Ahlam A. Othman , Hesham A. Katamish And Atef I. Shaker,

ABSTRACT
Statement Of Problem: Lack Of The Shock-absorbing Effect Of Periodontal Ligament Around Dental Implants Makes Them Highly Susceptible To Excessive Loads, Leading To Peri-implant Bone Loss And Implant Failure.

Purpose: The Aim Of This Study Was To Evaluate The Effect Of Implant Platforms, Abutment Designs And Crown Materials, On Strains Developed In The Implant Supporting Structures.

Materials & Methods: Thirty Titanium Fixtures Were Embedded In Thirty Especially Designed Mandibular Models In The First Molar Area. Titanium Or Customized Zirconia Abutments Were Fixed Over The Implants, Then Zirconia Or Lava Ultimate Crowns Were Fabricated And Cemented On Their Respective Abutments According To Experimental Groups. A Total Number Of 30 Samples Were Prepared. They Were Divided Into Five Groups ?6 Samples Each?? According To The Different Implant/abutment/crown Complexes: Group I: Switched Implant Platform With Two-piece Zirconia Abutment And Lava Ultimate Crown. Group II: Switched Implant Platform With Two-piece Zirconia Abutment And Zirconia Crown. Group III: Switched Implant Platform With Titanium Abutment And Lava Ultimate Crown. Group VI: Switched Implant Platform With Titanium Abutment And Zirconia Crown. Control Group: Regular Implant Platform With Titanium Abutment And Zirconia Crown. The Restorative Complex Was Fatigued In A Chewing Simulator Machine (ROBOTA). Strains Developed Around The Implants Were Measured Using Strain Gauges. Results Were Collected, Tabulated And Statistically Analyzed.

Results: The Highest Strain Was Observed In The Control Group With Regular Implant Platform (116.1 �m/m) In Comparison With The Other Four Groups With Platform Switching Concept. Within The Platform Switching Groups, There Was No Statistically Significant Difference In The Strains Generated Around The Two Abutment Designs Regardless Of Crown Materials. However, Lower Strains Were Developed Around Lava Ultimate Crowns (118.5 �m/m) When Compared To Zirconia Crowns (163.4 �m/m) Regardless Of Abutment Designs.

Conclusions: Platform Switching Concept And Softer (less Rigid) Crown Materials (Lava Ultimate Are Preferred In Implant-supported Crowns, Especially In High Stress Areas When Compared To Regular Platform And Zirconia Crowns. However, The Abutment Design Has No Influence On The Strains Induced In The Supporting Structures.