In- vitro evaluation of shear bond strength of three primer/resin cement systems to monolithic zirconia

PURPOSE: This in-vitro study aimed to evaluate the shear bond strength of several types of primer/ resin cements to monolithic zirconia with different levels of storage. MATERIALS AND METHODS: The disk-shaped specimens of monolithic zirconia (n=72) were prepared by CAD/CAM system (CORI TEC 350i Loader, Imes-Icore, Germany) (10mm x 3mm). All the specimens were polished with silicone carbide paper, then the bonding surface was prepared by surface pretreatment with air-borne particle abrasion (Al2O3, 120µm). Monolithic zirconia discs were divided into 3 groups (n=24), according to the 3 primer/ cement systems; 3M (Single bond universal adhesive/ Rely X Ultimate), Kuraray (Clearfil ceramic primer plus/ Panavia SA), and Bisco (Z prime plus/ Due-Link). After bonding procedure according to manufacturers` instructions, each group was further divided into 2 subgroups (n=12) according to the storage levels; 24-hours storage in water at 37C° and thermocycling (5000 cycles). After these procedures, shear bond strength tests were performed for all specimens. Failure types were also evaluated. The data were analyzed using one-way and two-way analysis of variance (ANOVA) and Tukey HSD test. Significance was set at p<0.005. RESULTS: There were significant differences between the mean shear bond strength values of 3 groups of adhesive systems in both storage levels (p<0.05). The highest shear bond strength value was observed in Kuraray adhesive system (12.52±1.34 MPa) and the lowest shear bond strength value was observed in Bisco adhesive system (5.32±0.54 MPa) in thermocycled groups (p<0.05). Similarly, in short-term storage groups, Kuraray had the highest (16.47±1.5 MPa) and Bisco had the lowest shear bond strength values (7.43±1.06 MPa) (p<0.05). Regardless to the type of adhesive systems, thermocycling significantly decreased the shear bond strength of all cement groups (p<0.05). The predominant failure mode was adhesive failure (49%) whereas mixed failure was 45% and cohesive failure was 6%. CONCLUSION: Thermocycling decreased the shear bond strength of all adhesive resin cements to monolithic zirconia. Kuraray adhesive system had the highest shear bond strength and Bisco adhesive system had the lowest shear bond strength. KEY WORDS: Monolithic zirconia, CAD/CAM, composite resin, primer agent, shear bond strength, thermocycling.