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Abstract
During the past 40 years, porcelain fused to metal technique has been extensively used in fixed partial dentures. Although this technique has improved the demand for more aesthetic materials with high strength properties for fabricating FPDs. However; the public scare about allergic adverse side effects of dental alloys has accelerated the development of alternatives to metallic dental restoration, therefore numerous attempt have been made to develop all ceramic systems which eliminate metal infrastructure.(1) However; dental ceramics are brittle and their low fracture resistance and relatively low flexural strength still limit the possibility of manufacturing FPDs using all-ceramic frameworks. Recently, yttrium oxide partially-stabilized zirconia (Y-TZP), has been made available to dentistry through the CAD/CAM-technique. Yttrium-Zirconia ceramics have been shown to have excellent mechanical performance, and superior strength and fracture resistance compared to other ceramics . Since Y-TZP has attractive mechanical properties, it could be of interest in the manufacturing of all-ceramic bridges intended for placement in premolar and molar regions The idea of using CAD/CAM techniques for the fabrication of tooth restorations was originated with Duret in the 1970s. Ten years later, Mormann developed the CEREC-system, first marketed by Siemens, which enable the first chair side fabrication of restorations with this technology