The Chroma Study Of Glass Infiltrated Alumina Ceramic Restorations

All-ceramic restorations without a metal substructure allow for greater light transmission within the restorations, thereby improving the color and translucency of the restorations. Color is one of the important factors which affect the esthetics of all-ceramic restorations. The chroma of all-ceramic material is getting more and more attention. All-ceramic restorations which are many layers of the component of ceramics have an optical behavior very similar to that of dental hard tissues. However, as some light passes through the ceramic to abutment substrate or post-and-core, many factors may negatively affect the final aesthetic appearance of the all-ceramic crown, such as the thickness of the porcelain, the color of the background and the luting agent. With the reference to the latest literatures, we have not concentrated on the chroma study of those factors related to the final color of glass infiltrated alumina ceramic.In this study, we made background specimens simulating the post-and-core in common use, overlaid the different thickness of GI-II glass/alumina composite with the same thickness of veneering porcelain on these background specimens, and measured the shifts in color with JY9800 Whiteness and Color Meter. The primary purpose of this study was to investigate the effects of thickness of all ceramic core, background color and luting agents on the final color of glass infiltrated alumina ceramic samples.The results showed that:1. All-ceramic restorations were easier to reproduce the appearance of the natural tooth than metal-ceramic restorations. Comparing withmetal-ceramic specimens, the lightness of glass infiltrated alumina ceramic specimens against the different background was higher, but C* values were lower and hue became redder. It seemed easy for the human eye to distinguish the differences in color between them (AE>6.0NBS).2. The different color of background and the thickness of all-ceramic core influenced the final color of all-cermaic specimens to a certain extent. L values of all-ceramic specimens against all-ceramic background were highest, lower against metal alloy background, and lowest against resin background. When the thickness of all-ceramic core increased, L values decreased regardless of the type of background. Changes in a* b* values were small but showed a tendency to become greater.3. When the thickness of all-ceramic core was more than 0.5mm with the standard thickness of veneering porcelain, we couldn't take the color of background into consideration. If not, all-ceramic post-and-core was selected to improve the esthetics.4. Luting agents had an effect on the final color of restorations. The influence of composite resin was least, followed by glass ionomer cement and Zinc Phosphate cement. The color difference between with and without Zinc Phosphate cement could be identified by the eye. So to reducing the effect of luting agents, composite resin is recommended to all-ceramic restorations' adhesion.