title: Influence of glass-fiber posts on the fracture resistance and failure pattern of endodontically treated premolars with varying substance loss: an in vitro study.
abstract: BACKGROUND
  It is unclear how the amount of substance loss affects whether the fracture strength of endodontically treated and crowned teeth is increased by post placement.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the influence of glass-fiber post placement on the fracture resistance of endodontically treated premolars with varying degrees of substance loss.
  
  
  METHODS
  Sixty-four extracted and endodontically treated mandibular premolars were divided into 4 test groups (n=16) depending on the number of residual coronal dentin walls that ranged from 3 to zero. Teeth in subgroups were either adhesively restored with composite resin without a post (-) or with an adhesively luted glass-fiber post (+). After receiving a 0.8-mm shoulder preparation, providing a ferrule of 0.5 mm, teeth were restored with complete metal crowns, which were cemented with glass ionomer cement. All specimens were subjected to dynamic loading in a masticatory simulator for 1.2 million loading cycles with a nominal load of 49 N at 1.2 Hz combined with thermal cycling (between 5 and 55°C, 30-second dwell time). Then specimens were quasi-statically loaded at 30 degrees in a universal testing machine until fracture. Data were analyzed with 2-way ANOVA, followed by multiple comparisons using Tukey HSD test (α=.05).
  
  
  RESULTS
  No specimen failed during masticatory simulation. Mean final fracture resistance ranged from 335.6 ± 39.7 N to 1064.9 ± 211.8 N. Two-way ANOVA revealed that both the number of residual coronal walls and post placement had a significant influence on the fracture resistance (P<.001). However, pair-wise comparisons of groups showed that in groups with 2 or 3 cavity walls, the post effect was not statistically significant (P=.378 and P=.175, respectively).
  
  
  CONCLUSIONS
  The fracture resistance of endodontically treated premolars was dependent on the number of residual coronal dentin walls. Placement of a glass-fiber post had a significant influence on the fracture resistance when fewer than 2 cavity walls remained but no significant influence when 2 or 3 walls were present.
authors.affiliation: Private Practice, School of Dentistry, Christian-Albrechts University at Kiel, Germany.
authors.forename: Jens T
authors.initials: JT
authors.lastname: Mangold
authors.forename: Matthias
authors.initials: M
authors.lastname: Kern
mesh_terms: D000704:Analysis of Variance; D001641:Bicuspid; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D003804:Dentin / Q000033:anatomy & histology; D005898:Glass; D006801:Humans; D011176:Post and Core Technique; D018709:Statistics, Nonparametric; D019228:Tooth Crown / Q000033:anatomy & histology; D014082:Tooth Fractures / Q000517:prevention & control*; D019553:Tooth, Nonvital / Q000473:pathology*
chemical_list: C009753:fiberglass