Tensile bond strength of immediately repaired anterior microfine hybrid restorative composite using nontrimmed hourglass specimens

To investigate the effect of different surface treatments on the tensile bond strength (TBS) of immediately repaired anterior microfine hybrid restorative composite using nontrimmed hourglass-shaped specimens.

Fifty-six nontrimmed hourglass composite specimens were prepared in this study. Eight specimens were used for the evaluation of the cohesive tensile strength as the control group. The remaining 48 were divided into 6 equal groups according to the method of proposed treatment. Groups IM1 and IM2: The specimens were repaired without intermediate treatment. Group IM3: A thin layer of Excite self-priming adhesive was applied to the proposed repaired area of each half-specimen. Group IM4: The repaired area was ground using an abrasive stone, each half-specimen was rinsed and dried, and the adhesive applied. Group IM5: Treatment consisted of 37% phosphoric acid etching of the proposed repair area. The adhesive was then applied. Group IM6: The repaired area was ground and acid etched before applying the adhesive. In all repaired groups except for IM2, repaired specimens were prepared and cured against a single layer of transparent polyester strip (matrix) to prevent the formation of an oxygen inhibition layer. In group IM2, specimens were cured in air without the polyester strip. Specimens were then tested for the repair tensile bond strength (TBS) in a universal testing machine at a crosshead speed of 0.5 mm/min until failure. Twelve more samples were used for SEM characterization of nontreated, ground, acid-etched, and ground/acid-etched samples. The failure mode was evaluated using a stereomicroscope at 30X magnification. All TBS data were expressed as mean and standard deviation, and were analyzed using StatsDirect 2.5.7. One-way ANOVA followed by Tukey-Kramer multiple-comparison post-hoc tests were used to compare the TBS between all tested groups. Differences were considered significant at p < 0.05.

Groups that were cured against a matrix and received no treatment or were repaired with adhesive only had significantly lower TBS than the control group. Groups which were cured without the matrix and received no treatment or grinding/adhesive, acid etching/adhesive, and grinding/acid etching/adhesive showed no significant difference in TBS compared to the control group. SEM evaluation showed that acid etching did not change the morphology of the composite surface. The ground specimens showed a grooved pattern with smeared grinding products. Ground/acid-etched specimens showed removal of the smeared products with a less distinct grinding-groove pattern. Stereomicroscopic evaluation of the debonded surfaces for all repaired groups showed that the failure mode was predominantly adhesive for all evaluated debonded surfaces in each repair group.

In the absence of an oxygen inhibition layer, the immediate repair bond strength was decreased. In contrast, in the presence of an oxygen inhibition layer, the immediate repair bond strength of composite was improved. The application of a thin adhesive layer did not improve the immediate repair bond strength as the other surface treatments did. When the composite was cured against a matrix, chemical and/or mechanical treatments of composite surface prior to application of the adhesive proved to be an effective method to improve the immediate repair bond strength.