African Journal of
Oral Health Sciences
AJOSHS 2015 V2 (2)
IS THE SAFETY OF DENTAL AMALGAM STILL IN
QUESTION: A LITERATUE REVIEW
Maina S.W, Nyaga J.M, Kisumbi B, Kassim A.B, Dienya
T.M, Simila H.O
Department of Conservative and Prosthetic Dentistry, School
of Dental Sciences, University of Nairobi
Abstract:
Objective: To review the scientific evidence on the adverse effects of dental amalgam in adults.
Study design and method: The key words “adverse effects” and “safety “of “dental amalgam” were used to search for
publications in peer reviewed journals on adverse health effects of dental amalgam.
Results: Forty three papers were accessed and reviewed. Several researchers have reported that mercury released from
dental amalgam restorations have not been demonstrated to contribute significant systemic effects on the immune system
or neurological diseases. The available scientific data are not sufficient to relate various complaints and mercury release
from dental amalgam especially due to other sources mercury like fish consumption. Moreover there are no controlled
studies that have demonstrated adverse effects on health from amalgam fillings. Remarkably, the literature reviewed
stated that amalgam restorations remain safe.
Conclusion: There is no validated scientific evidence that dental amalgam causes adverse health effects in adults.
Key words; - dental, amalgam, safety,
Introduction
Dental amalgam is made by mixing
approximately equal parts of elemental liquid mercury (43 to 54 %) and
an alloy powder (57 to 46 %) composed of silver, tin, copper and
sometimes smaller amounts of zinc,
palladium or indium. This material
has been extensively used as a tooth
filling material for many decades
(170 years). In the United States
alone, the American Dental Association estimates that amalgam fillings
have restored the teeth of 100 million Americans (1). Dental amalgam
has, beyond doubt, saved millions of
teeth that otherwise would have been
extracted. The fact that dental amalgam contains and releases elemental
3
mercury, concerns have been raised
over the years with respect to its potential health effects to the dental
personnel, the patient and lately to
the environment (2). Amalgam is the
most thoroughly studied and tested
filling material in use. After decades
of research projects undertaken
around the world, no controlled studies have ever been published demonstrating adverse effects from amalgam fillings (3). Compared to other
restorative materials, it is among
those which have been regularly improved in terms of its mechanical
properties and presentation. It is durable, easy to use, inexpensive and
its longevity in a wide range of clinical application has been tested and
reported to be 10-20years with an
average survival of 15years (4). Despite the increasing use of tooth coloured materials with advantages of
adhesion and aesthetics, amalgam is
still one of the most widely used
dental restorative materials (1).
However, the anti-amalgamist claims
that "sensitive" individuals can develop neurological disorders, various
emotional problems, cardiovascular
problems, collagen diseases and immunologic disorders. To support
their argument, several tests have
been used; breath, urine, blood, skin,
stool, electro-dermal testing and air
analysis (5-7). These tests have been
found to be inconclusive due to the
difficulties in demonstrating that the
A Publication of the School of Dental Sciences
African Journal of
Oral Health Sciences
AJOSHS 2015 V2 (2)
source of mercury is from amalgam
fillings or exposure from foods, water and air. It is, therefore, not known
if the amount of mercury released
from dental amalgam is enough to
cause illness, even in the most exposed or the most sensitive minority
of the amalgam-bearing population.
The Scientific Committee of the
European Commission in 2008 concluded that dental amalgams are effective and safe, both for patients
and dental personnel. It also noted
that alternative filling materials are
not without clinical limitations and
toxicological hazards (8). This is
supported by the World Health Organization (WHO), FDI World Dental Federation and United Nations
Environment Program (UNEP) report on the Future Use of Materials
for Dental Restoration (2) and the
U.S. Food and Drug Administration
(FDA) which stated that elemental
mercury levels released by dental
amalgam fillings are not high enough
to cause harm in patients (9).
Material and Methods
The key words “adverse effects”
and “safety “ of “dental amalgam”
in adults were used to search for
publications from peer-reviewed
journals and key dental organization
statements, declarations and resolution The abstracts of the listed papers
in English were reviewed to determine the relevance of the articles to
the topics. Using the online library of
the University of Nairobi and the
internet 43 relevant articles were
down -loaded and reviewed.
