الفهرس 
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Abstract
This study evaluated color stability of two machinable restorative materials, Resin nano ceramics Lava Ultimate and Polyetheretherketone ceramics (Bio Hpp ) luted to teeth with adhesive cement (Relay –x cement) after immersion in different staining solutions(coffee ,tea, pepsi and distilled water as control group).
Forty freshly extracted sound human upper central incisor were collected, sterilized, cleaned then stored in normal saline at room temperature. Copper molds were used for production of acrylic molds. Teeth were placed into molds randomly. The resultant acrylic molds were marked on their bases with red permanent marker for group (A) denoting teeth used for Lava ultimate samples and black permanent marker for group (B) denoting teeth used for Bio hpp samples .Samples numbers were crafted on the acrylic molds sides denoting their subgroups, where samples immersed in distilled water took numbers 1-5, those immersed in coffee were numbered 6-10, samples immersed in tea were 11-15 and those immersed in Pepsi were 16-20.
Standardized preparations were made by the same practitioner. Axial walls were reduced 1.5 mm with5° – 6°taper, incisal reduction was1.5 mm and a 1 mm shoulder finish line was made then all sharp line angles were rounded .
Optical impressions of the completed tooth preparation were made using the cerec system with laser based intraoral scanner BlueCam .Direct scanning was made and scan was evaluated for all the preparation. The Lava ultimate and bio Hpp ceramic blocks were placed in position in the milling unit, the information was sent to the milling unit through a wireless connection. Then start milling icon was selected and milling was started. Lava ultimate crowns were milled.
All samples of all sub groups were cemented according to the manufacturer instructions under constant static load with translucent dual-polymerizing resin cement. Forty crowns were divided into two equal groups according to the materials used , each group was further subdivided into four subgroups according tothe used staining solutions (coffee, tea ,Pepsi and distilled water as control group) . Color measurements were performed using a calibrated reflectance spectrophotometer before immersion and after a month. Data was collected, tabulated and statistically analyzed using SPSS.
Statistical analysis of Gp (L) Lava ultimate showed that the highest mean values of color change (ΔE) was recorded for coffee treated samples (7.91±2.43) followed by tea treated samples (6.02±2.86), then Pepsi treated samples (4.87±2.62) and that the lowest mean values of color change (ΔE) were recorded for control samples (1.60±0.55) . Whereas samples of Gp (B) Bio hpp showed that the highest mean values of color change (ΔE) were recorded for coffee treated samples (7.35±2.73) followed by tea treated samples (3.73±0.46), then Pepsi treated samples (3.08±0.54) and that the lowest mean values of color change (ΔE) were recorded for control samples (1.44±0.6). There was no statistical significant difference of color change values (ΔE) between the tested materials .