In vitro evaluation of the influence of ferrule effect and post length on the fracture resistance of endodontically treated teeth reinforced with glass fiber post

Background: The glass fiber post system with a similar elastic modulus to dentin is widely indicated to reinforce teeth after the endodontic treatment. Many studies emphasized the importance of ferrule effect and post length in strengthening endodontically treated teeth. However, the simultaneous influence of 2 factors on increasing fracture resistance is still controversial. Objectives: To evaluate the influence of ferrule effect and depth of glass fiber post insertion on the fracture resistance and the failure mode of endodontically treated teeth. Material and methods: In this in vitro study, sixty sound mandibular first premolars were performed endodontic treatment, and the crown was removed at 2 mm above the cementoenamel junction. Combinations of post lengths of 7 mm, 9 mm, and ferrule lengths of 0 mm and 2 mm formed four different groups consisting of 15 teeth each. The coronal sections were restored by composite build-up technique and received a full metal crown. The fracture load and failure pattern of each group were evaluated by applying a compressive load to the buccal surface of the tooth until the failure occurred. The data were analyzed with SPSS version 20.0. Results: The mean fracture load of 4 groups is 459.97 ± 115.92N, 495.96 ± 97.92N, 298.54 ± 82.46 N, 394.40 ± 88.67N, respectively. The difference in resistance to fracture between groups with ferrule and without ferrule or between groups with different post length insertions were statistically significant (p < 0.05). The number of favorable fractured teeth was highest in the group with ferrule effect and post length at 9 mm, whereas the lowest in the group without ferrule effect and with shorter post length. Conclusion: Both ferrule effect and post length play an important role in improving the fracture resistance to compressive load in endodontically treated teeth. The ferrule effect and the increased post length insertion create a more favorable fracture to restore. Key words: ferrule effect, endodontically treated teeth, fracture resistance, glass fiber post.