Results
4
Exposure to mercury from dental
amalgam can occur during placement, removal and in function. The
evaporation of mercury from amalgams is affected by several factors:
the concentration of tin in the Ag-Hg
(ƒÁ1) grains, which make up the
matrix of the amalgam structure and
are the main mercury-releasing
phase (10) , corrosion process (11),
the atmosphere in which the amalgam is placed (12) the incorporation
of indium into the triturated mercury
or alloy powder (13-15), alloying a
small amount of palladium with the
alloy powder (16), alloy powder
shape (17) among others. Ohmoto et
al (18) examined the relationship
between mercury content and mercury evaporation from amalgams
during setting using high-copper
amalgams single composition and
admixed types (Table 1).
They further stated that most of the
factors influencing the mercury
evaporation from amalgam are incorporated during the alloy manufacturing processes. When preparing amalgam with more resistance to condensation, caution is needed to prevent
irregularities and cracks by carefully
monitoring the amount of mercury
used in trituration.
In an earlier study, Haikel et al (19)
Table 1 demonstrated a significant
direct correlation between Hg vapor
concentrations in intra-oral air and
the sizes of amalgam restorations
during each procedure: removing,
setting, and polishing although there
was no statistic significant difference. It is important to note that no
control group was used in this study
and other factors may have affected
the result. The amount of Hg released from the mouth during function has been reported to be 0.03 μg /
day (20, 21). Björkman and Lind
(21) showed that while the age of
the amalgam and the amalgam type
influence the extent of mercury release during the initial non-steadystate conditions, the steady-state
value of mercury daily dose due to a
single amalgam filling is 0.03 μg /
day, which is well below the calculated threshold-limiting value (TLV)
of 82.29 μg/day considered dangerous for occupational exposure in the
United States.
The release of mercury from restorations in the mouth has been shown to
be extremely slow. Berglund et al
(22) found that the amount of mercury released from the oral cavity
was time-dependent and reported
that, the amount of mercury released
with the time kept constant was almost independent of the pumping
flow rate up to 8 litres per minute. In
a later study (23), the same authors
tested the release of mercury over a
24hr period under conditions that
were as normal as possible (Table 1).
The estimated average daily dose of
mercury vapor inhaled from the
amalgam restorations was 1.7 μg.
Jones (24) reported that it would take
1,680 years for a 0.65g amalgam
restoration to lose all of the combined mercury based on the established rate of release. The very slow
release of a very small amount of
mercury from amalgam restorations
can be put into perspective by the
fact that a patient with 10 amalgam
A Publication of the School of Dental Sciences
African Journal of
Oral Health Sciences
AJOSHS 2015 V2 (2)
Table 1: The findings of different investigations on evaporation of mercury from dental amalgam.
Author /year
Population/sample
Investigation
Findings/Conclusion
Ohmoto et al (18)
High-copper amalgams
single composition and
admixed types.
The relationship between mercury content and mercury evaporation amalgams during setting.
Mercury content influenced
mercury evaporation from admixed-type amalgam
Haikel et al (19)
242 subjects
Berglund (23)
Halbach et al (26)
WHO
*Accepted daily mercury intake
surfaces in his/her mouth would have
a mercury intake into the blood
which would be only 2% (0.8 μg/
day) of the World Health Organization’s Acceptable Daily Intake
(WHO ADI 40 μg/day) for mercury,
with no adverse health effects (24,
25). Further Halbach et al (26) evaluated the internal exposure and absorbed dose of mercury related to
amalgam (Table 1).They concluded
that the estimates obtained are below
the tolerable dose set by WHO.
Therefore the amount of mercury
released from amalgam restorations
and absorbed by the body is minuscule and unlikely to cause adverse
health effects.
The exposure to mercury vapor is of
greater concern for dentists and their
staff than for patients. Several re5
Analyzed the level of mercury
vapor of intra-oral air before and
after removing, setting and polishing dental amalgam using
atomic absorption spectrometry.
Mercury vapor released measured at intervals of 30-45 min
using atomic absorption spectrophotometry.
