الفهرس 
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Abstract
he task of restoring endodontically treated teeth is encountered almost daily. Endodontically treated teeth are known to present a higher risk of biomechanical failure than vital teeth. Posts are generally needed to allow clinicians to replace missing tooth structure and restore pulpless teeth. A post-and-core system is often required to provide retention and support for the restoration of teeth lacking coronal tooth structure. Posts are recommended to strengthen weakened endodontically treated teeth against intraoral forces by distributing torquing forces along the roots.
Aim of the study:
Comparison of the fracture strength and coronal leakage of endodontically treated teeth after insertion of zirconium, glass-fiber and titanium posts together with composite build up.
Material and Methods:
Ninety six human permanent incisors with mature apices were selected for the study. All the teeth were single rooted with single patent root canal of similar size and shape without any defect. The samples will be divided into 2 halves to be used in the 2 parts of the test (Fracture resistance and coronal leakage). Each part will be divided into 3 groups according to post type (Titanium, Glass fiber, Zirconia). Each group is divided into 2 sub-groups of irrigations (NaOCl, CHX).
All samples were endodontically treated and the clinical crown all samples were decoronated 1 mm coronal to cemento-enamel junction (CEJ) and standardizing the length of all roots to be 16mm. Post spaces were prepared to receive post in the canals then cementation to them. Composite core and all ceramic crowns are made in the fracture resistance test.
Fracture resistance test: A typical clinical model with a facio-lingual tooth inclination of 45o angle was chosen for fabrication of the fracture resistance test using a computer controlled testing machine [LRX-plus Llyod instrument ltd, Fareham, UK]. Failure loads were measured under a static loading test using the machine with a loadcell of 5kN and data were recorded using Nexygen computer software at a crosshead speed of 1 mm/min and at angle of 135° against the tooth axis. Failure manifested by audible crack sound and confirmed by sudden DROP along load-deflection curve recorded by Nexygen computer software.
Coronal leakage test: Coronal leakage was measured by fluid filtration test where all samples were sealed from their root side with cyanoacrylate adhesive to ensure perfect seal. Each root was then connected to the filtration apparatus for microleakage measurement. Then the system was allowed to equilibrate for 5 minutes before any measurement. After setting of the system, a small air bubble was introduced into the system by the microsyringe till reaching the centre of the micropipette. The linear movement of the air bubble was measured in millimeters knowing the volume of the micropipette. These readings were averaged and converted from mm/min to ml/min.
Results:
In fracture resistance test: Titanium posts recorded the highest fracture resistance with NaOCl irrigation (358.6 N±110) followed by glass fiber (216.9 N±26) then zirconia posts (214.2 N±81) with no significant differences with CHX irrigation; Titanium posts (360.6N±97), Glass fiber (244.6 N±21), Zirconia (230.1 N±24).
This may be due to the high strength properties of the titanium than glass fiber and the higher modulus of elasticity that results in lower stresses throughout the remaining dentin of tooth structure (22). Also post material with a higher modulus of elasticity induces more stresses on the post and less stress on the root.
In fluid filtration test: Zirconia post recorded the highest coronal leakage mean value with NaoCl irrigation (0.7 mL/min±0.16) followed by metal post (0.67 mL/min±0.15) while glass fiber post showed the lowest coronal leakage mean value (0.65 mL/min±0.19). There is a significance difference with CHX irrigation where the Glass fiber post recorded the highest coronal leakage mean value with CHX irriagation (1.2 mL/min ±0.22) followed by metal post (0.8 mL/min±0.1) while zirconia post showed the lowest coronal leakage mean value (0.7 mL/min±0.25).
Leakage may be due to that resin luting cement have lower elastic moduli compared to the 2 materials they join. Thus, a zone of highly concentrated loads and stresses is created. Glass fiber posts have elastic moduli lower than zirconia and metal posts, and their mechanical characteristics closely resemble dentin. Glass fiber systems might have distributed stresses over a wider surface and limited micro fractures inside the luting material. This may have resulted in less coronal leakage. The glass fiber showed the least coronal leakage than titanium posts may be due to that fiber posts allow the light transmission through fibers and resin matrix to a deeper penetration towards the apex more than titanium posts that prevent deeper penetration due to its opacity that may cause polymerization shrinkage or incomplete polymerization of the luting agent that leads to leakage.