الفهرس 
COVEROnly 14 pages are availabe for public view
 |  | from | 183 |  |  |
| | | from | 183 | | |
Abstract
One of the most difficult challenges in esthetic dentistry is obtaining an exact color match between natural teeth and an artificial restoration making the visual recognition of the inserted restoration a difficult task even for well-trained eyes. The achievement of an allceramic esthetic restoration that matches perfectly with adjacent teeth is the result of the interplay between two important optical factors: on one hand, the masking capacity of ceramics to block the background color with sufficient material thickness, and on the other hand, the amount of translucency the ceramic that will allow the natural background color shine throughout a translucent material and exhibit the most natural appearance. However, the final color result is unpredictable when the restoration is composed of different layers with unspecified thicknesses, which is the case for core veneered all-ceramic restorations. Recent developments in ceramic technology and evolutionary treatment methods have all increased the predictability of all-ceramic restorations. The introduction of partially stabilized zirconium dioxide to the dental field opened new design and application limits of all-ceramic restorations allowing a minimum framework thickness of 0.5 mm with the remaining thickness of the restoration used for building the ceramic veneer.
The following study was conducted to test the color reproduction ability of zirconia restorations veneered with CAD-on technique when using different core-veneer thickness ratios and different veneer translucencies.
A stainless steel die was machined to simulate an all-ceramic molar crown preparation with 1.5 mm rounded shoulder finish line
around the circumference, 7° occlusal convergence, and flat occlusal surface. Sixty zirconia (InCoris ZI) copings were constructed over the master die using the Cerec InLab CAD/CAM System, where the die was first scanned using the Cerec-3 infra-red camera, the restorations were then designed with InLab 3.88 software and finally milled in the InLab MC XL milling unit. The InLab 3.88 software was used to create the zirconia copings with three different thicknesses; 0.5 mm (n=20), 0.7 mm (n=20) and 1 mm (n=20). After completion of the milling process, complete sintering of the copings was done.
IPS e.max CAD blocks of different translucencies-HT and LT-were used for construction of the veneering caps using InLab CAD/CAM System, where the zirconia copings were first scanned using the Cerec-3 infra-red camera, the restorations were then designed with InLab 3.88 software and milled in the InLab MC XL milling unit. The InLab 3.88 software was used to create the IPS e.max CAD veneers with three different thicknesses; 1 mm (n=20), 0.8 mm (n=20) and 0.5 mm (n=20).
Low glass fusing porcelain (IPS e.max CAD Crystall/Connect) was used to create a homogenous bond between the copings and veneers. During the fusion cycle, crystallization of IPS e.max CAD was completed. After completion of the fusion process, the resulting restorations were used for color and translucency measurements on black and white backgrounds using spectrophotometer. Data were then statistically analyzed.
Results showed that change in core/veneer thickness ratio had significant over color change and that core/veneer thickness ratio, veneer translucency and interaction between them all hadsignificant effect over the absolute translucency measurements.