title: An in vitro evaluation of the effect of deep dry cryotreatment on the cutting efficiency of three rotary nickel titanium instruments.
abstract: BACKGROUND
  Cryogenic methods have been used to increase the strength of metals.
  
  
  OBJECTIVE
  The aim of this study was to evaluate the effect of deep dry cryotherapy on the cyclic fatigue resistance of rotary nickel titanium instruments.
  
  
  METHODS
  Twenty K3, RaCe and Hero Shaper nickel titanium instruments, size 25, 0.06 taper, were taken for this study. Ten files were untreated (control group) and 10 files were deep dry cryogenically treated. Both the untreated and cryotreated files were subjected to cyclic fatigue evaluation. Cyclic fatigue was evaluated as the number of cycles it took for fracture of the instrument within a stainless steel shaping block of specific radius and angle of curvature.
  
  
  METHODS
  Mean values were compared between different study groups by using one-way analysis of variance (ANOVA) with P < 0.05 considered as the level of significance.
  
  
  RESULTS
  The results showed a significant increase in the resistance to cyclic fatigue of deep dry cryotreated NiTi files over untreated files.
  
  
  CONCLUSIONS
  It may thus be concluded that deep cryotherapy has improved the cyclic fatigue of NiTi rotary endodontic files.
authors.affiliation: Department of Conservative Dentistry and Endodontics, Pushpagiri Dental College, Thiruvalla, India.
authors.forename: Gingu Koshy
authors.initials: GK
authors.lastname: George
authors.forename: Kavitha
authors.initials: K
authors.lastname: Sanjeev
authors.forename: Mahalaxmi
authors.initials: M
authors.lastname: Sekar