The influence of resin cement thicknesses on shear bond strength of zirconia treated with a universal adhesive

Objective: The study examined the influence of resin cement thicknesses on shear bond strength of zirconia treated with a universal adhesive. Materials and methods: Forty zirconia specimens (6 mm diameter, 4 mm thickness) were prepared, polished, surface treated with universal adhesive, and divided into 4 groups according to resin thicknesses (50, 80, 160 and 240 μm). All samples were stored in 37°C distilled water for 24 hours. The shear bond strength was performed using a universal testing machine at a crosshead speed of 0.5 mm/min. The results were statistically analyzed by one-way ANOVA and Tukey's multiple comparison test at a 95% confidence level. The failure modes were analyzed using stereomicroscope. Samples from each group were randomized and further analyzed under scanning electron microscope with the magnification of x2000Result: The shear bond strength for each group 1, group 2, group 3 and group 4 were 30.28±3.09, 26.86±2.21, 25.98±2.96, 18.22±1.71, respectively and Group1 showed significantly the highest bond strength than the other groups (P <0.05). There were no significant differences between Group2 and 3 (P > 0.05). Group 4 showed significantly the lowest bond strength than the other groups (P < 0.05). The adhesive failure and mixed failure were found in all groups. Conclusions: Resin cement thicknesses had the influence on zirconia shear bond strength treated with a universal adhesive. The thinner resin cement showed higher shear bond strength than the thicker resin cement thicknesses.