From: Steven Bornfeld on 18 Nov 2005 17:19
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Ilena Rose wrote:

Interesting bit of history--thanks!
I have heard that uranium WAS in fact used in denture teeth at one
time. I have been unable to find any evidence that this was done less
than about 50 years ago, however.

Steve

From: Ilena Rose on 18 Nov 2005 20:09
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On Fri, 18 Nov 2005 23:19:03 GMT, Steven Bornfeld
<dentaltwinmung@earthlink.net> wrote:

Here's some more:

Uranium Containing Dentures (ca. 1960s, 1970s)

http://www.orau.org/ptp/collection/consumer%20products/dentures.htm

Modern dentures are typically made from acrylic plastic, but at least
until the 1980s, porcelain was also very commonly used.

In the 1940s, manufacturers began adding uranium to the porcelain
powder used to make dentures. The idea was that the fluorescence of
the uranium would help mimic the look of real teeth under a variety of
natural and artificial light conditions. Uranium had the advantage
over some of the alternative materials because its fluorescence is
unaffected by the high temperatures (800 ? 1400 degrees centigrade)
used to bake the porcelain. According to NCRP 95, it seems that
manufacturers had stopped adding uranium to porcelain dentures by 1986
or so.

Papastefanou et al (1987) measured uranium levels in 22 samples of
porcelain powders used in Greece and found that the concentrations
ranged from 3.6 Bq/kg (0.1 pC/g) to 5600 Bq/kg (151 pCi/g). A more
limited study in 1977 by Binney and Scherpelz indicated an average
uranium concentration of 224 ppm (2,760 Bq/kg or 70 pCi/g). In England
, O?Riordan and Hunt estimated that the average concentration in the
porcelain powders might be as high as 5,060 Bq/kg (136 pCi/g).
Sairenji et al measured uranium concentrations in Japanese dental
powders ranging from 4.56 Bq/kg (0.12 pCi/g) to 1,000 Bq/kg (27
pCi/g).

Note that the naturally occurring potassium-40 in these dentures can
contribute significantly to their overall radioactivity.

It is likely that the dose to the oral mucosa as a result of the
uranium in dentures is primarily due to the beta particles emitted by
the decay products of U-238: Th-234 and Pa-234m. The contribution of
the alpha particles to the dose is hard to predict due to the
tremendous uncertainties in their attenuation.

One investigation in Great Britain (O?Riordan and Hunt 1974) estimated
that a set of porcelain dentures containing 0.1 % uranium might
deliver an annual dose to the oral mucosa of 600 rem by the emitted
alphas and 2.8 rem by the beta particles. A 1987 study by Papastefanou
et al calculated a similar dose: 400 rem per year. Don Thompson, with
the US FDA, calculated a dose of approximately 130 rem per year to the
oral mucosa due to the alpha emissions from dentures with a uranium
concentration of 0.044 %. NCRP Report No. 95 estimated that the annual
beta dose to the basal cells of the mucosa (the most sensitive portion
of the oral mucosa) was 0.7 rem. This dose was due to the betas
emitted by potassium-40 as well as the decay products of the uranium.
When they factored in the percent of the population that did not have
uranium-containing dental prostheses, the NCRP estimated that the
average beta dose to the basal cells of the mucosa in the US
population was approximately 0.13 rem. To permit a calculation of the
effective dose equivalent, the NCRP also employed a weighting factor
of 0.0001 for the basal cells of the mucosa.

The pertinent Nuclear Regulatory Commission regulations (2003), found
in 10 CFR 40.13a are as follows:

"40.13 Unimportant quantities of source material.

(a) Any person is exempt from the regulations in this part and from
the requirements for a license set forth in section 62 of the Act to
the extent that such person receives, possesses, uses, transfers or
delivers source material in any chemical mixture, compound, solution,
or alloy in which the source material is by weight less than
one-twentieth of 1 percent (0.05 percent) of the mixture, compound,
solution or alloy."

This limit of 0.05 % (500 ppm uranium) equates to approximately 167
pCi/g or 6,170 Bq/kg.

References

Binney, S. and Scherpelz, R. Technique for Rapid Analysis of Uranium
in Porcelain Dentures. Health Physics 33: 341-343; 1977

Dietz, C. US Patent Number 301,174; 1942.

NCRP. Radiation Exposure of the U.S. Population from Consumer Products
and Miscellaneous Sources. NCRP Report No. 95; 1987.

Papastefanou, C., Vitsentzos, S. and Garefis, P. Uranium in Dental
Porcelain Powders and Dose Induced in Oral Mucosa. Radiation
Protection Dosimetry 19(1): 49-53, 1987.

Thompson, D. Recommendations on the Use of Uranium in Porcelain Teeth.
in NUREG/CP-0001, Radioactivity in Consumer Products. August 1978.

From: Vaughn on 18 Nov 2005 18:21
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Of course, beryllium is STILL used...
http://www.osha.gov/dts/hib/hib_data/hib19990902.html

Vaughn

From: Steven Bornfeld on 18 Nov 2005 20:46
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Vaughn wrote:

Yeah, it is. Apparently if it ain't nuclear (or should I say nucular)
it ain't sexy enough for the media--even the alternative crowd.
I have to thank you Vaughn for bringing this to my attention.

Steve

Yes. I read this on the www too. Thing is what do they use to produce
fluorescence now and can it be distinguished?