This is quoted directly from a disinterested, scientifically respected
source. This textbook contains over 700 pages. The material that
follows was gleaned from only four of them. This source is a general textbook on
materials science who's main emphasis is NOT to refute the claims of
anti-amalgamists. The emphases on this page (in boldface) were added by me.
| ng |
One nanogram |
One billionth of a gram |
10-9 = 0.000 000 001 |
| µg |
One microgram |
One millionth of a gram |
10-6 = 0.000 001 |
| mg |
One milligram |
One thousandth of a gram |
10-3 = 0.001 |
| g |
One gram |
About the weight of a small paperclip |
| ng/ml |
nanograms per milliliter of blood |
| Clarification: The term "ng" refers to nanograms, or
billionths of a gram. It almost always refers to the level
of mercury found in a milliliter of blood or serum. The term
"μg" refers to micrograms, or
one millionth
of a gram. It generally refers to the level of mercury
inhaled or ingested into the body. |
From
Phillips Science of Dental Materials
For many years a controversy has raged
over the biocompatibility of amalgam restorations because of the presence of
elemental mercury. Another form that has received attention is methyl mercury
that is contained in ocean fish. Methyl mercury is generally formed by biologic
action on elemental mercury.
|
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The
Minamata disaster of the early 1970s
in Japan was the result of the release of large amounts of inorganic (elemental) mercury
in effluent from factories into local rivers. This mercury subsequently
underwent methylation by bottom-dwelling organisms in the Minamata Bay of Japan. This methylated
mercury accumulated, and was concentrated in the food chain, and humans were poisoned by eating
contaminated fish and shellfish. This incident created quite a stir worldwide,
and measurement of mercury in all forms of fish became a focal point for
environmental scientists. Later, however, scientists found that fish from
uncontaminated ocean waters, particularly tuna and swordfish, had high
concentrations of methyl mercury in their tissues. This mercury is derived from
areas of undersea volcanic activity and hydrothermal waters. Mercury accumulates
in the food chain, and large cold-water fish have concentrations that often
exceed FDA limits, even though the mercury is from natural sources. Virtually
100% of methyl mercury is absorbed in the gut. Thus, conversion of elemental
mercury to methyl mercury would greatly increase absorption via the
gastrointestinal route. This point is moot, however, because all the mercury in
seafood is methyl mercury, and all is absorbed. The average contribution of
one seafood meal per week to blood mercury levels of methyl mercury is many times
that of the average contribution of elemental mercury from the presence of 8 to
10 amalgam restorations in the mouth.
[Note: All mercury ingested
from dental amalgam is in the form of elemental mercury, while all of the
mercury ingested from seafood is in the form of methylated mercury. The
importance of this distinction lies in the relative solubility of each form.
Elemental mercury is not very soluble and is therefore not well absorbed via the
stomach and intestines, while the methylated form from seafood is well absorbed
via this route.....MS]
Less than 0.01% of
elemental
mercury ingested via the stomach is absorbed. However, it does have a high vapor pressure. Between 65%
and 85% of the mercury vapor that is inhaled is retained in the body; therefore,
this route is of concern in considering the contribution of mercury absorption
from dental amalgam. [See clarification of this point
below....MS]
Much of the confusion associated with the
biocompatibility of amalgam stems from ignorance of the signs and symptoms of
mercury poisoning. Headache, one of the symptoms most frequently claimed to
disappear on removal of amalgams, is not a symptom of mercury poisoning. The
recognized symptoms of chronic mercury poisoning include weakness, fatigue,
anorexia, weight loss, insomnia, irritability, shyness, dizziness, and tremors
in the extremities. These signs and symptoms of methyl mercury poisoning
[the symptoms mentioned above....MS]
are distinctly different from those of elemental mercury poisoning which
include the following: paresthesia [burning or tingling] of the extremities,
lips, and tongue; ataxia (gait disturbances); and concentric constriction of
visual fields (“tunnel vision”). [Note: all mercury
absorbed into the stomach from amalgam fillings is of the elemental variety.
(MS)]
When the most recent wave of antiamalgam
sentiment began, the claim was made that a few patients can react to extremely
small amounts of mercury with the signs and symptoms of mercury poisoning,
multiple sclerosis, epilepsy, and other diseases of unknown causes. It was
alleged that these patients had a condition that prompted some dentists to
diagnose this “micromercurialism hypersensity” through the use of the cutaneous
patch test.
In spite of attempts to demonstrate a
direct relationship between the presence of dental amalgams and elevated blood
levels of mercury, none has been found. The average mercury level in the blood
of subjects with amalgams was 0.7 ng/ mL (ng=billionths of a gram) (coefficient of variation = 78%),
whereas the level in subjects without amalgams was 0.3 ng/mL (billionths of a
gram-coefficient of
variation = 77%). In comparison, other investigators reported that ingestion of
one saltwater seafood meal per week raised the average blood mercury level from
2.3 to 5.1 ng/mL. Thus, one saltwater seafood meal per week can be expected to
contribute seven times more mercury to blood levels than the presence of
multiple dental amalgam restorations. The lowest level of total blood mercury at
which the earliest nonspecific symptoms occur is 35 ng/mL (after long-term
exposures). Thus, the widespread removal of amalgams is unwarranted.
