الفهرس 
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Abstract
This in-vitro study was designed to evaluate the fracture resistance and fit of hybrid implant abutment crowns using two materials; monolithic lithium disilicate (e max) and hybrid ceramics (Vita Enamic) and using two different CAD/CAM systems; five axis milling system (Vhf CAM S1) and four axis milling system (Cerec mcxl)
Twenty-eight implant dummies were embedded perpendicularly in an auto polymerizing resin (techno vit). Twenty-eight hybrid implant abutment crowns crown simulating a maxillary first premolar were designed and milled using two CAD/CAM system. These hybrid abutment crowns were divided into two main groups according to type of material (n=14): lithium disilicate (emax) and hybrid ceramics (Enamic). Each group was sub-divided into two subgroups according to the CAD/CAM system used (n=7): five axis and four axis.
Internal fit of each group was tested using the replica technique before cementation.
Titanium bases were cemented to their respective abutment crowns using self-curing resin cement after surface treatment of the bonding surfaces. Titanium bases were surface treated using 50 µm aluminum-oxide while lithium disilicate and hybrid ceramic bonding surfaces were treated using 5% hydrofluoric acid to roughen the surfaces and increase surface area for bonding. Universal primer was applied to all bonding surfaces before cementation. All restorations were cemented to their respective Titanium bases using self-adhesive resin cement then screwed to their respective implant models. Screw access channels were sealed with Teflon and composite resin. A light microscope was used to measure the marginal adaptation before loading samples to fracture in a universal testing machine.
Data was recorded, tabulated and analyzed. Statistical analysis was performed with IBM® SPSS® (SPSS Inc., IBM Corporation, NY, USA) Statistics Version 22 for Windows.
Data was explored for normality using Kolmogorov-Smirnov and Shapiro-Wilk tests. Internal fit (µ), Marginal adaptation (µ) and Fracture resistance (N) showed normal distribution, so Two way-ANOVA was used to study the effect of different Ceramic materials and CAD/CAM systems on mean Internal fit (µ), Marginal adaptation (µ) and Fracture resistance (N) between groups.
Independent sample t-test was used to study the effect of different Ceramic materials on mean Internal fit (µ), Marginal adaptation (µ) and Fracture resistance (N) within each subgroup. Also, Independent t-test was used to study the effect of different CAD/CAM systems on mean Internal fit (µ), Marginal adaptation (µ) and Fracture resistance (N) within each group. Paired samples t-test was used to study the effect of cementation on mean Marginal adaptation (N) (Before and After).
By analysis of failure modes, all failed samples had fractures in the restorations without fractures in the Titanium bases.