الفهرس 
Introduction .Only 14 pages are availabe for public view
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Abstract
Glass Ceramic restorations have gained fame and are now applied in daily practice. Their esthetics, durability, biocompatibility and ability to be machined, polished and glazedin short time made their use recently expanded, mainly due to their superior optical properties and the development of the cementation strategies. Porcelain laminate veneers of minimum thickness provide satisfactory esthetic results and conservative removal of tooth structure.
Clinicians and Patients are nowadays seeking esthetics with restorations of shade, shape and translucency close to natura teeth.
The current study evaluated the Translucency of different machinable CAD/CAD Lithium disilicate blockswith two thicknesses before and after aging.
Total of 60 ceramic discs were obtained in this study. The discs were divided according to the ceramic types into 3 groups:
group I: Ivoclar emax CAD
group U: Upcera CAD Blocks
group R: Rosetta SM CAD Blocks.
Each group was equally subdivided according to the thickness into Two sub-groups:
Subgroup A: 0.3 mm
Subgroup B: 0.7 mm
All Samples of Subgroup A & B were tested for translucency before and after hydrothermal aging using Vita Easyshade.
The Translucency parameters (TP) was calculated for each to assess translucency after obtaining the CIELAB coordinates with white and black background.
Results were tabulated and statistically analysed with R statistical analysis software version 4.1.3 for windows. Results showed material, thickness and aging all had a significant effect on translucency.
There was a significant difference between groups. Rosetta SM CAD showed the highest value of translucency, followed by IPS e.max CAD while the lowest value of translucency was found in Upcera CAD.
0.3 mm samples had a significantly higher value of translucency than 0.5 mm samples of all specimens.
Value of translucency measured before aging was significantly higher than value measured after aging.