title: The Effect of Isthmus on Vertical Root Fracture in Endodontically Treated Teeth.
abstract: BACKGROUND
  Vertical root fracture (VRF) from apical condensation of gutta-percha is a common failure mode in endodontically treated teeth. Virtually all previous studies of VRF are limited to 1-canal roots. In this study, we consider experimentally and analytically VRF in roots with 2 canals.
  
  
  METHODS
  The interior root morphology in mandibular molar teeth extracted from patients due to VRF or other reason was examined from a series of polished horizontal cross sections. A 2-dimensional fracture mechanics analysis was used to determine crack growth from the canal surface to the outer root surface and evaluate the apical load needed to cause VRF, Fmax.
  
  
  RESULTS
  From a mechanistic viewpoint, the isthmus connecting root canals can be regarded as a natural weak plane or crack. The results expose the prime role of isthmus in reducing Fmax, from ≈ 50 N with no isthmus present to ≈ 10 N.
  
  
  CONCLUSIONS
  Two-canal mesial roots are much more prone to VRF than 1-canal distal roots. We suggest that VRF may occur during clinical condensation of gutta-percha in mesial roots of mandibular molars as well as other roots with canals connected by isthmus.
authors.affiliation: School of Mechanical Engineering, Faculty of Engineering, Tel-Aviv University, Tel-Aviv, Israel. Electronic address: herzl@eng.tau.ac.il.
authors.forename: Herzl
authors.initials: H
authors.lastname: Chai
authors.affiliation: Goldschleger School of Dental Medicine, Tel-Aviv University, Tel-Aviv, Israel.
authors.forename: Aviad
authors.initials: A
authors.lastname: Tamse
mesh_terms: D000328:Adult; D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D006171:Gutta-Percha; D006801:Humans; D008334:Mandible; D008875:Middle Aged; D008963:Molar / Q000033:anatomy & histology; D012307:Risk Factors; D018915:Root Canal Preparation / Q000009:adverse effects*; D014082:Tooth Fractures / Q000209:etiology* / Q000473:pathology*; D014092:Tooth Root / Q000033:anatomy & histology*; D019553:Tooth, Nonvital / Q000473:pathology*
chemical_list: D006171:Gutta-Percha
keywords: Crack; gutta-percha; isthmus; root canal; vertical root fracture