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 Premo-lars 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 Fiberposts 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 Compres-sion 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 Mul-tiple 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 Re-corded 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 Dif-ference Between Different Materials Was Insignificant.Conclusion:1.The Deep Chamfer Finishline Marginal Design Increases The Fracture Resistance Of Endocrowns Than Butt-joint Marginal Design.2. Endocrowns With Sufficientferrule 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 Fiberpost And Core Supported E.max CAD Crowns In Terms Of Fracture Resistance .