title: Influence of different posts and cores on marginal adaptation, fracture resistance, and fracture mode of composite resin crowns on human mandibular premolars. An in vitro study.
abstract: OBJECTIVE
  To evaluate marginal adaptation, fracture modes, and loads to failure of composite crowns with different substructures on root-canal-treated premolars.
  
  
  METHODS
  Forty-eight mandibular teeth with single root canals were selected and assigned to six equal groups: group I, untreated; group II, root-canal-treated (RCT), access cavity restored with composite resin; group III, RCT, ferrule (2 mm), no post, standardized composite resin crown (SRCC); group IV, RCT, ferrule, glass fiber post, SRCC; group V, RCT, ferrule, zirconium post, SRCC; group VI, RCT, ferrule, cast gold post, SRCC. All teeth were subjected to thermocycling and mechanical loading (TCML) in a computer-controlled masticator (1,200,000 loads, 49N, 1.7Hz, 3000 temperature cycles of 5-50-5 degrees C). Marginal adaptation was evaluated before and after TCML with scanning electron microscopy at x200 at the tooth-to-luting-composite (IF1) and the luting-composite-to-crown (IF2) interfaces. After TCML, all specimens were loaded to failure in a universal testing machine at 0.5mm/min.
  
  
  RESULTS
  A significant decrease in marginal adaptation was found in groups III and IV after TCML at IF1. A significant decrease was observed at IF2 in group V. Mean loads to failure did not differ significantly between the groups with SRCCs. Those of groups II, III, and IV did not differ from that of unrestored teeth. Half the specimens exhibited partial root fractures, independent of the substructures used. No deep or vertical root fractures were observed in any group.
  
  
  CONCLUSIONS
  All studied posts had a positive effect on marginal adaptation at IF1, but not on failure modes or loads to failure of composite resin crowns.
authors.affiliation: Clinic for Preventive Dentistry, Periodontology and Cariology, Center for Dental and Oral Medicine, University of Zurich, Plattenstrasse 11, 8032 Zurich, Switzerland.
authors.forename: Elisabeth J
authors.initials: EJ
authors.lastname: Stricker
authors.forename: Till N
authors.initials: TN
authors.lastname: Göhring
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000704:Analysis of Variance; D001641:Bicuspid; D003188:Composite Resins / Q000737:chemistry*; D003442:Crowns; D018772:Dental Marginal Adaptation; D019232:Dental Restoration Failure; D006801:Humans; D008334:Mandible; D011140:Polyurethanes / Q000737:chemistry*; D011176:Post and Core Technique; D018709:Statistics, Nonparametric
chemical_list: D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; D011140:Polyurethanes