Effect of Location on Strength and Translucency of Multi-Layered Zirconias
Objectives: To examine how the biaxial flexure strength and the translucency change as a function of height in multilayered dental zirconias Methods: Ten cylinders with a 14.0 mm diameter (expanded for the shrinkage) from each of three multi-layered zirconia materials: e.max®ZirCAD MT-Multi, e.max®ZirCAD Prime and e.max®ZirCAD Prime were milled using PrograMill PM7 milling unit. Pre-fired cylinders were cut in a Buehler IsoMet 1000 saw to produce the top five layers of 1.6 mm thick specimens to produce 1.2 ± 0.2 mm fired specimens. The un-sintered discs were polished using 800 grit SiC. All discs from each layer were sintered at the same time according to the manufacturer's schedule. Specimens were measured using a Hunter Lab UltraScanVIS Spectrophotometer with a standardized white background and black background using glycerin. Yxy values were obtained for each disc specimen. Using the Y value from the black background and the white background, the contrast ratio was calculated by CR= Yblack/Ywhite. The disc specimens were loaded in a piston-on-three ball testing fixture detailed in ISO 6872. They were loaded at a loading rate of 0.5 mm/minute. The strength values were calculated by: σ = -0.2387 P(X-Y)/b2 where σ is maximum strength (MPa); P is fracture load (N), X and Y are loading constants derived from loading configuration and Poison’s ratio and b is thickness of specimen. Results: The means and standard deviations at each layer for the biaxial flexure strengths( Table 1) and contrast ratios (Table 2) were analyzed with ANOVA (α≤0.05) and are presented for each material below: Conclusions: Within the bounds of this study, all of the tested materials had the lowest strength values and highest translucency (lowest CR) in the incisal region (layers 1-2) while having the highest strength values and lowest translucency (highest CR) in the body region (layers 4-5).