الفهرس 
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Abstract
Summary
Two upper left central typodonts were prepared using dental surveyor for standardization, one prepared with horizontal preparation and the other one Verti prepared.
These two typodonts were scanned and then prototyped using 3D printing technology, resulting in 40 3D printed dies.
The printed dies were sprayed then scanned with DS Mizer extra oral scanner and the STL file exported to EXO-CAD in lab designing software to design the crowns.
Milling of the crowns were done from each group as per manufacturer instructions using 5 axis milling machine. Ten crowns from each group furtherly divided into (n=5) horizontally prepared and (n=5) vertically prepared crowns.
Crowns were retrieved and careful cleaning and inspection were done, then crowns were tried on their respective dies with careful margin detection.
Crowns were then cemented with transparent dual cure resin cement under intron loading device 3mn.
Measurement of color was done. Each crown was measured for L A B axis (Cie lab system): These samples received color measurements both prior to and following ageing using spectrophotometry. The specimens were subjected to color analysis using the CIE L*a*b* color space, and their corresponding values were determined using the color change formula. Measurement for all specimens for color difference (∆E) was executed in Agilent Cary 5000 UVic-NIR spectrophotometer.
After initial color measurements, samples were individually immersed in Thermocycler (SD mechatronic, feldkirchen Westerham, Germany) all crowns were subjected to cold water bath immersion for 30 seconds at 5 degrees and hot water bath immersion for 30 seconds at 55 degrees dwell time 10 seconds for 5000 cycles for 5 days equivalent to 6 months intra oral.
After the aging process, new color measurements were performed in the same way as described previously, the color stability of the restorations was calculated using the formula.
ΔE=√(L1-L2) +(a1-a2)2+(b1-b2)2
ΔE was the calculated between color after thermocycling and A2 color parameters of vita easy shade.
There was a significant difference between different groups (p<0.001). The highest value was found in Vita Suprinity (4.16±0.12), while the lowest value was found in Zircad (regular) (2.52±0.10). All post hoc pairwise comparisons were statistically significant (p<0.001) in horizontal preparations samples
There was a significant difference between different groups (p<0.001). The highest value was found in Vita Suprinity (4.47±0.05), while the lowest value was found in Zircad (regular) (2.51±0.14). All post hoc pairwise comparisons were statistically significant (p<0.001) in vertical preparations samples as well
The material and the preparation type have statistically significant impact on color change. The vertical preparations have higher values than horizontal preparations, yet the difference was not statistically significant except for vita suprinity.
Color changes from (A2) shade, both the material and the preparation design have significant interaction, for both horizontal and vertical preparations the highest value was in zircad reverse and the lowest value was in zircad regular group.
Both the vertical and horizontal preparation have significance, yet the vertical preparations have higher values than horizontal preparation and statistically significant. With highest value in vita suprinity and lowest in zircad regular.