Aim: The aim of this study was to evaluate in vitro effects of the combination of in-office and intracoronal bleaching on enamel and dentin bond strength and on dentin morphology.
Methods and materials: Bleaching treatment was performed on 128 bovine teeth for three weeks. Intracoronal bleaching was performed in groups G1 to G3, and in the other groups a combination of in-office and intracoronal bleaching was performed. The following agents and materials were used (n=16): G1- sodium perborate and water (SP); G2- 37% carbamide peroxide (CP); G3- 35% hydrogen peroxide (HP); G4- HP + cotton pellet soaked in water (CPW); G5- HP + SP; G6- HP + CP; G7- HP + HP; and G8- CPW (control). Seven days after bleaching treatment the teeth were sectioned into two halves. One half of each tooth was ground to obtain a flat dentin surface. Dentin and enamel fragments were treated with a dentin/enamel resin adhesive. Resin composite was inserted in two increments and polymerized for 20 seconds. Following the restorative procedures, specimens were sectioned into beams with a rectangular cross-sectional area of approximately 1 mm2. Microtensile testing was performed in a universal testing machine. Bond strengths (in MPa) were calculated and the data were submitted to an analysis of variance (ANOVA) and the Tukey test (a=0.05). For the scanning electron microscopy (SEM) observation, the exposed pulp chambers (n=5) were fixed, dehydrated, dried in a Critical Point dryer, and gold-sputter coated for analysis at standardized magnifications (500X, 1000X, and 2000X).
Results: None of the bleaching techniques reduced the enamel bond strength, the best results observed were with the intracoronal treatments with SP and HP. In dentin all bleaching techniques reduced the bond strength with the exception of the in-office HP application technique. The SEM results demonstrated similar dentin surfaces for the G1, G3, G6, and G7 groups with more open dentin tubules found than in the other groups.
Conclusion: None of the bleaching techniques tested reduced the bond strength of enamel, but they all reduced the bond strength of dentin with the exception of the group only treated with in-office bleaching using 35% HP. The worst bond strength results to dentin were observed in groups that received intracoronal bleaching with SP.