الفهرس 
Introduction.Only 14 pages are availabe for public view
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Abstract
The aim of this in vitro study is to examine the color stability of four different glass-ceramic materials with two different thicknesses: 1 mm and 2 mm thickness. The materials studied are IPS e.max Press by Ivoclar Vivadent, CeraMotion by Dentaurum and Rosetta SP by HASS Corporation which are lithium disilicate glass-ceramics and Celtra press by dentsply which is a zirconia reinforced lithium silicate glass-ceramic.
Two thicknesses were created from each of the four materials. Then, using a spectrophotometer and thermocycling (5000 cycles), color stability was assessed both before and after aging. 28 of each of the four different types of glass-ceramic materials indicated above, representing a total of 112 specimens, were made with standard dimensions of 1- and 2-mm thickness and 10 mm diameter. There were 14 specimens of each thickness for each material. In accordance with the finishing process, each group was splitted equally into two smaller sub-groups. The first sub-group’s specimens (n=7) were only glazed. The second sub-group’s specimens (n=7) were polished and subsequently glazed. Using digital software according to these dimensions, 3D virtual design was constructed then 3D-printed castable resin specimens were fabricated followed by spruing, investing and pressing.
All samples (n = 112) were measured for color stability on a grey background using a VITA easyshade spectrophotometer device. Each specimen was measured 3 times separately on the glazed surface with the tip of the device touching the specimen according to the manufacturer instructions. This procedure was repeated after thermocycling. The L, a and b coordinates were tabulated and then the mean was calculated for each separate coordinate. The VITA easy shade device was recalibrated every 10 measurement cycles.
Color formulas are designed to provide a quantitative representation of color differences between two objects within dental research. The most extensively used ΔE formula is derived from the CIE L*a*b* system, which approximates uniformed distances between color coordinates; ΔE*= [(ΔL*)2+ (Δa*)2 + (Δb*)2 ]1/2
All samples were aged through 5000 thermocycling cycles in a coffee solution. The coffee solution was made by combining 1 tablespoon of coffee with 177 mL of boiled tap water, as recommended by the manufacturer. Before filling the plastic containers, the coffee was allowed to sit for five minutes. Every 24 hours, fresh coffee was reintroduced to the plastic containers in the hot and cold baths. After 5000 total hot and cold cycles, coffee remnants were removed from the specimen surfaces by washing under running water, followed by rinsing under distilled water, and then drying with sterile gauze before measurements. All data were collected, tabulated and statistically analyzed.
Results
With glazing and ceramic thicknesses 1 mm as well as 2 mm, there was a statistically significant difference between ceramic types (P-value = 0.006, Effect size = 0.777) and (P-value = 0.001, Effect size = 0.994), respectively (emax showed the highest color change)
With glazing and polishing, ceramic thicknesses 1 mm, there was a statistically significant difference between ceramic types (P-value = 0.008, Effect size = 0.668), While with ceramic thickness 2 mm, there was a statistically significant difference between ceramic types (P-value = 0.005, Effect size = 0.742).