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

• 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.

The Benefits of Zirconium Implants and Dental Ceramics

Overall, Zirconium implants are highly resistant to corrosion and superior to other implant materials such as titanium and have a higher level of human biocompatibility and superior aesthetic value for patients. They are ideal for anyone whose immune systems are not compatible with titanium implants and for patients who may have metal allergies. Zirconium implants are far more durable with less risk of breakage. They are also capable of holding up to the extreme changes in temperature found in the human mouth

Furthermore, being bright white in color zirconium implants have a definite advantage or aesthetic value over titanium dental implants by eliminating the possibility of the unsightly grey appearance that titanium exhibits.

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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