| Endodontic treatment is performed often and that there is a high demand for the restoration of endodontically treated (ET) teeth. It has been suggested that ET teeth dry out over time and that the dentin in ET teeth undergoes changes in physic property. Therefore, they are less stiff and have lower rigid when loaded. Occlusal overload are distributed through the length of the root and generate stresses causing vertical root fracture and tooth loss. It has been suggested that ET teeth are more brittle and may fracture more easily than Non-ET teeth. Root fracture is the most serious complication. Metal posts have more risk of causing root fracture because of the higher modulus of elasticity. Fiber posts gained popularity recently .Their main proposed advantage was that they were more flexible than metal posts and had approximately (21GPa) the same modulus of elasticity (stiffness) as dentin (18GPa) and can decrease the incidence of root fracture. Teeth restored with less rigid posts trend have failures that are more likely to be restorable .When bonded in place ,it was thought that masticatory loading forces would be distributed more evenly in the root, resulting in fewer root fractures. Fiber-Posts are widely used in dental clinics these years,Fiber-Posts are composite materials. They are composed of fibers of carbon or silica surrounded by a matrix of polymer resin,usually an epoxy resin. According to the different fibers used,fiber-Posts can be divided into carbon-fiber Posts,glass-fiber Posts and quartz-fiber Posts. Fiber-posts have good flexure strength,tensile strength,biological safety,erosion resistance,aesthetic characteristic,radiopacity and can be easily removed from root canal. Fiber-Posts have a modulus of elasticity. Similar to dentine.The main advantage of the new biocompatible metal-free post is that it enables reconstruction of the destroyed tooth structure to its natural aesthetics. The physical properties of the metal-free post and the composite core are very close to those of dentin. They do not cause metal allergies or corrode. They offer good aesthetics in easily visible areas of the mouth. Finally, fiber-reinforced posts can be removed easily in case of an endodontic failure requiring re-treatment. The trend in clinical dentist is toward fiber posts, the dentists are generally favorable toward them Fiber-reinforced posts are relatively new, and data of different fiber-posts on their fracture resistance are not available yet.PURPOSE: Evaluation of the effect of 2mm ferrule designs on the fracture resistance of endodontically treated mandibular first premolar incorporating different fiber Posts (quartz posts; glass posts; carbon posts), composite cores .METHODS: The authors divided 36 first premolars into three groups according to the type of post they would receive: group A: quartz posts; group B: fiber glass posts; group C: carbon posts. We prepared teeth and cemented posts with Super-Bond C&B. After the specimens aged, For fracture testing, We placed the testing assembly in a universal testing machine and loaded each specimen to fracture on a 135degree angle at a speed of 1.0 mm/minute. For each specimen, we recorded the load to fracture (in Newton) and the load-displacement curve. All the results were analyzed by ANOVA, with the use of SPSS 13.0 software package. RESULTS : The median fracture values of groups were as follows: Group 1: 399.24±33.84N, Group 2: 220.32±23.98 N , Group 3: 358.11±22.82N. The quartz posts group showed a significantly higher level of fracture strength compared to the other groups, and the carbon posts showed a significantly higher level of fracture strength compared to the glass posts group (p<0.01). CONCLUSION: The quartz posts group showed a significantly higher level of fracture strength compared to the other groups, and the carbon posts showed a significantly higher level of fracture strength compared to the glass posts group (p<0.01),but the fracture model of the fiber posts allowed the possibility of re-preparation.
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