الفهرس 
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Abstract
With the advent of the new high performance ceramic strengthen PEEK polymer into dentistry, it has become imperative to evaluate its performance in orderto confirm its long term prognosis as a fixed prosthesis. The purpose of this in vitro study was to compare the fracture resistance; and marginal and internal fit of PEEK versus Zirconia all-ceramic crowns.
A master metallic die was first fabricated to simulate a prepared mandibular right first molar with standardized dimensions, from which twenty four epoxy resin dies were reproduced, then epoxy dies were randomly divided into two equal groups, twelve specimens each. group I received twelve PEEK crowns, while group II received twelve Zirconia crowns.
For standardization, copings of group I (breCAM.BioHPP) and copings of group II (IPS e.max ZirCAD) were milled using the same CAD/CAM technology with the same thickness and morphology. Veneers of group I (BreCAM.HIPC) were fabricated using CAD/CAM technology and bonded to their corresponding dies, while veneers of group II were milled from wax using the same CAD/CAM technology with the same thickness and morphology of veneers of group I, then pressed over ZirCAD copings using (IPS e.max Zirpress).
All crowns were adhesively luted to their corresponding dies with Dual-cure, Self-Adhesive, Universal Resin Cement (RelyX™ Unicem). Then crowns were subjected to thermal cycling and mechanical cyclic loading corresponding to one year clinical service.
Subsequently, eight specimens from each group were loaded until fracture using universal testing machine to indicate the fracture resistance. While remaining four specimens from each group were embedded completely in transparent acrylic resin and sectioned into four quarters then viewed under stereomicroscope to evaluate the precision of fit. Then statistical analysis was carried out.
The results showed significant difference between PEEK crowns and Zirconia crowns in fracture resistance, where PEEK crowns can resist higher fracture loads. There was also a significant difference between PEEK and Zirconia crowns in precision of fit, where PEEK crowns had significantly better fit.