Published Estimates of Hg Exposure in Adults With Dental Amalgam – Mercury Fillings

Why was this Report Prepared?

To date, no population-based assessment of Hg exposure from dental amalgam specific to the US general population has been undertaken. The quantification of Hg dose associated with dental amalgam is required to complete a proper risk assessment. Determining the amalgam associated dose can be directly compared to the dose associated with regulatory reference exposure levels (RELs) prescribed for the protection of the health of the general population. 

Such RELs are published by the USEPA (1995), the USATDSR (1999), the California EPA (2008), and others; these RELs are discussed in greater detail later in this report. 

dental amalgam is composed of approximately 50% elemental (liquid)

Hg by weight. It has been used in North American dentistry for perhaps 150 years (Clarkson

and Magos, 2006) and during that time has been the subject of repeated controversy, often

referred to as the Amalgam Wars (Clarkson and Magos, 2006). A brief historical account of its

introduction, use and controversy is provided by Molin (1992). Scientific articles regarding

amalgam’s potential toxicity date back at least to 1885 (Talbot, 1885). These wars or debates

have been due to the recurring concern for the potential health risks posed by exposure to the

Hg used in the manufacture of dental amalgam.

The quantity of Hg0 released from amalgam is often referred to as ‘minute’ (ADA, 2008; CDA,

2005) or ‘very small’ (AGD 2007). However, it is not the dose itself that determines safety, it is

how that dose compares to levels considered ‘safe’ or without anticipated harm that determines

whether or not the dose is significant (hazardous or free from harm). Irrespective of quantity, a

minute dose can be very hazardous if the substance is very toxic and the received dose

exceeds the toxic dose. Dental amalgam has been identified as the single largest source of

continuous Hg exposure for members of the general population who possess amalgam fillings

(WHO, 1991; Heath Canada, 1996). Also, previous assessments have demonstrated that the

dose of Hg received from amalgam exceeds what is considered to be a safe or reference dose

(see HC, 1995; Richardson and Allan, 1996).

The Academy of General Dentistry (AGD 2007) goes on to say that “mercury in dental amalgam

is not poisonous”. However, the mercury that evolves from amalgam, as for any other source, is

toxic; for example, Hg0 originating from amalgam has been shown to cause neurobehavioral

and other toxic effects in dental staff that place amalgam fillings. The Hg0 from amalgam is no

different chemically or toxicologically than the Hg0 from any other source. The American Dental

Association (ADA) recommends storing scrap amalgam and used amalgam capsules in airtight

containers (ADA 2007). The ADA’s mercury hygiene recommendations are predicated on

protecting the safety of dental professionals (ADA 2003; ADA Council on Scientific Affairs).

In a recent survey of members of the Society of Toxicology (STATS et al 2009) Hg was

surpassed as the primary toxic substance of concern only by smoking-related issues (direct use

of cigarettes, use of chewing tobacco, second-hand smoke).

Adding further to the controversy surrounding the continued use of amalgam in North America is

the fact that Norway has now banned the use of amalgam in dental treatment (with certain

minor exemptions) (Norway Ministry of Environment, 2007). Sweden has also banned the

further use of amalgam in general dentistry (Sweden Ministry of Environment, 2009). Those

bans were based predominantly on the health concerns related to exposure to Hg0 from this

dental material.

2.3 Who is Exposed and How are They Exposed?

Those people who possess one or more amalgam filled tooth surfaces will be directly exposed

to Hg from dental amalgam. The fetus is also exposed due to maternal amalgam load, as are

breast-fed infants as breast milk Hg content reflects maternal amalgam load. Excluding the

fetus and infants, the primary route of exposure to Hg from dental amalgam is via inhalation of

Hg0 emanating from in-place amalgam fillings (WHO, 1991; Richardson and Allan, 1996;

USFDA, 2009).

The chart below represents the estimated daily dose of mercury (from amalgam fillings) compared to mercury safety levels as established by the EPA and CalEPA. EPA safety levels were determined almost 20 years ago, whereas CalEPA was recently completed in 2008.

..it was determined that some 67.2 million Americans would exceed the Hg dose associated with the REL of 0.3 ug/m3 established by the US Environmental Protection Agency in 1995, whereas 122.3 million Americans would exceed the dose associated with the REL of 0.03 ug/m3 established by the California Environmental Protection Agency in 2008.”

Published Estimates of Hg Exposure in Adults With Dental Amalgam (Mercury Fillings)