Effect of two sintering protocols on translucency and flexural strength of different monolithic zirconia materials: An In vitro study

Abstract

Background: Dental ceramics and zirconia are increasingly being used with outstanding outcomes for various restorations such as fixed dental prosthesis, resin bonded FDPs, and implant restorations. Zirconia is a polymorphic ceramic that can be found in three various crystalline forms depending on temperature: monoclinic, tetragonal, and cubic. The monoclinic phase is stable at room temperature; unfortunately, its mechanical and optical properties are insufficient for clinical application; nonetheless, the tetragonal and cubic phases can be rendered stable at room temperature by applying stabilizing oxides. The multi-layered technology has shown an improvement in color of zirconia to mimic the natural teeth without affecting its mechanical properties. Aim of the Study: The aim of this In vitro study is to evaluate the effect of two sintering protocols: Conventional firing cycle and Speed firing cycle on translucency and Flexural strength of the novel color gradient zirconia and compare it to different monolithic zirconia material. Materials and Methods: 54 discs were constructed to be divided into 3 different groups each group sub divided to speed cycle group and conventional cycle group for materials: IPS e.max® ZirCAD® Prime, Katana ultra-translucent zirconia and BruxZir anterior, To compensate for sintering shrinkage, the zirconia samples were milled with dimensions bigger than the required final dimension. The discs were then sintered in a sintering furnace group conventional sintering and group speed sintering for each material. Results: Translucency for conventional firing, there was a significant difference between different groups the highest value was found in Katana UTML, followed by Zircad prime, while the lowest value was found at BruxZir and for speed firing there was a significant difference between different groups. The highest value was found in Katana UTML, followed by Zircad prime, while the lowest value was found at BruxZir. Flexural strength for conventional firing, there was a significant difference between different groups. The highest value was found in Zircad prime, followed by BruxZir, while the lowest value was found at Katana UTML; and for speed firing, there was a significant difference between different groups. The highest value was found in Zircad prime, followed by BruxZir, while the lowest value was found at Katana UTML. Conclusion: For all tested zirconia, zirconia samples sintered with the conventional sintering cycle showed a significantly higher translucency value than those sintered with the speed cycle. Katana UTML zirconia showed the highest translucency values while BruxZir zirconia exhibited the lowest values in both firing methods.