Dust in dental laboratories. Part I: Types and levels in specific operations.

The type and levels of dust in breathing air close to the workpiece produced through cutting, grinding, or polishing of alloys in dental laboratories have been characterized. The dust levels were compared with threshold limit values (TWA or STEL). In laboratories with improper local ventilation systems, dust levels considerably exceeding such values were recorded. Levels in excess of 10 times the threshold limit values were observed for solid mercury and silver present in amalgam dust, for cobalt present in nonprecious alloys, and for gypsum. Silver exceeded the threshold limit value 1,750 times in one case. Moderate excess of threshold limit values, that is less than 10 times, were measured for copper, nickel, tin, and porcelain in cases of insufficient ventilation. With the efficient outlet systems available on the commercial market, the dust levels could be reduced to levels consistent with criteria of threshold limit values except when trimming amalgam dies. Such systems comprise tubes with diameters of 35 mm connected to pumps with suction capacities of about 30 l/sec.