Magnetic strength and corrosion of rare earth magnets.
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.
Ahmad
Khalid A
KA
Department of Orthodontics, College of Dentistry, University of Illinois at Chicago, IL 60612-7212, USA.
Drummond
James L
JL
Graber
Thomas
T
BeGole
Ellen
E
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
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