الفهرس 
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Abstract
Ceramic restorations are used to satisfy patients’ aesthetic criteria; since they mimic the appearance of the tooth and are biocompatible as well. Furthermore, they are considered as a substitute to metal-ceramic restorations due to their great color and translucency. However, compared to metal crowns, ceramics have inferior mechanical properties. A variety of dental materials have been made available in the last decade thanks to the advent of new particle-filled and high-strength ceramics, hybrid composites, and techno-polymers, widening the clinical relevance in fixed prosthodontics.
Additionally, due to their increased optical and mechanical qualities, which increase patients’ acceptance of dental restorations, all ceramic materials are now best utilized for aesthetic restorations. As a result, scientific study has increasingly concentrated on these materials, particularly lithium disilicate and zirconia, in an effort to focus attention on the characteristics, uses, and restrictions of the new players in the prosthetic scene.
Translucency is a highly significant quality of dental ceramic materials since natural enamel has high translucency. It is proven to be a key element in determining the esthetic outcome because it gives restorations a more natural appearance. Translucency is defined as a state halfway between perfect transparency and opacity. The dispersion of light, ceramic size and composition, refractive index, frequency of firings, porosity and thickness are a few parameters that affect how translucent ceramics are.
In dentistry, a significant trend toward all-ceramic restorations has been seen during the past 3 decades. It is clear that it can be extremely difficult for dentists to restore anterior cosmetic flaws. Thanks to the recent advent of superior ceramic materials, however, one of the biggest obstacles in clinical practice is still getting patients to agree that ceramic restorations mirror real teeth in terms of translucency. Choosing the suitable restorative material as well as the correct ceramic shade are essential for achieving the color of a natural tooth. Today, all ceramics restorations are beneficial for handling anterior esthetic challenges. This is attributed to its ideal optical and translucency characteristics. In spite of this, information concerning the comparative optical properties particularly translucency of various thicknesses of glass-ceramic materials are few in literature.
The objective of this study is to examine the translucency 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), translucency 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 were measured for translucency on a black and white backgrounds using a VITA easy shade. This equation was used to calculate the translucency parameter (TP):
TP = [(Lb Lw)2 + (ab aw)2 + (bb bw)2] ½.
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.