Corrosion behavior of shape memory, superelastic, and nonsuperelastic nickel-titanium-based orthodontic wires at various temperatures.
OBJECTIVE
Nickel-titanium orthodontic wires have various temperature-dependent phases. The purpose of this study was to investigate temperature-dependent corrosion characteristics of shape memory, superelastic, and nonsuperelastic orthodontic wires.


METHODS
Four orthodontic wires were investigated: 27 and 40 degrees C copper Ni-Ti (superelastic and shape memory, respectively), superelastic Ni-Ti, and nonsuperelastic Nitinol Classic. Differential scanning calorimetry (DSC) was used to confirm phase/temperature behavior of the wires. Sectioned halves of as-received archwires were assessed electrochemically in artificial saliva at 5, 24, 37, and 45 degrees C. Open circuit potential (OCP) was monitored for 2h followed by polarization resistance and cyclic polarization tests.


RESULTS
DSC results showed Nitinol was primarily martensitic-stable whereas NiTi, 27 degrees C CuNiTi, and 40 degrees C CuNiTi possessed austenite-finish temperatures of approximately 19, 21, and 38 degrees C. The OCP of the CuNiTi wires was significantly greater than NiTi and Nitinol but no apparent trend in values was apparent with regard to temperature or phases present. Corrosion current density (i(corr)) increased with temperature for all wires, but not all were equally influenced. The two lowest austenite-finish temperature wires (27 degrees C CuNiTi and NiTi) approximately tripled in i(corr) from 37 to 45 degrees C. Greater incidence of pitting was observed in the CuNiTi wires.


CONCLUSIONS
This study showed the corrosion rate of various nickel-titanium wires increase with temperature and different phases present may influence corrosion rate trends.
Pun
Deo K
DK
Dental Biomaterials, School of Dentistry, Marquette University, Milwaukee, WI 53201, USA.
Berzins
David W
DW
D002152:Calorimetry, Differential Scanning; D003300:Copper / Q000737:chemistry; D003343:Corrosion; D003722:Dental Alloys / Q000737:chemistry*; D004548:Elasticity; D017097:Electric Impedance; D004563:Electrochemistry; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000737:chemistry*; D009969:Orthodontic Wires; D044367:Phase Transition; D011199:Potentiometry; D012464:Saliva, Artificial / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature; D014025:Titanium / Q000737:chemistry*; D044366:Transition Temperature
C415948:Copper NiTi; D003722:Dental Alloys; D012464:Saliva, Artificial; C040654:titanium nickelide; C093824:Martensite; C093826:Austenite; D003300:Copper; D009532:Nickel; D014025:Titanium