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. 2017:2017:6261248.
doi: 10.1155/2017/6261248. Epub 2017 Oct 12.

Zinc-Containing Hydroxyapatite Enhances Cold-Light-Activated Tooth Bleaching Treatment In Vitro

Yi Li  1   2 , Xinchang Shi  3 , Wei Li  1
Affiliations

Zinc-Containing Hydroxyapatite Enhances Cold-Light-Activated Tooth Bleaching Treatment In Vitro

Yi Li et al. Biomed Res Int. 2017.

Abstract

Cold-light bleaching treatment has grown to be a popular tooth whitening procedure in recent years, but its side effect of dental enamel demineralization is a widespread problem. The aim of this study was to synthesize zinc-substituted hydroxyapatite as an effective biomaterial to inhibit demineralization or increase remineralization. We synthesized zinc-substituted hydroxyapatite containing different zinc concentrations and analysed the product using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and energy dispersive spectrometer (EDS). The biological assessment of Zn-HA was conducted by CCK-8 assay and bacterial inhibition tests. pH cycling was performed to estimate the effect of Zn-HA on the enamel surface after cold-light bleaching treatment. The XRD, FTIR, and EDS results illustrated that zinc ions and hydroxyapatite combined in two forms: (1) Zn2+ absorbed on the surface of HA crystal and (2) Zn2+ incorporated into the lattice of HA. The results indicated that 2% Zn-HA, 4% Zn-HA, and 8% Zn-HA effectively inhibited the growth of bacteria yet showed poor biocompatibility, whereas 1% Zn-HA positively affected osteoblast proliferation. The XRD and scanning electron microscopy (SEM) results showed that the use of Zn-HA in pH cycling is obviously beneficial for enamel remineralization. Zinc-substituted hydroxyapatite could be a promising biomaterial for use in cold-light bleaching to prevent enamel demineralization.

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Figures

Figure 1
Figure 1
Physicochemical properties of Zn-HA (a) XRD pattern of Zn-HA. The diffraction pattern was analysed over 2θ range of 20°–70°. (b) The FTIR spectrum of Zn-HA. (c) Elemental chemical composition analysis using EDS.
Figure 2
Figure 2
Biological assessment of Zn-HA (a) cck-8 analysis of proliferation of MC3T3 cells cultivated with Zn-HA leaching solutions for 1, 3, and 7 days. Compared with the control group, 2%, 4%, and 8% Zn-HA leaching solution treatment significantly reduced cell viability, while for 1 day and 3 days 1% Zn-HA leaching solution has an effect of promotion on the cell proliferation. (b) Morphological changes of MC3T3 cells after 24 h incubation with Zn-HA leaching solutions. (c) Antibacteria test of Zn-HA with different zinc concentration after incubation with Zn-HA solution for 24 h. Groups 2% and 4% Zn-HA and 8% Zn-HA significantly inhibited Streptococcus mutans, Lactobacillaceae, and Streptococcus sobrinus growth (p < 0.05). ∗ means there are statistical differences between these group and control group.
Figure 3
Figure 3
XRD patterns of dental enamel specimen before/after bleaching and pH cycling treatment. (a) Group HA. (b) Group Zn-HA. (c) Group DW. “HA” and “CHA” refer to “hydroxyapatite” and “carbonated hydroxyapatite,” respectively.
Figure 4
Figure 4
Scanning electron microscopy (SEM) micrograph of dental enamel surface after pH cycling treatment. The images were obtained at 30000x magnification.
See this image and copyright information in PMC

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