The evaluatation of shear bond strenght between zirconia sintered with two different methods substructure and superstructure after various surface treatments

The aim of this in vitro study is to evaluate the effects of various surface treatments and sinterization methods on the shear bond strength between microwave and conventionally sintered zirconia substructure and superstructure ceramics. Noritake Alliance Y-TZP presintered blocks were used to prepare zirconia substructures. 96 disc shaped specimens were fabricated using YenaDent CAM unit and were divided in 2 groups according to the sinterization methods (n=48). 48 specimens were microwave sintered and the other 48 specimens were conventionally sintered. The specimens were then divided into 4 groups according to the surface treatments applied (n=12). The groups for microwave sintered substructure specimens were as; MK: untreated (control group), M1: Al2O3 sandblasted, M2: liner applied, M3: Al2O3 sandblasting followed by liner application; and the groups for conventionally sintered substructure specimens were as; KK: untreated (control group), K1: Al2O3 sandblasted, K2: liner applied, K3: Al2O3 sandblasting followed by liner application. Cerabien CZR powder-liquid slurry was placed using a custom made index and fired on zirconia substructures and then the specimens were thermocycled (5 ? -55 ? C, 6000 cycles). All specimens were then subjected to shear bond strength test using a universal testing machine at 0,5 mm/min. Fracture patterns of all specimens were evaluated under an optical microscope and classified as adhesive, cohesive or combination of adhesive and cohesive fracture patterns. A specimen of each fracture pattern was further evaluated under a scanning electron microscope. Data were statistically analyzed using the Shapiro Wilk, Levene, Post-hoc Tukey HSD and Student?s t tests, Two-Way Variance Analysis and One-Way Variance Analysis (p ? 0.05). Within comparisons of shear bond strength values among microwave sintered substructure groups were statistically insignificant (p=0.113). Shear bond strengths of K3 group specimens compared to that of K1 group (p=0.015), Kk group specimens compared to the Mk group (p=0.004) and K3 group specimens compared to the M3 group were statistically higher (p=0.005). While adhesive fracture pattern was not demonstrated in any of the groups, cohesive and combined patterns was seen in all groups. In conclusion, within the limitations of this in vitro study Al2O3 sandblasting followed by liner application on conventionally sintered Noritake Alliance zirconia substructures may be preferred.