Nesren M. Abo Elmagd Masry, Ahmed H Khalil And Rasha N M Sami ,

ABSTRACT
Statement Of Problem: All Ceramic Restorations Became A Popular Alternative To Esthetically Restore Missing Teeth. A Variety Of Different Cements Could Be Used For Cementation. Tooth Preparation With Different Convergence Angle Affect The Success Rate Of This Ceramic Restoration By Affecting The Cement Layer. However, The Quality Of The Selected Cement Cannot Be Evaluated Unless Determined After Being Subjected To Conditions Simulating Intraoral Stresses. Aim Of The Study: Was To Investigate The Route Of Failure Of Two Types Of Cement Lining Namely Glass Ionomer Conventional Cement, Rely X Ultimate Resin Adhesive Cement Under All Ceramic Crowns Fabricated From IPS E.max With Two Degrees Of Total Occlusal Convergence Namely, 10? And 18o. Materials And Methods Teeth Were Selected And Prepared By Computer Numerically Controlled CNC Milling Machine. A 5 Axis Line Scanner And Sirona Dental System Was Used For Ceramic Crown Fabrication, And Finally A (3D) Finite Element Model Was Constructed Under An ANSYS Environment. Fracture Resistance Was Measured With A Load Cell Of 6.5 KN By Instron Testing Machine. Two Way Analysis Of Variance ANOVA Test Of Significance Comparing Variables Affecting Mean Values (occlusal Convergence And Cement). One Way ANOVA Followed By Pair-wise Tukey?s Post-hoc Tests Were Performed To Detect Significance Interaction Between Subgroups. Statistical Analysis Was Performed Using Graph-Pad Statistics Software For Windows. P Values ? 0.05 Are Considered To Be Statistically Significant In All Tests.

Results: Regarding The Effect Of Occlusal Convergence Angle And Type Of Cement On Finite Element Analysis For IPS E.max Ceramic, Cement And Cortical Total Deformation There Was No Clinical Significance Difference Between The Two Types Of Cement At The Same Convergence Angle While Crowns, Root And Spongy There Is Moderate Clinical Significance Difference Between The Two Types Of Cement At The Same Convergence Angle. For Cement, Root, Crown, Spongy And Cortical Von Misses Stresses There Was A Clinical Significance Difference Between The Two Types Of Cement With 18o Occlusal Convergence Angle, Therefore 18oocclusal Convergence Angle Produced More Stresses On Cement Layer Than 10o Occlusal Convergence Angle. Regarding The Effect Of Cement Type On Fracture Resistance Of IPS E.max Ceramic Crowns, The Highest Bond Strength Was Obtained By Rely X Ultimate Cement, Which Was Statistically Significantly Higher Than Glass Ionomer Cement This Study Showed Less Prosperity For Cement Layer Failure And Crack Propagation.

Conclusions: Cementing IPS E.max -ceramic Crowns Using Adhesive Resin Cement Showed Superior Fracture Resistance Than Those Cemented Using Conventional Cement. Total Convergence Angle10ois Less Liable For Cement Layer Failure And Crack Propagation Than 18? Total Convergence Angle Of The Prepared Tooth In Order To Receive A Ceramic Crown.