title: Influence of sodium hypochlorite on fracture properties and corrosion of ProTaper Rotary instruments.
abstract: OBJECTIVE
  To evaluate the influence of immersion in NaOCl on resistance to cyclic fatigue fracture and corrosion of ProTaper NiTi Rotary instruments.
  
  
  METHODS
  A total of 120 new ProTaper NiTi Rotary files (F2) were randomized and assigned to three different groups of 40 each. Group 1 was the control group; 20 mm (excluding the shaft) of group 2 instruments were immersed in 5% NaOCl at 50 degrees C for 5 min; instruments in group 3 were completely immersed in 5% NaOCl at 50 degrees C for 5 min. All instruments were then tested for cyclic fatigue, recording the time in seconds to fracture. Data were analysed by the Kruskall-Wallis test and post-hoc multiple comparisons (P < 0.05). Micromorphological and microchemical analyses were also completed by means of a field emission scanning electron microscopy (SEM) on those instruments in group 3 that had undergone early fracture.
  
  
  RESULTS
  Instruments in group 3 had a significantly lower resistance to fracture because of cyclic fatigue than those in groups 1 and 2 (P < 0.001). In some instruments in group 3, early fracture occurred after only a few seconds of fatigue testing. SEM observations revealed evident signs of corrosion of the fractured instruments.
  
  
  CONCLUSIONS
  Group 3 had significantly reduced resistance to cyclic fatigue compared with instruments in groups 1 and 2. The phenomenon of early fracture may be attributed to galvanic corrosion induced by the presence of dissimilar metals, where one acts as the cathode of a galvanic couple, established when the instrument is immersed in NaOCl solution. The NiTi alloy may acts as the anode and thus undergoes corrosion.
authors.affiliation: Department of Endodontics, School of Dentistry, University of Turin, Turin, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Berutti
authors.forename: E
authors.initials: E
authors.lastname: Angelini
authors.forename: M
authors.initials: M
authors.lastname: Rigolone
authors.forename: G
authors.initials: G
authors.lastname: Migliaretti
authors.forename: D
authors.initials: D
authors.lastname: Pasqualini
mesh_terms: D003343:Corrosion; D003722:Dental Alloys; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004563:Electrochemistry; D004577:Electron Probe Microanalysis; D004868:Equipment Failure; D008855:Microscopy, Electron, Scanning; D009532:Nickel; D011897:Random Allocation; D012388:Root Canal Irrigants; D018915:Root Canal Preparation / Q000295:instrumentation*; D012973:Sodium Hypochlorite; D018709:Statistics, Nonparametric; D013499:Surface Properties; D014025:Titanium
chemical_list: D003722:Dental Alloys; D012388:Root Canal Irrigants; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium; D012973:Sodium Hypochlorite