Shear bond strength evaluation of composite resin on enamel and dentin after nonvital bleaching.

BACKGROUND

Studies have shown that bleaching agents interfere with the adhesion of composite resin placed immediately after bleaching.

PURPOSE

The aim of this study was to evaluate the shear bond strengths of composite resin after four different durations since the time of nonvital bleaching (1 d and 1, 2, and 3 wk).

MATERIALS AND METHODS

Two hundred seventy bovine teeth were assigned to nine groups (n = 30) according to the bleach used and the time between bleaching and restoration: group 1--sodium perborate (SP), 1 day after bleaching (AB); group 2--SP, 1 week AB; group 3--SP, 2 weeks AB; group 4--SP, 3 weeks AB; group 5--37% carbamide peroxide (CP), 1 day AB; group 6--CP, 1 week AB; group 7--CP, 2 weeks AB; group 8--CP, 3 weeks AB; group 9--control group (no treatment). After the bleaching treatment, the teeth in each group were sectioned and the enamel and dentin were separated. The teeth were cut, embedded in polyester resin, and polished to obtain flat enamel and dentin surfaces. The adhesive system was applied and a cylinder of composite resin was bonded on each flat surface. The specimens were stored in distilled water for 7 days at 37 degrees C. The shear bond strength test was performed in a universal test machine (Emic DL-500, São José dos Pinhais, São Paulo, Brazil) at a crosshead speed of 0.5 mm/min.

RESULTS

The data were subjected to analysis of variance, Dunnett's t-test, and Tukey's least significant difference at p < or = .05 and showed a statistically significant decrease in bond strengths of composite resin for enamel and dentin 1 day after the nonvital bleaching.

CLINICAL SIGNIFICANCE

The decrease in shear bond strength values is time dependent. A delay in bonding procedures for composite resin restoration is recommended. According to the results, a satisfactory time to perform the restoration of composite resin for both enamel and dentin is 2 weeks after bleaching.