الفهرس 
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Abstract
Statement of problem: Little quantitative and qualitative data exists on the full contour zirconia and lithium disilicate glass ceramic restoration wear against different ceramic restoration. Effect of fracture toughness, under wearing process, may vary according to the different antagonist.
Purpose: The purpose of this study was to assess the fracture toughness of different ceramic restorations influenced by wearing against different occlusal antagonists.
Materials and methods: 80 ceramic discs (13mm in diameter and 2mm in thickness) were divided into two groups; full contour zirconia (Zr) and lithium disilicate press on zirconia substrate (E.max) discs. Sixty antagonists were constructed.
The two groups were subdivided into four subgroups: -
Subgroup1 :(20) discs from each group wearing against extracted teeth. Subgroup2 :(20) discs from each group wearing against porcelain fused to metal. Subgroup3 :(20) discs from each group wearing against full contour zirconia. Subgroup4 :(20) discs from each group without wear.
Sample discs and antagonists were dynamically three-body loaded in dual axis chewing simulator with 49 N for 75000 loading cycles. Wear resistance for antagonist was calculated using surface roughness, height, and weight loss. Fracture toughness assessment for samples without wear and after wearing by different antagonist was measured using indentation fracture test. SEM for samples before and after wearing at x50 magnification were used. Fractography was applied using a digital camera to calculate fracture toughness.
Data were statistically analyzed with a 2-way analysis, followed by a Tukey test when showed significantly. Student t-test was done between main groups.
Results: E.max showed statistically significant higher wear rate than the Zr group. Teeth showed higher wear rate more than ceramic antagonist but the difference was statistically non-significant. The surface roughness for groups and subgroups were changed but the differences were statistically non-significant. SEM images after wear showed little scratch without cracks or flaws in the zirconia and E.max samples. Fracture toughness of ceramics without wear was the higher value than ceramic after wear and this was statistically non-significant. The zirconia group samples without wear and after wearing showed statistically significant difference while e. max group showed statistically non-significant.
Within the limitation of this in vitro study the following conclusions have been detected:
1- Full contour zirconia vs. lithium disilicate has more wear than full contour zirconia vs. full contour zirconia. The full contour zirconia has more wear resistance than lithium disilicate restoration.
2- No difference in wear value of human enamel, feldspathic porcelain and full contour zirconia restoration opposing ceramic restoration but human enamel was slightly more than other.
3- Full contour zirconia and lithium disilicate restorations exhibit acceptable wearing compatibility with the opposing feldspathic and full contour zirconia restoration.
4-The fracture toughness value for full contour zirconia and lithium disilicate glass ceramic are not affected by wearing with different antagonists but the full contour zirconia is affected more than lithium disilicate glass ceramic.