The integrated mercury absorbed
from amalgam restorations randomized controlled trial.
Acceptable Daily Intake of mercury with no health effects.
searchers have reported that most
people with fillings have less than 5
micrograms of mercury per liter of
urine. Nearly all practicing dentists
have levels below 10 micrograms per
liter, even though they are exposed
to mercury vapor when placing or
removing amalgam fillings Thus,
even with that exposure, the maximum levels found in dentists are
only slightly higher than those of
their patients and are far below the
levels known to affect health, even in
a minor way (27-31). Hence based
on this data and the WHO maximum
acceptable daily intake with no
health effects (ADI) of 40 μg Hg/
day, a dentist could carry out 1000
amalgam procedures a week and
keep within the WHO ADI limits.
The results of investigations on
amalgam and its effects on health for
Surface texture immediately
after condensation affected
mercury evaporation.
Vapor was released during any
procedure.
Estimated average daily dose
of mercury vapor inhaled from
the amalgam restorations was
1.7 μg.
Reported estimates of up to 3
μg per day for an average
number of restorations
7.4 μg per day for a high
amalgam load.
WHO ADI 40 μg/day*
dental personnel and the general
populations are shown in Table 2.
Mercury is found in the earth's crust
and is ubiquitous in the environment.
Hence even without amalgam fillings, small but measurable blood and
urine levels are found. Amalgam
fillings may raise these levels
slightly, but this has no clinical significance. The legal limit of safe
mercury exposure for industrial
workers is 50 micrograms per cubic
meter of air for 8 hours per day and
50 weeks per year. Regular exposure
at this level produce urine mercury
levels of about 135 micrograms per
liter. These levels are much higher
than those of the general public but
produce no symptoms and are considered safe (34). Other investigators, Kingman et al (35) (Table 2),
Clarkson et al (36) and Brownwell et
A Publication of the School of Dental Sciences
African Journal of
Oral Health Sciences
AJOSHS 2015 V2 (2)
al (37) have found no significant associations between amalgam exposure and clinical neurological signs
or clinically evident peripheral neuropathy or other health effects (Bates
et al (38) Table 2.
Some dentists and other health professionals advise people to avoid
amalgam and to have their amalgam
fillings replaced with other materials
and taking vitamins and other supplements to prevent trouble after
amalgam. "Amalgam toxicity" or
"amalgam illness” has been diagnosed in patients who suffer from
multiple common symptoms. Berglund and Molin (39) (Table 2) and
Herrstrom and Hogstedt (40) found
that patients and people with symptoms they related to amalgam fillings
had no significant higher mercury
levels in blood and urine than those
of a control group.
Discussion
For the past decades the public has
been bombarded by sensational, confusing and misleading reports about
health issues related to dental amalgam. Mobilization of irrational public fear is the strategy used by lobby
groups to pressure governments to
change public policy (41, 42). It is
important that governments adhere
to scientific principles and base
health policies on sound scientific
knowledge on dental amalgam. No
systematic scientific studies have
ever shown that dental amalgam
poses a health hazard to patients,
dentists, or to the dental assistant
when professionally used and safely
handled. Instead overwhelming scientific evidence has shown that dental amalgam is a safe dental restorative material (1-3, 8, 9, 23, 24, 34).
Most of the tests that have been used
such as breath, urine, hair, skin and
blood have been found to be inconclusive or misinterpreted. Mercury is
Table 2: The investigations on dental amalgam and its effect on health.
ubiquitous and the body absorbs and
excretes tiny amounts and hence is
commonly found in urine and blood.
Large-scale studies (33, 38) have
shown that the general population
has urine-mercury levels below 10
micrograms/liter. Industrial workers,
and dentists, who have regular exposure to mercury vapor also, have low
values (25, 27, 28). Urine testing
gives a fairly reliable indicator of
chronic exposure when performed on
a 24-hour urine specimen. Urine
mercury levels can be temporarily
raised by administering a chelating
agent such as DMSA or DMPS,
which concentrates them to be excreted. This results in artificially
raised urinary mercury levels. The
use of a chelating agent before testing mercury levels should be considered invalid and unreliable.
