BACKGROUND:Previous studies show that the fracture resistant force of endodonticaly treated teeth can be improved by post. But this idea has been controversial in recent years. Many scholars believe that the root canal preparation might weaken dental root the post increases the risk of tooth fracture. OBJECTIVE: To evaluate the fracture resistance ability of severe wedge-shaped-defect premolar to oblique loading, which was restored with fiber reinforced composite posts by different therapy methods. METHODS:A total of 50 human maxilary premolars were randomly divided into five groups, with ten teeth in each group. They were given folowing treatments: Group A: 10 untreated premolars; Rest 40 premolars of Groups B, C, D and E were prepared 1/3 bucco-lingual distance for artificial severe wedge-shaped defects at the buccal cervix. Group B: untreated severe wedge-shaped defects premolars; Group C: severe wedge-shaped defects premolars were endodonticaly treated, remaining dentin over hang above the wedge shaped defect, LuxaPost posts reinforced in buccal canal and lingual canal, LuxaCore composite resin restored dentin defect; Group D: severe wedge-shaped defects premolars were endodonticaly treated, LuxaPost posts reinforced in buccal canal and lingual canal, LuxaCore composite resin restored dentin defect, and then covered with ful metal crown; Group E: severe wedge-shaped defects premolars were endodonticaly treated, removing dentin over hang above the wedge shaped defect, LuxaPost posts reinforced in buccal canal and lingual canal, restored with LuxaCore composite resin, and then covered with ful metal crown. Fracture resistance of each specimen was measured in each group. RESULTS AND CONCLUSION: The fracture strength of each group were Group A (1 002.69±147.62) N, Group B (439.28±66.34) N, Group C (958.30±101.23) N, Group D (1 207.09±143.48) N, and Group E (1 056.44±139.30) N. Group D had the highest fracture strength (P < 0.01), while Group B had the lowest fracture strength (P < 0.01). There were no significant difference among the fracture strength of Group A, Group C and Group E. Our findings indicated that the fracture resistance of the severe wedge-shaped defected premolar can be improved by fiber reinforced composite post and dentin above wedge shaped defect remained.