Radioactivity of ceramic

Are Ceramic Dental Implants Radioactive?

Almost every element in nature has some measure of radioactivity associated with it including seemingly innocuous elements such as water, milk, vegetables and meat. So it is not surprising to learn that many materials used in dentistry today have some level of radioactivity including Zirconium based implants. By looking at the chart below you can see that Zirconium can contain a certain number of radioactive isotopes. In worst case scenarios, Radioactive Isotopes are known to increase the chance of various oral cancers, so knowing what level of radioactivity is involved is important for anyone who may be considering dental implant surgery.

“In the case of Zirconium, this natural radioactivity is related to natural exposure with other elements,” says James B. Francis, President Z-Systems USA, Inc. “The manufacturer of our raw material is the same manufacturer who has been making the Zirconia hip ball replacements for the past 30 years. Its process of removing the natural contamination is state of the art and results in the highest purity of raw Zirconia available.”

The Physics of Dental Ceramics (Zirconium) compared to other common elements

Element	Atomic # (Z)	Atomic Wt (A)	Density (p)	Radiation Len. (cm)	*DensityRL (g/cm2)**
Hydrogen	1	1.0079	0.0000818	717614	58.7008252
Nickel	28	58.7	8.907	1.42358	12.67982706
Zirconium	40	91.22	6.507	1.56678	10.19503746
Gold	79	196.97	19.281	0.33511	6.46125591
Mercury	80	200.59	13.546	0.47522	6.43733012
Uranium	92	238.03	19.05	0.31496	5.999988

The atomic number is the number of protons in the nucleus of an atom.
The atomic mass is the mass (weight) of all the components of the atom but is dominated by the nucleus composed of protons and neutrons. It is the mass of the atom at rest, measured in atomic mass units.
Electron density: the number of electrons per unit volume; volume charge density = electric charge per unit volume of a medium or body measured in coulombs per meter cubed; surface charge density = electric charge per unit area of a surface measured in coulombs per meter squared.
In physics, the radiation length is a characteristic of a material, related to the energy loss of high energy, electromagnetic-interacting particles with it. The mean distance traveled by a relativistic particle in a given medium before its energy is reduced by a factor e by its interaction with matter.
Relative density: The density of a substance divided by the density of water (formerly called specific gravity) which has a maximum density of 1000kg m-3; therefore the relative density of any substance is one-thousandth of its density.

Zirconia hip ball replacements weigh approximately 100g, which translates to a yearly natural radiological output of 1 mSv per year. Z-Systems Z-Look3 implants weigh approximately 1g, which translates to a yearly natural radiological output of 0.01 mSv per year. To put that in perspective, a look at the comparison levels of other items which have radioactive output might be helpful:

2.4 mSv/year the amount equal to the typical background radiation experienced by everyone (average 1.5 mSv in Australia, 3 mSv in North America).
Up to 5.0 mSv/year represents the typical incremental dose for aircrew in middle latitudes.
9.0 mSv/year equals the amount of exposure experienced by airline crew flying the New York – Tokyo polar route.
20 mSv/per year is the current limit (averaged) for nuclear industry employees and uranium miners.
50 mSv/per year is the former routine limit for nuclear industry employees. It is also the dose rate which arises from natural background levels in several places in Iran, India and Europe.

Uranium = White Teeth

Oral implants are produced from a highly purified form of Zirconia material which contains extremely low radiation emission levels, although all manufacturers of Zirconia dental implants are required to provide a declaration of radioactivity for their Zirconium based dental products. The use of radioactive compounds in dental ceramics has to do with cosmetic results and the need to copy the luster of natural teeth in an implant. Human dentine is naturally very bright in color and in an attempt to duplicate this characteristic, uranium is added to both artificial teeth and ceramic powders for the manufacturing of crowns and bridges, a practice that originated as far back as the 1920’s. A patent just a few decade later presented by inventors Lee and Müller describes a mixture of cerium and uranium as,”… creating an improved shade of white”.

