Analysis of the specimen shape and aging protocols in the adhesive strength between dentin and resin composite

The objective of this study was to evaluate the aging protocols and the specimen shape (sticks and dumbells) in the adhesive strength between dentin and resin composite during micro-tensile stress. The specimens were submitted to no aging protocol, mechanical cycling (using macro and micro-rotation methods), thermal cycling and micro-tensile test. The stress distribution for the two specimen shapes was performed by finite elements analysis. Data were submitted to 3-way ANOVA and Tukey Test (α = 0.05). There is no statistical difference considering the interactions among the factors: specimen shape, thermal cycling, and mechanical cycling. Also, the mechanical cycling, for both methods, micro or macro-rotation, and the thermal cycling did not affect the adhesive strength of the samples. However, the specimen with the dumbbell shape showed higher adhesive strength (16 ± 3 MPa) than the stick shape specimen (11 ± 2 MPa). The stress distribution in dumbbell shape was more homogeneous than in the sticks. It can be concluded that the aging protocols tested were not enough to degrade the adhesive interface and the dumbbell shape specimen is better to predict the real adhesive strength developed in the interface.