Mohamed S. Othman, Manal R. Hassan And Mohamed M. Shalaby,

ABSTRACT

Objectives: A Recently Introduced Pre-sintered Cobalt-chromium (Co-Cr) Alloy For Metal Ceramic Restorations Can Be Efficiently Processed With Computer-aided Design/computer-aided Manufacturing (CAD/CAM) Techniques. However, Little Or No Reliable Study Data Are Available Regarding The Marginal Fit And Bonding Ability Of Porcelain To Milled Co-Cr Alloys In Comparison To Conventional Casting Co-Cr Alloy. Aim Of The Study: The Aim Of This Study Is To Compare The Marginal Accuracy And Shear Bond Strength At The Interface In Porcelain Fused To Metal Crowns Made Of Cast Or Milled Cobalt Chromium.

Materials and Methods: For Marginal Accuracy Test, Twenty Anatomical Crowns (n=20) Were Fabricated Of Commercially Available Cobalt Chromium Alloy, 10 Crowns Constructed Using Conventional Lost Wax Technique Following The Manufacturer?s Instructions, Cast Cr-Co, And 10 Crowns Constructed Using Milling CAD/CAM Technique. The Crowns Were Seated On A Ni-Cr Die Which Was Fabricated After Duplication Of Prepared Mandibular Molar To Receive Cast And/or Milled Co-Cr Full Metal Crowns. After Sintering, Finishing And Polishing Of The Crowns, The Milled And Cast Crowns Were Checked For The Marginal Accuracy Under Scanning Electron Microscope At 75x Magnification. For Shear Bond Strength Test, Twenty Discs (n=20), 8 M Diameter With Thickness 1 Mm Were Fabricated Of Commercially Available Cobalt Chromium Alloy, (cast And Milled) And Will Be Divided Equally Into 2 Groups: 10 Discs Of Cast Co-Cr And 10 Discs Of CAD/CAM Milled Co-Cr .after Sintering And Polishing Of The Discs, Dental Ceramic Veneer 6 Mm In Diameter With Thickness 1 Mm Were Fused To The Cobalt Chromium Alloy Discs Following The Manufacture Instructions. The Veneered Discs Were Subjected To Shear Bond Strength Test By Universal Testing Machine. Data Were Tabulated And Statistically Analyzed With Student T-test Followed By Three Way ANOVA Test. P Values �0.05 Were Considered To Be Statistically Significant In All Tests.

Results: Best Fit Based On The Calculated Means �SD In �m, For All Measurement Points Surfaces Was In The Milled Group (17.55�7.5) While , In The Cast Group Was (19.20�7.8).Yet, Non-significant Differences Were Exist Between Marginal Fit Of Cast And Milled Crowns (p = 0.124) Although, The Two Groups Were Within The Acceptable Range Clinically. As Regarding Porcelain Veneer-metal Interface Bond Strength, Casted Discs Showed A Higher Boning To Porcelain (42.8�9.3) Than Milled Ones (33.8�8.8), (p<0.05). Conclusion: Crowns Produced By Using The Milling Or Sintering Techniques Can Be Considered Clinically Acceptable In Terms Of Marginal Gap And Showed Improved Marginal Fitting Adaptation Than The Conventional Casting Technique. The Bonding Ability, Of The Traditional Casting Produced Alloy-porcelain Veneer Interface, Was Higher Than That Of The Pre-sintered Milled Co-Cr Alloy.