title: Incidence of apical crack initiation and propagation during the removal of root canal filling material with ProTaper and Mtwo rotary nickel-titanium retreatment instruments and hand files.
abstract: BACKGROUND
  The aim of this study was to determine the incidence of crack initiation and propagation in apical root dentin after retreatment procedures performed by using 2 rotary retreatment systems and hand files with additional instrumentation.
  
  
  METHODS
  Eighty extracted mandibular premolars with single canals were selected. One millimeter from the apex of each tooth was ground perpendicular to the long axis of the tooth, and the apical surface was polished. Twenty teeth served as the control group, and no preparation was performed. The remaining 60 teeth were prepared to size 35 with rotary files and filled with gutta-percha and AH Plus sealer. Specimens were then divided into 3 groups (n = 20), and retreatment procedures were performed with the following devices and techniques: ProTaper Universal retreatment files, Mtwo retreatment files, and hand files. After retreatment, the additional instrumentation was performed by using size 40 ProTaper, Mtwo, and hand files. Digital images of the apical root surface were recorded before preparation, after instrumentation, after filling, after retreatment, and after additional instrumentation. The images were then inspected for the presence of any new apical cracks and propagation. Data were analyzed with the logistic regression and Fisher exact tests.
  
  
  RESULTS
  All experimental groups caused crack initiation and propagation after use of retreatment instruments. The ProTaper and Mtwo retreatment groups caused greater crack initiation and propagation than the hand instrument group (P < .05) after retreatment. Additional instrumentation with ProTaper and Mtwo instruments after the use of retreatment instruments caused crack initiation and propagation, whereas hand files caused neither crack initiation nor propagation (P < .05).
  
  
  CONCLUSIONS
  This study showed that retreatment procedures and additional instrumentation after the use of retreatment files may cause crack initiation and propagation in apical dentin.
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Erciyes University, Kayseri, Turkey. Electronic address: topcuogluhs@hotmail.com.
authors.forename: Hüseyin Sinan
authors.initials: HS
authors.lastname: Topçuoğlu
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Erciyes University, Kayseri, Turkey.
authors.forename: Salih
authors.initials: S
authors.lastname: Düzgün
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Erciyes University, Kayseri, Turkey.
authors.forename: Bertan
authors.initials: B
authors.lastname: Kesim
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Erciyes University, Kayseri, Turkey.
authors.forename: Oznur
authors.initials: O
authors.lastname: Tuncay
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D003786:Dental Pulp Cavity / Q000000981:diagnostic imaging / Q000293:injuries* / Q000473:pathology; D003804:Dentin / Q000000981:diagnostic imaging / Q000293:injuries* / Q000473:pathology; D004853:Epoxy Resins / Q000737:chemistry; D004867:Equipment Design; D006171:Gutta-Percha / Q000737:chemistry; D006801:Humans; D006813:Humidity; D007091:Image Processing, Computer-Assisted / Q000379:methods; D009532:Nickel / Q000737:chemistry*; D011859:Radiography; D019233:Retreatment; D012387:Root Canal Filling Materials / Q000737:chemistry*; D012389:Root Canal Obturation / Q000379:methods; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013696:Temperature; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*; D019227:Tooth Apex / Q000000981:diagnostic imaging / Q000293:injuries* / Q000473:pathology; D019553:Tooth, Nonvital / Q000000981:diagnostic imaging / Q000473:pathology; D019415:Torque
chemical_list: D003722:Dental Alloys; D004853:Epoxy Resins; D012387:Root Canal Filling Materials; C534916:epoxy resin-based root canal sealer; C040654:titanium nickelide; D009532:Nickel; D006171:Gutta-Percha; D014025:Titanium
keywords: Apical crack; retreatment; root canal