On the Instability of Amalgams...cont. -
Increased mercury vapor emission from modern non-gamma-two amalgams
Following the findings of deposits on the surface of non-gamma-two amalgams the logical question is if this phenomenon is linked to an increase in the emission of mercury vapor. Initial experiments showed that both conventional and non-gamma-two amalgams emitted easily measurable amounts of Hg-vapor. In both cases a dramatic increase in the emission could be observed when a piece of cotton wool was gently slided over the surface. A fragile layer of passivating nature was suspected.
Hg-vapor is regarded as the most concerning toxic substance emitted fromdental amalgam. It is indeed surprising that dental science has not looked for a link between the formation of droplets and an increased emission of mercury vapor. As mentioned before no scientific article has been published on the extraordinary phenomenon of droplets on modern amalgams so relevant for the understanding of this material.
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In 1988 a project was initiated at the department of chemistry at Linköping University, Sweden. It was performed by Cecilia Toomväli as a part of her Masters Degree in chemistry. The paper is unfortunately written in Swedish but with an abstract in English (41):
"The release of mercury vapor from dental amalgams has been studied. The
purpose has been to examine if there is a fragile passivating oxide layer
on the surface of the amalgams in air. To find out if there is an oxide
layer the amalgams have been exposed for a certain loading. The mercury
vapor released has been detected in different gases as air, argon and
nitrogen. Different parameters as time and temperature have been varied.
Another purpose has been to find out if there are any differences among
the five types of amalgams that have been tested.
The results indicate that a fragile, passivating oxide layer is built up
in air and that oxygen is adsorbed on the surface. The investigation also
shows a difference in mercury release between different amalgams. The
non-gamma-two amalgams with high copper content have a greater release of
mercury vapor than conventional amalgams."
Dental amalgams have been used for more than 160 years (42). It took however until the 1994
before any scientist found one of the mechanisms behind the emission of
mercury vapor from dental amalgams. Mahler, Adey and Fleming has shown
that the emission of mercury vapor is related to the amount of tin in the
gamma-1 phase (8). As can be seen from
Figure 2 it is the modern non-gamma-two amalgams that are at the top of
In a study by Berglund the author concludes: "In air during cyclic dipping
into the aqueous media, the conventional amalgam specimens released
mercury vapor at lower rates over the whole period than did the dispersed
and single-composition types studied"(43). They also included an in vivo
investigation into their study but failed to get any useful measurements
in subjects with non-gamma-two amalgams as well as in those with
Boyer says: "High-copper, admixed amalgam emitted higher amounts of mercury
vapor than the conventional amalgam under the experimental conditions of
this study" (44).
Psarras et al say: "High copper, non-gamma 2-amalgams, released more
mercury vapor than the conventional one throughout the experiment" (45).
Ferracane et al has performed investigations on a number of experimental
amalgams with different amounts of gamma-one tin (46).
Amalgams with compositions according
to the new standard ISO 1559 ed. 2 emits considerably more mercury vapor
than those with ingredients in accordance with the old ISO 1559 ed. 1, see Figure 3.
In his long term corrosion studies of amalgam Moberg says: "In general,
the high copper amalgams released more corrosion products into the
solution than the conventional one" (47). In his doctoral dissertation he
concludes: "Placing the conventional amalgam in contact with the blended
high-Cu amalgam caused an increased amount of Cu in the solutions probably
due to the easily corrodable Cu-phases of the high-Cu amalgam. The high
release of Cu from high-Cu amalgams is in accordance with earlier results
(Espevik 1977)" (48). He also states
that: "The amounts of corrosion products increased exponentially with the
Non-gamma-two amalgams were introduced on the market to increase strength
and corrosion resistance. Decades later when relevant scientific work has
been done on this material it is obvious that a giant sub optimization has
taken place. Strength and corrosion resistance have been paid for by means
of a drastic increase in emission of mercury vapor - the form of mercury
regarded as the most hazardous emitted from dental amalgam.
On Reality. Publisher and editor: Bo Walhjalt. ISSN 1650-9323.
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Latest update 2002-12-05
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