Inhaled mercury
The most significant contribution to mercury
assimilation from dental amalgam is via the vapor phase. The patient’s encounter
with mercury vapor during insertion of the restoration is brief, and the total
amount of mercury vapor released during function is far below the “no effect”
level. The most reliable estimates suggest that mercury from dental amalgam does
not contribute a significant amount to the total exposure of patients. The
results of one study in which patients with amalgam restorations were monitored
with mercury vapor detectors over a 24-hour period showed that the amount of
vapor inhaled was 1.7 µg/day [millionths of a gram] . Three other studies have confirmed that the
magnitude of vapor exposure for a patient with 8 to 10 amalgam restorations is
in the range of 1.1 to 4.4 µg/day. The threshold value for workers in the
mercury industry is 350 to 500 µg/day, depending on activity level, and is based
on an exposure of 40 hours per week. [Note that these measurements are in
"micrograms" of mercury found as inhaled vapor. This is in contrast to the
"nanogram" units discussed above which relate to the amount of mercury found in
blood serum...MS]
Mercury blood levels that were measured in one
study indicated that the average level in patients with amalgam was 0.7 ng/ml
[billionths of a gram]
compared with a value of 0.3 ng/mL for subjects with no amalgam. This difference
was found to be statistically significant (P 0.01). However, one
should be aware of a study in Sweden that demonstrated that one saltwater
seafood meal per week raised average blood levels of mercury from 2.3 to 5.1 ng/mL,
a sevenfold increase (2.8 ng/mL) compared with that (0.4 ng/mL) associated with
amalgam restorations. The normal daily intake of mercury is 15 µg from food,
1 µg from air, and 0.4 µg from water.
Quoted from
Phillips Science of Dental Materials
Tenth edition, W.B. Saunders C0.
pp83-84 and pp403-404.
References and suggested reading cited in the textbook:
Berglund
A: Estimation of a 24-hour study of the daily dose of intra-oral mercury
vapor inhaled after release from dental amalgam.
J
Dent Res
69:1646, 1990.
A
pioneering study conducted by measuring the intraoral vapor levels over
a
24-hour
period in patients with at least nine amalgam restorations. The average
daily dose of inhaled mercury vapor was 1.7 µg (range from 0.4 to 4.4
µg), which is approximately 1% of the threshold limit value of 300 to
500 µg/day established by the World Health Organization, based on a
maximum allowable environmental level of 50 µg/day in the workplace.
Eames WB: Preparation and condensation of amalgam with a low
mercury:alloy ratio. I Am Dent Assoc 58:78, 1959.
This technique revolutionized the procedure in constructing an
amalgam restoration by use of minimal amounts of mercury in the original
mix
Fédération Dentaire Internationale: Technical Report 33: Safety of
dental amalgam. hit Dent 39:217, 1989.
This authoritative organization reviewed the literature on mercury
toxicity and concluded that there is no documented scientific evidence
to show adverse effects from mercury in amalgam restorations except in
rare cases of mercury hypersensitivity.
Mackert JR Jr: Factors affecting estimation of dental amalgam mercury
exposure from measurements of mercury vapor levels in intra-oral and
expired air. J Dent Res 66:1775, 1987.
This analytical study demonstrates that a previous paper on vapor
release based on animal models was flawed and that the investigators in
this previous study overestimated the daily dose by a factor of 16 or
more.
Marshall GW, Marshall SJ, and Letzel H: Mercury content of amalgam
restorations. Gen Dent November-December:473, 1989.
Amalgam restorations removed after prolonged clinical use contained
nearly all the original mercury present, suggesting that mercury loss
contributes only a minor amount to total daily dosage.
Mjor IA: The safe and effective use of dental amalgam. Int Dent J
37:147, 1987.
Many pertinent matters related to the amalgam restoration are
discussed in this review, including mercury toxicity, longevity of the
restoration, common causes for failure, and certain properties that
relate to performance.
Powell LV, Johnson GH, and Bales DJ: Effect of admixed indium on mercury
vapor release from dental amalgam. J Dent Res 68:1231, 1989.
Addition of indium decreased the release of mercury by reducing
the amount of mercury required to wet the, alloy particle.
Rogers KD: Status of scrap (recyclable) dental amalgams as
environmental health hazards or toxic substances. J Am Dent Assoc
119:159, 1989.
A review presenting available evidence to show amalgam
scrap is not a toxic substance or environmental health hazard.
It also covers portions of the literature indicating that intraoral
amalgams do not present an adverse health hazard.
