title: Reduced contraction stress formation obtained by a two-step cementation procedure for fiber posts.
abstract: OBJECTIVE
  In a previous study, a 60% increase in push-out strength was obtained in vitro with a two-step cementation of fiber posts, a procedure equivalent to the layering technique of composite restorations. The aim of this study is to find the rationale for this increase in push-out strength with finite element analysis (FEA).
  
  
  METHODS
  FEA models were created of the push-out test set-up of fiber posts cemented according to a one-step and two-step procedure and of the complete root with post. The failure loads of glass-fiber posts cemented with RelyX Unicem as obtained in a previous study were used as the load in the push-out FEA models. For the complete root model, a load of 100N was used. The stresses due to the shrinkage of the cement layer and the applied load were determined for the one-step and two-step procedure of the push-out test specimens and for the one-step procedure of the complete root.
  
  
  RESULTS
  Even though the load in the two-step push-out model was 60% higher compared to the one-step model, the combined stresses were comparable. The stresses due to shrinkage alone in the complete root approached or exceeded the bond strength of resin cements to dentin in the coronal and apical areas.
  
  
  CONCLUSIONS
  FEA of this test set-up explains the results of the in vitro study. Two-step cementation of fiber posts leads to a decrease in internal stresses in the restoration which results in higher failure loads and possibly in less microleakage.
authors.affiliation: Department of Dental Materials Science, ACTA, Universiteit van Amsterdam and Vrije Universiteit, Gustav Mahlerlaan 3004, 1081 LA Amsterdam, The Netherlands. L.Jongsma@acta.nl
authors.forename: Leontine A
authors.initials: LA
authors.lastname: Jongsma
authors.forename: Niek de Jager
authors.initials: Nde J
authors.lastname: Ir
authors.forename: Cornelis J
authors.initials: CJ
authors.lastname: Kleverlaan
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Feilzer
mesh_terms: D002484:Cementation / Q000379:methods*; D003198:Computer Simulation; D003481:Cuspid; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis / Q000379:methods; D003804:Dentin; D055119:Elastic Modulus; D020342:Finite Element Analysis; D005898:Glass; D006801:Humans; D058105:Polymerization; D011176:Post and Core Technique; D019279:Resin Cements / Q000737:chemistry*; D013314:Stress, Mechanical; D014092:Tooth Root
chemical_list: D019279:Resin Cements; C009753:fiberglass