الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
Dental ceramics have varying degrees of translucency. The translucency of porcelain is dependent on how light scatters, absorbs, reflects and transmits through the ceramic material. This is dependent on the crystal number inside the core matrix, the particle size of the crystals and their chemical composition as compared to the incident light wave length. Consequently, matching dental ceramic translucency to natural tooth translucency is the optimal esthetic goal.
A new group of machinable ceramics has recently been introduced for CAD/CAM techniques, Zirconia-reinforced lithium silicate (ZLS) ceramics, with 8-10% by weight zirconium oxide incorporated in lithium disilicate matrix providing superior mechanical and optical properties when compared to Lithium disilicate glass ceramic.
In this studyten ceramic specimens were obtained for each material (A2 shade ceramic blocks), 5 of which were 1.5 mm thick and the other 5 were 1 mm thick to be veneered by 0.5 mm of the corresponding veneering material according to manufacturer’s instructions. All ceramic specimens were cemented to A2 composite resin specimens of thickness 1.5mm.
Spectrophotometric analysis was carried out for the forty ceramic specimens. Light transmission and light reflection were measured using spectrophotometer. Whereas, light absorption was calculated using the Beer Lambert’s law (A= - log T) where A is light absorption and T is light transmission.
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Light transmission
All Zirconia reinforced lithium silicate sub-groups (Sub-group Ia,Sub-group Ib, Sub- group IIa and Sub- group IIb) showed significantly higher mean value of light transmission than their corresponding Lithium disilicate sub-groups (Sub- group IIIa, Sub-group IIIb, Sub-group IVa and Sub-group IVb). Moreover, veneering showed significant increase in light transmission for both materials Sub-groups.
Light reflection
All Zirconia reinforced lithium silicate sub-groups showed significantly lower mean value of light reflection when compared to their corresponding Lithium disilicate sub-groups. Also, veneering showed significant increase in light reflection for both materials sub-groups.
Light absorption
All Zirconia reinforced lithium silicate sub-groups showed significantly lower mean value of light absorption when compared to their corresponding Lithium disilicate sub-groups.Veneering showed significant decrease in light absorption for both materials sub-groups.
Based on the results of our study the following conclusions can be drawn:
1. Translucency of Zirconia reinforced lithium silicate is better than that of Lithium disilicate.
2. Veneering improved optical properties for both Zirconia reinforced lithium silicate and Lithium disilicate.