The effect of different bonding agents on the shear bond strength between monolithic zirconia and indirect composite

In clinical practice, indirect composites are used as veneering materials in the zirconia supported restorations as alternative materials. In this study, investigation of the effect of different bonding agents, application of feldspathic porcelain, and thermocycling on the shear bond strength between monolithic zirconia and indirect composites was aimed. In this study, 200 monolithic zirconia disks with 11 mm diameter and 2.5 mm thickness were milled with CAD/CAM system. After the application of airborne abrasion on the sintered disks, porcelain glaze was applied on the half of the disks. Five different bonding agents were applied on the zirconia disks according to the manufacturer's recommendations. 5000 cycles of thermocycling were applied to half of the disks. The results of the shear bond testing with a universal testing device were recorded for all of the samples. The broken interfaces of the samples were examined under light microscope (10x magnification) and under scanning electron microscope (SEM; 1000x magnification). For the statistical analysis, Mann Whitney U and Kruskal Wallis test were utilized. The results were evaluated with 95% confidence interval and the significance level was accepted as p<0.05. 8th generation bonding agents (GP, TU) provided a significantly higher bonding in comparison to the recommended primers for the bonding between the dental materials and composite resins. Application of porcelain glaze did not have a significant effect on the shear bond strength when GP, TU or SZ bonding agents were utilized as the bonding material between monolithic zirconia and indirect composite, whereas it significantly increased the shear bond strength when ZP or CCP were utilized. Thermocycling should be considered in the studies evaluating the shear bond strength and primers. Adhesive failure was observed in all of the primers used in this study.