Comparison of Contrast Ratio, Translucency Parameter, and Flexural Strength of Traditional and "Augmented Translucency" Zirconia for CEREC CAD/CAM System

Purpose: Tetragonal zirconia polycrystals (TZP) can be used via CAD/CAM technique as metal replacement for fixed partial dentures. However, its intense white color and high opacity may represent an aesthetic limit. New TZPs with a claimed higher degree of translucency were recently marketed. The aim of the study was to investigate contrast ratio (CR), translucency parameter (TP), flexural strength (sigma), Weibull characteristic strength (sigma(0)), and Weibull modulus (m) of three traditional (IPS e.max Zir-CAD, inCoris ZI, VITA In-Ceram YZ) and two increased translucency (inCoris TZI, VITA In-Ceram YZ HT) Y-TZPs. Methods: For flexural strength, ISO 6872:2008 was followed. Bars (N=40) were cut from pre-sintered blocks. Dense-sintering, finishing, and polishing were performed in order to obtain specimens of 15x4x1.2mm. Samples were tested with three-point bending setup in a universal testing machine. For CR and TP, specimens (N=10) were cut perpendicularly to the long axis from pre-sintered blocks. After the dense-sintering, specimens were finished and polished in order to obtain tiles of 12x15x1mm. CR and TP were measured with a spectrophotometer equipped with an integrating sphere. Results: No significant difference was found regarding flexural strength. A significant difference was found both for CR and TP among tested groups. VITA In-Ceram YZ HT and inCoris TZI showed the higher translucency. The difference was not statistically significant when compared with VITA In-Ceram YZ, and statistically significant when compared with IPS e.max Zir-CAD and inCoris ZI. Conclusion: The new "augmented translucency" TZPs showed higher translucency and similar flexural strength than "traditional" TZPs.