|
3.
Organizzazione mondiale della Sanità (OMS) su
mercurio e amalgama
-
vedi:
Materiali Dentari e denti tossici
(documento W.H.O.,
1991)
W.H.O. 1991 -
Environmental Health Criteria for inorganic mercury
The
general population is primarily exposed to mercury from dental amalgam and
the diet.
Table 2 indicates the average daily intake and retention of
total mercury and mercury compounds in the general population not
occupationally exposed to mercury.
|
Table 2 |
|
exposition
source (mg/ day)
|
mercury
vapour
|
inorganic
mercury
compounds
|
methylmercury
|
|
air
|
0.03
(0.024)
|
0.002
(0.001)
|
0.008
(0.0064)
|
|
food:
fish
|
0
|
0.6
(0.042)
|
2.4
(2.3)
|
|
food:
no-fish
|
0
|
3.6
(0.25)
|
0
|
|
drinking
water
|
0
|
0.050
(0.0035)
|
0
|
|
dental
amalgam
|
3.8–21
(3–17)
|
0
|
0
|
|
total
|
3.83–21
(3.1–17)
|
4.3
(0.3)
|
2.41
(2.31)
|
Human
studies
The release of mercury vapour from dental amalgam fillings has been
known for a very long time (Stock, 1939). The next major contribution to
this field was that of Frykholm (1957). Using a radioactive mercury tracer, he showed that the insertion of amalgam in both humans and dogs
resulted in significant concentrations of mercury in urine and faeces. In
humans the concentrations of urinary mercury increased during a 5-day
period following the insertion of 4-5 small occlusal fillings. A new
higher peak occurred a couple of days after removal of these fillings.
Faecal elimination showed a similar pattern, appearing on the second day
after amalgam insertion. Another maximum appeared 1-2 days after amalgam
removal. Frykholm (1957) also measured the concentration of mercury in the
oral cavity during amalgam placement in teeth. Recently, concern over
amalgam usage has been revived by the pubblication of a number of
experimental studies showing that, among other elements, inorganic mercury
is released from amalgam in vitro (Brune 1981, Brune & Evje 1985).
More importantly, mercury vapour released in the mouth in vivo leads to an
increased uptake of mercury in body tissues (Gay 1979, Svare 1981, Abraham
1984, Ott 1984, Patterson 1985, Vimy & Lorscheider 1985a,b, Vimy 1986,
Langworth 1988, Nylander 1987, 1989, Berglund 1988, Aronsson 1989). Vimy
and Lorscheider (1985b) showed that the release rate of mercury vapour
increases dramatically when the amalgam is stimulated by continuous
chewing, reaching a plateau within 10 min. After the cessation of chewing,
it takes approximately 90 min for the mercury release rate to decline to
the basal pre-chewing value. (Fig.1) A confirmatory study has recently
been published by Aronsson (1989) who also made daily dose estimates.
Critical
reviews have been made of published information on mercury release and
exposure from amalgam (Enwonwu 1987, Friberg & Nylander 1987, Langan
1987, Mackert 1987, Olsson Bergman 1987, Clarkson 1988a). Several studies
have correlated the number of dental amalgam fillings or amalgam surfaces
with the mercury content in brain and kidney tissue from human autopsy.
Subjects with no dental amalgam had a mean mercury level of 6.7 ng/ g in
the occipital cortex; whereas subjects with amalgams had a mean level of
12.3 ng/g (Friberg & Nylander 1987; Nylander 1987). Amalgam free
subjects had a mean mercury level in kidneys of 49 ng/g, whereas subjects
with amalgam fillings had a corresponding level of 433 ng/g. In a similar
investigation, Eggleston & Nylanber (1987) showed mean mercury levels
of 6.7 ng/g and 3.8 ng/g in grey and white brain matter, respectively, in
subjects with no amalgam fillings. In subjects with amalgam fillings,
mercury levels were 15.2 ng/g and 11.2 ng/g for grey and white matter,
respectively. In a more recent extensive study, Schiele (1988) showed a
mean brain occipital mercury concentration of 10 ng/g for 44 subjects with
an average of 14 amalgam surfaces each. Kidneys from the same subjects
showed a sex difference in the mercury concentrations, mean values being
484 ng/g for the 16 females and 263 for the 28 males.
