Shear Bond Strength of Composite Cement to Lithium-Disilicate Glass-coated Zirconia Versus Alumina Air-abraded Zirconia.

Purpose: To compare the shear bond strength of composite cement to lithium-disilicate glass-ceramic coated zirconia vs to alumina air-abraded zirconia and to analyze the residual stresses on both of lithium-disilicate glass-ceramic coated zirconia vs alumina air-abraded zirconia specimens.

Materials and methods: One hundred eighty zirconia disks (diameters 10 mm and 5 mm, 4.5 mm thick) were divided into two groups: lithium-disilicate glass-ceramic coating followed by hydrofluoric acid etching and Monobond N Primer (LiDi) or alumina air-abrasion (AA). For each group, two different sizes of identically pre-treated zirconia specimens were bonded with Multilink Speed Cement. A total of 90 specimens were stored in distilled water at 37°C for 24 h and then assigned to three subgroups (n = 15/test group): 1. short-term test; 2. thermocycling for 5000 cycles; 3. 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 (α = 0.05). Failure mode and surfaces were analyzed with optical and scanning electron microscopy. X-ray diffraction was used to analyze t-m phase transformation and residual stresses on mechanically pre-treated LiDi and AA surfaces.

Results: The LiDi groups recorded higher mean bond strength than AA groups after thermocycling (p < 0.05). Thermocycling did not affect the bond strength of either LiDi or AA groups (p > 0.05). Most of specimens in AA groups exhibited mixed failure. Alumina air-abraded surfaces exhibited higher residual compressive stresses than did surfaces with a lithium-disilicate glass-ceramic coating.

Conclusion: Following thermocycling, composite-zirconia bond strength of specimens with a lithium-disilicate glass-ceramic coating was greater than that of alumina air-abraded specimens.