الفهرس 
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Abstract
This work was designed for exploring the effect of autoclaving of the mechanical properties of dental monolithic zirconia crowns. Yttrium-stabilized-tetragonal-zirconia-polycrystal(Y-TZP) is used in dental crowns and implant prosthesis manufacturing due to superior strength and toughness comparing to other porcelains. Before implantation, autoclaving process is obligatory for sterilization, which badly effect the mechanical properties of the material. Y-TZP blocks were used in this study. Specimens were sterilized by autoclaving at 134 oC for 10 hours. The specimens were divided into two groups; sintered as the control group and autoclaved. The mechanical properties of both groups were measured. Results showed that control group hardness is higher than the autoclave group, XRD test shows that tetragonal phase is stable. Crown Fracture testing showed that the fracture resistance of the monolithic zirconia crowns increased (mean rank=24.00) when subjected to autoclaving, then that of control group (mean rank=8.5) The Aim of the thesis This thesis aims to obtain scientific information regarding the effect of autoclave used for sterilization on some physical and mechanical properties of monolithic zirconia restoration regarding 1. Surface roughness 2. Surface microhardness 3. Surface crystalline structure 4. Surface topography and chemical analysis 5.Fracture resistance of zirconia premolar crown.