Fatigue and fracture properties of yttria partially stabilized zirconia crown systems.

Objectives: The purpose of this study was to test in vitro the fatigue and fracture properties of the Zirconia Everest core material after being veneered with a sintered or a heat-pressed veneer material.

Methods: Fifty zirconium copings were made using Kavo Everest ZS-blanks and the CAD/CAM technology. These were divided equally into two groups. Group one was veneered by a heat-pressed material (IPS e.max ZirPress) and group two was veneered by a sintered material (IPS e.max Ceram). All the crown shapes were subjected to 50,000 cycles of cyclic loading in water between 20 and 200 N, at a rate of 1 Hz and then loaded dynamically at a crosshead speed of 1 mm/min, until failure. Specimens of the core and the veneering materials were characterized using X-ray diffraction (XRD) and secondary electron imaging (SEI).

Results: There was no statistically significant difference in the mean failure load (N+/-S.D.) between group 1: 2135.6+/-330.1 and group 2: 2189.9.1+/-317.6 (p>0.05). No difference was found in the Weibull modulus and characteristic failure load values between the two groups (p>0.05). The specimens displayed mainly cohesive failure within the veneering material. XRD of the zirconium powder before sintering revealed tetragonal and monoclinic phases while after sintering only tetragonal zirconia could be identified.

Significance: There was no difference in the fatigue properties of the Zirconia Everest core material following sintering or heat pressing of the veneering material (p>0.05).