Answer to Question #8568 Submitted to "Ask the Experts"
Category: Medical and Dental Patient Issues — Dental
The following question was answered by an expert in the appropriate field:
Regarding porcelain in the mouth, problems I find are (1) just because we are exposed to other radiation sure does not mean it is okay to be exposed to more, (2) the radiation is not directly up against us (including the mucosa, which is more vulnerable), (3) it is 24 hours a day forever, and finally (4) what about those who had some in from 20 years ago? Any suggestions? Is there an accurate way to measure it? Am I going to have to replace it all? Cancer is something that is rather difficult to turn back once it hits.
Your question shows concerns for radiation that most people share. However,
to determine potential risk from any source of radiation there are several
questions that we need to answer. First of all, what types and amounts of
radiation are involved? What part of our body may be exposed and how? And
lastly, how much radiation dose will we receive? After we answer these
questions, we can gain some insight into possible consequences by comparison
with other sources of radiation exposure.
To address your concerns for radiation from porcelain in dentures and
crowns, we need to consider the type of radiation. The National Council on
Radiation Protection and Measurements (NCRP) Report 95 indicates that porcelain
dentures and crowns are made of feldspar materials that contain small
quantities of radioactive potassium-40. In addition, beginning in the 1940s
until the mid-1980s, the practice was also to add small amounts of uranium to
give the dentures the natural color and fluorescence of real teeth. Uranium and
its decay products of thorium and palladium are sources of alpha, beta, and
gamma radiation. However, for several reasons discussed in Report 95, only the
beta particles from uranium and potassium are likely to deposit any significant
radiation dose to cells of the oral mucosa or skin inside the mouth. Several studies in Report 95 show that for typical concentrations of uranium
and potassium in porcelain dentures, the average beta dose to a person in the
U.S. population is about 1.3 mSv a year to the basal mucosa or skin inside the
mouth. The millisievert (mSv) is a
measure of radiation energy deposited in tissues. For comparison, NCRP Report
116 recommends a skin dose limit of 50 mSv a year for members of the public.
Thus, the radiation dose contribution from porcelain dentures is only a small
fraction of the recommended limit. When the beta dose to skin in the mouth is
adjusted to an equivalent whole-body dose and the proportional amount of skin
irradiated, the number drops to 0.00013 mSv a year. This report further
recommends that any corresponding whole-body dose of less than 0.01 mSv a year
is considered a negligible risk. For comparison, a recent report (NCRP 160)
shows an average person in the United States receives an equivalent whole-body
radiation dose of 6.2 mSv a year from natural and man-made sources. All of the
reported studies would seem to indicate that you do not need to remove or
replace porcelain dentures or crowns. There are also no reports in the
literature to indicate any cancer attributed to radiation from porcelain. You also asked about measurements. The only accurate way to measure
radioactivity in dentures or crowns would be to take a sample to a laboratory
where the materials may have to be ground up or dissolved for analysis. This
would be an expensive analysis and may not be warranted in light of the studies
described above. For more information on radiation from dentures, you may wish to consider
the answer to Question #8152 on the HPS Web site Ask the
Experts feature. Helpful information on uranium in dentures is also provided on the Oak Ridge Associated
Universities Web site. Ray Johnson, MS, PE, FHPS References
Available at www.ncrponline.org. National Council on Radiation Protection and Measurements (NCRP) Report No.
95, “Radiation exposure of the U.S. population from consumer products and miscellaneous
sources,” Bethesda, MD 1987 National Council on Radiation Protection and Measurements (NCRP) Report No.
116, “Limitations of exposure to ionizing radiation, “Bethesda, MD 1993 National Council on Radiation Protection and Measurements (NCRP) Report No.
160, “Ionizing radiation exposure of the population of the United States,”
Bethesda, MD 2009
Certified Health Physicist