The idea of using magnets in stomatology is more than 60 years old. Magnets were considered to bean interesting alternative to mechanical attachments and force systems traditionally used in prosthetic and orthodontic treatment. The first to see the potential applications of magnets in dentistry were the clinicians working to develop dental prostheses.
The first clinical studies used magnets to fix removable dentures. At the time magnets were made of materials like platinum-cobalt (Pt-Co) or aluminium-nikel-cobalt (AlNiCo) alloys. Conceived in the ’30s and made available on the market in the ’50s, Pt-Co alloys can be considered the most precious permanent magnet alloys as they contained they contain 78% weight platinum. As opposed to AlNiCos which are hard and brittle, Pt-Co alloys are ductile and also have higher coercivity. As expected, they showed excellent corrosion resistance and biocompatibility comparing to the AlNiCos which were later found to corrode rapidly in saliva. In spite of their superior qualities Pt-Co alloys were never widely used and were eventually abandoned by clinicians because of their extremely high cost.
Iron-cobalt-chromium (Fe-Co-Cr) magnets which were first prepared in 1971 brought the advantage of being formable at room temperature besides the magnetic properties that are similar to those of the AlNiCo magnets. Cold workability enabled the fabrication of the first magnetic orthodontic brackets used in maxillary and mandibular arches to correct the position of teeth.
Few successes were registered during the initial stages of research as various difficulties like low magnetic forces, large implant sizes, corrosion and high costs were encountered but a new way for the clinical use of magnets was opened.
Research in the field gained momentum in the late ’70s when samarium-cobalt (Sm-Co) magnets were put to practical use in dentistry. Showing a significantly improved magnetic properties, Sm-Co magnets made a great step ahead of the AlNiCos just as the AlNiCos had been a massive revolution compared to cobalt containing steels and ferrites. Their high magnetization and coercivity lead to the improvement of prosthetic and orthodontic systems design as miniaturization became possible. Announced in 1983, Nd-Fe-B magnets still represent the apogee in the evolution of magnetic materials. The highest stored magnetic energy per unit volume was achieved therefore the magnetic forces necessary in dental applications were attainable with very small magnets. Nd-Fe-B alloys are less costly to produce than Sm-Co alloys and hence are now the main rare earth permanent magnet in use today.
Because they have low corrosion resistance (especially in chloride containing media like saliva), rare earth permanent magnets that are used in vivo need to be encapsulated or coated in order to prevent corrosion and the possible side effects of corrosion products. The latest technologies use magnetic stainless steel capsules that are laser welded together in order to seal the magnet and covered with titanium nitride for abrasion resistance. Titanium nitride coatings are also meant to protect the patient from exposure to Ni which is contained in the welding alloy.3
Due to the development of rare earth magnetic alloys magnets are now popular in dentistry being successfully used for purposes such as the retention of dentures, maxillofacial prostheses and in orthodontic applications. Although they have not been unanimously accepted by clinicians as they might present the risk of corrosion in the presence of saliva, Nd-Fe-B permanent magnets have proved the power to help people who deal with dental problems show a confident and healty smile.
1. Rupali Kamath, Sarandha D.L, Anand M, Clinical Use of Magnets in Prosthodontics â€“ A Review, Int. Journal of Clinical Dental Science 2 (2), 2011;
2. Karl J. Strnat, Modern Permanent Magnets for Applications in Electro-Technology, Proceedings of the IEEE, Volume 78, Number 6, June 1990, pp. 923;
3. Paola Ceruti, S. Ross Bryant, Jun-Ho Lee, Michael I. MacEntee, Magnet-Retained Implant-Supported Overdentures: Review and 1-Year Clinical Report, J Can Dent Assoc 2010;
4. Vidya S. Bhat, K. KamalakanthShenoy, Priyanka Premkumar, Magnets in dentistry, Archives of Medicine and Health Sciences, Jan-Jun 2013, Vol 1, Issue 1;