Seif Eldin Mohamed Mounir, Lamia Sayed Kheiralla And Rana Mahmoud Sherif,

ABSTRACT
Statement Of Problem: Fixed Prosthodontic Dentistry Owns Many Updates Including Preparation Design, Luting Cements And A Great Variety Of Restoration Materials. One Of The Most Important Factors Influencingthe Success Rate And Longevity Of The Fixedrestoration Is The Preparation Design Including Many Parameters Specially The Convergence Angle Of The Tooth And How It Is Affecting The Retention Of The Restoration. The Type Of The Crown Material Which Is Shifted To High Esthetic Option Represented In All Ceramic Restorations With Variety Of Types And Techniques Of Manufacturing. Also We Cannot Forget The Leading Role Of The Luting Cement In The Success Rate Of The Fixedrestorations Which Is Its Main Function Is To Retain The Restoration In Place For Life Time Depending On Either Conventional Cements Or Self-adhesive Cements Or The Recent Bioactive.Aim Of Study: To Assess The Efficacyof Convergence Angle On The Retention Of E-max Restoration Bonded With Adhesive Bioactive Cement Vs Adhesive Resin Cements.Methodology: In This In Vitro Study, 40 Sound, Sterilized, Freshly Extracted Human Molar Teeth Free Of Caries, Cracks And Fractures Are Collected From The MIU Bank. Teeth Will Be Machine Milled By Surveyor At Standardized Degree Of Taper 10? Or 20?. Teeth Will Be Divided According To Different Degree Of Taper Into Two Main Groups; Group (1) 10? (n=20) And Group (2) 20? (n=20). E-max Crowns Will Be Constructed According Manufacturer Recommendations, And Then Each Group Will Be Further Subdivided Into Two Subgroups According To The Type Of Luting Agent Used For Cementation; Subgroup (C) E-max Crowns Will Be Cemented Using Ceramir Cement (n=10) And Subgroup (R) E-max Crowns Will Be Cemented Using RelyX Ultimate Adhesive Resin Cement (n=10). Universal Instron Testing Machine Will Be Used For Evaluation Of Retention Of Each Cemented Crown. Values Will Be Expressed In (N), The Investigators Will Code The Samples Into Numbers & Randomize Them Using Computer Guided Randomization. Two-way Analysis Of Variance (ANOVA) Will Be Used To Study The Effect Of Convergence Angle, Cement Type And Their Interaction On Mean Retention Force. The Significance Level Will Be Set At ? 0.05

Results: Among The Two Cement Types (Ceramir & RelyX Ultimate); Teeth Prepared With 10 Degrees Of Convergence Angle Showed Statistically Significantlyhigher Mean Retention Bond Strength Than Those Prepared With 20 Degrees Convergence Angle, While Among The Two Degrees Of Convergence Angle (10o & 20o); Crowns Cemented With RelyX Ultimate Cement Showed Statistically Significantly Higher Mean Retention Bond Strength Than Those Cemented With Ceramir Cement.Conclusion: Increasing The Convergence Angle To 20o Decreased The Retention Of E-max Crowns Significantl, The Mean Retentive Strength Of E-max Crowns Prepared With Two Convergence Angles; 10o & 20o And Cemented With Ceramir Bioactive Cement Was Less Than That Of Crowns Cemented With RelyX Ultimate Resin Cement.