Background: Many post systems are available to clinicians, yet no consensus exists about which one is better in restoring endodontically treated teeth.Purpose: This study evaluated the fracture resistance of weakened roots restored with custom made metal posts, zirconia custom made posts and fiber reinforced custom made posts.Methods: Forty five maxillary central incisors had their crowns removed 2mm above the cemento-enamel junction and were endodontically treated. The canals were prepared for post fixation, and the canal walls were flared using a taper diamond bur. The prepared roots were randomly divided into three groups according to the post system. All posts were cemented with adhesive resin cement. For the fiber-reinforced resin posts, cores were built up using microhybrid composite. Specimens were loaded at 45 degrees in a universal testing machine at a crosshead speed of 0.5 mm/min until failure. The mode of failure was classified as favorable or unfavorable.Results: Teeth restored with cast posts had the highest fracture resistance. Fiber-reinforced resin posts failed at a compressive force comparable to clinical conditions, but most failures were repairable. Thinner root dentin walls significantly decrease the fracture resistance of endodontically treated teeth.Conclusion: Fracture resistance and mode of failure in anterior teeth with flared canals varied according to the type of post used to support a crown.