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Canadian review - dental amalgam

Dagfinn Reiersol reiersol at telepost.no
Mon Jan 1 16:28:01 EST 1996


It seems that the readers of bionet.toxicology have been receiving the
tail end of a rather chaotic debate between Brian Sandle and myself,
originating in sci.med.dentistry, which has a lot of discussion of
fluorides and amalgam. I didn't realize until now that Brian had been
cross-posting these articles. Anyway, since you have been receiving
this type of material, I think you deserve something more structured.
Here is part of a recent Canadian review of dental amalgam.

Dagfinn Reiersol



ASSESSMENT OF MERCURY EXPOSURE AND RISKS FROM DENTAL AMALGAM
by G. Mark Richardson, PhD.,
Medical Devices Bureau, Environmental Health Directorate,
Health Canada, August 18, 1995,
Final Report (released November 27, 1995, in Toronto, at the 
stakeholders' meeting)

Executive Summary
For Canadians with amalgam-filled teeth, it was estimated that total 
mercury (Hg) exposure averages: 3.3 ug Hg/day in toddlers (aged 3 to 4

years); 5.6 ug Hg/day in children (aged 5 to 11 years); 6.7 ug Hg/day
in teens (aged 12 to 19 years); 9.4 ug Hg/day adults (aged 20 to 59
years; and 6.8 ug Hg/day in seniors (aged 60+ years). Of this
exposure, amalgam was estimated to contribute 50% to total Hg exposure
in adults, and 32 to 42% for other age groups. Estimates, based on two
independent models, of exposure from amalgam alone were: 0.8 - 1.4 ug
Hg/day in toddlers; 1.1 - 1.7 ug Hg/day in children; 1.9 -2.5 ug
Hg/day in teens; 3.4- 3.7 ug Hg/day in adults and 2.1 - 2.8 ug Hg/day
in seniors.

There are insufficient published data on the potential health effects 
of dental amalgam specifically to support or refute the diverse
variety of health effects attributed to it. Numerous studies
constantly report effects on the central nervous system (CNS) in
persons occupationally exposed to Hg. Virtually all studies failed to
detect a threshold for the effects CNS measured. A tolerable daily
intake (TDI) of 0.014 ug Hg/kg body weight/day was proposed for
mercury vapour, the principal form of mercury to which bearers of
amalgam fillings are exposed. This TDI was based on a published
account of sub-clinical (i.e. not resulting in overt symptoms or
medical care) CNS effects in occupationally exposed men, expressed as
a slight tremor of the forearm. An uncertainty factor of 100 was
applied to these data, to derive a reference dose (TDI) which should, 
in all probability, prevent the occurrence of CNS effects in
non-occupationally- exposed individuals bearing amalgam fillings.

The number of amalgam-filled teeth, for each age group, estimated to 
cause exposure equivalent to the TDI were: 1 filling in toddlers; 1
filling in children; 3 fillings in teens; and 4 fillings in adults and
seniors. It was recognized that filling size and location (occlusal
versus lingual or buccal) may also contribute to exposure. However,
data suggest that no improvement in prediction of exposure is offered
by any particular measure of amalgam load. Therefore, the estimates of
exposure derived from the number of filled teeth were considered as
reliable as those that might be based on size and position of amalgam
fillings, were such data available for the Canadian population.

Effects caused by allergic hypersensitivity to amalgam or mercury, 
including possible auto- immune reactions, can not be adequately 
addressed by any proposed tolerable daily intake. Individuals
suspecting possible allergic or auto-immune reactions should avoid the
use of amalgam selecting suitable alternate materials in consultation
with dental care (and possibly health care) professionals.

Preface
This report has been prepared in response to concerns that exposure to

mercury from dental amalgam may adversely impact on health. Recent 
reviews (USDHHS 1993, Swedish National Board of Health, 1994) have 
concluded that there is no evidence to suggest that dental amalgam, 
specifically, is injurious to health. However, the data base relating 
health impacts in humans or animals to amalgam specifically is small
and weak. This suggests that indirect evidence relating mercury vapour

exposure (the predominant form of mercury released by dental amalgam)
to human health effects (for which a large data base exists) is a
necessary basis for an evaluation of the possible health risks of
dental amalgam. In the reports previously mentioned, exposure to
mercury arising from amalgam was not adequately quantified, and a
level of mercury vapour exposure which is, in all probability,
tolerable to the vast majority of persons bearing amalgam fillings,
was not defined. This report attempts to address these previous
deficiencies.

This report is not exhaustive. Recent reviews on mercury (WHO 1990, 
1991; IARC 1993; ATSDR 1994) adequately review many aspects of mercury

toxicity and exposure. Instead, this report focuses on studies which 
report on health effects in dental care practitioners and other 
occupational groups exposed to relatively low levels of mercury. This 
report also examines recent research which hypothesizes a link between

mercury exposure, and thereby dental amalgam, and Alzheimers' Disease.

This report concentrates on effects associated with long term mercury 
vapour exposure (via inhalation) in humans. Other reviews (WHO 1990, 
1991; IARC 1993; ATSDR 1994) examined acute and sub-chronic exposure
in animals, and all aspects of the toxicology of exposure to other
forms of mercury via other routes of exposure (ingestion, dermal
absorption), in extensive and adequate detail such that this is not
repeated here.

Any medical or dental material, such as amalgam, will have associated 
with it some degree of health risk. The purpose of this report is to 
attempt some determination of what that risk is (i.e. what effect(s)
it may cause), how significant it is (i.e. what level of exposure
should be free from effect), and what proportion of the population
might be at some degree of risk (i.e. how many exceed the level
considered to be free from effect).





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