I find this to be an interesting read. MJ
Volume 41, Supplement 3, August 2013, Pages e24–e30
Full-ceramic systems can be produced by different techniques (layering, heatpressing, CAD/CAM) and have various compositions with different crystalline contents that may affect the optical properties of laminate restorations.
A total of 60 specimens were prepared from e.max Press, e.max CAD, Empress Esthetic, e.max Ceram, Inline, and ZirPress systems (A1 shade; diameter 10 mm; thickness 0.5 ± 0.05 mm). The L*, a*, and b* values, chroma and translucency (TP) of each system were recorded before and after ageing. The statistical analyses were performed by ANOVA, Tukey's tests and the paired sample t-test (p < 0.05).
The L* value of the shade guide was significantly different from those of the full-ceramic systems; however, there were no significant differences between the a* values of Ceram, Esthetic, Inline and Zirpress. There were significant differences between the b* values of the shade guide compared with the full-ceramics except for e.max Press. The L* values decreased, and the a* and b* values increased after the ageing process for all groups. There were no significant differences between the ΔE values of the ceramic systems (p > 0.05). The TP values decreased, and the chroma value increased significantly after the ageing process (p > 0.05). The chroma of the shade guide was found to be the highest.
None of the full-ceramic systems was able to match the color of the shade guide. The chemical structures of the ceramic systems were more effective for determining the optical parameters than the fabrication techniques. Ageing caused full-ceramics to become more opaque, darker, reddish and yellowish.