الفهرس 
Glass ceramicsOnly 14 pages are availabe for public view
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Abstract
The continuous search for better qualities and properties will never stop. As the advancements in dentistry continue, new materials and techniques are being introduced to the market to meet the increasing demand for superior esthetics and best physical properties. The integration of the restoration with the biological tissues and the achievement of normal function are the goals that clinicians and technicians aspire to achieve in everyday dental practice
Several types of all ceramic systems have been developed to meet the increased demands of patients and dentists for highly esthetic, biocompatible, and long-lasting restorations
With all improvements accomplished in the physical properties of ceramic blocks used, two main drawbacks of ceramics still exist. The chipping of the material in thin sections, either during the milling process or during try-in, caused by intrinsic brittleness of ceramic materials, and the high hardness relative to enamel resulting in wear of the opposing natural dentition. So there is a great need in determining which material is best in every clinical situation.
The aim of this in vitro study was to evaluate and compare the effect of aging on biaxial flexural strength, surface roughness and wear resistance of zirconia reinforced lithium silicate, polymer reinforced ceramic and resin nano ceramic to that of lithium disilicate to obtain optimum mechanical and optical properties. Each material was divided into two groups (n=10). Control group, and aged group. Extracted human premolars from patients in the age range from 15-20 years as part of orthodontic treatment were collected.
The control group was fractured in a universal testing machine to test the biaxial flexural strength.
All materials and enamel samples were weighted using a sensitive balance with an accuracy of 0.0001 grams. The mean surface roughness (Ra) of all samples as well as enamel samples were measured using an optical interference microscope.
The materials and enamel samples were mounted opposing each other in a wear-simulating device designed at the department of mechanical engineering Faculty of Engineering, Ain Shams University. The wear simulation was done for 10,000 cycles at a frequency of 120 cycle/min for a horizontal traveling distance of 1 mm under a load of 2 kg.
After the wear test, all materials and enamel samples were weighted and the differences in weight before and after the test were calculated. The surface roughness (Ra) of all materials and enamel samples were also measured and the difference in Ra was calculated. After that, all the samples were fractured in a universal testing machine to gather data about the change in biaxial flexural strength after aging.
Results showed that in wear resistance, the resin nano ceramic had the least amount of wear followed by zirconia reinforced lithium silicate and polymer reinforced ceramic. The lithium disilicate showed the highest amount of material loss.
While results for opposing enamel wear showed that resin nano ceramic had the best enamel response followed by zirconia reinforced lithium silicate, lithium disilicate and polymer reinforced ceramic but there was no statistical difference between the materials.
Regarding surface roughness zirconia reinforced lithium silicate had the roughest surface followed by lithium disilicate, polymer reinforced ceramic, while resin nano ceramic had the least surface roughness.
For the biaxial flexural strength tests in the control group, lithium disilicate had the highest results followed by zirconia reinforced lithium silicate, resin nano ceramic and polymer reinforced ceramic. After aging, the tested samples showed that there was a decline in the strength values of lithium disilicate to be comparable with zirconia reinforced lithium silicate but still it was the highest.