الفهرس 
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Abstract
This study was determined the effect of different thicknesses of hybrid ceramics (vita Enamic and lava ultimate) and different luting agent shades on the perceived final color.
Forty disc shaped samples were fabricated (20 sample of each ceramic material). Samples of vita Enamic were represented in group V whereas samples of lava ultimate were represented in group L.
According to thickness samples of each group was divided into two subgroups; subgroup V1 & subgroup L 1 representing 0.5 mm thick discs and subgroup V2& subgroup L2 representing 1mm thick discs (10 samples each). Samples of each subgroup was divided into two classes according to the used luting agent shades (A3 opaque / translucent) that were represented in class V1O, V1T, V2O, V2T, L1O& L1T, L2O, and L2T (5 samples each).
Samples were obtained from CAD/CAM blocks cut with a water-cooled diamond at speed 200-5000rpm in 50rpm increments using a linear precision saw machine (Isomet 4000, Buehler, Illinois, USA). Samples of both materials were finished and polished using vita Enamic Technical Kit. After that all samples were cleaned by ultrasonic cleaner.
A Specially designed split copper mold was constructed for resin patterns build up. It consists of a split ring with a hole in the center 10 mm in diameter, 2 mm in thickness and a sleeve to hold the assembled ring. Composite resin shade A4 (Filtek Z250 XT, 3M ESPE, USA) was used to simulate the color of a dark underlying substrate. Composite were packed into the hole of the ring and light cured then finished and polished by 3M™ Sof-Lex™ Finishing and Polishing System. After that all composite discs were ultrasonically cleaned.
Glycerin was used to secure contact between samples of both tested materials to composite discs and color measurement were done by a portable spectrophotometer (VITA Easyshade Advance 4.0, Vita Zahnfabrik, Bad Säckingen, Germany) for all the samples and served as base line (total numbers of forty samples).
All Samples were removed from composite discs and ultrasonically cleaned and then dried using compressed air and stored in containers till cementation.
Vita Enamic samples were degreased using alcohol then etched with (5% hydroflouric acid gel) into the fitting surface for 60 seconds. Lava ultimate samples were sandblast with aluminum oxide grain size ≤ 50 μm at two bars (30 psi) until entire bonding surface appears matte. Then samples were rinsed by a copious amount of water for at least 5 seconds and dried using compressed air. Silane Primer (Silane coupling agent) was brushed on the treated surface according to the manufacturer instructions.
Composite substrate discs were pretreated by 37% phosphoric acid for 30 seconds then washed off with water for 30 seconds to remove debris and dried using compressed air for 10 seconds. A resin bonding agent (Tetric N-Bond Universal, Ivoclar Vivadent) was brushed and agitated for 20 seconds after that adhesive was dispersed with compressed air for 5 seconds and light-cured for 10 seconds.
Two different shades (A3 opaque and translucent) of resin cement (Rely X veneer, 3M ESPE, USA) were used for cementation. The pretreated surfaces of all samples were loaded with resin cements then adhered to composite substrate discs under constant static load of 0.5 kg to standardize the cement thickness and light cured for 30 seconds according to the manufacturer’s instructions. Curing was repeated for another 20 seconds from both surfaces to ensure complete polymerization of resin cement.