Alterations in Bovine Enamal Surface Properties by Bleaching with Hi-Lite®

Abstract

Bleaching does not require tooth grinding, and it has become the preferred initial choice for patients who want to improve the color of their teeth. Although there are clinical reports on bleaching, few have evaluated the bleached enamel surface properties. The purpose of this study was to examine the effrece of 35% hydrogen peroxide on the surface properties of extracted bovine enamel. The bleaching agent used was the Shofu Hi-Lite® bleaching system. We investigated the change in the surface micro-hardness (Vicker's hardness) and nanohardness (Universal hardness) in enamel surface before and after exposure in vitro to the bleaching agent. Creck resistance indirectly related to the fracture toughness was also measured. A Vicker's hardness indenter was used to initiate crackes into bleached enamel surface. In addition the microstructure and compositional changes (Ca, P) of the bleached enamel surface and its cross section were assessed using scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). A laser fluorescence diagnostic device (DIAGNOdent™) was also used to detect degenerate organic substance in the bleaching enamel surface. This investigation revealed no significant differences in micro and nanohardness values and fracture touthness values among the surface of bleached enamel treated three and 18 times. Following Vicker's micro-hardness indentation on the bleaching enamel, significant cracking fracture and deformation pattern were not observed. However, results of the bleached enamel in a cross section at 0-50 μm depth showed a statistically significant (p<0.05) decrease in micro and nano-hardness compared with the control. The analysis of the SEM, EPMA, and DIAGnodent™ measurement showed differences in surface topography and composition and peak value for enamel treated with the bleaching agent. Surface destruction was seen; however, it was not as severe as that seen in the control. The bleaching caused a decrease of Ca and P at 0-50 μm depth compared with the polished surface.