How "Universal" is Adhesion? Shear Bond Strength of Multi-mode Adhesives to Enamel and Dentin

Purpose: The purpose of this in vitro study was to compare the shear bond strength of different universal adhesives to enamel and dentin with and without additional phosphoric acid etching before and after thermocycling (TC). Materials and Methods: The mesial, distal, lingual, and buccal surfaces of the teeth were ground flat to expose two enamel areas and two dentin areas. Specimens were randomly divided into 36 groups (n = 10). Four adhesives were tested: Scotchbond Universal (SBU), Prime & Bond Elect (PBE), All-Bond Universal (ABU), and iBond Universal (IBU). The application was performed in the self-etch mode (SE) or in the etch-and-rinse mode (ER). Optibond FL (OFL) was used as an etch-and-rinse control. After composite buildups were made, half of the groups were tested before and the other half after TC. The failure mode was evaluated using a light microscope. Results: In enamel, mean bond strengths ranged from 13.4 to 21.9 MPa in the SE mode before TC. When used as an ER adhesive, mean bond strengths exceeded 30 MPa. TC did not influence the mean bond strengths in either application mode. Regarding dentin, significant differences in the SE mode were adhesive dependent. Differences were only detected between SBU and IBU before TC and were not present after TC. When SBU, PBE, and ABU were used as ER adhesives, no differences were detected before TC. TC only affected IBU when compared to the other adhesives. Conclusion: Universal adhesives benefit from phosphoric acid etching, as bond strengths increased especially at enamel surfaces. Keywords: universal adhesives, shear bond strength, self-etch, etch-and-rinse, enamel, dentin