title: The influence of elastic modulus mismatch between tooth and post and core restorations on root fracture.
abstract: OBJECTIVE
  To investigate the influence of elastic modulus mismatch between tooth and post and core restorations on mechanisms of root fracture.
  
  
  METHODS
  Three-dimensional mathematical models of a root filled maxillary premolar tooth with supporting periodontium were constructed. The tooth was restored with a cast Ni-Cr alloy or fibre-reinforced composite post and core that was bonded or nonbonded to dentine. In the nonbonded simulation, a nonlinear contact analysis was executed to simulate a friction and a potential sliding phenomenon in the interface between tooth and post and core. Risks of root fracture and debonding at the bonded interface were estimated based on the principal stress of the root and the shear stress on the interface, respectively.
  
  
  RESULTS
  The fracture risk of the bonded cast post and core was lower than that of the composite post and core, although the cast restoration exhibited eight times greater stress than the composite. The risk of root fracture based on the tensile stress of the tooth structures was higher with the bonded composite post and core than that with the cast post and core. These stresses doubled when the restorations were not bonded to the tooth structures. The risk of debonding of the cast post and core based on the shear stress was approximately twice that of the composite post and core.
  
  
  CONCLUSIONS
  The elastic modulus mismatch appears to be a factor responsible for the debonding of post and cores from root canals, with the potential to increase the risk of root fracture indirectly.
authors: Department of Removable Partial Prosthodontics, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
authors: M
authors: M
authors: Ona
authors: N
authors: N
authors: Wakabayashi
authors: T
authors: T
authors: Yamazaki
authors: A
authors: A
authors: Takaichi
authors: Y
authors: Y
authors: Igarashi
mesh_terms: D000328:Adult; D001641:Bicuspid / Q000293:injuries / Q000473:pathology; D002858:Chromium Alloys / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D003198:Computer Simulation; D001840:Dental Bonding / Q000379:methods; D003764:Dental Materials / Q000737:chemistry; D017267:Dental Prosthesis Design; D003786:Dental Pulp Cavity / Q000473:pathology; D019232:Dental Restoration Failure; D003804:Dentin / Q000473:pathology; D055119:Elastic Modulus; D020342:Finite Element Analysis; D017276:Friction; D005898:Glass / Q000737:chemistry; D006171:Gutta-Percha / Q000737:chemistry; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008954:Models, Biological; D011176:Post and Core Technique; D012387:Root Canal Filling Materials / Q000737:chemistry; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D014082:Tooth Fractures / Q000209:etiology*; D014092:Tooth Root / Q000293:injuries*; D019553:Tooth, Nonvital / Q000473:pathology*
chemical_list: D002858:Chromium Alloys; D003188:Composite Resins; D003764:Dental Materials; D012387:Root Canal Filling Materials; C009753:fiberglass; D006171:Gutta-Percha