Bond strength of veneering ceramics to zirconia framework

Objectives: The aim of this research was to investigate the bond strength between one type of zirconia substructure material and a variety of veneering ceramic materials using Shell-Nielsen bond strength test. Methods: Fifty Zirconia rods (ICE Zirkon) were milled in the green state then sintered. After firing, the rods (4mm diameter and 20mm height) were sand-blasted and ultrasonically and steam cleaned. The zirconia rods were randomly assigned to five veneering groups (n=10/group) and veneered with five ceramics (Matchmaker Zr, Cerabien ZR, Ice Zirconia Ceramic, IPS E-max Ceram, ZirkonZahn, Vita VM9) in 2 mm height and 2 mm thickness circumferentially around the rods and were thermocycled for 6,000 times (5/55 degrees C per 30 seconds). The specimens were placed in a special mold and loaded from the top of the zirconia rods with a ball point at a crosshead speed of 0.5 mm/min on a universal testing machine (Autograph) until fracture. The Shell-Nielsen bond strengths of the specimens were calculated and expressed in Mpa. The surfaces of the zirconia rods were evaluated under SEM following testing. The measurements were statistically analysed using 1-way analysis of variance test (ANOVA) and a Tukey multiple comparisons tests at significance level of á=0.05. Results: Mean bond strengths (MPa) for Cerabien ZR(42.2+,7,2), Vita VM9 (43.6+,6,4) were significantly higher than those Matchmaker Zr (38.6+8,1), Ice Zirconia Ceramic (35.3+,6,7), IPS E-max Ceram (36.2+,8.4) (P<.05). Conclusions: Shell-nielsen bond strength test to evaluate the core-veneer bond strength is a useful method to study the behavior of core veneered all-ceramic restorations when subjected to shear stresses. The zirconia veneer bond strength was affected by the type of the layering ceramic used. Coefficient of thermal expansion plays an important role on the bond strength of the veneering ceramic to the high strength core materials.