الفهرس 
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Abstract
The current study evaluated the marginal gap width of recently introduced monolithic high translucent zirconia crowns compared to Ips e.max CAD crowns with deep chamfer finish line with two different thickness.
A total of thirty-two (n=32) crown samples were constructed from monolithic highly translucent zirconia (n=16) and Ips e.max CAD (n=16) using CAD/CAM system on specially designed stainless die representing an all ceramic crown preparation for maxillary central anterior tooth.These dies were machined in a standardized manner using an engineering lathe machine (6mm inciso-gingival height, 120 total incisal convergence)
The preparation ended with either:
1- 0.8mm deep chamfer finish line.
Or
1. 1mm deep chamfer finish line.
The crown samples were divided into two equal groups:
group I: (n=16) monolithic highly translucent zirconia (Bruxzir anterior, glidwell)
group II: (n=16) lithium disilicate glass ceramic (Ips emax CAD, ivoclare vivadent)
Each group was subdivided into two equal subgroups:
Subgroup I: (n=8) deep chamfer finish line with 0.8 mm thickness
Subgroup II: (n=8) deep chamfer finish line with 1mm thickness
Each of the stainless-steel dies was powder sprayed with telescan spray then scanned by the identica scanner which showed a three-dimensional virtual image of the scanned die on the screen. Using EXOCAD software, a virtual die appeared on the screen to start the designing step.
The Roland Milling Unit was used to mill the anterior solid bruxzir blank to produce the CAD/CAM milled monolithic zirconia crowns.The CAM 5-S1 IMPRESSION was used to mill the IPS-emax CAD blocks to produce IPS-emax CAD crowns.
Each specimen was photographed using measuring Stereomicroscope (Nikon Eclips E600, Tokyo, Japan) connected with an IBM compatible personal computer using a fixed magnification of 45X.
Measuring marginal gap:
Total effect of ceramic type,
regardless to totally it was found that e.max group recorded statistically significant higher marginal gap mean value (85.21±6.55μm) than Zr group (56.84±11.83μm) as indicated by two-way ANOVA (P=<0.0001< 0.05).
Total effect of finish line thickness,
regardless to material group totally it was found that 1mm thickness subgroup recorded statistically non-significantly higher marginal gap mean value (74.66±10.48μm) than 0.8 mm thickness subgroup (67.39±7.9μm) as indicated by two-way ANOVA (P=0.1037> 0.05).
Results showed that the marginal accuracy was not significantly different between the two test groups. In other words, the narrower finish line thickness did not affect the marginal accuracy compared to the conventional finish line thickness.