Bond Strength of CAD/CAM Resin Blocks After Various Surface Treatments

Objectives: To evaluate the shear bond strength of CAD/CAM resin blocks to dentin after various surface treatments.
Methods: Bovine coronal tooth were embedded with epoxy resin in rings which were polished until dentin was exposed. CAD/CAM resin blocks (Block HC, SHOFU) were prepared into cylindrical specimens 3 mm in diameter and 2 mm in thickness. All adhesive surfaces were polished with 600 grit abrasive paper. A total of 30 specimens were prepared and divided into 3 groups according to type of surface treatment: no treatment (control), sandblast, and sandblast and silane treatment. Roughness of specimens after surface treatments were determined using the 3D laser microscope (LEXT OLS4000, Olympus). Two types of cements, adhesive resin cement（RelyX^TM Ultimate Adhesive Resin Cement, 3M ESPE）requiring a bonding agent and a self-adhesive resin cement (RelyX^TM Unicem 2 Automix, 3M ESPE), were applied on specimens and bonded to bovine dentin where the adhesive surface was standardized using a vinyl ring with an internal diameter of 3 mm. After 24 hours of storage in distilled water at 37°C, shear bond strength was determined using a universal testing machine (EZ Graph, Shimadzu). Specimens were stressed parallel to the bonded surface at a crosshead speed of 0.5 mm/min. Statistical analysis was performed using two-way ANOVA and Tukey’s multiple comparison tests.
Results: Surface roughness of resin blocks increased after sandblast treatment. Shear bond strength was significantly higher in both treated groups than the control (p<0.05). Self-adhesive resin cements showed significantly lower bond strength compared to conventional resin composite cements. Fracture mode consisted mostly of adhesive failure between resin block and adhesive resin cement.
Conclusions: Within the limitations of this study, the surface treatments performed on CAD/CAM resin blocks improved the bond strength between dentin by increasing its roughness.