Comparison of Bleaching Effect of At-home and In-office Bleaching

Objectives: Vital bleaching is generally classified into at-home and in-office bleaching. With at-home bleaching people can bleach their teeth by themselves, while with in-office bleaching their teeth are bleached by dental practitioners. It has been clinically recognized by many practitioners that the appearance of the enamel surface after bleaching is different between at-home and in-office bleaching, presenting a chalky-white appearance after in-office bleaching and a translucent natural-white after at-home bleaching. We assumed that for in-office bleaching the bleaching effect is limited to the enamel and the outer dentin at deepest, while for at-home bleaching the bleaching effect can reach to deep dentin. The science of color explains that the appearance of objects is perceived through the cross-interaction of their color, transparency, surface gloss, light diffusion and fluorescence. Among these factors, color is assumed to be a dominant factor controlling the appearance of enamel surface after bleaching. In this study, therefore, we examined the color change by calculating the whiteness (W) from the value of L*, a* and b* in the CIE system, from which we compared the bleaching effect of at-home and in-office bleaching. Materials and Methods: An extracted human pre-molar was sectioned lingo-buccally avoiding pulp exposure so that a tooth specimen having a thickness of 2.45±0.05 mm was obtained. Bleaching was performed on either a buccal or a lingual surface of the enamel surface in the specimen. At-home bleaching using 10% carbamide peroxide (Hi-Lite Shade Up, Shofu) was performed in half of the specimens (n=9) where the bleaching was done for 6 hours once a day during which the specimen was kept at 37℃ and 100% RH (relative humidity). At-home bleaching was continued for 2 or 4 weeks. The other half of the specimens were treated by in-office bleaching using 35% hydrogen peroxide (Hi-Lite, Shofu) according to the manufacturer's instructions where the bleaching was repeated three times in a single day that continued for 5 days. Simulating vital teeth the hydrostatic fluid pressure of 34cmH₂O was applied constantly to the pulp chamber of every specimen throughout the experimental period. Colorimetric measurement was done for each cross-section of the specimen at two measuring points in enamel and at four measuring points in dentin. Values of L*, a* and b* in the CIE system were assessed before and after the bleaching, by which W was calculated using an equation. Results were statistically analyzed by two-way ANOVA and Tukey's multiple comparison (p< 0.05). The image of the specimen before and after the bleaching was taken with a scanner of which RGB (red-green-blue) values were transformed to values of L*, a* and b* through a mathematical process. From these values W was calculated, and then a color-contour map before/after the bleaching was developed. Results: Results from the colorimetric measurements and the image-scanning statistically treated by two-way ANOVA demonstrated that there was no interaction between the depth from surface enamel and the bleaching methods. The tendency that the change of A W (difference of W at before and after bleaching) with the depth from the surface enamel to the deep dentin was not different between at-home bleaching for 2 weeks and at-home bleaching for 4 weeks and in-office bleaching. In at-home bleaching for 4 weeks and in-office bleaching, the results from a color-contour map before and after the bleaching were similar regarding the area showing increased W and the value of ΔW. Conclusions: Under the limited conditions employed in this study, it was not concluded that the bleaching effect of in-office bleaching is limited to the enamel and the outer dentin at deepest, while for at-home bleaching the bleaching effect can reach to deep dentin.