Friday, January 25, 2008

Has Dental Amalgam Been Torpedoed and Sunk?

J Dent Res 87(2):101-102, 2008
© 2008 International and American Associations for Dental Research

GUEST EDITORIAL
Has Dental Amalgam Been Torpedoed and Sunk?
Derek W. Jones

Professor Emeritus of Biomaterials, Dalhousie University, Halifax, NS, Canada

dwjones@dal.ca

KEY WORDS: Mercury • amalgam • environment • scientific principles

For the past 20 years, the public has been bombarded by sensational, confusing, and misleading media reports about health issues related to dental amalgam. The public opinion on this issue has been modified by minority, non-scientific views driven and supported by media sensationalism. Mobilization of irrational public fear is the strategy used by lobby groups to pressure governments to change public policy (Jones, 1993). It is important that governments adhere to scientific principles and base health and environmental policies on sound scientific knowledge. Dentistry is an applied science and needs to bring issues such as those dealing with dental amalgam to the attention of governments.

I recently read a news item regarding the ban being imposed on dental amalgam in Norway. As a scientist, I was appalled to read of the decision taken by the Norwegian Government (Ministry of Environment) on December 14, 2007. This legislation aims to prohibit the production, importation, exportation, sale, and use of substances that contain mercury. However, the prohibition does not cover mercury that occurs naturally in coal, ore, and ore concentrations (presumably cinnabar could be included in this category). According to the Norwegian government, the regulation covering dental amalgam will come into effect on January 1, 2008, and for more limited use on December 31, 2010 (Norwegian Ministry of the Environment, 2008). In a prepared statement, Norwegian Minister of the Environment Erik Solheim said that the reason for the ban is the risk to the environment that mercury may pose. "Mercury is among the most dangerous environmental toxins. Satisfactory alternatives to mercury in products are available, and it is therefore fitting to introduce a ban," said Solheim.

My strong objection to this bureaucratic travesty relates to the following:

1. At least 50% of environmental mercury pollution comes from natural sources.
2. Some 42% of environmental mercury pollution comes from the burning of fossil fuels (and yet for the moment they exclude coal) (Jones, 2004).
3. No valid scientific studies have ever shown that dental amalgam poses a health hazard to patients, to dentists, or to the environment.
4. A patient with 10 amalgam surfaces in his/her mouth would have a mercury intake into the blood which would be only 2% of the World Health Organization’s Acceptable Daily Intake (WHO ADI 40 µg/day) for mercury, with no adverse health effects.
5. I have calculated that the environmental impact of mercury from 800,000 dental offices worldwide would represent between 0.04 and 0.2% of the total worldwide environmental mercury pollution from all sources (this would be significantly reduced by the use of amalgam traps [ISO 11143, 1999], which are increasingly being used).
6. I have also calculated that the worldwide environmental impact of mercury discharges into the sewers from 20 billion amalgam surfaces in people’s mouths represents between 0.01 and 0.07% of the total environmental mercury pollution.

I could understand if all industrial use of mercury, such as the burning of fossil fuels, was banned in Norway, together with the unsafe disposal of mercury-containing batteries and lamps. Each year, close to 8000 kg of mercury from fluorescent lamps end up in landfills and incinerator plants in North America alone (Chong, 1997). Without question, it is the emerging industrial countries that represent the major threat to increased mercury pollution. Estimates of mercury put into sewer systems by dentistry are incredibly small in comparison with the worldwide release of mercury, which has been estimated as 6.3 million kg (Chong, 1997). However, another estimate puts the global figure at between 22 and 33 million kg of mercury discharged into the environment each year as a result of human activities (Chin et al., 2000). Whatever the real number is for total mercury released into the environment on a global scale, the amount released from dental procedures and dental amalgam is not a significant contributor to the problem.

