Core Buildup Composite Resins Bond Strength to Dentin and Microhardness Using Universal Adhesives

The peer-reviewed literature on the use of universal adhesives (UAs) with core build-up composite resins (CBCRs) is limited. UAs may enhance the polymerization of dual-cured composite resins, leading to increased microhardness due to the "touch-cure" effect. This study compared the dentin bond strengths and microhardness of CBCRs bonded with UAs. A total of 480 bovine incisors were randomly allocated into 20 groups (n=24). Two dual-cured CBCRs, ParaCore (PrCore) and Gradia Core (GrCore), one light-cured CBCR, Clearfil Photo Core (PhotoCore), and Filtek Z250 (Z250) were evaluated. For the dual-cured CBCRs, the UAs from the respective manufacturers were mixed with a dual cure activator (Act): One Coat 7 Universal (OC7+Act) and G-Premio Bond (GrPB+Act). Three additional UAs were evaluated: Tokuyama Universal Bond II (TUB), Scotchbond Universal Plus Adhesive (SBUP), and Scotchbond Universal Adhesive with Dual Cure Activator (SBU+Act). Shear bond strength was evaluated after 24 hours. Additional specimens were prepared for Vickers microhardness (VHN) evaluation, with or without UA application to the bottom surface. Bond strengths ranged from 7.4±4.0 to 37.0±7.5 MPa. GrCore and PrCore showed higher bond strengths with SBU+Act than with their manufacturer-recommended adhesives. Dual-cured CBCRs exhibited lower dentin bond strengths and lower VHN than the light-cured composite resins, and the touch-cure effect was more effective for GrCore and PhotoCore.