Effect of No Ferrule on Failure of Teeth Restored with Bonded Posts and Cores

Four to five millimeters of remaining tooth structure coronal to crestal bone has been shown to improve failure resistance of endodontically treated teeth restored with cast posts and cores. Objectives: This study investigated the effect of the absence of ferrule on failure resistance of teeth restored with bonded fiber posts and resin cores. Methods: Twenty extracted maxillary anterior teeth were decoronated 18mm from their apices. Endodontic treatment was completed, leaving 4mm of gutta percha for apical seal. Stratified randomization was used to assign teeth into two groups of ten specimens. Teeth were embedded in acrylic resin with the coronal 5mm exposed. A 2mm ferrule was prepared on the Ferrule Group. The NonFerrule Group was further reduced, leaving 3mm of tooth exposed. Post spaces were prepared and prefabricated fiber posts (DT light-post, Bisco) were cemented using resin cement (Duolink, Bisco). Composite resin (Lightcore, Bisco) cores were made using core formers and crown preparations were completed with high-speed diamond burs. Preparation height for both groups was identical. Cast metal crowns were fabricated and seated using resin cement (Nexus 2, Kerr). A universal testing machine compressively loaded tooth specimens at a crosshead speed of 0.5cm min^-1, at an angle of 135^o to the long axis of teeth until failure occurred. Results: There was a significant difference (p < 0.001) between load to failure of the Ferrule Group (Mean = 615N, SD = 111) and NonFerrule Group (Mean = 173N, SD = 58). Root fracture was the predominant mode of failure for the Ferrule Group while debonding failures were predominant in the NonFerrule Group. Conclusion: A 2mm ferrule improves failure resistance of endodontically treated teeth restored with bonded fiber posts and resin cores. This study was partially supported by NIH-NIDCR Grant DE 13358.