The erosion of enamel was observed in acidic bleaching solutions and resulted in a slight whitening effect. However, the neutral or alkaline bleaching agent shows a more obvious whitening effect, without the evidence of enamel erosion. SUMMARYThis study investigated the influence of pH values of bleaching agents on the properties of the enamel surface. Sixty freshly extracted premolars were embedded in epoxy resin and mesiodistally sectioned through the buccal aspect into two parts. The sectioned slabs were distributed among six groups (n¼10) and treated using different solutions. Group HCl was treated with HCl solution (pH¼3.0) and served as a positive control. Group DW, stored in distilled water (pH¼7.0), served as a negative control. Four treatment groups were treated using 30% hydrogen peroxide solutions with different pH values: group HP3 (pH¼3.0), group HP5 (pH¼5.0), group HP7 (pH¼7.0), and group HP8 (pH¼8.0). The buccal slabs were subjected to spectrophotometric evaluations. Scanning electron microscopy investigation and MicroRaman spectroscopy were used to evaluate enamel surface morphological and chemical composition alterations. pH value has a significant influence on the color changes after bleaching (p,0.001). Tukey's multiple comparisons revealed that the order of color changes was HP8, HP7.HP5, HP3.HCl.DW. No obvious morphological alterations were detected on the enamel surface in groups DW, HP7, and HP8. The enamel surface of groups HCl and HP3 showed significant alterations with an erosion appearance. No obvious chemical composition changes were detected with respect to Micro-Raman analysis. Within the limitations of this study, it was concluded that no obvious

Luting composites could slightly modify the final color of ceramic veneers. Color matching of a try-in paste to the corresponding luting composite was not always achieved in the 0.7 or 0.5 mm thicknesses.

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