Background: A reduction in bond strength of bleached enamel has been confirmed in the literature. Although limited information is available, it is conceivable that the veneer preparation process may remove the impacted enamel and further eliminate the compromised bond strength between the composite resin and bleached enamel. This study aimed to evaluate the effect of surface removal following bleaching on the micro-shear bond strength (μSBS) of bleached enamel.
Methods: Forty-eight specimens were prepared from bovine incisors and were randomly divided into 2 groups (n = 24): group B (bleaching with 40% hydrogen peroxide for 2 × 45 min with a 1-week interval) and group C (control group without bleaching treatment). Immediately after receiving the treatments, 0.5 mm of the enamel was removed from the specimen surface, followed by bonding of composite resin to the enamel surface. Each group was further divided into 2 subgroups of 12 specimens each: subgroup T (with 5000 thermocycles in water baths at 5 °C and 55 °C), and subgroup N (without thermocycling). The μSBS values were measured using a universal testing machine and subjected to two-way analysis of variance (α = 0.05). The fracture modes of the specimens were observed using a stereomicroscope.
Results: The μSBS values of the different groups ranged from 21.42 to 25.21 MPa. Following a surface reduction of 0.5 mm, bleaching treatment and thermocycling did not significantly affect the μSBS values (P = 0.348 and P = 0.507, respectively). No significant interaction was found between the bleaching treatment and thermocycling (P = 0.514). All the groups exhibited a high percentage of mixed failures. Compared with group C, group B exhibited higher percentage of adhesive failure.
Conclusion: The results suggested that the bonding procedure could be performed on the bleached enamel following a surface reduction of 0.5 mm immediately after the bleaching treatment.
Keywords: Enamel; Hydrogen peroxide; Shear bond strength.