Amr Hussein Aziz , Hanaa Ibraheem Sallam And Rasha Nabil Sami,

ABSTRACT
Statement Of The Problem: Zirconia Hybrid Abutment On Implant Achieves High Mechanical Properties And Moderate Esthetic Requirements. The Increase Of Esthetic Demands Has Renewed Interest In The Search For New Materials With Enough Mechanical Properties And Better Esthetic Qualities Than Zirconia Like Lithium-disilicate Materials Which Has Been Used Recently For Construction Of Hybrid Abutments On Implants. Aim Of The Study: The Aim Of This Study Was To Evaluate The Fracture Resistance Of E.max CAD Implant Superstructures Cemented On Two Types Of Customized Hybrid Abutments Made Of Lithium-disilicate And Zirconia. Materials And Methods 14 Internal Connection Titanium Dummy Implants Were Embedded In Epoxy Resin Molds And Randomly Divided Into Two Groups ( N= 7 Each ) According To The Hybrid Abutments Material Used ; Group I : Yttria Stabilized Polycrystalline Zirconia (Y-TZP) (Katana Zirconia) And Group II: Lithium Disilicate Glass Ceramic E-max CAD .All Abutments Were Fabricated By The CAD/CAM Technique. 14 Monolithic Lithium Disilicate Glass Ceramic(e.max CAD) Crowns Simulating A Maxillary First Premolar Were CAD/CAM Fabricated And Cemented Onto The Hybrid Abutments. All Samples Were Compressively Loaded Under Axial Static Load Till Fracture Using A Universal Testing Machine With A Load Cell Of 5 KN At A Cross-head Speed Of 1mm/min. The Load Required To Fracture Was Recorded In Newton And Failure Modes Were Visually Analyzed. Statistical Analysis Was Performed Using Student T-test (P ?0.05 ). Frequent Distribution Of Failure Modes (%)was Performed By Chi Square Test (P<0.05).

Results: The Results Showed That E Max CAD Superstructures Cemented On Hybrid Zirconia Abutments Recorded Statistically Significantly Higher Mean Fracture Resistance Mean Values Than Those Cemented On Hybrid Lithium Disilicate Abutments. Regarding Failure Mode Results, All Superstructures Showed Catastrophic Fracture With Cracking And Chipping Of The E Max Cad Hybrid Abutments. On The Other Hand , Custom Made Zirconia Abutments Did Not Exhibit Any Crack Lines Or Actual Fractures. The Difference In Frequent Distribution Of Failure Modes (%) Between Groups Was Statistically Significant . Conclusions Fracture Resistance Of E.max CAD Implant Superstructures Was Affected By The Hybrid Abutment Material, With The Superiority Of Those Cemented On Zirconia Hybrid Abutments. All Tested Superstructures Could Withstand The Masticatory Forces In The Premolar Region In The Oral Cavity.