الفهرس 
Composition of Dental porcelain:-
Predictable shade matching protocolOnly 14 pages are availabe for public view
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Abstract
Color stability is an important factor to ensure the long- term clinical success of ceramic restorations. There is a lack of information on how color is affected by fabrication procedures, such as the number of firings. The present study was performed to evaluate the influence of repeat firing cycles on the color of PFM, Empress2, and Zirconia samples. (A3) color was evaluated by spectrophotometer. Fabrication of PFM discs: Acrylic pattern was prepared into the mold to give 0.5mm thick acrylic discs. Discs were casted in nickal chromuim alloy. Opaque layer was applied in 0.3mm thickness using cylinder and plunger set up. Followed by application of body porcelain using the cylinder and plunger set up to give a standard sample thickness of 1.5mm. Fabrication of Empress discs: By lost acrylic method by using a copper mold. The acrylic patterns discs (1.5 mm) were sprued and attached to the base of rubber ring. The IPS Press VEST Speed powder, liquid and water were mixed according to manufacturer′s recommendation and poured slowly into the IPS silicone ring. After complete setting the ring was then burning to eliminate the acrylic pattern. Ingot of shade MOA3was pressed into the mold cavity. After finishing the press cycle, the ring was left to bench cool to room temperature. The pressed discs were then divested, finished, stained, and glazed. Conclusion 71 Fabrication of zirconia discs: Zirconia discs were fabricated by 5-motion system as manufacture, s instructions with diameter of 10mm width and 0.5mm thickness and finally veneered with porcelain veneering material to a thickness of 1.5mm. Grouping of the specimens: In this study a total of 30 ceramic specimens ( 10mm in diameter and 1.5mm in thickness) were used and divided into three main groups each according to the type of ceramic used (PFM, Empress, and Zirconia). The ceramic specimens were subjected to two additional firing cycles. The color coordinates of the ceramic specimens before and after additional firing cycles were detected using spectrophotometer. The color difference between different types of specimens after burning also was calculated. Results The effect of repeated firing cycles on the ceramic discs were, Empress 2 showed the highest decrease in L* value followed by zirconia ,and PFM showed the lowest decreased in L*value. Empress and zirconia both showed the statically significantly highest mean (Δa) values. PFM showed the statistically significantly lowest mean (Δa). Empress showed the statistically significantly highest mean ((Δb). There was no statistically significantly lowest mean (Δb) value. Empress showed the statistically significantly highest mean (ΔE). Zirconia showed statistically significantly lower mean (ΔE). PFM showed the statistically significantly lowest mean (ΔE).