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The metal constituents in dental amalgam can be purchased separately and mixed in the appropriate amounts or can be purchased in prepackaged capsules. A tooth is filled by packing the amalgam into the cavity and carving off the excess amalgam before it sets.
There are at least three waste streams that may result from this process:
Large amalgam particles that are carved off the cavity - should be collected and recycled.
Amalgam particles that enter the wastewater:
Some are collected by the filtration system;
Because filtration systems are not 100% effective, some are not collected by the filtration system and enter the wastewater discharge from the office.
Unused amalgam - should be collected and recycled.
Removal of old mercury amalgams from teeth also results in mercury waste. As in the new fillings procedure, large amalgam particles that result from the removal process should be collected and recycled. Particles that enter the wastewater may be removed by the filter or may enter the discharge from the office. The municipalities of Metropolitan Seattle and San Francisco have estimated that 23 mg of mercury waste results from each amalgam removal procedure.
Most dental facilities have a basic chairside filter (or trap) to capture amalgam particles and many have secondary vacuum filters just upstream of the vacuum pump. In addition, separator technologies are now available that can potentially remove over 90% of the mercury from wastewater.
Estimates of the amount of mercury discharged daily per dentist range from 35 mg (San Francisco) to 300 mg (Duluth).
Other devices in dental offices that may contain mercury include blood pressure devices containing visible liquid mercury, fever thermometers with a silver bulb, and thermostats containing mercury in glass ampoules.
Sources: Water Environment Federation, "Controlling Dental Facility Discharges in Wastewater: How to Develop and Administer a Source Control Program," 1999; Kunkel et. al., "The Fate of Mercury in Dental Amalgam," Water Environment and Technology, December 1996.