Aim: The aim of this in vitro study was to evaluate the influence of time after treatment with a 35% hydrogen peroxide bleaching agent on the shear bond strength between composite resin and sound enamel and dentin.
Methods and materials: Eighty dental slabs - 40 enamel (E) slabs and 40 dentin (D) slabs - were embedded, flatted, and divided into four groups (n=10). In G1 the E and D slabs were kept in artificial saliva for 14 days. For the G2, G3, and G4 groups the E and D slabs were submitted to bleaching treatment with a 35% hydrogen peroxide bleaching agent. At different times after bleaching treatments (G2=immediate; G3=seven days; G4= fourteen days), composite resin cylinders were made using an adhesive system. Tests were performed in a universal testing machine at a speed of 0.5 mm/min to obtain the values in MPa.
Results: For enamel, the Kruskal-Wallis test and Dunn Method showed G1 differed significantly from G2 (G1=13.40 a; G2=6.64 b; G3=16.76 a; G4=11.64 ab). For dentin, the analysis of variance (ANOVA) and Tukey tests showed that G1 differed significantly from G2 and G3 (G1=12.11 a; G2=4.97 b; G3=8.67 c; G4=11.86 ac).
Conclusion: It is recommended adhesive restorative procedures in enamel be delayed for seven days post-bleaching treatment with 35% hydrogen peroxide, while restorations in dentin should be delayed for 14 days following bleaching treatment.