الفهرس 
Marginal accuracy and Fracture resistance of milled Zirconia restorations using two veneering Techniques
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Abstract
The aim of the present study is to evaluate the marginal accuracy and fracture resistance of zirconia restoration using two finish line types, two veneering techniques and two margin designs. A total of 40 zirconia crowns were used. The samples were divided into 2 groups and two sub groups and two sub division groups; according to two finish line types, two veneering technique and two margin designs. Two specially constructed metal dies were machine milled representing upper first premolar preparation to receive all-ceramic restoration. The first die had deep chamfer finish line, while the second die had shoulder finish line. A total number of forty zirconia copings were constructed. They were divided in two main groups, 20 samples each. group (A): Samples with deep chamfer finish line. group (B): Samples with shoulder finish line. Samples of each group were subdivided into two equal subgroups (10 samples) according to the technique of veneer application. Sub group }: Veneering material was applied using layering technique. Sub group {u2161}: Veneering material was applied using press on technique. Each subgroup was further sub divided into two equal sub divisions (5 samples each) according to the type of the material at the restoration margin. Sub division }: Coping margin was made up of zirconia material (zirconia margin). Sub division {u2161}: Coping margin was cutback by 1 mm and IPS e.max was added cut back margin (e.max margin). Zirconia copings were constructed on prefabricated metal dies using the Zirkonzahn CAD/CAM system; Also CAD wax was constructed for press on technique with the same system. Either layering or pressing veneering techniques were performed according to manufactures instructions. Marginal accuracy and fracture resistance were used as testing methods. Scanning electron microscope was used to detect the mode of failure