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Abstract
This study was conducted to evaluate the effect of finish line design on theMarginal fit, and fracture resistance of the Hybrid ceramic Vita Enamic. According to the sample size calculation, a total of 16 crowns were constructed. The samples were divided into two equal groups (n=8) according to the finish line design: group (A): 8 samples (n=8) Chamfer finish line design1mm (Ac). group (B): 8 samples (n=8) Shoulder finish line design 1mm (Bs). Two stainless steel dies were machine milled to simulate a tooth preparation for a ceramic crown of a mandibular second molarwith two finish line configurations 1mm chamfer and 1 mm shoulder. Each die was 6-mm in height, 8-mm in cervical diameter, 6mm in occlusal diameter and had a total occlusal convergence of 16o. Digitalization of both dies and milling of hybrid restorations was made using CAD-CAM technology .The stainless steel dies were duplicated into epoxy resin ones using Silicone impression material, and the marginal gap was evaluated on the stainless steel dies using digital microscope,while fracture resistance was measured using epoxy resin die with the corresponding hybrid restoration. The restorations were surface treated according to the manufacturer{u2019}s instructions, and cemented on the epoxy resin dies using self-adhesive resin cement, after 24 hours of storage in distilled water, the fracture resistance of the restorations was measured using universal testing machine with load of 5 kN and at a cross head speed of 1mm/min