title: Cyclic fatigue resistance of D-RaCe, ProTaper, and Mtwo nickel-titanium retreatment instruments after immersion in sodium hypochlorite.
abstract: OBJECTIVE
  The aim of this study was to investigate the effect of immersion in sodium hypochlorite (NaOCl) on cyclic fatigue resistance of three different rotary nickel-titanium (NiTi) retreatment files.
  
  
  METHODS
  A total of 90 new ProTaper, D-RaCe, and Mtwo retreatment files were tested. Thirty files of the same brand were randomly assigned to two groups (n = 15). Group 1 was no immersion (control group) and 16 mm of group 2 instruments were immersed in 5 % NaOCl at 37 °C for 5 min. All instruments were then tested for cyclic fatigue. Resistance to cyclic fatigue was determined by counting the numbers of cycles to failure in a 60° curve with a 5-mm radius, recording the time in seconds to fracture. Data were analyzed by two-way analysis of variance.
  
  
  RESULTS
  Resistance to cyclic fatigue decreased significantly for D-RaCe retreatment files after immersion in NaOCl. ProTaper and Mtwo retreatment files were not affected from immersion to NaOCl. D-RaCe retreatment instruments showed better cyclic fatigue resistance than ProTaper and Mtwo retreatment instruments, and the difference was statistically significant (p < 0.05). There was no significant difference between ProTaper and Mtwo retreatment instrument groups (p > 0.05).
  
  
  CONCLUSIONS
  D-RaCe retreatment instruments had the highest cyclic fatigue resistance among retreatment files tested in this study, but immersion to NaOCl decreased the cyclic fatigue resistance of D-RaCe retreatment instrument.
  
  
  CONCLUSIONS
  It should be considered that cyclic fatigue resistance of D-RaCe can decrease in contact with NaOCl during the removal of canal filling material.
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Erciyes University, Melikgazi, Kayseri, 38039, Turkey. sindent8@hotmail.com.
authors.forename: Hüseyin Sinan
authors.initials: HS
authors.lastname: Topçuoğlu
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Erciyes University, Kayseri, Turkey.
authors.forename: Kanşad
authors.initials: K
authors.lastname: Pala
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Erciyes University, Melikgazi, Kayseri, 38039, Turkey.
authors.forename: Ahmet
authors.initials: A
authors.lastname: Aktı
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Erciyes University, Melikgazi, Kayseri, 38039, Turkey.
authors.forename: Salih
authors.initials: S
authors.lastname: Düzgün
authors.affiliation: Department of Pedodontics, Faculty of Dentistry, Erciyes University, Kayseri, Turkey.
authors.forename: Gamze
authors.initials: G
authors.lastname: Topçuoğlu
mesh_terms: D003762:Dental Instruments; D019544:Equipment Failure Analysis; D007101:Immersion; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D019233:Retreatment; D018915:Root Canal Preparation / Q000295:instrumentation*; D012973:Sodium Hypochlorite / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry*
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium; D012973:Sodium Hypochlorite
keywords: Cyclic fatigue; Retreatment; Rotary instrument; Sodium hypochlorite