Background
major loss of natural tooth, fracture, incisors, tooth, trauma
FRAGILITY, DENTAL CARIES, AIDS, ENDODONTICALLY TREATED TEETH
The restoration of endodontically treated teeth is controversial and remains a challenge to the dental clinicians, as a result of major loss of natural tooth structure due to dental caries or trauma; which is mandatory for the retention of the coronal restoration. The remaining tooth structure is the most crucial factor for the good prognosis as they are devoid of mechanical properties including loss of strength, fragility as well as the liability to fracture [Endodontically treated teeth are traditionally restored with a post-core and crown foundation system which depend mainly on the design, material and modulus of elasticity of dental posts as they play a major role in retention and fracture resistance of coronal restoration of endodontically treated teeth [Posts are classified according to their material into metallic or tooth-colored posts. Tooth-colored posts are further classified into pre-fabricated and custom-made posts. Among the prefabricated type, fiber posts are the most appropriate to select as they acquire simple technique of application in addition to the optimum mechanical properties; dentin-like modulus of elasticity that aids in dissipation of occlusal forces and the decrease of incidence of root fracture [Fiber posts contain either carbon fibers or quartz fibers, embedded in epoxy or methacrylate resin matrix. The fibers are parallel to the long axis of the post with diameter ranging between 6 to 15 mm. While the number of fibers range between 25 and 35 per mmCustom-made tooth-colored posts include ceramic and zirconia posts. They are used when high esthetic demand is required in the anterior zone of teeth to prevent long term discoloration. However, these posts show difficult retrievability in the retreatment cases as the removal require rotary instruments which might lead to root fracture or perforation [Zirconia post and core system offers chemical stability and its similarity to natural tooth structure whereby the tooth-colored translucency of all-ceramic crowns that provides high stiffness and distributes stresses better to the root; providing greater clinical longevity, light transmission and radio-opacity as well as the promising esthetic restorative outcome to the patients [Grewal et al. and Khaldi et al. stated that the success of various post systems depend on length, diameter, design of the post, canal shape and preparation, ferrule, luting cement, technique of cementation along with its location in the dental arch and proper retention of the post is mandatory in order to sustain the vertical occlusal forces [Sughaireen et al. and Mou et al. recommended the optimum diameter of the post preparation to stay at one-third of root’s diameter or have 1:4 ratio approximately. This wide preparation of posts aided in resisting occlusal forces but led to root fracture [In spite of different statements concerning the effect of post space diameter on the fracture resistance of endodontically treated teeth, more information regarding fracture resistance and the effect of different post space systems/materials and diameters is required. This study aimed to evaluate fracture resistance of endodontically treated teeth, restored with two post-core systems in different post space diameters. The null hypothesis of this study was that there would be no significant difference between fracture resistance of endodontically treated maxillary central incisors, restored with glass-fiber posts and composite resin core and zirconia post-core one-piece restoration in different post space diameters.