title: Torsional superelasticity of NiTi archwires.
abstract: OBJECTIVE
  To reproduce and compare the intraoral torsional behavior of 10 commonly used preformed upper NiTi 0.017 x 0.025 archwires in 0.018-slot brackets at 20 degrees C, 35 degrees C, and 55 degrees C.
  
  
  METHODS
  Ten upper preformed NiTi archwires were compared to a multibraided stainless steel wire. An original testing bench was used to reproduce palatal root torque applied onto an upper central incisor with a maximum value of 1540 g x mm. Ten samples of each wire type were tested at 20 degrees C, 35 degrees C, and 55 degrees C each.
  
  
  RESULTS
  Loading and unloading at 20 degrees C revealed three categories of wires: a group of four NiTi wires of relative stiffness bereft of any superelasticity, a group of six NiTi wires displaying some horizontal plateau, and finally the stainless steel wire of lesser stiffness. Testing at the average oral temperature of 35 degrees C produced the same three categories of wires, with only 2 of 10 NiTi wires displaying a superelastic effect (Copper NiTi 35 degrees C and 40 degrees C). None of the NiTi wires was superelastic at 55 degrees C. Moments increased with temperature as the martensite was replaced by the more rigid austenite.
  
  
  CONCLUSIONS
  This study showed that most NiTi wires did not exhibit in torsion the superelastic effect traditionally described in bending. The combination of straight-wire prescriptions and rectangular superelastic NiTi archwires did not provide optimal constant moments necessary to gain third-order control of tooth movement early in treatment. A braided stainless steel rectangular archwire displayed better torsional behavior at 35 degrees C than most NiTi archwires of the same dimensions.
authors.affiliation: Department of Orthodontics, Nancy Université, Nancy, France. bolender@wanadoo.fr
authors.forename: Yves
authors.initials: Y
authors.lastname: Bolender
authors.forename: Anne
authors.initials: A
authors.lastname: Vernière
authors.forename: Christophe
authors.initials: C
authors.lastname: Rapin
authors.forename: Marie-Pierryle
authors.initials: MP
authors.lastname: Filleul
mesh_terms: D003300:Copper; D003722:Dental Alloys; D003799:Dental Stress Analysis; D004548:Elasticity; D008422:Materials Testing; D009532:Nickel; D009969:Orthodontic Wires; D013193:Stainless Steel; D013696:Temperature; D014025:Titanium; D054159:Torsion, Mechanical
chemical_list: C415948:Copper NiTi; D003722:Dental Alloys; C040654:titanium nickelide; C093824:Martensite; C093826:Austenite; D013193:Stainless Steel; D003300:Copper; D009532:Nickel; D014025:Titanium