Zirconium compounds are refined for dental use from naturally occurring ores, notably zircon, which usually contain trace amounts of other elements depending upon the source of the original ore, including trace amounts of radioactive nuclides. In 1992 ceramic radioactivity was 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…”

Further research pointed out that the radiation emitted by a dental ceramic powder (3 mol% Y2O3-ZrO2) was the same as alumina powder (note: aluminum is an element, and alumina is an aluminum containing compound), 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 Y-TZP artificial hip joints 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 recommended for the human body including local internal exposure of organs and tissue. It was documented to be no more than the ambient radiation of environmental surroundings.

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

In the United States, the primary raw material used in the manufacture of zirconium dioxide is zircon silicate (ZrSiO4), which is rendered into a higher form of purity (ZrO2) when melted with coke and lime. Since extremely pure initial products must be used for high-performance ceramics such as those used in dental implants and 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.

Where does the radiation go?

Research has shown that all radiation is absorbed withinto the bulk of the material in such extremely dense ceramics. For example, in the case of artificial hip joints, any radiation from the femoral head is absorbed primarily by the surrounding artificial materials.

Continuous testing and research from the medical implant field demonstrates 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.

————–

Resources:
World Nuclear Association (The World Nuclear Association http://www.world-nuclear.org/info/inf05.html):

Radiation Length Package (data taken from Particle Data Booklet) by R.J.Apsimon

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

NOTE: the above information was taken from https://naturaldentistry.us in the interest of advancing patient awareness.

"Radioactive burden resulting from Zirconia implants"

[Article in German]

Fischer-Brandies E, Pratzel H, Wendt T.

Klinik und Poliklinik fur Kieferchirurgie der Universitat Munchen.

Due to its mechanical properties zirconia is an interesting implantation material. However, it may contain a certain amount of radioactive isotopes. The measurement of alpha-emission reveals varying amounts of radiation. As a result, a declaration of radioactivity should be required for zirconia implants and only zirconia with low emission levels should be used for implantation purposes.

PMID: 1817864 [PubMed]

"Zirconia Ceramics as Biomaterials – Radioactivity Issues"

Background

Zirconium compounds are refined from naturally occurring ores, notably zircon, and usually contain trace amounts of other elements depending upon the source of the original ore.

In particular, zirconia typically contains trace amounts of radionuclides of the actinide series such as 226Ra and 228Th.

As a consequence there have been some concerns about the use of zirconia ceramics as implant materials.

However, the radioactivity of zirconia is negligible.

For example, the radiation emitted by a 3 mol% Y2O3-ZrO2 powder 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 (in Europe).

The radioactivity of Y-TZP zirconia femoral heads were shown to be similar to that of alumina and cobalt-chrome alloy femoral heads accepted for human implantation.

The radiation dose of each material was 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 no more than the ambient radiation of the surroundings.

The Radioactivity of Commercially Available Zirconia Powders
Similarly, the radiation levels of several commercially-available zirconia powders (Nilcra Ceramics, Melbourne, Australia) measured by the Australian Radiation Laboratory were found to be minimal and well below acceptable limits.

The Radiation Health Committee of the National Health and Medical Research Council of Australia consider that magnesia partially stabilised zirconia femoral heads made from these powders would pose very little hazard to surrounding tissue.

Radiation Absorption

In a dense ceramic, almost all the radiation will be absorbed within the bulk of the material. Any external radiation could come only from radionuclides at the surface in the case of a-emission, or from radionuclides in the first few millimetres in the case of b-emission.

Furthermore, in the case of artificial hip joints, any radiation from the femoral head will be absorbed mostly by the ultra high molecular weight polyethylene acetabular cup or the metal femoral stem.

The radiation risk of zirconia ceramics is negligible and certainly no more than that of alumina.

Primary author: Dr. Owen Standard.
Source: Abstracted from Ph.D Thesis “Application of Transformation-Toughened Zirconia Ceramics as Bioceramics”, University of New South Wales, Australia, 1995.

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