Influence of surface pretreatment on the short term bond strength of composite resin to a zirconia-based material. A microtensile bond strength test

Purpose: To evaluate the influence of airborne-particle abrasion of zirconia before and after sintering, on the bond strength between a zirconia core and an indirect resin composite material. Methods: 9 disks of Y-TZP zirconia core were prepared and divided into three equal groups. In Group 1 pre-sintered Y-TZP zirconia was airborne-particle abraded with 120 μm alumina oxide. In Group 2 sintered Y-TZP zirconia was airborne-particle abraded with 120 μm alumina oxide. In Group 3 sintered Y-TZP zirconia was not treated and thus served as the control group. A 10-methacryloylooxydecyldihydrogenphosphate (MDP) containing bonding agent and silane coupling agent mixture was applied to the disks in all three experimental groups. Resin composite for indirect restorations was incrementally layered in a plastic mold to a final thickness of 3 mm. Specimens were sectioned under water cooling to obtain microsticks 6×1×1 mm in dimension. 30 microsticks per experimental group were generated. Microtensile bond strength test was conducted with a universal testing machine. Fractured microsticks and sections from each group were also examined under an optical microscope and a scanning electron microscope to evaluate respectively the mode of failure and the zirconia-composite interface. T-test for independent samples was selected to analyze the data. The level of significance was set at P< 0.05. Results: Airborne-particle abraded groups resulted in mean (SD) bond strength values of 25.65 (7.23) MPa for Group 1 and 24.65 (12.33) MPa for Group 2. Bond failures were mainly interfacial. In the control group a high number of premature failures occurred during cutting process and the mean (SD) bond strength recorded was 3.36 (4.17) MPa. It was concluded that airborne-particle abrasion of a zirconia substrate combined with application of a MDP-containing bonding/silane coupling agent mixture resulted in an adequate resin composite bond. Airborne-particle abrasion performed before sintering zirconia did not produce any significant differences.