Purpose: To determine the influence of mechanical properties of resin-based composites on the microtensile bond strength to dentin of all-in-one adhesives.
Materials and methods: Microtensile bond strengths were measured with the non-trimming technique for the experimental groups: 1) Bond Force/Estelite Σ (Tokuyama); 2) G-Bond Plus (GC)/Estelite Σ; 3) Bond Force/Gradia Direct Anterior (GC);4) G-Bond Plus/Gradia Direct Anterior; 5) Bond Force/Gradia Direct LoFlo (GC); 6) G-Bond Plus/Gradia Direct LoFlo. The following mechanical properties of the resin-based composites were assessed: tensile strength, flexural strength, tensile elastic modulus, shear elastic modulus, Poisson's ratio, Vicker's hardness, contraction stress. Three-dimensional models of microtensile beams were created for finite element analysis of the first principal stress values and distribution in the adhesive layer during microtensile testing. Statistical tests were applied to microtensile bond strength values (two-way ANOVA) and to data from mechanical tests (one-way ANOVA). In all the analyses, the level of significance was set at p < 0.05.
Results: While the adhesive did not significantly influence microtensile bond strength, the composite was a significant factor. Regardless of the adhesive, Estelite Σ yielded significantly higher bond strengths than Gradia Direct Anterior and Gradia Direct LoFlo, that were comparable. Adhesive-composite interactions were not statistically significant. Estelite Σ had the highest Vicker's hardness, the highest tensile and shear elastic moduli, the lowest and closest to dentin Poisson's ratio. A more favorable stress distribution in the adhesive layer occurred in the Estelite Σ model.
Conclusions: When comparing the bonding potential of several adhesives with the microtensile technique, the same resin composite should be used in all the experimental groups for building up the coronal portion.