The effect of tooth bleaching on the bond strength of an experimental primer to enamel

This study evaluated the effect of tooth bleaching on the microtensile bond strength (microTBS) of an experimental primer to enamel. Materials used were an experimental tooth manicure system (Shofu) composed of primer and light-cured flowable resin composite. Flattened enamel surfaces of bovine teeth were bleached with Nite White Excel (Discus Dental) or Hi-Lite (Shofu), with nonbleached teeth used as a control group. Each bleaching group was subdivided into three bonding modes. These were group A, application of primer for 3 s, followed by 5 s of air blowing; group B, application of primer for 10 s, followed by 5 s of air blowing; and group C, application of 20% phosphoric acid for 10 s, spraying with water for 5 s, and then air blowing for 5 s. The flowable resin paste was placed and polymerized after each enamel surface treatment. Using a low-speed diamond saw, the specimens were sectioned into beam-shaped samples with a cross-sectional area of approximately 1 mm(2) at the bonded interface. The samples were subjected to the microTBS test with a 1.0 mm/min crosshead speed. Data were statistically analyzed using two-way analysis of variance (ANOVA) followed by the Bonferroni/Dunn post-hoc test. The two-way ANOVA revealed significant differences in the effects of the bleaching systems and bonding mode, and significant differences were also found for the interaction between them (P < 0.01). There were no statistically significant differences in microTBS values among the specimens in groups A and B regardless of bleaching or nonbleaching (P > 0.05). In contrast, the microTBS value of group C without bleaching was significantly higher than that of all other experimental groups (P < 0.01).