Bond Strength of Hybrid Ceramic Blocks for CAD/CAM Crowns

Objectives: The purpose of this study is to evaluate the shear bond strength of resin cements to hybrid ceramic blocks for CAD/CAM crowns. Hybrid ceramic blocks that contain 60% or more inorganic fillers may have a weak bond strength. Therefore, we investigated the bond strength of CAD/CAM ceramic blocks using the shear bond test with different adhesive resin cements.
Methods: Three different types of hybrid ceramic blocks were used: 1) CERASMART270 (GC Co.), 2) SHOFU BLOCK HC (SHOFU INC.), and 3) KZR-CAD HR2 (YAMAKIN CO.LTD). These were each divided into three adhesive resin cement groups: 1) RelyX Ultimate resin Cement (3M), 2) Block HC Cem (SHOFU INC.), and 3) G-CEM LINKFORCE (GC Co.)). These hybrid ceramic blocks (n=5/gp) were bonded to composite resins for core (UNIFIL CORE EM (GC Co.)) using adhesive resin cements according to each manufacturer's instructions. All cemented specimens were stored (37°C, 24 hours). Shear bond strength was measured at a crosshead speed of 0.5mm/minute. The collected data was statistically analyzed (two-way ANOVA, Tukey’s, p<0.05).
Results: The highest bond strength was achieved with KZR-CAD HR2 and LINKFORCE (19.8±6.1Mpa), while the lowest bond strength was with KZR-CAD HR2 and Block HC Cem (15.1±5.0Mpa). However, all specimen groups did not show significant statistical differences. The fracture surface of specimen groups that used LINKFORCE or RelyX Ultimate resin Cement showed cohesive failure without interfacial failure. The fracture surface of specimen groups that used Block HC Cem showed mixed cohesive failure and interfacial failure.
Conclusions: From the above results, it is inferred that the bond strength of these adhesive cements to CAD/CAM crown materials is suitable for clinical application.