Radiation Exposure from Denture Containing Uranium
(last updated 18 Aug 2003)
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Up to the early 1980s, natural and depleted uranium has been widely used for dental porcelains to obtain a natural color and fluorescence of dentures and the superficial parts of crowns.
The original patent [Dietz 1942] describes the denture as having a body portion with a uranium contents of 0.01% to 0.1%, and an enamel portion with a uranium contents of 0.009% to 0.032%.
A further patent [Lee 1959] describes improvements obtained by the addition of cerium and, optionally, samarium. The uranium percentage range given in this patent is 0.004% - 0.15% uranium oxide.
In addition, increasingly, depleted uranium (DU) was used rather than natural uranium. This had two benefits ľ it was cheaper and it was less radioactive.
Later the uranium has been replaced by rare earth elements, such as cerium, terbium, dysprosium or samarium.
- Uranium concentrations of 170 to 13,300 ppm (0.017 - 1.33 wt-%) were found in 15 types of porcelain powders of one manufacturer [Noël1988].
- Uranium concentrations of 0.5 - 24.7 ppm were found in 8 types of porcelain powders marketed in Sweden [Sairenji1982].
Exposure of Workers Manufacturing Denture
- Inhalation of powder dust
For a dental technician working in a room in which porcelain powder (with 0.05% by weight of uranium) is lost during tooth construction, and using conservative assumptions for the concentration of uranium in dust in air and for exposure time, the whole-body dose was estimated to be 0.02 ÁSv (2 Árem). [NUREG/CR-1775 / NUREG-1717]
- Uranium concentrations of 31 - 145 ppm were found in 4 types of porcelain denture teeth marketed in Sweden [Sairenji1982].
- Uranium concentrations of 0.6 - 2.8 ppm were found in 6 types of porcelain powders marketed in Sweden, baked and fired on gold plates (simulating use for superficial parts of crowns) [Sairenji1982].
U.S. NRC standard for uranium in denture [NUREG-1717]:
- 0.05 weight-percent (500 ppm)
German standard for uranium in denture [Zinke1994]:
- 0.03 weight-percent (300 ppm) (0.1 wt-% until 1987)
In the early 1980s, the last of the U.S. major manufacturers had phased out the addition of uranium in dental ceramics [NUREG-1717]. A 1993 (?) survey among German producers showed that none of them added uranium to their products at this time any longer.
Exposure of Denture Wearers
- Skin dose
NRPB-R25 (1974) contained calculations and measurements of doses to soft tissue in the mouth assuming DU
was used. The doses were nearly 30 mSv per year to the basal layer of the epithelium in
the mouth, and this was in breach of the UK Medical and Dental Code of Practice in the 1970s.
This code set a limit of 15 mSv per year averaged over any organ, for practices with no
obvious therapeutic or diagnostic benefit. [NRPB 2001, p. 3]
NCRP 95 (1987) estimated that the annual dose equivalent to the basal mucosa of a dental prostheses wearer from beta particles was 5 mSv (0.5 rem) at 0.02% (200 ppm) by weight of uranium. On the basis of a weighting factor of 0.01 for the human skin, and assuming that irradiation of the basal mucosa is equivalent to irradiation of 1% of the skin, the effective dose equivalent (EDE) was estimated to be 5 · 10-4 mSv (0.05 mrem). [NCRP 95 / NUREG-1717].
The annual dose equivalents from alpha particles at the surface of the teeth range from 1 to about 4 Sv (100 to 400 rem) for teeth containing 0.05% by weight of uranium. However, since the maximum range of the alpha particles in tissue is 30 Ám, essentially the entire dose to tissues of the mouth would be received by superficial cells on the surface and the dose to radiosensitive cells in the basal layer of the tissues would be zero. [NUREG/CR-1775 / NUREG-1717]
[Dietz 1942] Dietz C.: Fluorescent Artificial Teeth - United States Patent No. 2,301,174 (1942) *)
[Lee 1959] Lee P W, and Müller G.: Fluorescent Artificial Teeth - United States Patent No. 2,895,050 (1959) *)
[NCRP 95] National Council on Radiation Protection and Measurements , NCRP Report No. 95, "Radiation Exposure to the U.S. Population From Consumer Products and Miscellaneous Sources." 1987
[Noël1988] A. Noël, A. Goengrich, J.-P. Louis: Céramiques dentaires et radioactivité, in Radioprotection Vol. 23 (1988) No. 3, p.291-300
[NRPB 2001] Radiological Protection Bulletin, No. 229, National Radiological Protection Board , March 2001
[NRPB-R25] O'Riordan M. C., Hunt G. J.: Radioactive Fluorescers in Dental Porcelains, National Radiological Protection Board , Report R25, 1974)
[NUREG-1717] Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials, Final Report, NUREG-1717, U.S. Nuclear Regulatory Commission, 2001
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[NUREG/CR-1775] U.S. Nuclear Regulatory Commission , NUREG/CR-1775, SAI01380-469LJ/F, Buckley, D. W., et al. "Environmental Assessment of Consumer Products Containing Radioactive Material." NRC: Washington, D.C. 1980
[Sairenji1982] Eiko Sairenji, Rune Söremark, Kunikazu Noguchi, et al.: Uranium cotent in porcelain denture teeth and in porcelain powders for ceramic crowns, in Acta odontologica Scandinavia Vol. 40 (1982), No. 5, p.333-339
[Zinke1994] A. Zinke: Radioaktivität in zahnärztlichen Keramikmassen?, in ZWR Zahnärztliche Welt Zahnärztliche Rundschau Vol. 103 (1994) No.1, p. 18-28
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