title: [Is the shape memory effect a reality for 35° Copper Ni-Ti(®)? Study by means of differential scanning calorimetry].
abstract: BACKGROUND
  Copper-nickel-titanium alloys are supposed to deliver a shape memory effect: when they are brought to a low temperature phase and subjected to a plastic deformation, they should recover their initial shape by simple heating. Nickel-titanium alloys can display different crystallographic phases: martensite, austenite and an inconstant intermediate R-phase. The shape memory effect is generally associated with the transition from martensite to austenite but it could also accompany the transition from R-phase to austenite. Since oral temperatures are not compatible with a fully martensitic alloy, this study aims, for 35° Copper Ni-Ti(®), to assess the R-phase presence at oral temperatures and to verify the possibility of using the R-phase shape memory effect under clinical conditions.
  
  
  METHODS
  Thirty consecutive 35° Copper Ni-Ti(®) archwires from two different batches were examined by differential scanning calorimetry with partial cycles limited to temperatures encountered within the oral cavity (from 0 °C to 50 °C). The presence of an intermediate crystallographic phase was assessed on the thermograms. The transformation temperatures were determined and the two batches were compared using the Mann-Whitney U Test.
  
  
  RESULTS
  Upon heating, all wires transformed directly from martensite to austenite. Af (mean  = 33.5 °C, SD  = 0.8 °C) was generally below the temperature stated by the manufacturer and a statistically significant difference (p ≤ 0.01) was found between the two batches.
  
  
  CONCLUSIONS
  No R-phase was detected and transformation temperatures were not constant. This study questions the supposed shape memory effect displayed by 35° Copper Ni-Ti(®) wires under clinical conditions.
authors.affiliation: Département d'Orthopédie Dento-Faciale, Faculté d'Odontologie de Nancy, Université de Lorraine, 96 avenue du Maréchal de Lattre de Tassigny, 54000 Nancy, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kanter
authors.forename: Yves
authors.initials: Y
authors.lastname: Bolender
authors.forename: Christophe
authors.initials: C
authors.lastname: Rapin
authors.forename: Marie-Pierryle
authors.initials: MP
authors.lastname: Filleul
mesh_terms: D000497:Alloys / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D003300:Copper; D008422:Materials Testing; D009969:Orthodontic Wires
chemical_list: D000497:Alloys; D003300:Copper