C21 Demonstrate your awareness that mercury is released from amalgam during mixing, insertion, and removal, as well as from amalgam fillings in situ. Relate the amount of mercury being released from amalgams to its contribution to both blood and urine Hg-values, and to the threshold value for mercury in blood and urine. Identify the sources of mercury in general, and also identify the risk groups for mercury toxicity.
The mercury threshold levels accepted today are listed below. OSHA's level is expected to decrease to 30 µg/m3 within a near future.
The amount of mercury being released from dental amalgams to blood and urine are quite small. The figures presented below are based on values measured after 4-5 amalgam restorations were placed. Some of the detected mercury relates to mercury vapor released from old amalgams being removed before the new amalgams were placed.
Blood: 2.5 µg/l five days after placement, a value that the decreases to undetectable levels with time.
Urine: Max 5 µg/l initially after removal. This value decreased toward undetectable levels
The above values should be compared to the threshold values (exposure to 50 µg/m3 eight hours per day during five days per week)
Blood: 30 µg/l
Urine: 80 µg/l
As seen from the above, the amount mercury from amalgam fillings is low compared to the threshold values. In fact, the amount of mercury present in some seafood (e.g. tuna) contributes more to the blood and urine levels. In a study from 1991, A. Berglund showed that the amount of mercury being released in a mouth with 16-20 amalgam fillings was only 1-2% of the threshold level.
Despite the low amount of mercury being released from dental amalgams, it is important to realize that mercury passes the placenta barrier. The latter suggests that excessive amalgam use should be avoided during pregnancy. It is also important to realize that people working in certain industries (alkali and mercury lamp industries) may already be exposed to high mercury levels, and that a rather small increase could result in a critical increase.
To conclude:
Dentists and dental personnel, rather than patients, should be concerned about the mercury level released from dental amalgams.
