Answer to Question #12162 Submitted to "Ask the Experts"

I have a question about the radiation risk from gold metal crowns. In Ask the Experts Question 11372 about zirconia (zinc oxide) porcelain crowns, you mention negligible risk but acknowledge that the risk is not zero. How about gold crowns (which are usually not pure but combined with other alloys)? How about ceramic reconstruction (CEREC) method crowns (which have multiple suppliers of the many proprietary materials in them, some which include zinc oxide)?

Given a choice between gold, CEREC, or zirconia crowns, which would provide the least radioactivity? Should radioactivity even be a factor in determining which one to pick for a crown?

All of these materials result in a negligible radiation dose, well below the level of background radiation. And there are many other factors besides radioactivity that should be considered when deciding what type of crown to choose.

In the United States, we each receive a background radiation dose of approximately 3.1 millisieverts (mSv) each year (approximately 8.5 microsieverts [µSv] per day). This radiation comes largely from cosmic and terrestrial sources. A large contributor is the natural breakdown of uranium into radon. In addition, we receive trace amounts of radiation from the foods that we eat. For example, bananas give off radiation from potassium-40 (⁴⁰K). In fact, there is a "banana-equivalent" dose of approximately 0.1 µSv for one banana. It is important to keep this in mind when it comes to discussions about dental materials, particularly those that have materials that are mined from the earth. Therefore, we can never say that a dental restorative material has absolutely zero radiation and would instead state that the radiation dose is negligible.

With that in mind, let me respond in detail to your questions. First let's discuss the radioactivity of dental materials.

• Dental gold contains approximately 75% gold with the addition of small amounts of palladium and silver. Rarely, other trace amounts of platinum, copper, and zinc are used. Platinum, copper, and zinc have antimicrobial properties which can make them an excellent choice for restorative properties. Gold is soft and malleable and a great restorative property for a patient with a history of grinding their teeth. The radioactivity of gold crowns is negligible.
• CEREC crowns are made from a variety of ingredients, and their exact composition is proprietary and not made public. However, the CEREC blocks may be either ceramic (perhaps derived from feldspathic porcelain) or resin and would therefore contain radioactive properties consistent with other dental ceramic materials such as zirconia.
• Zirconia materials are refined for dental purposes from naturally occurring elements such as zircon. They may contain trace amounts of other elements depending on their original source which may include trace amounts of radionuclides. The radioactivity of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) artificial hip joints has been widely researched. A ceramic femoral head of approximately 100 grams (g) emits a radiation dose of approximately 0.13–0.53 mSv per year (Porstendorfer et al. 1996). In comparison, an all-ceramic dental implant weighs less than 2 g and results in a radiation dose of approximately 10 µSv per year. That is little more than a day of background radiation. A zirconia crown weighs even less than a dental implant and therefore the radiation dose is considered to be several orders of magnitude less than that typically measured for water, milk, vegetables, and meat (based on European standards). Therefore, we can say that the dose for both zirconia and CEREC-based crowns, while not completely zero, is below the level of background radiation and thus negligible.

Now let's consider whether radioactivity should be a factor in choosing a crown. There are many other factors that should be considered when deciding what type of crown to choose, particularly when it is known that the radioactivity of the material used is well below the level of background radiation.

Of greater concern would be dietary and functional habits. As stated previously, gold is a great option for patients who routinely grind and wear down their teeth. However, it is not as aesthetically pleasing as zirconia or CEREC crowns. If the tooth to be crowned is in an aesthetic area, patients usually desire the more natural appearance that can be attained by zirconia or CEREC crowns.

Time may be another factor. CEREC crowns are milled from a machine and are usually available the same day. This is a great aesthetic option for those with minimal time to waste in the dental chair or for those who don't want to wear a temporary crown for a few weeks while they wait for a lab to produce their crown and the dentist to have time to see them for a second visit.

Most dentists are excellent at helping a patient to decide which crown options are best suited for their unique oral environment and habits. Please also note the answers given to Ask the Experts Questions 11372 and 8152 concerning dental materials and radioactivity.

Heidi Kohltfarber, DDS, MS, PhD
Diplomate of the ABOMR

Reference

Porstendorfer J, Reineking A, Willert HC. Radiation risk estimation based on activity measurements of zirconium oxide implants. J Biomed Mater Res 32:663–667; 1996.