The effect of ferrule length on fracture resistance of endodontically treated teeth restored with different post-and-core materials.

Objective To investigate the effect of a crown lengthening ferrule on the fracture resistance of endodontically treated teeth restored with two dowel-core systems.Methods Thirty-two extracted mandibular first premolars were each sectioned perpendicular to the long axis at a point 1.0mm occlusal to the buccal cementoenamel junction. Following endodontic treatment, the teeth were assigned randomly to 4 groups: cast Ni-Cr alloy dowel-core with no ferrule (Group A1), cast dowel-core with 2.0mm ferrule (Group A2), prefabricated carbon fiber-reinforced dowel-resin core with no ferrule (Group B1), and fiber-reinforced dowel-resin core with 2.0 mm ferrule (Group B2). Each specimen was embedded in a self-cured acrylic resin block from 2.0mm apical to the margins of a cast Ni-Cr alloy crown, and then loaded at 150 degrees from the long axis in a universal testing machine at a crosshead speed of 1.0mm/min until fracture. Data were recorded and analyzed using ANOVA and Fisher's exact tests, with а=0.05.Results Mean failure loads (kN) for groups A1, A2, B1, B2 were: 1.46 (S.D. 0.45),1.07(0.21),1.13(0.30),1.02(0.27). Teeth restored with cast Ni-Cr dowel-cores and 2.0mm ferrules demonstrated marginally, significantly lower fracture strengths,PP=0.04.There were significant differences between the two dowel systems in their fracture site patterns, P0.05.Conclusion Crown lengthening with a 2.0mm ferrule resulted in reduced fracture strengths for endodontically treated teeth restored using two dowel-core systems and cast metal crowns. The fiber-reinforced dowel-resin core system reduced the severity of the root fractures.