Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 3 2 2006 06 15 69 76 M. Sadeghi 2015 10 03 Statement of problem: It is yet unclear whether fiber-reinforced composite posts can enhance the mechanical properties and prevent vertical fractures of teeth under chewing loads. Purpose: The purpose of this study was to compare the fracture resistance and failure mode of endodontically treated teeth restored with three different post systems. Materials and Methods: Thirty-six maxillary canines were randomly divided into three groups (n=12). All teeth received endodontic therapy and one of three post systems of cast post-and-core, zirconia fiber post, and quartz fiber post. Cast posts-and-cores were cemented using zinc phosphate cement, fiber posts were luted with dual-cured resin cement, and composite cores were prepared. Compressive load was applied at a 135° angle to the long axis of the tooth at a crosshead speed of 1mm/min until fracture occurred. One-way ANOVA and Tukey-Karmer test were used to determine the difference of the failure loads between the groups (α=0.05). Results: The mean values (SD) for fracture resistance were 1631(803), 513(348) and 789(390) N in the cast post-and-core, zirconia fiber post and quartz fiber post groups, respectively. Teeth restored with cast posts-and-cores exhibited significantly higher resistance to fracture (P https://fid.tums.ac.ir/index.php/fid/article/view/84 https://fid.tums.ac.ir/index.php/fid/article/download/84/84