Shear bond strength of composite cement to alumina-coated versus tribochemical silica-treated zirconia

Objectives: To compare the shear bond strength of composite-resin cement to nano-structured alumina-coated versus to tribochemical silica-treated zirconia, and to analyze the residual stresses on both of nano-structured alumina-coated versus tribochemical silica-treated zirconia specimens. Methods: One hundred and eighty zirconia disks (10 mm and 5 mm in diameter, 5 mm thickness) were divided into two groups: nano-structured alumina coating (H.C.Starck, AlN) and tribochemical silica treatment (CoJet) followed by RelyX Ceramic Primer (COJ). For each group, two different sizes of identically pre-treated zirconia specimens were bonded together with RelyX Unicem 2 Cement. A total of 90 specimens were stored in distilled water at 37 degrees C for 24 h and then further assigned to three groups (n = 15/test group): short-term test, thermocycling for 5000 cycles, and thermocycling for 10,000 cycles. Bond strength was tested in shear mode and results were analyzed using two-way ANOVA, followed by one-way ANOVA and Tukey's HSD (alpha = 0.05). Failure mode and surfaces were analyzed with optical microscopy and SEM. X-ray diffraction (XRD) were used for t-m phase transformation and residual stress analysis on mechanically pre-treated AlN and COJ surfaces. Results: The mean bond strengths of AlN and COJ groups were not statistically different after thermocycling (p > 0.05). However, when compare to 24 h only the bond strength of the COJ groups decreased significantly after thermocycling (p < 0.05). Most of specimens in both AlN and COJ groups exhibited adhesive failure. Compressive stresses were detected on both mechanically pre-treated AlN and COJ surfaces, with significant differences in stress values. Conclusion: Following thermocycling, composite-zirconia bond strength of nano-structured alumina coating was comparable to that of tribochemical silica treatment.