Sara Alaa El-Din Mohammed Kamal, Shereen Adel Ameen And Zeinab Nabil Emam,

ABSTRACT
The Aim Of The Present Study Is To Evaluate The Marginal Accuracy And Fracture Resistance Of Milled Zirconia Restorations Using Two Finish Line Types, Two Veneering Techniques And Two Margin Designs.

Materials and Methods: Two Specially Constructed Metal Dies Were Machine Milled Representing Upper First Premolar Preparation To Receive All-ceramic Restoration. The First Die Had Deep Chamfer Finish Line; While The Second Die Had Shoulder Finish Line.A Total Number Of Forty Zirconia Copings Was Constructed. They Were Divided In Two Main Groups, 20 Samples Each (deep Chamfer And Shoulder Finish Lines) And Were Subdivided Into Two Equal Subgroups (10 Samples Each) (layering And Pressing Techniques) And Further Sub Divided Into Two Equal Sub Divisions (5 Samples Each) (zirconia Margin And E.max Margin). Zirconia Copings Were Constructed On Prefabricated Metal Dies Using The Zirkonzahn CAD/CAM System; Also CAD Wax Was Constructed For Press On Technique With The Same System.Either Layering Or Pressing Veneering Techniques Were Performed According To Manufactures Instructions.Marginal Accuracy And Fracture Resistance Were Used As Testing Methods.Scanning Electron Microscope Was Used To Detect The Mode Of Failure.

Results: Mann-Whitney U Test Was Used To Compare Between The Two Finish Line Types, Two Techniques As Well The Two Margin Types. It Was Found That No Difference When Using Either Finish Line Type, Veneering Technique Or Either Margin Designs On Marginal Accuracy Or Fracture Resistance Values. Conclusion: A More Conservative Finish Line Might Be Preferred With All Ceramic Restorations. The Pressing Veneering Technique Would Positively Influence The Longevity Of All Ceramic Restorations. When Fracture Resistance Is Considered, Zirconia Margin Would Yield To Outstanding Longevity Of All Ceramic Restorations.