Download Radioactive Compounds In Dental Materials?

Radioactive Compounds in Dental Materials. Ed. 2
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2000-01-01
Is There A Renewed Trend of
Radioactive Compounds
In
Dental Materials?
Ulf Bengtsson
2000-01-01
Radioactive Compounds in Dental Materials. Ed. 2
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Radioactive Compounds in Dental Materials.
Abstract.
In order to mimic the fluorescence of human dentine radioactive compounds including
both natural and depleted uranium have been used in artificial teeth and ceramic
powders. This use of uranium has been going on at least since 1925.
Strong indications point at a new and accelerated use of radioactive compounds in other
dental materials. Especially thorium but also uranium and perhaps others might have
been added to some of the new composite resins dominating the market today. The main
reason is to achieve the necessary X-ray opacity. Non-radioactive alternatives do
however exist.
When used as a fluorescent agent in artificial teeth and ceramic powders uranium must
not exceed 0.03% by weight according to the only standard regulating radioactive
compounds in dental materials (USA). This standard explicitly says that the limitations
are only valid for uranium in dental porcelain. When used as radiopaque agents in dental
composites it will be necessary to add radioactive or other heavy metals up to a
considerably higher level, perhaps as high as 10% or more.
In one scientific article an acrylic resin for polymeric appliances is proposed to contain
11 – 14% of uranium. It is uncertain whether this has materialized into a marketed
product.
One patent describes a dental cement containing uranium in order to render the product
X-ray opacity.
No relationship between radioactive dental materials and cancer has been established. In
fact it has not even been investigated. No scientific article discussing a possible trend
towards modern radioactive dental materials has been found.
The use of radioactive compounds in dental materials has to be investigated. It has to be
established if radioactive fillings are used and if so, the problem has to be quantified.
Dental materials are ground and polished in the patients’ mouth, sometimes with
unintentional damage to the oral mucousa thus resulting in an imbedding of dental
material. This possibility has to be taken into account when examining the
biocompatibility of these dental materials. The possibility that the patient is swallowing
radioactive particles due to teeth grinding or dental treatment has to be addressed.
Possible inhalation of radioactive compounds by patients, technicians and dentists has to
be taken into account.
The use of intentionally radioactive implants where radioactivity is not used for its
therapeutic effects but for technological reasons alone has to be carefully reviewed.
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Ingredients of dental materials.
It has been argued that the ingredients of dental materials should be openly declared, as is
the case with drugs. Many have been in favor of such a listing. Dental trade in Sweden
has for example taken the initiative to declare different dental products and their
ingredients – the database DentMR found on the Internet at:
http://www.dentmr.dentalhandel.se/
Due to very imprecise listing of ingredients and very poor quality of information this
database is however of limited use to professionals. This especially holds true for the
more complex materials such as composites.
Cahn et al say (1):
“The components of composite resins are often disclosed by manufacturers in general
terms, but significant information may only be attained by chemical analysis.”
There are only two valuable sources of information openly available – scientific articles
and patents.
Scientific articles are of course of value when published. Especially so when showing
results of chemical analysis. It should however be pointed out that dental science has an
ethically troublesome situation because of the heavy involvement with the dental
industry. Most dental materials manufacturers are members of several worldwide dental
scientific organizations making monetary contributions to their activities. These dental
organizations own a number of scientific journals and counts most dental scientists and
many governmental officers in the field of dentistry as members. Members from the
dental industry hold official positions in dental scientific organizations. Few, if any,
scientific areas shows such a heavy organizational amalgamation with industry as dental
science does. In 1964 The American Dental Association Board of Trustees established
The American Dental Association Health Foundation, ADAHF. At present ADAHF
holds some 60 patents and a number of these deals with composites. New products are
developed and patents are licensed to dental manufacturers on commercial grounds. None
of the ADAHF patents mentions uranium or thorium.
The heavy organizational amalgamation between dental science and industry can be
further studied at: http://vest.gu.se/~bosse/ybftBEN95a.html
Patents are often overlooked as a source of information. Patents are legal documents and
therefore of special interest. Information otherwise regarded as secrets of the trade can
be found there.
It should be pointed out that the fact that a product has received a patent does not mean
that this particular product can be found on the market. However, background
information in the patents for the proposed invention often reveals ingredients of products
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currently on the market. This is for example true in the case of radioactive compounds in
dental composites.
Radioactive compounds in dental ceramics.
The use of radioactive compounds in dental ceramics is one of long standing. In these
materials radioactive ingredients are used for pure cosmetic reasons alone. Human
dentine is weakly fluorescent and in an attempt to mimic this characteristic uranium has
been added to both artificial teeth and ceramic powders for the manufacturing of crowns
and bridges. Moore and MacCulloch reveal that this was done as early as 1925 (2).
