Compatibility of new universal simplified adhesives with dual-cured composite and effect of hydrophobic resin coat

Abstract

1. ObjectiveThe purpose of this study was to evaluate the influence of two different universal adhesive on microshear bond strength of dual-cured composite to dentin. Also we evaluated the effect of application of a hydrophobic resin coat on the bond strength within the hybrid layer of a one-step self-etch adhesive system.2. Materials and methodsThe flat dentin surfaces were prepared from freshly extracted, caries-free, human third molars. Four recent adhesive systems including two universal adhesive (Single Bond Universal, All-Bond Universal), one-step self-etch system (Tetric N-Bond Self-Etch), etch-and-rinse system (XP bond) and hydrophobic adhesive resin for coating (Heliobond) were evaluated with dual-cured type composite. As a control group, light-cured type flowable composite, with similar flexural strength as dual-cured composite was selected.Microshear bond test was carried out using a universal testing machine and all debonded specimens with dual-cured composite were observed under X40 stereoscope to determine the mode of failure. Furthermore, specimens in each group with different adhesives were observed under scanning electron microscope for detailed evaluation of surface morphology.3. ResultSingle Bond Universal exhibited the highest bond strength (28.5 ± 6.2 MPa). On the other hand, All-Bond Universal showed low microshear bond strength (14.1 ± 5.1 MPa) and statistically no difference with Tetric N-Bond Self-Etch (8.8 ± 6.7 MPa). Also, with an additional hydrophobic resin coat, Single Bond Universal exhibited significantly higher bond strength than All-Bond Universal. When used with an additional hydrophobic resin coat, the bond strength of all adhesives increased significantly except for Single Bond Universal.The failure mode of Single Bond Universal was predominantly mixed failure. In case of other adhesives, high percentages of adhesive failure appeared. When a hydrophobic resin coat was applied, Single Bond Universal and All-Bond Universal did not show much difference, whereas Tetric N-bond Self-etch and XP bond showed an increased percentage of mixed failure.4. Conclusion(1) With respect to the influence of universal adhesives, Single Bond Universal showed the highest microshear bond strength but not incompatibility with dual-cured composite. However All-Bond Universal showed relatively low microshear bond strength and statistically no difference with Tetric N-Bond Self-Etch as existing one-step self-etch system. (2) Hydrophobic resin coat may be considerable alternation for solving the problem of incompatibility between single step adhesive system and dual-cured composite, and can improve microshear bond strength of these materials.