Document 9w2OmnozmrjNw5Q7GXZwmw9q

FILE NAME: Dental Asbestos (DEN) DATE: 1981 DOC#: DEN002 DOCUMENT DESCRIPTION: Journal Article - Levels of Methylmethacrylate, Formaldehyde, and Asbestos in Dental Workroom Air Levels o f m ethylm ethacrylate, form aldehyde, and asbestos in dental workroom air ^ DAG BRUNE AND HANS BELTESBREKKE Jff OM - Scandinarim lastttaU */ Dmtal Materials, Oslo, Norway Brune, D. 4 Beltesbrckke, H .: Levels o f methylmethacrylate, formaldehyde, and asbestos in dental workroom air. Scand. J . Dent. Res. 1981: 89: 113-116. Abstract - The levels of methylmethacrylate and formaldehyde in workroom air of a dental laboratory following finishing and polishing a pour type denture base resin have been measured. The levels of these compounds did not exceed the respective hygienic threshold limit values in the general workroom air or in breathing air close to workpiece. The content of asbestos fibers in breathing air released during dismantling molds from gold casting was measured. During the dismantling procedure the fiber content in the air could exceed threshold limit values by up to about 12 times. However, about 10 min after terminating this process the fiber content had declined to a level below the established requirements. Key words: asbestos; dental hygiene; dental laboratories; dental materials; formaldehyde; methylmethacrylate. . Dag Brune, NIOM - Scandinavian Institute of Dental Materials, Forskningsveien 1, Oslo 3, Norway. Accepted for publication 24 August 1980. In workroom a ir o f d e n ta l laboratories dust levels following handling o f c h ro m iu m -co b a lt alloys, am algam dies, porcelain or gypsum models could a tta in values m arkedly in excess of hygienic requirem ents (2, 3). . In the finishing and polishing procedure for denture base m aterial, particulate m atter as well as fumes are released to 'th e am b ien t breathing air. T he p articu late m a tte r J composed of polymers as well as particles o f abrasives from the tools, i.e. wheels a n d stones. In a com parison o f '.he levels o f this kind o f p a rticu la te m atter with men mineral dust, the hygienic threshold limit value was n o t exceeded (3). Release of form aldehyde from d enture base material has previously been studied by R uyter (5). He observed th at form aldehyde could be released in quantities o f ab o u t 1-10 m g/m ' from surfaces of polymers exposed to w ater for 3 d. During preparation of denture base materials m ethylm ethacrylate vapors can be transferred to the workroom air due to release o f unreacted monomers as well as due to depolym erization of the polymer m atrix (6). I n various casting procedures an asbestos liner is used to allow expansion. D uring the heat treatm ent at a tem perature of about 850C the asLestos liner becomes brittle. Consequently, asbestos fibers will be released to breathing air during dism antling the mold. The present measurements of the levels of m ulhylm ethacrylate, formaldehyde and asbestos fibers in dental workroom air are part of a general survey of the internal environm ent of dental laboratories (2,3). / '" N ? * 1 D E FE N D A N T 'S EXHIBIT II 5 114 bru ne and beltesbrekke M aterial and methods MtOijimtAacgilalt - During finishing aad polishing a type demure base resin <Swe Flow. Svedia Denwl-Indus.ri AB, Sweden), air was collected in the breathing posmon about 30 cm away from the workpiece usmg suetfon into , 2-liter bag constructed polyethylene and aluminum laminate. T hu baa was elected for gas collection because of negligible dwrpuon of methylmethacrylate to the walls o f the *ORMALDHY0 i D BK "aM X The air sample was then sucked through a column contammgabout 2 mg active carbon in order to adsorb methylmethacrylate before the ga, was injected into a 8 ,,m atograph (Model 3920, Perkin Elmer Corp 7 U -S'A' ) for-quandtadve chemical analysis. The iInnd"?u5s?tr-ial ReseCaarrTcihC,<JOsloU.` " Cintr:d Im titute of O.Ol * Tff* nil III Fii-l. Level, of formaldehyde in breathing air close to Fcrmaldehydt - Formaldehyde released during finish workptece well as in general workroom air o f , ' durins fini5hin` ^ mg ami polishing of the pour type denture base resin " n,C " above> wa* collected in breathing air at a is l z z z distance of about 30 cm from the workpiece. The air was sucked into a solution of sodium bisulfite retaining formaldehyde. Formaldehyde was then quantitatively assayed by means of the chromotropic acid technique comprising a colorimetric measurement (4). It is known that the capacity of the sodium bisulfite solution for fixing formaldehyde will decrease during Results and discussion The contents of form aldehyde and methylmeth acrylate vapors in breathing air in a dental workroom following finishing and polishing a suction of air through the solution due to oxidation of ; 5UlfaV 4)- F r th" andard, of formaldehyde in the range 25-150 pi 0.01 HCHO were injected into a 1-1 bulb filled with either nitrogen Z Z o n l T T ' " t,f'CnSUCked throuSh * e bisulfite solution. The chem.cal recovery o f formaldehyde wa, " T 'TM mCd