الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
evaluation the stability of the color of different veneering restorations after being subjected to different firing cycles. Materials and methods: A total of 20 disc-specimens were constructed and veneered (12 mm diameter and 1.5 mm thickness). Samples were divided into four groups according to the type of core material into: gold-based alloy (n=5), nickel-chromium based alloy (n=5), lithium Disilicate ceramic (n=5) and a Zirconia-based ceramic (n=5) using veneer porcelain shade (A3). Repeated firings (3&5 firings) were performed for the specimens, and color differences (∆E) were determined using a spectrophotometer. Color changes (∆E) as well as ∆L, ∆a and ∆b values were calculated using Commissun Internationale de l’eclairge Lab (CIE-LAB) uniform color scale. Results: Results showed that core material, firing cycles and the interaction between the two variables had a statistically significant effect on mean (∆E). Nickel chromium core material showed the statistically significantly highest mean color change values following repeated firing cycles (∆E). This was followed by Zirconia core, then Lithium core samples. Gold core samples showed the statistically significantly lowest mean color change values (∆E). Conclusion: The mean color difference received following repeated firings (3&5 firing cycles) were perceivable and considered clinically unacceptable (∆E ≥ 3.7) for all tested groups.