RESUMEN
<p><b>OBJECTIVE</b>To compare the fracture resistance and failure modes of endodontically treated human upper premolars restored with different post-core systems.</p><p><b>METHODS</b>32 extracted human upper premolars were endodontically treated and crowns were sectioned at 2 mm above the labial cement enamel junction (CEJ). The teeth were randomly and equally divided into 4 groups: Group A, teeth restored with cast metal post and metal crown; group B, Tenax Fiber White fiber post and metal crown; group C, EverStick fiber post 1.5 mm in diameter and metal crown; group D, EverStick fiber post 1.5 mm in diameter and add another 1.2 mm diameter EverStick fiber post and metal crown. All the teeth were embedded in acrylic resin blocks, and were subjected to a compressive load at 1 mm/min crosshead speed which delivered at a 45 degrees to the long axis until the first sign of failure was noted. The fracture load and the mode of fracture were recorded.</p><p><b>RESULTS</b>Fracture resistances of the four groups of restored teeth were not significantly different (P>0.05). However, fracture modes in fiber post groups were nearer to CEJ than cast metal post group.</p><p><b>CONCLUSION</b>Fracture resistance of endodontically treated teeth restored with EverStick fiber post is enhanced that it can meet the clinical need, although the flexural resistance of EverStick fiber post itself is the weakest. Fracture modes of all fiber post groups are more favorable than cast metal post group.</p>