title: Stiffness and frictional resistance of a superelastic nickel-titanium orthodontic wire with low-stress hysteresis.
abstract: BACKGROUND
  Stress-induced martensite formation with stress hysteresis that changes the elasticity and stiffness of nickel-titanium (Ni-Ti) wire influences the sliding mechanics of archwire-guided tooth movement. This in-vitro study investigated the frictional behavior of an improved superelastic Ni-Ti wire with low-stress hysteresis.
  
  
  METHODS
  Improved superelastic Ni-Ti alloy wires (L & H Titan, Tomy International, Tokyo, Japan) with low-stress hysteresis were examined by using 3-point bending and frictional resistance tests with a universal test machine at a constant temperature of 35 degrees C, and compared with the former conventional austenitic-active superelastic Ni-Ti wires (Sentalloy, Tomy International). Wire stiffness levels were derived from differentiation of the polynomial regression of the unloading curves, and values for kinetic friction were measured at constant bending deflection distances of 0, 2, 3, and 4 mm, respectively.
  
  
  RESULTS
  Compared with conventional Sentalloy wires, the L & H Titan wire had a narrower stress hysteresis including a lower loading plateau and a higher unloading plateau. In addition, L & H Titan wires were less stiff than the Sentalloy wires during most unloading stages. Values of friction measured at deflections of 0, 2, and 3 mm were significantly (P <.05) increased in both types of wire. However, they showed a significant decrease in friction from 3 to 4 mm of deflection. L & H Titan wires had less friction than Sentalloy wires at all bending deflections (P <.05).
  
  
  CONCLUSIONS
  Stress-induced martensite formation significantly reduced the stiffness and thus could be beneficial to decrease the binding friction of superelastic Ni-Ti wires during sliding with large bending deflections. Austenitic-active alloy wires with low-stress hysteresis and lower stiffness and friction offer significant potential for further investigation.
authors.affiliation: Dental Department, Taipei Veterans General Hospital, Taipei, Taiwan.
authors.forename: Yu-Cheng
authors.initials: YC
authors.lastname: Liaw
authors.forename: Yu-Yu M
authors.initials: YY
authors.lastname: Su
authors.forename: Yu-Lin
authors.initials: YL
authors.lastname: Lai
authors.forename: Shyh-Yuan
authors.initials: SY
authors.lastname: Lee
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation* / Q000379:methods; D004548:Elasticity; D017276:Friction; D008422:Materials Testing / Q000295:instrumentation / Q000379:methods; D009532:Nickel / Q000737:chemistry*; D009969:Orthodontic Wires; D013314:Stress, Mechanical; D013696:Temperature; D014025:Titanium / Q000737:chemistry*; D014087:Tooth Movement Techniques / Q000295:instrumentation*; D016474:Weight-Bearing
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium