title: Effect of irrigation on surface roughness and fatigue resistance of controlled memory wire nickel-titanium instruments.
abstract: OBJECTIVE
  To investigate the effect of irrigation on the surface roughness and fatigue resistance of HyFlex and M3 controlled memory (CM) wire nickel-titanium instruments.
  
  
  METHODS
  Two new files of each brand were analysed by atomic force microscopy (AFM). Then, the instruments were dynamically immersed in either 5.25% sodium hypochlorite (NaOCl) or 17% ethylene diamine tetraacetic acid (EDTA) solution for 10 min, followed by AFM analysis. The roughness average (Ra) and root mean square (RMS) values were analysed statistically using an independent sample t-test. Then, 36 files of each brand were randomly assigned to three groups (n = 12). Group 1 (the control group) was composed of new instruments. Groups 2 and 3 were dynamically immersed in 5.25% NaOCl and 17% EDTA solutions for 10 min, respectively. The number of rotations to failure for various groups was analysed using the one-way analysis of variance software.
  
  
  RESULTS
  For M3 files, the Ra and RMS values significantly increased (P < 0.05) after the immersion. For the HyFlex file, the Ra and RMS values significantly increased (P < 0.05) only in EDTA, but not (P > 0.05) NaOCl. The resistance to cyclic fatigue of both HyFlex and M3 files did not significantly decrease (P > 0.05) by immersing in 5.25% NaOCl and 17% EDTA solutions.
  
  
  CONCLUSIONS
  Except the HyFlex files immersed in NaOCl, the surface roughness of other files exposed to irrigants increased. However, a change in the surface tomography of CM wire instruments caused by contact with irrigants for 10 min did not trigger a decrease in cyclic fatigue resistance.
authors.affiliation: Nanjing Stomatological Hospital, Medical School of Nanjing University, Nanjing, China.
authors.forename: J-J
authors.initials: JJ
authors.lastname: Cai
authors.affiliation: Nanjing Stomatological Hospital, Medical School of Nanjing University, Nanjing, China.
authors.forename: X-N
authors.initials: XN
authors.lastname: Tang
authors.affiliation: Nanjing Stomatological Hospital, Medical School of Nanjing University, Nanjing, China.
authors.forename: J-Y
authors.initials: JY
authors.lastname: Ge
mesh_terms: D003762:Dental Instruments; D004492:Edetic Acid / Q000737:chemistry; D004868:Equipment Failure; D019544:Equipment Failure Analysis; D008422:Materials Testing; D018625:Microscopy, Atomic Force; D009532:Nickel; D011897:Random Allocation; D012388:Root Canal Irrigants / Q000737:chemistry*; D018915:Root Canal Preparation / Q000295:instrumentation*; D012973:Sodium Hypochlorite / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium
chemical_list: D012388:Root Canal Irrigants; C040654:titanium nickelide; D009532:Nickel; D004492:Edetic Acid; D014025:Titanium; D012973:Sodium Hypochlorite
keywords: atomic force microscopy; controlled memory wire nickel-titanium instruments; cyclic fatigue resistance; irrigation