Background: Endodontically treated teeth often have a varying remaining coronal tooth structure, is an important factor in the successful of post-core with crown restoration.
Objective: This study compared the fracture resistance of pulpless teeth with variable amounts of remaining coronal tooth structure restored with fiber-reinforced composite posts and composite core.
Material and Method: Fifty extracted human premolars were endodontically treated and divided into 5 groups of 10 teeth each. Four groups were prepared having axial wall heights of 4 mm around the preparation circumferences. In 3 of the groups with axial tooth structure, mesial axial tooth structure was removed, mesial and lingual axial tooth structure were removed, mesial-lingual and distal axial tooth structure were removed. For the fifth group, all axial tooth structure was removed to the level of the prepared finish line. All 50 prepared teeth were restored with fiber-reinforced composite posts (FRC Postec Plus) and composite resin cores (Multicore Flow). Testing was conducted with a universal testing machine with the application of a static load to the lingual incline plane of buccal cusp at a crosshead speed of 5 mm/min at 45 degrees to the long axis of the tooth. The load at failure was recorded. The data were subjected to 1-way analysis of variance.
Results: The mean value + standard deviation for the failure load of group 1 to 5 were 237.48 + 81.87, 242.97 + 66.80, 257.67 + 70.42, 239.56 + 70.42 and 297.70 + 99.42 (N), respectively. There were no significant differences in the fracture resistance (p < 0.01). No root fractures occurred in any of the groups.
Conclusion: The varying remaining coronal tooth structure of endodontically treated tooth had no influenced on the fracture resistance when restored with fiber-reinforced composite posts and composite core.

Keywords: Endodontically treated tooth, Fiber-reinforced composite posts, Composite core, Fracture resistan