The World Health Organization exposure limit for metallic mercury vapor is 25 micrograms per cubic meter of air in order to prevent neurological symptoms of the Central Nervous System. Neurological signs do not seem to occur at levels below 10 micrograms per cubic meter. The ceiling level of mercury exposure from all sources has been established at 42.9 micrograms. Mercury exposure from 20 average amalgams is 25.74 micrograms per day. Mercury vapor levels as high as 88 and 150 micrograms per cubic meter of air have been recorded following chewing.
Chemical reactions occur when the metals are being mixed.
Mercury diffuses into the metallic alloy particles, reacting with silver and tin. A number of setting phases occur next, thus changing the potency of some of the compounds. Once the tooth has been prepared for the filling and the filling put in the tooth, mercury begins to pass into the body. Higher concentrations of mercury are found around the margins, or edges, of the filling. Teeth are usually overfilled and then carved down to eliminate the excess amalgam.