Rana A. Abdulatif And Cherif A.Mohsen,

ABSTRACT
Objective: The Aim Of This Study Is To Evaluate In An In Vitro Study, The Influence Of Straight And Angulated Implant In Lower First Molar And Upper Central Incisor On The Fracture Resistance And Failure Location Of Zirconia Crowns Fabricated Using CAD\CAMtechnology.

Materials and Methods: In This Study 20 Casts Were Used , Epoxy Resin Mixed And Loaded In The Sockets, Then Implant Was Loaded And Fixed Into All 10 Missed Lower Molar And 10 Upper Central Incisor. According To Position Of Implants The Samples Divided Into Two Groups Anterior And Posterior. Each Group Divided Into 2 Subgroups (5 Samples Each) According To The Degree Of Abutment Angulation Straight Abutment And 15 Degree Angulation. The Specimens Were Then Subjected To Compressive Loading By Universal Testing Machine (Shimadzu Autograph AG-50kNE, Shimadzu Co., Ltd, Japan) . The Force Required (N) To Cause Fracture Of The Crown, And The Mode Of Failure Were Recorded Using A Classification Designed For The Investigation.

Results: The Mean Values ?SD Of Loads At Failure (n -5) For Each Group Were As Follows In Newton (N): Posterior Straight Angle (A- I) 1361.6?245.3-,posterior 15 Angulation,(A-II) 1820.6?168 , Anterior Straight Angulation(B-I) 1117.5?112, Anterior 15 Angulation (B-II) 1435?135.9 0There Was Significant Increase In The Maximum Resistance At Angle 15 Compared With Angle 0 At Anterior E And Posterior Site.(p<0.05). Conclusion: Within The Limitations Of The Invitro Study, The Following Can Be Concluded: (I) Angulation 150 Abutment Increases Fracture Resistance Of The Overlaying CAM-milled Zirconia Single Crowns Than Straight Abutment. (II) All The Values Of Fracture Resistance Obtained In This Study Were Higher Than The Average Of Normal Occlusal Forces . (III) There Was Insignificant Difference Between The Posterior And Anterior Sites At Straight And Angulated.