Ahmed Y. El-Refaay, Manal R. Hassan And Raiesa M. Mohammed,

ABSTRACT
Objective: The Purpose Of This Study Was To Assess Fracture Resistance Of Endocrown Of Premolars Constructed Of Two Different Materials Namely IPS E.max CAD And Hybrid Ceramic Compared To Conventional Post And Core And IPS E.max Full Coverage Crown. Materials And Methods : Thirty Sound Extracted Human Single Rooted Premolars (N =30) Were Endodontically Treated. Standardized Preparations Were Done With 5 Mm Intracoronal Extensions Into The Pulp Chamber And Divided Into 3 Groups Of Each (n=10). Group A: Specimens Involved Endodontically Treated (ET) Premolars Restored With Glass Fiber Posts Cemented With Rely X Cement, Composite Cores Were Built Up And IPS E.max CAD Full Coverage Crowns (control Group) .Group B: Specimens Involved ET Premolars Restored With Hybrid Ceramic Vita Enamic Endocrown. Group C: Specimens Involved ET Premolars Restored With IPS E.max CAD Endocrown. Each Group Was Subdivided Into Two Sub-groups According To Marginal Design, 5 Specimens With 1.5 Mm Ferrule And 5 Specimens Without Ferrule. Specimens Were Subjected To Thermal Cycling (5000 Cycles) And Fatigue By Cyclic Loading (75,000 Cycles) In Order To Simulate A Clinical Service Time Of 6 Months And Were Mounted In A Universal Testing Machine(instron) And Then They Subjected To Vertical Compression Load Until Failure. Data Were Collected, Tabulated And Statically Analyzed). Two-way ANOVA Used To Show The Effect Of Different Groups And Design On Fracture Resistance (N) Followed By Multiple Comparison With Bonferroni Correction. Chi-square Test Used To Show The Effect Of Different Groups And Design For Failure Mode Analysis. Result: The Highest Fracture Resistance Mean Value Was Recorded For E.max CAD Endocrown With Ferrule Group (1409.62�255.01 N) While The Lowest Fracture Resistance Mean Value Was Recorded For E.max Crown Without Ferrule Group (723.48�43.46 N). Difference Between Different Treatment Modalities And Different Marginal Design Preparation Was Significant (p<0.05) While Difference Between Different Materials Was Insignificant. Conclusion:1.The Deep Chamfer Finish Line Marginal Design Increases The Fracture Resistance Of Endocrowns Than Butt-joint Marginal Design.2. Endocrowns With Sufficient Ferrule Were Found To Be A Successful Mean Of Restoring Mutilated Endodontically Treated Single Rooted Premolars.3.VITA ENAMIC And E.max CAD Endocrowns Are Better Than Fiber Post And Core Supported E.max CAD Crowns In Terms Of Fracture Resistance .