Abstract: Objective: To explore the interaction effects of ferrule height and fiber post dimension on the fracture resistance of endodontically treated teeth. Methods: Sixty endodontically treated incisors were randomly assigned into four groups (n=15), and decoronated at 0 mm, 1 mm, 2 mm, and 3 mm to the proximal cemento-enamel junction (CEJ). The roots were restored using fiber posts with various dimensions. All specimens were subjected to fracture failure tests, loaded with an incremental force at an angle of 45° to the long axis of the roots. Fracture failure loads were recorded and analyzed using two-way analysis of variance (ANOVA), followed by the Tukey's post hoc comparisons. The fracture modes were investigated using fractographic analysis. Results: The interaction effects of ferrule height and post dimension were detected (P=0.006). Post dimension significantly influenced the fracture failure loads of specimens with 0 mm and 1 mm ferrule. No significant difference was found between 2# and 3# posts in 2 mm ferrule, or among all the dimensions of posts in 3 mm ferrule. Increasing of ferrule height decreased the probability of the debonding at the core/dentin interface. Conclusion: The effect of post dimension on fracture resistance decreases with the increasing of ferrule height. Increasing of ferrule height potentially postpones the processing of the ultimate fracture failure.

Key words: Interaction effect, Ferrule height, Post dimension, Fracture resistance, Post-restored teeth