Optical and Mechanical Properties of Different Zirconia Generations

Objectives: To evaluate the effect of fatiguing and thermocycling on bi-axial flexural strength and optical properties of different zirconia generations as a function of thickness.
Methods: Third generation fully stabilized zirconia (FSZ, 5-6 mol% Yttria) and first generation partially stabilized zirconia (PSZ, 2-3 mol% Yttria) (Bruxzir, Glidewell) were evaluated. Specimens (14 mm diameter discs) were prepared to different thicknesses: 0.7 mm and 1.2 mm from each zirconia type and according to ISO 6872. A total of 4 groups (n=16/group) are tested before (baseline) and after fatiguing to 1.2 million cycles at 100N load with simultaneous thermocycling 5-55°C (Chewing Simulator, SD Mechatroniks). Translucency parameter (TP), contrast ratio (CR) and light blockage percentage are recorded using a spectrophotometer before and after fatiguing and thermocycling. Data will be analyzed by two- way ANOVA.
Results: Baseline bi-axial flexural strength of PSZ was higher than FSZ at both thicknesses. Baseline ranking from most to least translucent according to TP and CR measurements: FSZ (0.7 mm), PSZ (0.7 mm), FSZ (1.2mm), PSZ (1.2mm). Higher light blockage percentage was recorded in PSZ groups, 62%, 56% at 1.2 mm, 0.7 mm thickness respectively. FSZ had 60.2%, 52.5% light blockage at 1.2mm, 0.7 mm respectively. The 0.7 mm thickness group were more translucent and had lower light blockage percentage than the 1.2 mm thickness group. Post-fatiguing and thermocycling mechanical and optical properties are being collected.
Conclusions: Different generations of zirconia according to yttria concentration display different mechanical and optical properties. Third generation FSZ is weaker and more translucent than the first generation PSZ.