Zinc is incorporated into toothpaste formulations for its ability to reduce calculus and halitosis. Considerably less work is reported on interaction of zinc with dental enamel and its putative role in demineralization and remineralization. Zinc has been shown to reduce enamel solubility and demineralization, but its mechanism of interaction with enamel is unclear. The aim of this study was to understand the fundamental chemistry of zinc in inhibiting enamel demineralization by determining whether zinc is incorporated into the apatite lattice structure during demineralization, or if it is forming complexes at the surface. To understand zinc’s mechanism of potential cariostatic action, ultra-low energy secondary ion mass spectrometry (uleSIMS) was used for depth profiling of zinc in demineralized enamel surfaces at the nanometre level (10-100 nm). The application of this technique for profiling in enamel is very novel.
Method:
Control and test enamel samples were immersed in demineralizing solution (0.1 acetic acid, pH 4.0) for 24 h at 37˚C. Test sample was subjected to a zinc-containing demineralizing solution for a further 96 h. uleSIMS was used to measure the zinc depth profile in samples using 500 eV and 3 keV beam energy.
Result:
uleSIMS analysis for control showed no zinc incorporation. Test sample showed ~10% increase in zinc concentration on enamel surface (~10 nm). Depth profile showed a sharp decline in zinc concentration from outer surface layer of atoms to deeper penetration depths. A zinc concentration gradient was identified at different depth regions in the enamel surface (~100 nm).
Conclusion:
uleSIMS shows that zinc reacts with a few layers of the crystalline apatite lattice at the enamel surface during demineralization. These results have a significant implication on the understanding of the fundamental chemistry aspects of zinc in toothpastes and demonstrate the therapeutic potential of zinc in preventing tooth mineral loss.