Effects of various ferrule lengths on in vitro fracture resistance of premolars restored using prefabricated fiber post-and-core system

Objective To investigate the effect of various ferrule lengths on the fracture resistance of endodontically treated teeth restored with prefabricated carbon fiber post-and-core system.Methods Thirty-two extracted endodontically treated mandibular first premolars were sectioned perpendicular to the long axis at a point 1.0 mm occlusal to the buccal cementoenamel junction(CEJ).All the prepared endodontically treated root models were divided into four groups according to the ferrule lengths from 0.0 mm to 3.0 mm with 1.0 mm interval each(Group A,B,C and D).After restoration with prefabricated carbon fiber post-and-core system,each specimen was embedded in a self-cured acrylic resin block from 2.0 mm apical to the margins of a cast Ni-Cr alloy crown,then loaded at 150 degrees from the long axis in a universal testing machine at the crosshead speed of 1.0 mm/min until fracture.Data were recorded and analyzed using ANOVA and Fisher's exact tests,with α=0.05.Results Compared with Group C and Group D,Group B demonstrated significantly higher fracture strengths(P0.05).Conclusions Crown lengthening with a ferrule length more than 2.0 mm resulted in reduced fracture strengths for endodontically treated roots restored with prefabricated carbon fiber post-and-core system and cast metal crowns.