title: Damage to root dentin during retreatment procedures.
abstract: BACKGROUND
  The aim of this study was to explore the influence of retreatment procedures on the appearance of defects on the root canal walls.
  
  
  METHODS
  Two hundred mandibular premolars were divided into 4 groups. One group was left unprepared. The rest of the teeth were prepared with ProTaper files up to size F4 and filled with gutta-percha and AH26. One group was left filled and received no further treatments. The filling material was removed from the remaining teeth either with ProTaper retreatment files or with Hedström files. Roots were then sectioned and inspected under a microscope. Data were analyzed with the nominal regression test (α = 0.05).
  
  
  RESULTS
  No defects were observed in the unprepared group. Retreatment groups showed significantly more defects than the initial treatment group (P < .05).There was no difference between the appearance of defects after retreatment with Hedström files and ProTaper retreatment files. The remaining dentin thickness and level of the root did not significantly influence the appearance of defects.
  
  
  CONCLUSIONS
  Retreatment procedures result in more defects than initial treatment. When assessing the outcomes of endodontic retreatment, the substantial damage to the root canal walls should be considered.
authors.affiliation: Department of Endodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands. hshemesh@acta.nl
authors.forename: Hagay
authors.initials: H
authors.lastname: Shemesh
authors.forename: Alida C
authors.initials: AC
authors.lastname: Roeleveld
authors.forename: Paul R
authors.initials: PR
authors.lastname: Wesselink
authors.forename: Min-Kai
authors.initials: MK
authors.lastname: Wu
mesh_terms: D001641:Bicuspid; D003762:Dental Instruments / Q000009:adverse effects; D003786:Dental Pulp Cavity / Q000293:injuries* / Q000601:surgery; D003804:Dentin / Q000293:injuries*; D006801:Humans; D008334:Mandible; D019233:Retreatment / Q000009:adverse effects; D018915:Root Canal Preparation / Q000009:adverse effects / Q000295:instrumentation*; D012390:Root Canal Therapy / Q000009:adverse effects* / Q000295:instrumentation; D014082:Tooth Fractures / Q000209:etiology*; D014092:Tooth Root / Q000293:injuries*