinc acetate, were studied as a combination to lower fluoride concentration in NaF and were surprisingly found to promote lesion remineralization 24,25) by acting as a mineral regulator to control the porosity at the lesion surface. It was of interest to include fluoride and zinc together because they are both powerful elements for remineralization.…”

Inhibitory Effects of Zinc Ions on Enamel Demineralisation Kinetics in vitro

“…It has also been shown that this concentration can increase the remineralisation of subsurface lesions, by retarding fluoride-induced lesion arrest and increasing lesion consolidation [Lynch et al, 2011]. However, Lippert [2012] reported that the effect is dependent on relatively high fluoride concentrations, and high Zn 2+ concentrations can reduce remineralisation. While data from caries clinical trials suggest that Zn 2+ has no net effect on caries reductions resulting from the use of fluoride toothpastes [Stephen et al, 1988;Ripa et al, 1990], it seems unlikely that any effect on demineralisation exactly outweighs any possible effect on remineralisation, and that caries status risk should also be considered.…”

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

“…Zinc ions are commonly added to toothpaste formulations to reduce malodour by chemically binding to volatile odour molecules [12,13] and by inhibiting malodour-generating plaque bacteria [14]. Zinc has an affinity for enamel surfaces via binding to surface phosphate groups and so also has the potential to interfere with fluoride's action against caries [15,16]. Since a further benefit of use of zinc toothpastes is a reduction in calculus formation [17] via inhibition of formation of apatites and their precursors [18], it has the potential to interfere with enamel remineralisation.…”

“…Since a further benefit of use of zinc toothpastes is a reduction in calculus formation [17] via inhibition of formation of apatites and their precursors [18], it has the potential to interfere with enamel remineralisation. In vitro mechanistic studies have demonstrated the potential for this to occur in both a positive and negative fashion [15,16]. Furthermore, like phytate, zinc may offer its own protection against demineralisation.…”