Investigation of the effects of 30% hydrogen peroxide on human tooth enamel by Raman scattering and laser-induced fluorescence

Abstract

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.

Compositional, structural and mechanical comparisons of normal enamel and hypomaturation enamel

“…Similar to FTIR, Raman spectroscopy has the ability to analyze chemical composition at a molecular level. It is known that laserinduced fluorescence can provide useful information about organic matter [12,25]. Consequently, the higher FI value in the hypomaturation enamel also indicated a higher organic content.…”

“…It was found that hypomaturation enamel showed a lower mean RRI value than normal enamel. Since the RRI from the Raman spectra is linearly proportional to the phosphate group concentration within HAP molecules [43,44] and phosphate group concentration is a good indicator of the degree of mineralization in enamel [12,24,25,44], a lower mean RRI value is expected for the lower mineral content of hypomaturation enamel.…”

“…BWSpec 4 spectroscopic software (BWSpec, B&W TEK Inc.) was used to analyze the acquired spectra. The Raman absolute intensity (RAI), Raman relative intensity (RRI), fluorescence intensity (FI) and full width at half maximum (FWHM) at 960 cm À1 were defined and calculated from the Raman spectra according to previous investigations [12,[27][28][29]. RAI is the intensity of the Raman peak at 960 cm À1 before the spectrum is baselined and RRI is the intensity of the same peak after the spectrum is baselined between 990 and 930 cm À1 .…”

“…They reveal that is has an intricate organic-inorganic hybrid organization with hierarchical levels. First, needle-like hydroxyapatite (HAP) crystals pack tightly into groups and the organic matrix binds these crystals together [11,12]. The crystals are then organized into the base structural unit, the enamel prism, in a species-specific manner.…”

Beneficial effects of hydroxyapatite on enamel subjected to 30% hydrogen peroxide

“…Some studies reported that there was no evident change in enamel microhardness and morphology after bleaching treatment. [4][5][6][7] But others have found calcium loss, [8][9][10] alterations of surface morphology, [11][12][13][14][15] changes in chemical composition, 10,[15][16][17][18] decrease in hardness 10,15,[19][20][21][22] and fracture resistance 23 of enamel. The divergence in these results is probably related to different methodologies (in vivo or in vitro, time of evaluation, bleaching agents used, time of application, immersion of the specimens in artificial saliva between treatments, type of storage, bleaching agent pH, usage of fluoride, etc.).…”