Effect of Nonvital Tooth Bleaching on Resin/Enamel Shear Bond Strength

This study evaluated the effect of nonvital tooth bleaching on shear bond strength (SBS) of the composite resin/bovine enamel interface at different periods of time after bleaching. Three hundred twenty teeth were randomly divided into four groups according to bleaching agent: SPH: sodium perborate and 30% hydrogen peroxide; SPW: sodium perborate and distilled water; CP: 37% carbamide peroxide; and PLA: distilled water (placebo). The bleaching agents in the pulp chambers were replaced every 7 days for 4 weeks. For SBS testing, each of these groups was randomly divided into four subgroups (n = 20) according to the postbleaching periods of time: 0 (baseline), 7, 14, and 21 days. At the respective time, enamel slabs were embedded in polyester resin and flattened. Composite resin cylinders (Z100/Single bond, 3M) were bonded to the enamel surface and subjected to the SBS test using a universal testing machine. The ANOVA and Tukey's test (α = 0.05) showed statistically significant differences (expressed by different letters) among the bleaching agents only at follows: PLA (a), CP (ab), SPW (ab), and SPH (b). The SPH group, showing the lowest mean value, differed significantly from the control group. At 7, 14, and 21 days, no significant differences were observed. Nonvital tooth bleaching affected the resin/enamel SBS values when sodium perborate mixed with 30% hydrogen peroxide was used.