According to the American Dental Association the use began before 1935 (3). In a patent
by Lee and Müller in 1959 the inventors describes a mixture of cerium and uranium
giving an improved shade of white (4). In recent years the question of radioactive
ceramics has been addressed by Anusavice KJ (5): “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,…”
At the end of the seventies and beginning of the eighties Prof. Eiko Sairenji et al at Nihon
University placed the issue of radioactive dental ceramics firmly on the table with a
number of articles (6, 7, 8, 9, 10, 11, 12). This was some fifty-five years after the use of
uranium in dental ceramics began. A number of articles by other investigators have been
published (13, 14, 15, 16, 17)
In Sweden Prof. Rune Söremark established a cooperation with Prof. Sairenji (6). In 1979
Prof. Söremark also contacted The National Board of Health and Welfare (SoS) and
requested an immediate halt to all use of dental ceramics containing over 100 ppm of
uranium (18). The case was handed over to The Swedish Radiation Protection Institute,
SSI. Their policy is to remove all radioactive compounds from the market if the benefits
are non-existing or could be achieved otherwise (19). Due to the lack of expertise in the
area of dental materials SSI requested the view of SoS concerning the necessity to
include uranium in dental porcelain. SoS never answered that request. The case was
reported to The Parliamentary Ombudsmen, JO. Since the case was older than two years
JO saw no possibility to act. They did however find that the case was closed by SoS in
1982 without ever answering the request from SSI (20).
The only radioactive compound regulated for use in dental material is – to my knowledge
– uranium when used in dental porcelain and porcelain teeth in the USA. This standard is
explicitly limited to defining maximum uranium content in prefabricated artificial teeth
made from fused porcelain and porcelain powders for making custom crowns and
bridges. The uranium content is rather low and must not exceed 0.03% (3).
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In recent years it seems as though depleted uranium, a waste product from the
manufacturing of nuclear weapons and fuel has been favored. Natural uranium has
however also been used.
It has been argued that uranium mainly emits -radiation that can not penetrate the oral
mucosa. There are however several occasions when for example crowns are grinded
within the mouth of the patient. Unintentional injury of the oral mucosa is not
uncommon. Imbedding of dental materials into the mucousa is well known.
For example Levison DA et al say (21):
“X-ray energy spectroscopy (XES) of all particulate matter found by light microscopy in
histological sections of 222 oral lesions revealed a much wider range of elements than
expected from dental amalgam. Subsequent XES of a variety of endodontic materials,
impression materials and toothpastes indicated possible sources for virtually all elements
identified in the histopathological lesions. “
“…possible implications of local implantation and large scale ingestion of such
substances are discussed. “
Inhalation and swallowing of radioactive powder during dental treatment or teeth
grinding is not unlikely.
Radioactive compounds in some dental composites and other materials
I would like to bring into the open the question if the use and concentration of radioactive
compounds in dental materials has accelerated during later years. No scientific articles
have been found dealing with this subject. However, several patents reveal the use of
radioactive compounds in dental composites. One of the big changes that have taken
place within dentistry in recent years is that of the introduction of dental composites. As
being the main alternative to dental amalgam its use has risen greatly over the last
decades.
Polymers used in dental composites are X-ray translucent. In composites X-ray opacity
has been achieved by adding various heavy metal fillers, some being toxic, others being
radioactive. Proposed fillers include uranium, thorium, lead, mercury, barium, bismuth
etc. Fillers are also added to achieve wear-resistance, reduced shrinkage etc. The total
amount of all sorts of fillers can be as high as 87% - the rest being polymer (1).
According to Cahn et al X-ray opacity is readily achieved by non-radioactive substitutes:
“Radiopacity of composites, which is essential for restorations in posterior teeth, is
readily achieved by incorporation of Ba, Sr, or Zn in the glass formulation.” (1)
Rheinberger V et al reveals in their patent that thorium is used as one such filler (22):
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“Disclosed as X-ray opaque fillers in EP-PS 0 011 735 are solid, sparingly soluble heavy
metal compounds, such as barium sulfate, barium fluoride and barium silicate, bismuth,
zirconium, lanthanum and thorium compounds and compounds of the rare earth metals.”
“It is a disadvantage of these materials that the heavy metals frequently used are toxic
and sometimes radioactive, whilst the oxides of the rare earths can lead to undesired
discolorations of the filling or prosthesis.”
Masuhara E et al. Further establishes the use of radioactive fillers in dental composite
(23):
“… dental filling material which has been ordinarily used in dental application. Examples
of such a dental filling material are apatite, soda-lime glass, silica, quartz, silica gel,
borosilicate glass, synthetic sapphire (alumina) and radioactive opaque filling materials,
such as barium oxide and zirconium glass.” In this example it is more likely that the
authors mean radioactive impurities rather than intentionally added isotopes of barium
and zirconium.
