الفهرس 
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Abstract
Esthetics and minimally invasive procedures are two main concepts that our patients today seek for and we should make sure our esthetic conservative crown has enough fracture resistance to withstand the occlusal forces.
This study was designed to investigate the effect of finish line configuration and cement type on the fracture resistance of yttrium partially stabilized zirconia copings with stress analysis of the marginal area.
Standardized four master stainless steel dies were manually machined all have the same dimensions of 5.5 mm crown height, 8mm gingival diameter, 6 degree taper except of different finish line configuration. The first one had a Knife edge finish line, the second a Chamfer finish line with 0.5 mm thickness, the third had a Deep chamfer finish line with 1 mm thickness and the last one had a Shoulder finish line with 1 mm thickness.
The master models were used to duplicate forty epoxy resin dies divided into four groups ten dies each according to the finish line, then each group was divided to two subgroups according to the cement type intended to cement the copings.
A total of forty zirconia (InCoris ZI) copings were constructed by Cerec InLab CAD/CAM milling machine, ten for each finish line group (n=10),five cemented with self adhesive resin cement (G-CEM)31 and five with glass ionomer cement (GC Fuji I)32.
Two KYOWA strain gauges of 1 mm length were attached one on the lingual and one on the buccal surfaces of the coping 1mm above the margin.
All specimens were subjected to a continuous compressive testing in a universal testing machine while measuring the margin strain in the same time, Fracture loads and strain measurements were recorded. Data were tabulated, statistically analyzed using Two-Way ANOVA test and Tukey pair wise comparisons test.
The results of this study revealed that finish line configuration and cement type had no significant effect on fracture resistance of TZP copings although had a significant effect on the strain produced in zirconia copings during load application.
Within the limitations of this study, the following conclusions can be drawn:
1. Different finish line configurations did not affect the fracture resistance of YPS zirconia copings whereas, knife edge finish line copings showed comparable loads with chamfer, deep chamfer and shoulder finish line copings.
2. Whatever the type of cement used either adhesive or conventional, the fracture resistance of YPS zirconia copings was not affected.
3. Knife edge margin copings measured the highest strain values than all other margin configurations.
4. Adhesively cemented copings using resin cement showed higher strain than conventionally cemented copings using glass ionomer cement.
Clinical recommendations:
1. Less invasive finish line configuration is the optimum choice for zirconia crowns as increasing the finish line thickness didn’t improve the fracture resistance.
2. Adhesive bonding or conventional cementation can be used safely with TZP copings.