title: Influence of surface layer on mechanical and corrosion properties of nickel-titanium orthodontic wires.
abstract: OBJECTIVE
  To analyze the effect of various coating formulations on the mechanical and corrosion properties of nickel-titanium (NiTi) orthodontic wires.
  
  
  METHODS
  Uncoated, rhodium-coated, and nitrified NiTi wires were observed with a three-point-bend test, surface roughness (Ra) measurement, scanning electron microscopy, energy dispersive spectroscopy, and electrochemical testing (open circuit potential, electrochemical impedance spectroscopy, and cyclic polarization scan). Differences in the properties of tested wire types were analyzed with analysis of variance and Tukey post hoc test.
  
  
  RESULTS
  Uncoated and nitrified NiTi wires showed similar mechanical and anticorrosive properties, while rhodium-coated NiTi wires showed the highest Ra and significantly higher modulus of elasticity, yield strength, and delivery of forces during loading but not in unloading. Rhodium-coated NiTi wires also had the highest corrosion current density and corrosion potential, lowest impedance modulus, and two time constants on Bode plot, one related to the Rh/Au coating and the other to underlying NiTi.
  
  
  CONCLUSIONS
  Working properties of NiTi wires were unaffected by various coatings in unloading. Nitrification improved corrosion resistance. Rhodium coating reduced corrosion resistance and pronounced susceptibility to pitting corrosion in artificial saliva because of galvanic coupling between the noble coating and the base alloy.
authors.affiliation: a  Research Assistant, Department of Pediatric Dentistry and Orthodontics, School of Medicine, University of Rijeka, Rijeka, Croatia.
authors.forename: Višnja
authors.initials: V
authors.lastname: Katić
authors.forename: Helena Otmačić
authors.initials: HO
authors.lastname: Curković
authors.forename: Damir
authors.initials: D
authors.lastname: Semenski
authors.forename: Gorana
authors.initials: G
authors.lastname: Baršić
authors.forename: Katarina
authors.initials: K
authors.lastname: Marušić
authors.forename: Stjepan
authors.initials: S
authors.lastname: Spalj
mesh_terms: D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D003343:Corrosion; D003722:Dental Alloys / Q000737:chemistry*; D058266:Dielectric Spectroscopy; D055119:Elastic Modulus; D004572:Electrolysis; D006046:Gold / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000737:chemistry*; D009969:Orthodontic Wires; D018583:Pliability; D011048:Polarography; D012238:Rhodium / Q000737:chemistry; D012464:Saliva, Artificial / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D020099:Coated Materials, Biocompatible; D003722:Dental Alloys; D012464:Saliva, Artificial; C040654:titanium nickelide; C041500:titanium nitride; D006046:Gold; D009532:Nickel; D014025:Titanium; D012238:Rhodium
keywords: Corrosion; Electrochemical testing; NiTi; Surface coating; Three-point-bend test