الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Dental composite is considered one of the fastest developing materials in the dental field in the last few years. Dental composite is used in both anterior and posterior teeth. Its use in posterior teeth requires high mechanical properties to withstand forces of mastication without fracture.
Dental composite is exposed to several factors inside the patient’s mouth such as temperature changes, hydrolysis in saliva and pH changes which affect its mechanical and physical properties. In vitro studies tend to simulate these conditions to investigate their effect on the properties of dental composite.
Recently a new fiber-reinforced dental composite has been developed to increase the mechanical properties of dental composites in order to be used in posterior teeth to withstand forces of mastication without fracture.
The aim of this study was to compare the effect of aging in distilled water at 37°C for 1 day, 3months and 6 months on the flexural strength and fracture toughness of a fiber-reinforced composite (EverX Posterior), a nano-hybrid ceramic filled composite(IPS Empress Direct) and a nano-hybrid zirconia filled composite(Z250 XT).The three composites were chosen to have different types of fillers to test whether there will be a difference in the mechanical properties after aging.
For the flexural strength test, sixty three specimens were fabricated, twenty one specimens from each of the three dental composites. The twenty one specimens of each composite were then subdivided into three subgroups of seven specimens each according to the three aging periods.
For the fracture toughness test, sixty three specimens were fabricated, twenty one specimens from each of the three dental composites. The twenty one specimens of each composite were then subdivided into three subgroups of seven specimens each according to the three aging periods.
For both tests, the specimens were fabricated in teflonsplit molds to prevent the adherence of the composite to the mold to prevent any internal or external stresses during removal of specimens from the mold. The specimens were cured with a LED light curing unit .For the fracture toughness test a sharp blade was used to create a precrack in the specimen.
After storage of the specimens in an incubator at 37°C for 1 day, 3months and 6 months, each specimen was fractured in a Universal testing machine. Results were tabulated and analyzed using ANOVA and post hoc test (Fisher’s LSD).After the aging period of 6 months, for both tests, fractured specimens were viewed using the scanning electron microscope (SEM).
Results showed that the fiber-reinforced composite had the highest flexural strength and fracture toughness in all the three aging periods followed by the nano-hybrid zirconia filled composite and the least was the nano-hybrid ceramic filled composite. Although the mechanical properties of the fiber-reinforced composite decreased after aging, it still remained higher than the two nano-hybrid composites.