الفهرس 
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Abstract
Nowadays, the need of esthetics is highly demanded, the use of dental ceramics and zirconia, is increasing with excellent results for different restorations types. Zirconia is polymorphic ceramic, it can be found in 3 different crystalline forms; monoclinic, tetragonal and cubic. the mechanical and optical properties of the of zirconia differs according to the type of zirconia. The multi-layered technology has shown an improvement in color of zirconia to mimic the natural teeth without affecting its mechanical properties.
A drawback of conventional zirconia is the long-time sintering process, this became a problem with the evolution of ceramics and the increased use of single visit chairside restorations. It has been claimed that changing the sintering parameters have several effects on the structure of the zirconia and thus its physical properties such as translucency flexural strength.
Objective: This investigation was to test the biaxial flexural strength, optical properties of the novel color gradient zirconia using conventional and high-speed sintering and to test the effect of aging on them and compare them to lithium disilicate.
Methods: 35 discs were constructed to be divided into 3 different groups according to their materials; IPS e.max CAD, Katana TM Zirconia Ultra Translucent Multi- layered, IPS e.max® ZirCAD® Prime. The zirconia samples were milled with dimensions larger than the desired final dimension to compensate for the sintering shrinkage. Then, the discs were sintered in a sintering furnace according to the proposed sintering cycles in the specimen grouping.
Summary
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All samples were tested for translucency and color stability using
Aligent Cary 5000 spectrophotometer before and after aging.
All samples were tested for biaxial flexural strength using a universal testing machine before and after aging.
Results: There was a significant difference between different groups, IPS e.max ZirCAD Prime had the least translucency before and after aging, in both normal and speed cycles. It also has the highest biaxial flexural strength in both normal and speed cycles. Normal and speed cycles have no significant difference on biaxial flexural strength