The safety of tooth bleaching, which is based upon hydrogen peroxide (HP) as the active agent, has been questioned. Our aim was to investigate the effects of 30% HP on human tooth enamel. The specimens were divided randomly into three groups and treated with distilled water, HCl, and HP, respectively. Raman scattering and laser-induced fluorescence of enamel were determined before and after treatment. Microhardness testing and scanning electron microscopy were also used. The results of Raman scattering showed that the Raman relative intensity of enamel changed significantly after HP and HCl treatment. These findings were consistent with the results of microhardness testing and morphological observations. In addition, a small band at 876 cm(-1) due to O-O stretching of HP became pronounced during HP treatment, which provided direct evidence that HP has the ability to penetrate enamel. Meanwhile, the results of laser-induced fluorescence revealed that HP caused the greatest fluorescence reduction. This suggested that the organic matter in enamel might be greatly affected by HP, which was also supported by the results of microhardness. It can be concluded, therefore, that the 30% HP may have adverse effects on the mineral and the organic matter of human tooth enamel.

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The electrophoretic deposition (EPD) is a versatile and cost-effective technique for fabricating advanced coatings. In this study, chitosan/gelatin (CS/G) coatings were prepared on titanium substrates via EPD. The prepared coatings were characterized using fluorescence microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and shear bond strength testing. It was found that CS/G coatings had a similar macroporous structure. The gelatin content in the CS/G coatings gradually increased with the increase of the gelatin in the blend solutions. The shear bond strength of the CS/G coatings also increased with the increasing gelatin content. In vitro biological tests demonstrated that human MG63 osteoblast-like cells achieved better affinity on the coatings with higher gelatin content. Therefore, it was concluded that EPD was an effective and efficient technique to prepare CS/G coatings on the titanium surface and that CS/G coatings with higher gelatin content were promising candidates for further loading of functional agents.

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