THE QUESTION OF RADIATION IN DENTAL CERAMICS

It may be surprising that one of the ‘risks’ associated with Zirconium based implants is radioactivity. But what does the research say, and is there really any risk to patients? The truth is that Zirconium just like aluminium and many other commonly used materials can contain a certain number of radioactive isotopes, which in extreme cases can increase the chance of oral cancers. However, oral implants are produced from a highly purified and stabilized form of Zirconium also called zirconia or zirconium dioxide which contains extremely low radiation emission levels. Furthermore all manufacturers of zirconia dental implants are required to provide a declaration of radioactivity for their zirconium based dental products. Therefore all zirconia products and materials are not created equal, because the quality and safety of each lies in the the processing of the raw material zirconium.

THE RADIOACTIVITY OF COMMERCIALLY AVAILABLE ZIRCONIA POWDERS

Zirconium compounds are refined from naturally occurring ores, notably zircon, which usually contain trace amounts of other elements depending upon the source of the original ore. In particular, zirconia typically contains trace amounts of radionuclides. As a consequence there were some concerns about the use of zirconia ceramics as implant materials.

In 1992 the question of radioactive ceramics was officially addressed by Anusavice KJ in an article titled ‘Degradability of dental ceramics’ which observed in part that … “The degradation of dental ceramics generally occurs because of mechanical forces or chemical attack. The possible physiological side-effects of ceramics are their tendency to abrade opposing dental structures, the emission of radiation from radioactive components…”

However alarming that may sound further research indicated that the radiation emitted by a dental ceramic powder (3 mol% Y2O3-ZrO2) was the same order of magnitude as alumina powder, both of which were several orders of magnitude less than that typically measured for water, milk, vegetables and meat (based on European standards). The radioactivity of zirconia femoral heads (Y-TZP artificial hip joints) for example, has been shown to be similar to that of alumina and cobalt-chrome. The radiation dose of each material was recorded at that time to be well below European radiation limits specified for general external exposure of the human body and also for local internal exposure of organs and tissue, and was well recognized as no more than the ambient radiation of environmental surroundings.

In another similar study, radiation levels of several commercially available zirconia powders commonly used to manufacture implants in Australia (Nilcra Ceramics, Melbourne) were declared to be minimal and well below acceptable limits. The Radiation Health Committee of the National Health and Medical Research Council of Australia now consider that magnesia partially stabilized zirconia artificial hip joints made from these powders pose “very little hazard to surrounding tissue”.

The main raw material for the manufacture of zirconium dioxide (zirconia) in the US is the mineral zircon silicate (ZrSiO4) which is translated to a higher form of purity zirconium dioxide (ZrO2) when melted with coke and lime. Since extremely pure initial products must be used for the production of high-performance ceramics used in dental implants, special synthesis methods have been developed specifically for this product; a process that works to create the strongest, most durable dental ceramic product available today.

RADIATION ABSORPTION

Research has shown that in a dense ceramic almost all radiation is absorbed within the bulk of the material. In the case of artificial hip joints, any radiation from the femoral head is absorbed primarily by the surrounding artificial materials.

From these tests and others, it is widely recognized in the medical implant field that the actual radiation risk of zirconia ceramics is negligible, certainly no more than that of alumina – and consistent with the level of radiation found to occur naturally in healthy environments.

THE BENEFITS OF ZIRCONIUM IMPLANTS AND DENTAL CERAMICS

Overall, Zirconia (zirconium oxide) implants are valued by dentists and patients alike for being highly resistant to corrosion and superior to other available implant options such as titanium, both as related to biocompatibility and resultant color. They are ideal for those patients whose immune systems do not accept titanium implants and for patients who may have allergic reactions to metals. Zirconia implants are far more durable with less risk of breakage and is capable of holding up to the drastic changes in temperature and chemistry found in the oral environment. Being bright white in color, zirconia implants have a definite advantage or aesthetic value over titanium dental implants by eliminating the possibility of corrosion and the unsightly grey appearance that titanium exhibits.

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RESOURCES:

Is There A Renewed Trend of Radioactive Compounds In Dental Materials? — Ulf Bengtsson, 2000-01-01

Abstracted from Ph.D Thesis “Application of Transformation-Toughened Zirconia Ceramics as Bioceramics”, University of New South Wales, Australia, 1995.

Anusavice KJ. Degradability of dental ceramics. Adv Dent Res 1992 Sep 6:82-9