Some of the alleged allergic reactions associated with dental amalgam
are concluded from skin testing
(patch test) done with a dilute solu-
Author
Population /sample
Investigation
Health effects
Ritchie, et al
(25)
180 dentist against a
control group
Svenden et al
(32)
Dentist and dental
nurses in Norway
Well-controlled using a questionnaire the health and cognitive
effects
Exposure level and mercury level
in urine
Urinary mercury concentrations
Dentist report having a disorder of the
kidney more than control group but the
difference was not significantly
Levels of exposure seemed low
Kingman
al (35)
et
1663 dentate Vietnam
veterans
Bates et al
(38)
20,000 Defence Force
persons New Zealand
Berglund and
Molin (39)
18 Patients referred
physicians and control
group
6
Exposure to amalgam and its effect to clinical neurological signs,
vibrotactile thresholds and peripheral neuropathy.
Association between amalgam
restorations and disorders related
with nervous system and kidney
Any correlation between subjective symptoms and amalgam restorations- mercury levels in
plasma, erythrocytes, and urine
No significant association with reported
memory disturbance
no significant associations between
amalgam exposure and clinical neurological signs or clinically evident peripheral neuropathy
No significant correlation between
amalgam restorations and chronic fatigue syndrome or kidney disease was
observed.
The symptom group had neither a
higher estimated daily uptake of inhaled mercury vapor, nor a higher mercury concentration in blood and urine
than the control group.
A Publication of the School of Dental Sciences
African Journal of
Oral Health Sciences
AJOSDS 2015 V2 (2)
7
tion of corrosive mercury salts that
cause the skin to redden and possibly
swell (5). The reaction is misinterpreted as a sign of mercury allergic
reaction or toxicity. The other test
used is hair which contains trace
amounts of mercury from food, water, and air, regardless of whether the
person has amalgam fillings. Because hair can absorb mercury from
external sources, the amount of mercury it contains may not necessarily
reflect the amount of mercury within
the body. In addition, hair mercury
testing cannot be standardized because hair thickness, density, shape,
surface area and growth rate may
vary from person to person. Further
the laboratory reporting process has
been stated to be invalid (6).
amalgam as the main source of mer- 7. Zimmer, H., Ludwig, H., Bader,
cury exposure. Studies have shown
M., Bailer, J., Eickholz, P.,
even in the sick individuals who reStaehle, H.J and Triebig, G.
lated their illness to mercury from
Determination of mercury in
amalgam (7, 38) their mercury levels
blood, urine and saliva for the
in blood and urine was similar to
biological monitoring of an
those of the general population. Thus
exposure from amalgam fillings
the alleged symptoms are common to
in a group with self-reported ad
other ailments, are self reported usverse health effects. Int J Hyg
ing questionnaires which have been 8. E nvi r o n H ea l t h. 2 0 0 2 ; 20 5
found to be subjective and in some
(3):205- 11. U.S. Food
a n d
cases psychosomatics.
Drug Administration (FDA). Issues Final Regulation on Dental
Amalgam. July 2009;pg
Conclusion
There is no validated scientific evidence that dental amalgam causes 9. Ferracane, J.L., Adey, J.D., Nakajima, H. and Okabe, T.: Mercury
adverse health effects in adults even
vaporization from amalgams with
with the minimal amount of mercury
varied alloy compositions, J Dent
released from it.
Res 1995; 74: 1414-1417.
Autopsy studies are the most valuable and most important for examining the amalgam-caused mercury
body burden. Guzzi et al (43) reported that total mercury levels were
significantly higher in subjects with
a greater number of occlusal amalgam surfaces (9) compared with
those with fewer occlusal amalgams
(0-3).They also stated that mercury
levels were significantly higher in
brain tissues compared with thyroid
and kidney tissues in subjects with
more than 12 occlusal amalgam fillings. Mutter (43) stated that dental
amalgam is by far the main source of
human total mercury body burden as
proven by autopsy. This has, however, been disputed by the fact that
humans are mainly exposed to methymercury from seafoods and fresh
water fish. This source of mercury
exposure has not been controlled for
by researchers who have reported
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Corresponding Author:
Nyaga J.M.
Email: [email protected]
A Publication of the School of Dental Sciences