Using pubblished experimental data (Svare 1981, Abraham 1984, Patterson
1985, Vimy & Lorscheider 1985b), the amalgam mercury release rate
average daily mercury uptake, and its steady-state contribution to blood,
urine, brain, and kidney were estimated by Clarkson (1988). These
estimations gave brain, kidney and urine values that are similar to data
reported from human studies (brain and kidney autopsy samples: Friberg
1986, Nylander 1987, Schiele 1988, urine: Nilsson & Nilsson 1986b,
Olstad 1987, Langworth 1987). Estimates of daily dosages of mercury
attributed to amalgam have also been reported by Mackert (1987) and Olsson
& Bergman (1987), although they are somewhat lower than those of
Clarkson et al. (1988).
Snapp (1989) studied the blood mercury level before and 18 weeks after the
removal of amalgam fillings. After the removal, nine of the ten subjects
examined exhibited a statistically significant mean decrease of 1.13 ng
mercury/ml in the blood mercury level.
Recently Molin (1990) studied mercury concentrations in human plasma,
erythrocytes and urine before and up 12 months after removal of amalgam
fillings and replacementds with gold alloy restorations. They noted an
initial increase in all recorded mercury levels after amalgam removal.
About three months thereafter, plasma and erythrocyte levels decreased
markedly. A continuous reduction in urine mercury levels took place,
reaching a plateau of approximately 25% of the pre-removal mercury level
within 9 months.
It is important to note that, in the studies cited, both the predicted
mercury uptake from amalgam and the observed accumulation of mercury in
the body are average values. It is also clear from the original reports
that substantial individual variations exist.
Animal
experiments
- Frykholm (1957), using radioactive mercury in amalgam, studied the
release and uptake of mercury in dogs and monkeys. He concluded that the
mercury exposure from amalgam was essentially limited to the immediate
placement procedures. This is in contrast to more recent studies that
examined the disposition of radioactive mercury released from amalgam
restorations in sheep (Hahn 1989, Vimy 1990).
Hahn
(1989) demostrated by whole-body image scan that amalgam mercury could be
readily visualized in the kidney, liver, jawbone, and gastrointestinal
tract after only 29 days of chewing with amalgam. Vimy (1990a)
demostraterd that the mercury levels in maternal blood, fetal blood, and
amniotic fluid reached a peak within 48h after amalgam placement and
remained at that level for the duration of the studies (140 days). Mercury
levels of 4 ng/g in maternal blood and amniotic fluid and of 10 ng/g in
fetal blood were found. The erythrocyte/plasma ratios of mercury from
amalgam in both the ewe and the fetal lamb were less than unity. The
maternal urine mercury concentration ranged from 1- 10 ng/g during a 16
day period. approximately 7.7 mg of mercury could be eliminated per day in
faeces.
All tissues examined displayed mercury accumulation. By 29 days, kidney
mercury levels rose to approximately 9000 ng/g, and these levels were
mantained throughout the duration of the study. A similar pattern was
observed in the liver, but the levels remained at approximately 1000 ng/g.
The fetal kidney contained mercury levels of 10-14 ng/ g, whereas fetal
liver had levels of 100-130 ng/g.
The maternal brain (cerebrum, occipital lobe, and thalamus) showed a
mercury accumulation ranging from 3-13 ng/g. In the pituitary, thyroid and
adrenal glands, concentrations ranged from approximately 10-1100 ng/g. In
the fetal cerebrum, occipital cortex, and thalamus the highest levels were
approximately 10 ng/g. the fetal pituitary gland had mercury
concentrations of more than 100 ng/g, whereas the thyroid and adrenal
glands contained less than 10 ng/g.
Milk obtained at lamb parturition or within several days following birth
(25-41 days after amalgam placement) contained levels of mercury from
dental amalgam that reached as high as 60 ng/g.
Other recent reports indicate that both kidney function (Vimy 1990b) and
intestinal bacterial population (Summers 1990) may be affected when
animals are exposed tio dental amalgam mercury.
Dossier:
Pag. 1 -
Pag. 2 -
Pag. 3 -
Pag. 4 +
Dossier 2
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