title: The effect of post type and length on the fracture resistance of endodontically treated teeth.
abstract: BACKGROUND
  Few studies have been conducted to determine a correlation between the flexural modulus of metal and fiber-reinforced posts and the fracture resistance and failure mode of teeth restored with posts. Questions remain as to whether a longer post length or a post with a higher flexural modulus will significantly improve the fracture resistance of a tooth restored with a prefabricated post and core.
  
  
  OBJECTIVE
  The purpose of this study was to compare the fracture resistance and mode of failure of endodontically treated teeth restored with 3 different post systems, including 2 fiber-reinforced posts (Light-Post and Snowlight) and a stainless steel post (ParaPost XP).
  
  
  METHODS
  Seventy single-rooted premolars were sectioned at the cemento-enamel junction and then endodontically treated. Teeth were distributed into 7 groups. Three different prefabricated posts were cemented into a post space either 5 or 10 mm in depth, and composite resin (ParaPost ParaCore automix) cores were fabricated. A composite resin core group without a post served as a negative control. Specimens were loaded at 90 degrees to the longitudinal axis until ultimate failure occurred. An initial failure load and mode of failure were also recorded. Statistical analysis was performed for initial and ultimate failure loads of groups by using 2-way ANOVA (P=.05).
  
  
  RESULTS
  The groups with ParaPost XP posts demonstrated significantly higher initial and ultimate mean failure loads when compared with the fiber-reinforced post groups. The highest mean (SD) initial failure load was with the ParaPost XP group with a 10-mm post length (170.05 (60.08) N), and the lowest was with the Snowlight group with the 5-mm post length (62.85 (18.47) N).
  
  
  CONCLUSIONS
  The stiffness and the load to initial fracture of the teeth restored with ParaPost XP posts were higher compared with the fiber-reinforced post groups.
authors.affiliation: Department of Cariology, Restorative Sciences and Endodontics, University of Michigan School of Dentistry, Ann Arbor, Mich 48109-1078, USA.
authors.forename: John D
authors.initials: JD
authors.lastname: McLaren
authors.forename: Charles I
authors.initials: CI
authors.lastname: McLaren
authors.forename: Peter
authors.initials: P
authors.lastname: Yaman
authors.forename: Mohammed S
authors.initials: MS
authors.lastname: Bin-Shuwaish
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Dennison
authors.forename: Neville J
authors.initials: NJ
authors.lastname: McDonald
mesh_terms: D000704:Analysis of Variance; D001641:Bicuspid / Q000293:injuries; D003188:Composite Resins / Q000737:chemistry*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D005898:Glass; D006801:Humans; D011176:Post and Core Technique / Q000295:instrumentation*; D014082:Tooth Fractures / Q000517:prevention & control*; D019553:Tooth, Nonvital / Q000503:physiopathology*
chemical_list: D003188:Composite Resins; C009753:fiberglass