Dust in dental laboratories. Part III: Efficiency of ventilation systems and face masks.

The efficiency of local and electrostatic ventilation systems installed in dental laboratories has been measured. With local exhaust systems, dust amounts could be reduced in breathing air close to the emission source to levels lower than threshold limit values for various elements or compounds in dust produced through cutting, grinding, or polishing various dental materials such as chromium-cobalt, nickel, or gold alloys, porcelain, gypsum models, or denture base material. However, the local exhaust system did not enable a dust reduction from handling amalgam dies consistent with criteria of threshold limit values for mercury and silver. The efficiency of electrostatic filters installed in dental laboratories for general ventilation purposes was found to range from 37% to 73% based on weight reduction. Various ventilation systems with bag filters possessing a high efficiency based on weight reductions allowed small, respirable particles less than 5 micrometers to recirculate within the working environment. The efficiency of face masks for the reduction of inhaled dust revealed efficiencies for two commercial masks ranging from 70% to 95% based on weight reduction. However, such masks only partly retained the respirable dust.