The proposed implementation by Norway to ban a very sound and effective dental material makes no scientific, economic, or environmental sense at all. Unlike composite-resin-based materials (alternatives to amalgam fillings), amalgam has an elastic modulus (stiffness) similar to that of natural tooth enamel. This lends support to the tooth structure by the filling material. Composite resin fillings, in contrast, are less stiff than natural tooth enamel and are unable to support the tooth structure at the margins to the same extent. Unlike amalgam, composite resin materials take up water, which is detrimental to their mechanical properties. Amalgam has wear characteristics similar to those of natural teeth, while composite materials wear more readily. In addition, interproximal placement of amalgam is much easier than for composite. Composite resin materials retain a greater amount of plaque compared with amalgam, which can predispose to dental caries adjacent to the composite restorations. Composite resin materials are required to be replaced more frequently than dental amalgam. Each time a restoration has to be replaced, additional natural tooth structure is lost.

At present, there is no conclusive evidence in the scientific literature to demonstrate a link between the cause of irreversible neurological disorders or of impaired kidney function and mercury vapors from dental amalgam. Animal experiments to date have not been able to establish conclusively any cause-and-effect link that can be extrapolated to human exposure to mercury from amalgam restorations (Jones, 1999).

Although it is generally accepted that some 50% of mercury pollution comes from natural sources, the relative contribution from natural vs. anthropogenic mercury sources remains unclear, and the natural source may be considerably higher. Pollution from dentistry is insignificant compared with that from industrial use and natural sources. Clearly, the above information leads to the logical conclusion that banning "dental amalgam" is a political issue that will have no impact on total worldwide mercury pollution.

A colleague (C Lloyd, personal communication) recently brought to my attention the very significant mercury pollution problem faced by the Norwegian government. This involves a German submarine U864 that was torpedoed off Bergen in February, 1945. It was carrying some 65 thousand kg of mercury and heading for Japan (Oziewicz, 2006; Cowell and Gibbs, 2007). The wreck was discovered in 2003, and the Norwegian government has been criticized for mishandling this mercury pollution problem. It is tempting to consider whether the banning of dental amalgam by Norway is in fact a political diversion.

FOOTNOTES

About the author: Derek Jones is a Past President, Canadian Association for Dental Research (CADR, 1992-95), Past President of the IADR Dental Materials Group (1990-91), and Chair of the Canadian Dental Association’s Dental Materials and Devices Committee (1993-1998). He is currently Chair of ISO/TC 106 Dentistry (2005-2010). He was Secretary of ISO/TC/SC1 Dental Filling and Restorative Materials from 1979 to 1997, and Chair of ISO/TC/SC1 from 1998-2005, as well as Chair, Canadian Standards Association Technical Committee on Dentistry, and Chair, Canadian Advisory Committee to the International Standards Organization, 1979-2005.

Received January 10, 2008; Accepted January 10, 2008

REFERENCES

Chin G, Chong J, Kluczewska A, Lau A, Gorjy S, Tennent M (2000). The environmental effects of dental amalgam. Aust Dent J 45:246–249.[ISI][Medline]

Chong R (1997). Mercury reduction and product stewardship. Paper presented at Mercury Elimination and Reduction Symposium Pollution Probe, May 5–6, 1997, Toronto.

Cowell A, Gibbs W (2007). German sub menaces North Sea 61 years after sinking, International Herald Tribune Europe, January 10.

ISO 11143 (1999). Dental equipment-amalgam separators. Geneva, Switzerland: ISO Central Secretariat.

Jones DW (1993). The enigma of amalgam in dentistry. J Can Dent Assoc 59:155–166.[Medline]

Jones DW (1999). Exposure or absorption and the crucial question of limits for mercury. J Can Dent Assoc 65:788–792.

Jones DW (2004). Putting dental mercury pollution into perspective. Br Dent J 197:175–177.[ISI][Medline]

Norwegian Ministry of the Environment: Amendment of regulations of 1 June 2004 #922 relating to restrictions on the use of chemicals and other products hazardous to health and the environment (product regulations). The amendment will come into effect 1 January 2008. WHO (2004). International Digest of Health Legislation. Reg 1479 amending Reg 922, 17 Nov 2004, and Reg 818 amending Reg 922, 11 July 2005.

Oziewicz E (2006). Toxic shield guards U-864’s secrets. The Globe and Mail, December 7.

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