Abstract:A low-concentration hydrogen peroxide solution containing titanium dioxide as a photocatalyst has attracted attention as a safe office bleaching agent. In this study, the influence of different kinds of light on the bleaching effect of this agent was examined. The bleaching agent was applied to hematoporphyrinstained paper strips that were then irradiated with a 405-nm diode laser (800 mW/cm 2 ), a halogen lamp (720 mW/cm 2 ), or an LED (835 mW/cm 2 ) for 5 minutes. The color was measured spectrophotometrically before treatment and every 30 seconds thereafter, and the effects of bleaching on the strip were assessed using the CIE 1976 L * a * b * color coordinate system. Of the three different irradiation conditions, 405-nm laser irradiation gave the strongest bleaching effect with 3.5% hydrogen peroxide containing titanium dioxide. The laser provides strong irradiance at 405 nm, which corresponds to the absorption range of the bleaching agent, and consequently the largest effect was obtained.

This study determined the bond strengths to Er:YAG laser-irradiated and non-irradiated bovine enamel of three one-step self-etch adhesives (AQ Bond Plus (AQP), G-Bond (GB), and Clearfil Tri-S Bond (TS)) and one two-step self-etch adhesive (Clearfil Megabond (MB)). Eighty SiC paper-ground bovine enamel surfaces were used, of which half were laser-irradiated. The enamel surfaces were bonded to a resin composite with each adhesive, and tensile bond strengths were determined after 24 hours. For non-irradiated enamel groups, MB achieved greater bond strength to enamel than GB and TS (p<0.05), but no significant difference was found between MB and AQP (p>0.05). For laser-irradiated enamel groups, no significant differences were found among the four adhesives (p>0.05). Additionally, for each adhesive, no significant differences were found between laser-irradiated and non-irradiated enamel. It was thus concluded that Er: YAG laser irradiation of enamel did not affect the tensile bond strength of one-step and two-step self-etch adhesives.

Abstract:To establish a safer and more effective bleaching method for discolored pulpless teeth, we examined bleaching from the pulpal dentin side using a 3.5% hydrogen peroxide solution containing titanium dioxide. The twenty bovine bloodstained discolored enamel-dentin plates of 1.0 mm enamel thickness and 2.0 mm dentin thickness were used. The bleaching agent was applied to the dentin side that was then irradiated with a 405-nm diode laser (800 mW/cm 2 ) or a halogen lamp (720 mW/cm 2 ) for 15 minutes. The bleaching effect was assessed by spectrophotometric measurement of the color of the specimens from the dentin and enamel side for every 5 minutes, and then dentin or enamel surface was examined with a scanning electron microscope. The 3.5% hydrogen peroxide solution containing titanium dioxide proved to have a strong bleaching effect. The color difference after laser irradiation was higher than that after halogen lamp irradiation, however, there was no significant difference between them. No changes in the enamel surface morphology were found and open dentinal tubules with no smear layer were clearly observed at the pulpal dentin surface in both groups. SEM observation of the dentin surface at a non-bleached area (a) and a bleached area (b) after bleaching for 15 minutes with 405-nm diode laser irradiation