Smid J et al says (24):
“It is therefore an object of this invention to provide means for imparting radiopaque
characteristics to a wide range of polymers.
It is a further objective of this invention to provide radiopaque composites containing
heavy metal atoms which are evenly distributed within a polymer.”
“Most preferred heavy metals include barium, bismuth, lead, mercury and uranium.”
In another patent Sid et al say (25):
“The most preferred bismuth, mercury and uranium salts are bismuth tribromide, bismuth
nitrate and acetate; uranyl bromide, nitrate and acetate; mercury nitrate and acetate, and
the like.”
In a third patent Smid et al say (26):
“Abstract
Novel radiopaque materials comprise heavy metal salts, such as bismuth and uranium
salts complexed with a polymer. The metallic complexes which are permanent,
nonleachable and have radiopacities at least equivalent to that of aluminum do not
adversely affect the mechanical and physical properties of compositions. They are useful
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as medical and dental resins, in fabricating medical and dental appliances, prosthetic
devices, ...”
Temin SC of Colgate Palmolive Co holds a patent titled: Radio-opaque dental restorative
composition using one or both of thorium and tantalum oxides as the only x-ray
absorbent (27):
“The radiopaque dental filling compositions based on liquid polymerisable organic resin
binders and finely divided inert inorganic radiopaque filler particles essentially contain as
the only X-ray-absorbing component of the radiopaque filler particles 3 to 10 % by
weight of the total filler particles of thorium dioxide or tantalum pentoxide or a mixture
of thorium dioxide and tantalum pentoxide.”
A passage from the British patent GB695278:
“A dental cement contains uranium compounds, e.g. uranyl compounds and red coloring
materials, e.g. gold oxide, chrome-alumina colours, copper aluminate and manganic
oxide, which give the cement an appearance similar to natural teeth both in natural and
artificial light.” (28)
Rawls HR et al say in their article (29):
“It was found that, when present in PMMA at 11 to 14%, several compounds of either
bismuth or uranium or 35% of an organo-zirconium compound impart radiopacity
equivalent to that of aluminum.”
Michl , et al. (30):
“European Pat. No. 11,735 describes dental filling materials containing as the contrast
medium compounds of barium, bismuth, lanthanum, thorium and rare
earth metals, preference being given to the use of barium sulphate. “
From Walkowiak , et al. (31)
“Abstract
The invention provides dental materials which are opaque to X-rays and are based on
organic plastics in paste form, which comprises (a) a polymerizable binder, (b) a
crosslinked bead polymer and (c) an X-ray contrast medium.”
“The materials are useful, inter alia, for filing dental cavities.”
“Barium compounds, for example barium sulphate, barium silicate and barium fluoride,
are very particularly suitable. However, compounds of bismuth, for example bismuth
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oxynitrate, zirconium, for example zirconium dioxide, and lanthanum, for example
lanthanum oxide and compounds of thorium and the rare earth metals are also suitable.”
A translation of Botezatu E et al could perhaps be fruitful (32).
Thorotrast
The record of thorium in medicine is one of great sadness. A thorium based radiological
contrast medium known as Thorotrast has previously been used in medicine. Its use has
been abandoned because it induced cancer in a number of patients treated with the
product. A great number of Thorotrast studies have been performed worldwide – over
1000 hits in Medline. Thorotrast is considered a dark story in medical history (33, 34,
35).
Ways of administration and dose from Thorotrast are not comparable to those of thorium
in dental materials. It however shows that radioactive compounds should be treated with
the greatest respect when used within the body.
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References
1/
Cahn RW, Haasen P, Kramer EJ. Materials Science and Technology. A
Comprahensive Treatment.
Volume 14. Medical and Dental Materials. Volume editor Williams DF. VCH,
Weinheim, 1992.
2/
Moore JE, MacCulloch WT. The inclusion of radioactive compound in dental
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3/
Council on Dental Materials and Devices. American National Standards
Institute/American Dental Association Specification No. 52 for Uranium Content
in Dental Porcelain and Porcelain Teeth. JADA 1979;98:755-759.
4/
Smith DC, Williams DF. Biocompatibility of dental materials. Volume IV.
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5/
Anusavice KJ. Degradability of dental ceramics. Adv Dent Res 1992 Sep;6:82-9
6/
Sairenji E, Soremark R, Noguchi K, Shimizu M, Moberg LE. Uranium content in
porcelain denture teeth and in porcelain powders for ceramic crowns. Acta
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Sairenji E, Moriwaki K, Shimizu M, Noguchi K. Estimation of radiation dose
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Sairenji E, Moriwaki K, Shimizu M, Noguchi K, Anzai I, Ikeda N. Determination
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Sairenji E, Moriwaki K, Shimizu M, Noguchi K. Determination of uranium in
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Dec;19(4):159-64.
