Sarah Alaa Hussien Mohammed, Gihan Abd-El-hady El-Naggar And Iman Salah El-Din Hamdy,

ABSTRACT
Statement Of The Problem: Conservative Approach In Modern Dentistry Aims To Restore The Missing Part Of Tooth Structure With A Material That Has Improved Mechanical And Esthetic Properties. One Of Recently Introduced Material For Construction Of Fixed Restoration Is Vita Suprinity. It Is A Glass Ceramic Reinforced With A 10% Zirconia. It Was Assumed That This Modification Improved The Mechanical Properties Of Fixed Restorations. It Is Not Yet Known Whether This Modification In The Microstructure Enabled The Material To Be Used Successfully With Conservative Tooth Preparation Using Feather Edge Finish Line Without Compromising Restoration Strength. Aim Of This Study: Evaluation Of The Fracture Resistance Of Zirconia Reinforced Lithium Silicate (vita Suprinity) Single Crowns With Two Margin Geometries (feather Edge And Chamfer Edge) Under Thermal And Cyclic Loading.

Materials and Methods: A Total Of Twenty Six Samples (epoxy Resin Dies) Were Used In The Present Study (n=26) That Were Divided Into Two Groups (n=13 For Each Group). These Epoxy Dies Were Duplicated From Two Stainless Steel Dies, One Of These Dies Was Prepared With Chamfer Finish Line And Other Was Prepared With Feather Finish Line. Then Scanning Of Stainless Steel Dies Was Carried Out For Milling Of Vita Suprinity Crowns With Two Finish Line Configurations. After That Crowns Were Cemented To Epoxy Dies And Then Exposed To Thermo-mechanical Aging That Was Repeated For 37,500 Cycles Which Simulate 3 Months Of Clinical Usage. Then Fracture Resistance Test Was Carried Out Using A Computer Controlled Universal Testing Machine With A Loadcell Of 5 KN And Data Were Recorded Using Computer Software.

Results: It Was Found That, The Chamfer Finish Line Group Recorded Statistically Non-significant Higher Fracture Resistance Than The Feather Edge Group At (p Value>0.05).

Conclusions: Feather Edge Margin Geometry Is A Promising Conservative Alternative To Chamfer Margin When It Is Used For Construction Of Zirconia Reinforced Lithium Silicate (vita Suprinity) Crowns Without Adverse Effect On The Fracture Resistance.