Effects of ethanol concentrations of acrylate-based dental adhesives on microtensile composite-dentin bond strength and hybrid layer structure of a 10 wt polyhedral oligomeric silsesquioxane (POSS)-incorporated bonding agent

Abstract

Background: The aim of this study was to assess for the first time the effects of different amounts of ethanol solvent on the microtensile bond strength of composite bonded to dentin using a polyhedral oligomeric silsesquioxane (POSS)-incorporated adhesive. Materials and Methods: This experimental study was performed on 120 specimens divided into six groups (in accordance with the ISO TR11405 standard requiring at least 15 specimens per group). Occlusal dentin of thirty human molar teeth was exposed by removing its enamel. Five teeth were assigned to each of six groups and were converted to 20 microtensile rods (with square cross-sections of 1 mm x 1 mm) per group. The "Prime and Bond NT" (as a common commercial adhesive) was used as the control group. Experimental acrylate-based bonding agents containing 10 wt POSS were produced with five concentrations of ethanol as solvent (0, 20, 31, 39, and 46 wt). After application of adhesives on dentin surface, composite cylinders (height = 6 mm) were bonded to dentin surface. The microtensile bond strength of composite to dentin was measured. The fractured surfaces of specimens were evaluated under a scanning electron microscope to assess the morphology of hybrid layer. Data were analyzed using one-sample t-test, one-way analysis of variance (ANOVA), and Tukey tests (alpha = 0.05). Results: the mean bond strength in the groups: "control, ethanol-free, and 20, 31, 39, and 46 ethanol" was, respectively, 46.5 +/- 5.6, 29.4 +/- 5.7, 33.6 +/- 4.1, 59.0 +/- 5.5, 41.9 +/- 6.2, and 18.7 +/- 4.6 MPa. Overall difference was significant (ANOVA, P < 0.0001). Pairwise differences were all significant (Tukey P < 0.05) except those of "ethanol 0 versus 20" and "20 versus 31." All groups except "0 and 46 ethanol" had bond strengths above 30 MPa (t-test P < 0.05). Conclusion: Incorporation of 31 ethanol as solvent into a 10 wt POSS-incorporated experimental dental adhesive might increase the bond strength of composite to dentin and improve the quality and morphology of the hybrid layer. However, higher concentrations of the solvent might not improve the bond strength or quality of the hybrid layer.