10/
Noguchi K, Shimizu M, Sairenji E. Uranium content and 235U/238U isotopic
ratio in dental porcelain powders determined by neutron activation analysis. Int J
Appl Radiat Isot 1981 Jan;32(1):56-7
11/
Shimizu M, Noguchi K, Moriwaki K, Sairenji E. [Distribution of uranium in
dental porcelains by means of the fission track method]. [Article in Japanese].
Radioisotopes 1980 Jul;29(7):326-31.
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12/
Noguchi K, Shimizu M, Sairenji E, Ikeda N. [Non-destructive neutron activation
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13/
Papastefanou C, Vitsentzos S, Garefis P. [Uranium concentration in dental
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14/
Goengrich A, Noel A, Louis JP. [Ceramics and radioactivity]. [Article in French]
Inf Dent 1987 Nov 26;69(41):3789, 3791, 3793 passim
15/
Kao Hsiung I Hsueh Ko Hsueh Tsa Chih. [Measurement of the uranium content in
materials used for porcelain teeth]. [Article in Chinese] 1986 Mar;2(3):149-52
16/
Caruso C, Crapisi S, Conz A. [Determination of the uranium content of dental
porcelains and of porcelain teeth]. [Article in Italian] G Stomatol Ortognatodonzia
1984 Oct-Dec;3(4):720-1
17/
Gorban G. [Optical behavior, especially under ultraviolet rays, of certain dental
porcelains]. [Article in French]. SSO Schweiz Monatsschr Zahnheilkd
1972;82(6):645-70
18/
Söremark R. Karolinska Institutet 1979-05-23. Socialstyrelsen Dnr L 517:697/79.
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Snihs J, Bergman C. About radioactive materials in odontologicalk rehabilitation.
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Norell Söderblom G. 1989-04-26. Dnr 2605-1988.
21/
Levison DA, Crocker PR, Lee G, Shepherd NA, Smith AP. Unexpected inorganic
elements in oral lesions: results of X-ray energy spectroscopy (XES) on
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22/
Rheinberger V, Moszner N, Salz U.X-ray opaque dental materials .United States
Patent 5,780,668. July 14, 1998 . Ivoclar AG, Schaan, Lichenstein
23/
Masuhara E, Kadoma Y, Matsumoto T, Komai T, Yamada E, Nakachi O,
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May 8, 1990. Nippon Oil and Fats Co., Ltd.,Tokyo, Japan.
24/
Smid , et al. Homogeneous radiopaque polymer-organobismuth composites.
United States Patent 5,256,334, October 26, 1993
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25/
Smid , et al. Novel radiopaque heavy metal polymer complexes, compositions of
matter and articles prepared therefrom. United States Patent 5,024,232, June 18,
1991.
26/
Smid , et al. Novel radiopaque heavy metal polymer complexes, compositions of
matter and articles prepared therefrom. United States Patent 4,882,392.
November 21, 1989
27/
Temin SC. Radio-opaque dental restorative composition using one or both of
thorium and tantalum oxides as the only x-ray absorbent. Patentnumber
CH646600. December 14 1984. COLGATE PALMOLIVE CO (US).
28/
Patentnummer: GB695278. EC klassifikation: A61K6/06 Ekvivalenter:
CH281900
29/
Rawls HR, Starr J, Kasten FH, Murray M, Smid J, Cabasso I. Radiopaque acrylic
resins containing miscible heavy-metal compounds. Dent Mater 1990
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30/
Michl et al. Radiopaque dental materials. United States Patent ,629,746
December 16, 1986.
31/
Walkowiak , et al. Dental materials which are opaque to X-rays and are based on
organic plastics in paste form. United States Patent 4,302,376. November 24,
1981.
32/
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33/
Beer TW, Carr NJ, Buxton PJ. Thorotrast associated nodular regenerative
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34/
Stover BJ. Effects of Thorotrast in humans. Health Phys 1983;44 Suppl 1:253-7.
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Mays CW. Cancer induction in man from internal radioactivity. Health Phys 1973
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Other references of interest
A/
Terzakis JA, Blake MN, Weaver SC, Reidy JJ. Radiation-induced lesion of the
oral cavity: thorium depositions detected by x-ray microanalysis. Oral Surg Oral
Med Oral Pathol 1985 Apr;59(4):399-404
B/
Goren AD, Harley N, Eisenbud L, Levin S, Cohen N. Clinical and radiobiologic
features of Thorotrast-induced carcinoma of the maxillary sinus. A case
report.Oral Surg Oral Med Oral Pathol 1980 Mar;49(3):237-42
C/
Baran GR. [Fluorescence of dental ceramics by means of non-radioactive
materials]. Dtsch Zahnarztl Z 1977 Dec;32(12):962-4