by * of the chromotropic acid S t0lbSOrPtin" thCWaVe,C"^ of c S T c T ' r rCC Very W" eXpreWd in ' m s of , . , (4)' Thc recovery t v e for formaldehyde standards m nitrogen atmosphere served as reference ppm 1000 too m eth ylm eth acryla te O SSH StB S B SB rSfcB L , JWJOIT*H*oWuMrurrito*. WOMHeou AM air A 3-The relCaSC <;asbes`os fiber, to breathing r ' , r"* d" mant'mg a mold conuining a Pennwaid finer (Jelenko, New Rochelle, NY, U.S.A was measured in a laboratory which wa, not equipped with local ventilation. Asbestos fibers wcrt ^ membrane filter installed about 30 cm away from the workpiece. Samples were collected during dismantling he mold as well a , during two periods afier terminating the procedure. The asbestos fibers were counted using light microscopy at the Institute of Occupational Health L/SIO. _ * g. 2. Levels of methylmethacrylate in breathing air close to workpiece as well as in general workroom air of a dental; laboratory during fi,,i5hi,,g and denture base resin. m ethylm ethacrylate, form aldehyde and asbestos 115 HCHO W NITROGEN HCHO IN AM HCHO ITANOMO Fig. 3. Recovery o f formaldehyde in sodium biiulGte soludoo in air and nitrogen atmosphere. Recovery is expressed in terms of extinction referring to the chromotropic acid technique (). demure base resin are presented in Figs. 1 and 2, respectively. H ygienic threshold limit values referring to 15 m in a n d 8 h daily exposure (8) are included on the illustrations. According to the present Gndings neither methylmethacrylate nor formaldehyde were found to exceed the respective hygienic threshold limit values even in cases w ith no ventilation. Local ventilation resulted in a strong decrease of the levels o f these vapors (Figs. 1 a n d 2). Fig. 3 presents the recovery of formaldehyde from nitrogen o r a ir atm osphere accomplished through fixauon in sodium bisulfite solution followed w ith the chrom otropic a d d colorim e tric m easurem ent (4).' A ccording to Fig. 3 formaldehyde is quantitatively retained in nitro- gen atmosphere whereas anomalies appear when the gas is present in air. H ow ever, when form aldehyde was present in air a t low levels, a quantitative uptake was also dem onstrated (Fie 3) . T h e present study involves the analysis of formaldehyde at low concentrations in air in the dental laboratory. The linear relationship o f the yield curve in Fig. 3 was consequently used in the quantitative assay of form aldehyde. ftR- 4 presents the num ber o f asbestos fibcrs/cm* in breathing a ir released during dism antling molds. In two experim ents values of 21 a n d 27 Cben/cm * w ere m easured d u rin g the dismantling procedure. According to Norwegian regulations concerning limits o f pollutant levels in the working environment, asbestos should not exceed two fibcrs/cm* (7). According to American threshold lim it values for chemical substances in workroom a ir the asbestos fiber content should not exceed 5 fibcrs/cm* (8). Consequently, the asbestos levels in dental laboratories could exceed threshold lim it requirem ents u p to 12 times in short-tim e intervals. T he dismantling procedure m ay ac count for a time o f about 5 m in. However, about 10 m in after term inating the procedure the asbestos fiber content had declined to levels low er than 2 fibers/cm*. In the present laboratory no access to local ventilation was available. W ith a good local ventilation system the asbestos fiber content' w ould most likely be reduced to levels lower than tw o fibcrs/cm* even during the dism antling procedure. Efficiencies o f local ventilation for purifying polluted dental workroom air may a tta in values close to 99% (3). F'g. 4- Amount of asbestos fibers in breathing air close to workpiece following demolishing a mold in a dental laboratory. Levels of threshold limit values according to U.S. and Norwegian regulations are indicated. Acknowledgments - The authors wish to express their gratitude to Dr. N. Berg at Central Insdtute of Industrial Research, Oslo, and M r. J . R. P edersen at Institute of Occupational Health for analysis of methylmethacrylate and asbestos fibers, respectively. References 1. Bero, N.: Central Institute of Industrial Research, Oslo: Personal communication. 116 brune and beltesbrekke 2. Brume, D. 4 Bectesbreiim, H.: Levels o f . 6. Ruytsr, I. E. 4 Svendsen, S. A.: Flexural mercury and silver in dust from the trimming of properties of denture base polymers. J . Pmttk. amalgam dies. Seand. J . Dmt. Res. 1979:87 462 Dmt. 1980: 43r 95-104. 455. / 7. Direlctoratet for ArbeidstUsynet: Admimslrutim 3. Brume, D. 4 Beltesbkekke, H.: Dust in dental anntr Jar Jorurensninger i arbeidsatmosferc, Ojkp laboratories. J . Presth. Dm t. 1980: 44r 211-215. 1978: No. 361. 4. Share, I. 4 Dahlner, B.: Bestamning av aldehyder 1 lull. Arbeit Halso 1973; 6i 1-91. 5. R uyter, I. E.: Release of formaldehyde from denture base polymers. Acta Odontel. Seand. 1980- 8. Threshold Umii taints fo r chemical snbslanets it workroom air 1976: The American Conference of Governmental Industrial Hygienists, Cincinnati, M r 17-27. ' '