Osama S. Selim, Jihan F. Younis And Tamer A. Hamza,

ABSTRACT
Statement Of Problem: The Mechanical Properties Of Recently Introduced Zirconia Reinforced Lithium Silicate Materials As Full Anatomical Restorations Require More Evaluation. The Lack Of Documentation Studying The Effect Of Different Finish Line Curvatures On The Mechanical Behaviour Of Ceramics Necessitated Investigation. The Purpose Of This In-vitro Study Is To Compare The Fracture Resistance Of Recently Introduced Zirconia Reinforced Lithium Silicate To Lithium Disilicate Using Two Different Finish Line Curvatures.

Materials and Methods: Twenty-eight Crowns Were Milled And Fabricated Using CAD/CAM System On Epoxy Dies Duplicated From A Stainless-steel Master Die. They Were Divided Into 2 Equal Groups (n = 14) According To The Ceramic Material Type Used: Group I, Monolithic Lithium Disilicate (IPS E.maxCAD) And Group S, Monolithic Zirconia-reinforced Lithium Silicate (Vita Suprinity). According To The Finish Line Curvature; Zero And 3mm Curve, Each Group Were Subdivided Into Two Equal Subgroups (n=7). All Specimens Were Cemented On Epoxy Dies Using A Self-adhesive Resin Cement (TOTALCEM, Itena), And Then Loaded Until Fracture Using A Universal Testing Machine. Kruskal-Wallis Test Was Used To Compare Between The Two Ceramic Types. Mann-Whitney U Test Was Used To Compare Between The Two Finish Line Curvatures. The Significance Level Was Set At P ? 0.05. Hypothesis: The Two Different Finish Line Curvatures Will Affect The Fracture Resistance Of The Tested Monolithic Crowns

Results: With Both Ceramic Types, There Was No Statistically Significant Difference Between Mean Fracture Resistance Values Of The Two Finish Line Curvatures. IPS E.maxCAD Showed The Statistically Significantly Higher Mean Fracture Resistance Than Vita Suprinity. Conclusion: The Finish Line Curvature Had No Effect On The Fracture Resistance Of The Tested Ceramic Restorations. The Strength Of Tested Ceramic Is A Material Dependant Where IPS E.maxCAD Crowns Showed Higher Fracture Resistance Mean Values Than Vita Suprinity