الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Enormous development in the dental field, and the continuous research in the scope of dental materials yielded the production of new dental ceramics. The new materials produced always look up to match ideal properties of natural teeth . So , they should be both mechanically sufficient and esthetically pleasing and in harmony with the human dentition.
A ceramic with these two essential qualities serves properly in the oral environment . However, No sufficient data is available on how long these materials will attain their smooth surface and how rough they can be after long time under function, which might jeopardize the success of the restoration, and in addition, damage the opposing dentition.
The present study was designed to assess and evaluate the wear of different zirconia types ( tetragonal and cubic) in addition to Zirconia reinforced lithium silicate against an enamel antagonist. Using glazing and polishing and a combination of both as different surface finishing methods to detect which produces the best wear resistance property. The results were compared to a control enamel group to detect how it might affect the daily clinical applications.
The Ultra-Translucent Multi-Layered (UTML) cubic zirconia and the Multi Layer (ML) tetragonal zirconia blanks were sectioned under coolant with dimensions 25% larger than the final dimension required to compensate for the sintering shrinkage using a low speed diamond coated saw. Each blank was vertically sectioned into a series of long blocks. Each block was fixed to an attatchment 90◦ angle to get cut into smaller blocks.
The final blocks were secured to an attatchment and Cut into slices of dimension (18x15x2.5mm) to produce the same dimensions of Celtra DUO specimens (14x12x2mm) after sintering shrinkage. The Celtra DUO size C14 blocks was sectioned to sliced of 2 mm to produce 14x12x2mm slices. CZ and TZ specimens each was sintered in the zirconia furnace according to the recommended manufacturer program. All specimens were confirmed to be accurate within 0.2 mm with a digital caliper.
Each group of the 3 (n=21): Cubic Zirconia (CZ) , Tetragonal Zirconia (TZ) and Zirconia reinforced Lithium Silicate (ZLS) was subdivided into 3 sub groups Polished(P) , Glazed(G) and Polished then Glazed (PG) (n=7).
CZ and TZ were polished using Zirconia polishing rubber diamond kit, and ZLS were polished using the Silicate Polishing rubber diamond kit. Specimens were cleaned in ultrasound device containing distilled water before glazing. CZ and TZ were glazed using CERABIEN™ ZR (FC Paste Stain) according to manufacturers instructions.While , ZLS were glazed using DENTSPLY Universal Overglaze (High Flu) as recommended by manufacturer.
The antagonist premolar cusps were selected according to Strict selection criteria : Recently extracted, Sound ,Youthful , Cusp angle ranging from 100-110° and cusp width 4mm ±0.2 . This was aided by using an intraoral scanner (3 shape TRIOS 3) and analysis by Dentalcad Galway 3.0 software.
Specimens were wear tested using a ROBOTA Chewing simulator against a sound buccal cusp of a human upper first premolar for 120,000 cycle, load 100 N to simulate 1 yr of clinical function, distance of 3mm motion and frequency of 1.6 HZ, Using 33% glycerine as lubricant. The upperc compartment consists of a chuck that held the half premolar. And the lower compartment contained a Teflon mold in wich the specimen was firmly secured to.
The samples were imaged before and after the wear testing and using a special software 3d images were processed and superimposed so that the volumetric change was calculated. The specimens’ surface topograghy was evaluated using optical profilometry by a camera attatched to a digital microscope to detect roughness change. Moreover, One specimen from each zirconia group underwent x-ray diffraction to determine the amount of zirconia phase transformation after wear. Imaging by SEM was used to demonstrate the wear pattern of the specimens.
The results of the volumetric loss revealed that the TZ had the best wear resistance property as a material, and that polishing provides more resistance to wear than glazing. ZLS showed the least wear resistance of all the 3 materials.
However , TZ showed some phase transformation according to the X-ray diffraction analysis. While CZ didn’t show a significant change.