title: Heat treatment of nickel-titanium rotary endodontic instruments: effects on bending properties and shaping abilities.
abstract: OBJECTIVE
  To evaluate the bending properties and shaping abilities of nickel-titanium endodontic instruments processed by heat treatment.
  
  
  METHODS
  K3 files were heated for 30 min at 400 °C (group 400), 450 °C (group 450) and 500 °C (group 500). Files that were not heat treated served as controls. A cantilever-bending test was used to evaluate changes in specimen flexibility caused by heat treatment. Curved root canal models were prepared. The times required for preparation, deformation and fracture were recorded. Pre- and postoperative images were superimposed. The amounts of resin removed from both the inner and the outer sides of the curvature in the apical 6 mm were determined.
  
  
  RESULTS
  In the cantilever-bending test, load values of the control group and group 500 were higher than those of groups 400 and 450 at the elastic range (P<0.05). At the superelastic range, the bending load of the control group was the highest amongst all groups (P<0.05). Regarding shaping ability, in the control group, root canals at the apex were transported more to the outer side of the curvature compared with those of all heat-treated groups (P<0.05). Root canals of group 400 at 3 mm from the apex were transported less compared with those of other groups (P<0.05). No significant difference was found in working time amongst the groups. In group 450, there was no plastic deformation or fracture of the file.
  
  
  CONCLUSIONS
  Heat treatment of files might improve their flexibility, making them more effective for preparation of curved canals.
authors.affiliation: Pulp Biology and Endodontics, Department of Restorative Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Ebihara
authors.forename: Y
authors.initials: Y
authors.lastname: Yahata
authors.forename: K
authors.initials: K
authors.lastname: Miyara
authors.forename: K
authors.initials: K
authors.lastname: Nakano
authors.forename: Y
authors.initials: Y
authors.lastname: Hayashi
authors.forename: H
authors.initials: H
authors.lastname: Suda
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D004868:Equipment Failure; D006358:Hot Temperature; D006801:Humans; D008669:Metallurgy; D009532:Nickel / Q000737:chemistry*; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D014025:Titanium / Q000737:chemistry*
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium