title: Electropolishing enhances the resistance of nickel-titanium rotary files to corrosion-fatigue failure in hypochlorite.
abstract: BACKGROUND
  The aim of this study was to examine the fatigue behavior, especially at the low-cycle fatigue (LCF) region, of an experimentally electropolished FlexMaster and a commercial electropolished nickel-titanium (NiTi) instrument (RaCe) in a corrosive environment.
  
  
  METHODS
  A total of 90 NiTi rotary instruments were subjected to rotational bending at various degrees of curvatures while immersed in 1.2% sodium hypochlorite solution until broken. The maximum surface strain amplitude, calculated from the curvature of the instrument and the diameter of the cross section at break, was plotted against the LCF life. The results were compared with data for a non-electropolished commercial product tested by using the same methodology.
  
  
  RESULTS
  The fatigue life of both instruments generally declined with increasing surface strain amplitude; there was a significant difference between the 2 instruments. Comparing the surface-treated FlexMaster with its commercially available non-electropolished counterpart, an improved resistance to fatigue breakage as a result of electropolishing was noted (P < .05).
  
  
  CONCLUSIONS
  The LCF life of a NiTi instrument rotating with a curvature in a corrosive environment is enhanced by electropolishing. The design, both cross-sectional and longitudinal, appears to have an effect on the fatigue behavior of NiTi rotary instruments.
authors.affiliation: Area of Endodontics, Comprehensive Dental Care, Faculty of Dentistry, University of Hong Kong, Hong Kong.
authors.forename: Chonrada
authors.initials: C
authors.lastname: Praisarnti
authors.forename: Jeffrey W W
authors.initials: JW
authors.lastname: Chang
authors.forename: Gary S P
authors.initials: GS
authors.lastname: Cheung
mesh_terms: D003343:Corrosion; D003722:Dental Alloys / Q000737:chemistry*; D003775:Dental Polishing / Q000379:methods*; D055664:Electrochemical Techniques; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008280:Magnetics; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D012973:Sodium Hypochlorite / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium; D012973:Sodium Hypochlorite