Youssef Y. Ashour, Samir I. Bakry , Sanaa H. Abd Elkadr And Fayzal Elabbasy,

ABSTRACT
BACKGROUND: Veneered All-ceramic Restorations Are Associated With A High Incidence Of Chipping And Veneer Delamination From The Inner Core. Monolithic All-ceramic Crowns Facilitate The Fabrication Process And Minimize Residual Stresses Between Core And Veneer. A New Material, Zirconia-reinforced Lithium Silicate (ZRL), Celtra Duo Was Recently Introduced For Fabrication Of Monolithic Anterior Crowns To Overcome The Aesthetic Drawbacks Of Traditional Zirconia And Also To Improve The Strength Of The Lithium Disilicate. Aim Of The Study: To Evaluate The Biaxial?flexural?strength Of CAD/CAM: Zirconia Reinforced Lithium Di Silicat And To Compare It With Lithium Silicate Glass-ceramic Crowns.

Materials and Methods: Thirty Monolithic Ceramic Specimens Will Be Fabricated And Divided Into THREE Main Groups; Group I: CAD/CAM ZLS Celtra Duo Milled And Polished, Group II CAD /CAM ZLS Celtra Duo Milled And Glazed & Group III: CAD/CAM Lithium Silicate Glass-ceramic (e.max CAD). For Evaluation Of The Biaxial?flexural?strength 30 Ceramic Disc Specimens (10mm Diameter ? 1.5mm Thickness) Ten Specimens From Each Material(N=10), Subgroups Ia, IIa, IIIa Will Be Fabricated According To The Manufacturers? Instructions And Thermocycled To Simulate One Year Clinical Service. Biaxial Flexural Strength Will Be Measured For The Same Specimens (Ia, IIa, IIIa). For Evolution Of Marginal Fit 30 Ceramic Crowns Will Be Fabricated, Ten Crowns From Each Material (N=10), Subgroups Ia, IIa, IIIa.