鋳造床フレームワーク研磨作業で飛散する粉塵に関する産業衛生学的研究

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  • Study on scattered dust from the polishing of cast framework of denture from the viewpoint of industrial hygiene.

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Dental laboratory work includes frequent cutting and polishing, which are always accompanied by scattering of dust. It is well known that microscopic particles are deposited in lung alveoli when inhalated for long periods, so that dentists and dental technicians may have their health affected by inhalation of dust.<BR>In a preliminary measurement of cutting dust from various laboratory procedures, I found that polishing cast framework for dentures caused the highest concentration of dust.<BR>Chromium-cobalt alloy is commonly used in denture framework. Cobalt exposure can cause interstitial pulmonary fibrosis, and chromium has cell toxicity and exerts corrosive action on mucous membranes.<BR>Therefore, I investigated dust from framework polishing from the viewpoint of occupational hygiene.<BR>Air samplings during work were performed with a low volume air sampler (flow rate 15 l/min.) at 7 dental laboratories in the Tokyo area, and personal exposure was measured with a size-selective personal dust sampler (flow rate 1.4-1.5 l/min.) which sorted dust particles 7 μm increments.<BR>Dust collected by both atmospheric air sampling and personal sampling was measured as dust concentration, and cobalt and chromium concentrations were measured with atomic absoption analysis and neutron activation analysis.<BR>The free silica and chromium content of the polishing materials were also analyzed.<BR>The following results were obtained:<BR>1. The atmospheric dust concentration in polishing workplaces was 0.07-0.26 mg/m3.<BR>2. Although a low atmospheric dust concentration was maintained in the workplaces, personaldust exposure was several times higher than the atmospheric dust concentration. The average dust exposure of dental technicians differed greatly according to working conditions, such as the type of work, working posture of the technician, and the use of a local exauster. In 13 cases of dental technicians who polished framework under the condition using local exaust systems, the average concentration of dust did not exceed the threshold limit value (JAIH) in any case, but 8 of 11 cases without local exaust systems exceeded the threshold limit value.<BR>3. The atmospheric cobalt concentration in polishing workplaces was from 0.001 to 0.016 mg/m3. Chromium concentration was from 0.001 to 0.008mg/m3.<BR>4. The average cobalt exposure of dental technicians was 0.1mg/m3, which ACGIH indicated as the TLV·TWA for cobalt, in 1 of 14 cases with local exaust systems, and more than 0.1mg/m3 in 3 of 10 cases without local exaust systems. Therefore, I suggest that cobalt exposure is hazardous to the health of dental technicians under some polishing conditions.<BR>5. The average chromium exposure of dental technicians was less than 0.5mg/m3, which ACGIH indicated as the TLV·TWA for chromium, independently of the use of a local exaust system.<BR>6. Free silica content was 11.3% in abrasive for sandblasting, and less than 5% in the other polishimg materials for cast framework.<BR>7. Cr2O3 was confirmed as a main component of“green polishing agents”by X-ray diffraction analysis, and buffing with“green polishing agents”caused a high degree of chromium exposure.

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