title: Evaluation of Retention of two Different Cast Post-Core Systems and Fracture Resistance of the Restored Teeth.
abstract: BACKGROUND
  The survival of pulpless teeth restored with different post and core systems is still a controversial issue.
  
  
  OBJECTIVE
  This study compared the retention of two different post and core systems and also the fracture resistance of teeth restored with these systems.
  
  
  METHODS
  Eighty endodontically treated maxillary central incisors were sectioned perpendicular to the long axis at a point 2mm incisal to the cemento-enamel junction (CEJ) and then the root canals were obturated. The restored teeth were randomly divided into two equal groups of 40. One group was restored with Nickel-Chromium (Ni-Cr) post and core system and the other group with Non-Precious Gold alloy (NPG) system. For evaluation of fracture resistance of the restored teeth, the specimens (n=20 per each group) were mounted in acrylic resin blocks and a layer of polyvinyl siloxane was applied to cover the roots. Loads were applied at an angle of 45 degrees to the long axis of the teeth and measured with a universal testing machine. The axial retention values of the studied groups (no=20) were measured on an Instron testing machine at a crosshead speed of 0.5 mm/min. Statistical analyses were performed using SPSS version 19.00 and student's t-test (α=0.05).
  
  
  RESULTS
  Although retention failure load for Ni-Cr system was lower than NPG system, there was no significant difference between the two systems (p= 0.7). However, fracture resistance of the teeth restored with Ni-Cr post and core system was significantly higher than NPG group (p= 0.000).
  
  
  CONCLUSIONS
  There was no significant difference between the retention of the studied post and core systems. Although significantly higher fracture thresholds were recorded for Ni-Cr post and core group, the failure loads of both systems may rarely occur clinically.
authors.affiliation: Dept. of Prosthodontic, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran;
authors.forename: Amir Ali Reza
authors.initials: AA
authors.lastname: Khaledi
authors.affiliation: Students' Research Committee, School of Dentistry, International Branch, Shiraz University of Medical Sciences, Shiraz, Iran;
authors.forename: Shekufe
authors.initials: S
authors.lastname: Sheykhian
authors.affiliation: Students' Research Committee, School of Dentistry, International Branch, Shiraz University of Medical Sciences, Shiraz, Iran;
authors.forename: Arash
authors.initials: A
authors.lastname: Khodaei
keywords: Cast metallic post-core; Fracture resistance; Pulp less teeth; Retention