Magnetic strength and corrosion of rare earth magnets

Am J Orthod Dentofacial Orthop. 2006 Sep;130(3):275.e11-5. doi: 10.1016/j.ajodo.2006.01.024.

Abstract

Introduction: 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.

MeSH terms

  • Boron
  • Coated Materials, Biocompatible*
  • Corrosion
  • Ions
  • Iron
  • Magnetics / instrumentation*
  • Metallurgy
  • Metals, Rare Earth*
  • Neodymium
  • Orthodontic Appliances*
  • Polymers
  • Polytetrafluoroethylene
  • Saliva, Artificial
  • Xylenes

Substances

  • Coated Materials, Biocompatible
  • Ions
  • Metals, Rare Earth
  • Polymers
  • Saliva, Artificial
  • Xylenes
  • parylene
  • Neodymium
  • Polytetrafluoroethylene
  • Iron
  • Boron