title: Deformation of HyFlex CM instruments and their shape recovery following heat sterilization.
abstract: OBJECTIVE
  To assess the deformation of HyFlex CM instruments (Coltene Whaledent) when used in two instrumentation sequences and to assess their shape recovery after heat sterilization.
  
  
  METHODS
  Simulated root canals with four different shapes were prepared with HyFlex CM instruments using a single-length technique (n = 40) or a crown down technique (n = 40). Pre-preparation, post-preparation and post-sterilization standardized images of each instrument were recorded. Assessment of instrument deformation and their subsequent shape recovery was carried out visually and by comparing the digitised images. Data analysis was carried out using chi-square tests.
  
  
  RESULTS
  None of the 400 instruments fractured. Visual assessment of instruments post-preparation revealed that 30.5% had unwound and 0.5% had reverse winding. Following sterilization 8.5% remained unwound and 0.5% remained with reverse winding. When assessing instrument shape using digital images, 35.25% were unwound post-preparation, which reduced to 11% post-sterilization. Nine size 25, 0.08 instruments deformed, but none fully regained their original shape after sterilization; however, other sizes of deformed instruments did regain their shape (P < 0.001).
  
  
  CONCLUSIONS
  Approximately one third of instruments became deformed as a result of use. However, two thirds of these fully recovered their shape following sterilization. The number of deformed instruments was underestimated when no magnification was used for assessment. Instrument size was related to incidence of deformation and shape recovery.
authors: Endodontology Research Group, School of Dentistry, College of Biomedical and Life Sciences, Cardiff University, Cardiff, UK.|Bneid Algar Dental Speciality Centre, Ministry of Health, Kuwait City, Kuwait.
authors: M
authors: M
authors: Alfoqom Alazemi
authors: Endodontology Research Group, School of Dentistry, College of Biomedical and Life Sciences, Cardiff University, Cardiff, UK.
authors: S T
authors: ST
authors: Bryant
authors: Endodontology Research Group, School of Dentistry, College of Biomedical and Life Sciences, Cardiff University, Cardiff, UK.
authors: P M H
authors: PM
authors: Dummer
mesh_terms: D003722:Dental Alloys; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004867:Equipment Design; D004868:Equipment Failure; D006358:Hot Temperature; D008422:Materials Testing; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D013242:Sterilization; D013499:Surface Properties
chemical_list: D003722:Dental Alloys
keywords: HyFlex CM; defect; deformation; endodontic file; instrument fracture; nickel-titanium instrument