title: Magnetic strength and corrosion of rare earth magnets.
abstract: BACKGROUND
  Rare earth magnets have been used in orthodontics, but their corrosion tendency in the oral cavity limits long-term clinical application. The aim of this project was to evaluate several; magnet coatings and their effects on magnetic flux density.
  
  
  METHODS
  A total of 60 neodymium-iron-boron magnets divided into 6 equal groups--polytetrafluoroethylene-coated (PTFE), parylene-coated, and noncoated--were subjected to 4 weeks of aging in saline solution, ball milling, and corrosion testing.
  
  
  RESULTS
  A significant decrease in magnet flux density was recorded after applying a protective layer of parylene, whereas a slight decrease was found after applying a protective layer of PTFE. After 4 weeks of aging, the coated magnets were superior to the noncoated magnets in retaining magnetism. The corrosion-behavior test showed no significant difference between the 2 types of coated magnets, and considerable amounts of iron-leached ions were seen in all groups.
  
  
  CONCLUSIONS
  Throughout the processes of coating, soaking, ball milling, and corrosion testing, PTFE was a better coating material than parylene for preserving magnet flux density. However, corrosion testing showed significant metal leaching in all groups.
authors.affiliation: Department of Orthodontics, College of Dentistry, University of Illinois at Chicago, IL 60612-7212, USA.
authors.forename: Khalid A
authors.initials: KA
authors.lastname: Ahmad
authors.forename: James L
authors.initials: JL
authors.lastname: Drummond
authors.forename: Thomas
authors.initials: T
authors.lastname: Graber
authors.forename: Ellen
authors.initials: E
authors.lastname: BeGole
mesh_terms: D001895:Boron; D020099:Coated Materials, Biocompatible; D003343:Corrosion; D007477:Ions; D007501:Iron; D008280:Magnetics / Q000295:instrumentation*; D008669:Metallurgy; D008674:Metals, Rare Earth; D009354:Neodymium; D009967:Orthodontic Appliances; D011108:Polymers; D011138:Polytetrafluoroethylene; D012464:Saliva, Artificial; D014992:Xylenes
chemical_list: D020099:Coated Materials, Biocompatible; D007477:Ions; D008674:Metals, Rare Earth; D011108:Polymers; D012464:Saliva, Artificial; D014992:Xylenes; C011055:parylene; D009354:Neodymium; D011138:Polytetrafluoroethylene; D007501:Iron; D001895:Boron