The Effect of Nonvital Bleaching on the Shear Bond Strength of Composite Resin Using Three Adhesive Systems

To evaluate the effect of nonvital bleaching on the shear bond strength of composite resin using three adhesive systems. Two hundred seventy bovine teeth were assigned to 3 groups (n = 90): SP, paste of sodium perborate and water; CP, 37% carbamide peroxide; CO, control group (no treatment). After the bleaching treatment, the teeth in each group were cut into enamel (E) and dentin (D) sections. The teeth were embedded in polyester resin and polished in order to obtain a flat E or D surface. Each group was divided into 6 subgroups (n = 15) according to substrate (E and D) and adhesive system: SB, Single Bond (solvent: water/alcohol); PB, Prime & Bond NT (solvent: acetone); CLF, Clearfil SE Bond (solvent: water). The adhesive system was applied on each flat surface according to the manufacturer's instructions and a cylinder of composite resin Z-250 was overlaid. The specimens were stored in distilled water for 7 days at 37°C. The SBS test was performed in a universal testing machine with crosshead speed of 0.5 mm/min. The data obtained (in MPa) were statistically analyzed with two-way ANOVA and Tukey's test (p = 0.05). The bleaching treatment influenced the SBS, regardless of the adhesive system used. On enamel, the SP and CP bleaching treatments reduced the SBS values. On dentin, the SP bleaching agent reduced the SBS values, but the CP bleaching did not. Nonvital bleaching treatment with sodium perborate may adversely affect shear bond strength of composite resin for both enamel and dentin. Similar effects can be expected from 37% carbamide peroxide bleaching agent on enamel but not dentin bonding strength. The use of water/alcohol and acetone-based adhesive systems cannot reverse the effects of bleaching treatments on bond strengths. Keywords: bleaching agent, bond strength, adhesive system