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3. How can dental patients and workers be exposed to mercury from amalgams?

Patients are mainly exposed when fillings are placed or removed © Therese Chase

Mercury occurs in the environment mainly naturally, but also as a result of human activities. Mercury is present in different forms: either as a pure metal, in various minerals, or in organic compounds, such as methylmercury, which can bioaccumulate in living organisms and reach high levels in fish and marine mammals.

It can be released into the atmosphere by volcanic eruptions, natural weathering of rocks, and through human activities such as the burning of fossil fuels.

The general population can be exposed to mercury through food, water and air as well as through the use of cosmetics, medicinal products and medical devices that contain mercury, including dental amalgams.

The exposure of individuals to mercury varies widely depending on their lifestyle and on the levels of mercury in the local environment. An important source of mercury for the general population is the diet. In particular, eating large amounts of some fish and seafood products can result in exposure to organic mercury above tolerable levels.

Those who work in mercury-related industries and practices may be particularly exposed.

Patients are also exposed to mercury from their dental restorations, particularly through the release of mercury vapour from amalgams, which can be breathed in directly. The level of exposure is highest during placement and removal. Exposure to mercury from fillings that are in place depends on the number of fillings, the filling size, composition, surface, age and placement, the chewing habits, food texture, grinding and brushing teeth and many other physiological factors.

In general, once they are in place, exposure to mercury from amalgam fillings is well below recognised tolerable limits, even for individuals with a large number of restorations. Since the main exposure happens when placing or removing amalgam fillings, it is better to leave them in place unless there is a medical reason to remove them.

Although dental workers do not touch amalgam and usually wear gloves and face masks, they breathe in mercury vapours, particularly during placement and removal of fillings. As a result, and despite improvements in technique and in mercury hygiene measures, exposure to mercury is normally higher for dental workers than for the general population.

During pregnancy and early life, children can be exposed from a variety of sources to organic and inorganic mercury– through their mothers in the womb and during breast-feeding. However, exposure levels are extremely low and no adverse effects have been reported during pregnancy and early life. The concentration of total mercury in human breast milk is considered to be too low to pose any risk to infants.

Once it is taken in, mercury spreads throughout the whole body. Depending on the form of mercury, different samples are most telling about exposure, blood and urine giving the best information. Measurements of total mercury in the urine tend to reflect inorganic mercury exposure and total mercury levels in whole blood are more indicative of methylmercury exposure. More...