DENTISTS WORLDWIDE USE RARE EARTH MAGNETS TO HELP PEOPLE WIN BACK THEIR SMILE

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.[1] 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.[2] As expected, they showed excellent corrosion resistance and biocompatibility comparing to the AlNiCos which were later found to corrode rapidly in saliva.[3] 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.[4]
Few successes were registered during the initial stages of research as various difficulties like low mBild1agnetic 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.

References
1. Rupali Kamath, Sarandha D.L, Anand M, Clinical Use of Magnets in Prosthodontics – 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;

Radioactive lanthanides in medicine

Radiation is energy in the process of being transmitted. It may take such forms as light or tiny particles much too small to see. Visible light, the ultra-violet light we receive from the sun, and transmission signals for TV and radio communications are all forms of radiation that are common in our daily lives. These are all generally referred to as ‘non-ionizing’ radiation, though at least some ultra-violet radiation is considered to be ionizing.

Radiation particularly associated with nuclear medicine is ‘ionizing’ radiation, which means that the radiation has sufficient energy to interact with matter, e.g. the human body, and produce ions [1].

Nuclear medicine is a branch of medicine that uses ionizing radiation to provide information about the functioning of a person’s specific organs or to treat disease. In most cases, the information is used by physicians to make a quick, accurate diagnosis of the patient’s illness (diagnostic techniques). The thyroid, bones, heart, liver and many other organs can be easily imaged, and disorders in their function revealed. In some cases radiation can be used to treat diseased organs, or tumors (radionuclide therapy). Five Nobel Laureates have been intimately involved with the use of radioactive tracers in medicine [2].

Diagnostic techniques in nuclear medicine use radioactive tracers which emit gamma rays from within the body. These tracers are generally short-lived isotopes linked to chemical compounds which permit specific physiological processes to be scrutinized. They can be given by injection, inhalation or orally. Emitted rays are detected by a gamma camera which can view organs from many different angles. The camera builds up an image from the points from which radiation is emitted; this image is enhanced by a computer and viewed by a physician on a monitor for indications of abnormal conditions [2]. Most common diagnostic techniques in nuclear medicine are computed X-ray tomography (CT) and positron emission tomography (PET).

Rapidly dividing cells are particularly sensitive to damage by radiation. For this reason, some cancerous growths can be controlled or eliminated by irradiating the area containing the growth which is the basis of radionuclide therapy (RNT).

The role of radioactive isotopes of lanthanides in nuclear medicine is continuously growing due to the combination of imaging and therapy properties (the isotopes of an element have the same number of protons in their atoms (atomic number) but different numbers of neutrons) [3].

Whilst the therapy effect of radioisotopes of lanthanides originates from its radioactivity the imaging effect can result from either magnetic or radioactive properties (radioimaging) of isotopes. Thus magnetic resonance imaging (MRI) technique based on measuring magnetic properties of human tissues exploits compounds of stable gadolinium(III) as a contrast agent which differs this method from CT.

Naturally occurring isotopes of lanthanides are feebly radioactive, having extremely long half-lives (e.g. half-life of 144Nd is 2.3∙1015 years). The unstable radioactive isotopes are produced in many ways — e.g., by fission, neutron bombardment, radioactive decay of neighbouring elements, and bombardment of neighbouring elements with charged particles [4].

An ideal therapeutic radioisotope is a strong beta emitter with just enough gamma to enable imaging, e.g. lutetium-177. This is prepared from ytterbium-176 which is irradiated to become Yb-177 which decays rapidly to Lu-177.

Yttrium-90 is used for treatment of cancer, particularly non-Hodgkin’s lymphoma and liver cancer, and it is being used more widely, including for arthritis treatment. Lu-177 and Y-90 are becoming the main RNT agents [2].

Lutetium-177 dotatate or octreotate is used to treat tumours such as neuroendocrine ones, and is effective where other treatments fail. A series of four treatments delivers 32 GBq. After about four to six hours, the exposure rate of the patient has fallen to less than 25 microsieverts per hour at one metre and the patients can be discharged from hospital. Lu-177 is essentially a low-energy beta-emitter (with some gamma) and the carrier attaches to the surface of the tumour [2].

 

https://www.youtube.com/watch?v=6lqnMIwplcE

 

Many therapeutic procedures are palliative, usually to relieve pain. For instance, samarium-153 is used for the relief of cancer-induced bone pain.

Unfortunately the high price of some radioisotopes of lanthanides restrains its wide application in nuclear medicine.

 

Radioisotopes of lanthanides and yttrium and its medical application [2]:

(half-life indicated)

Dysprosium-165 (2 h): Used as an aggregated hydroxide for synovectomy treatment of arthritis.

Erbium-169 (9.4 d): Use for relieving arthritis pain in synovial joints.

Holmium-166 (26 h): Being developed for diagnosis and treatment of liver tumours.

Lutetium-177 (6.7 d): Lu-177 is increasingly important as it emits just enough gamma for imaging while the beta radiation does the therapy on small  tumours. Its half-life is long enough to allow sophisticated preparation for use.  It is usually produced by neutron activation of natural or enriched lutetium-176 targets.

Samarium-153 (47 h): Sm-153 is very effective in relieving the pain of secondary cancers lodged in the bone, sold as Quadramet. Also very effective for prostate and breast cancer. Beta emitter.

Ytterbium-169 (32 d): Used for cerebrospinal fluid studies in the brain.

Ytterbium-177 (1.9 h): Progenitor of Lu-177.

Yttrium-90 (64 h)*: Used for cancer brachytherapy and as silicate colloid for the relieving the pain of arthritis in larger synovial joints. Pure beta emitter and of growing significance in therapy, especially liver cancer.

* fission product

 

References:

  1. http://www.world-nuclear.org/info/Safety-and-Security/Radiation-and-Health/Nuclear-Radiation-and-Health-Effects/
  2. http://www.world-nuclear.org/info/non-power-nuclear-applications/radioisotopes/radioisotopes-in-medicine/
  3. Sander Wilhelm Zielhuis. Lanthanide Bearing Radioactive Particles for Cancer Therapy and Multimodality Imaging. PhD thesis, 2006. http://dspace.library.uu.nl/handle/1874/8851
  4. http://global.britannica.com/EBchecked/topic/491579/rare-earth-element/307501/Giant-magnetocaloric-effect#toc307503