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 with fiber posts of various dimensions. All specimens were subjected to fracture failure tests, loaded with an incremental force at an angle of 135° to the long axis of the roots. Fracture failure strengths were recorded and analyzed using analysis of variance (ANOVA), followed by Tukey's post hoc comparisons (α=0.05). The fracture modes were investigated using fractographic analysis.
Results: The interaction effect of ferrule height and post dimension was detected (P=0.006). Post dimension significantly influenced the fracture failure strengths of specimens with 0 mm and 1 mm ferrule. No significant difference was found between 2# and 3# posts in 2 mm group, or among all the dimensions of posts in 3 mm group. Debonding of the crown/dentin interface occurred in all specimens. And increasing of ferrule height decreased the probability of the debonding at the core/dentin interface.
Conclusions: 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.