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FILE NAME Dental Asbestos DEN DATE 1981 DOC DEN002 DOCUMENT DESCRIPTION Journal Article - Levels of Methylmethacrylate Formaldehyde and Asbestos in Dental Workroom Air Levels of methylmethacrylate formaldehyde and asbestosin dental workroom air DAG BRUNE AND AND HANS BELTESBREKKE NIOM Scandinavian Institute of Dental Materials Oslo Norway Brune D. & Beltesbrekke H Levels of methylmethacrylate formaldehyde and asbestos in dental workroom air ScandJ. 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 methylmethacrylate dental hygiene dental laboratorics dental materials formaldehyde Dag Brune NIOM - Scandinavian Institute of Dental Materials Forskningsveien , Oslo 3 Norway Accepted for publication 24 August 1980 In workroom air of dental laboratories dust levels following handling of chromium alloys amalgam dies porcelain or gypsum models could attain values markedly in excess of hygienic requirements 2 3 In the finishing and polishing procedure for denture base material particulate matter as well as fumes are released the ambient breathing air The particulate matter is composed of polymers as well as particles ofabrasives from the tools i.c. wheels and stones In a comparison of the levels of this kind ofparticulate matter with inert mineral dust the hygienic threshold limit value was not exceeded 3 Release of formaldehyde from denture base material has previously been studied by RUYTER 5 He observed that formaldehyde could be released in quantities of about 1-10 mg from surfaces of polymers exposed to water for 3 d During preparation of denture base materials methylmethacrylate vapors can be transferred to the workroom air due to release of unreacted monomers as well as due to depolymerization of the polymer matrix 6 In various casting procedures an asbestos liner is used to allow expansion During the heat treatment at a temperature of about 850 the asbestos liner becomes brittle Consequently asbestos fibers will be released to breathing air during dismantling the mold The present measurements of the levels of methylmethacrylate formaldehyde and asbestos fibers in dental workroom air are part of a general survey of the internal environment of dental laboratories 2 , ^' ~~ e DEFENDANT'S EXHIBIT 5 Cohen 3-26-08 114 BRUNE AND BELTESBREKKE DOM | Material and methods 10 Methylmethacrylate - During finishing and polishing a pour type denture base resin Swe Flow Svedia Industri AB Sweden air was collected in the " breathing position about 30 cm away from the ; workpiece using suction into a liter bag constructed ofpolyethylene and aluminum laminate This bag was selected for gas collection because of negligible adsorption of methylmethacrylate to the walls of the bag ) FORMALDEHYDE THRESHOLD THRESHOLD LIMIT J Ea EXPOSURE . BS WITHOUT & GENERAL WORKROOM AM 1 NEN The air sample was then sucked through a column 8 S N s \ | R le NY containing about 2 mg active carbon in order to adsorb methylmethacrylate before the gas was injected into a gas chromatograph Model 3920 Perkin Elmer Corp. C.T. U.S.A. quantitative chemical analysis The analysis was carried out at Central Institute of Industrial Research Oslo a NN \.) ce NN : NN VAN 0.01 P N_ Fig 1. Levels of formaldehyde in breathing air close to Formaldehyde - Formaldehyde released during finishing and polishing of the pour type denture base resin same as above was collected in breathing air at a distance of about 30 cm from the workpiece The air workpiece as well as in general workroom air of a dental laboratory during finishing and denture base resin polishing 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 of capacity the sodium bisulfite solution for fixing formaldehyde will decrease during of suction air through the solution due to oxidation of bisulfite to sulfate 4 For this reason standards of formaldehyde in the range 25-150 ...l 0.01 w HCHO were injected into a 1-1 bulb filled with either or air The nitrogen gases were then sucked through the bisulfite solution The chemical recovery of formaldehyde then determined by means of the was chromotropic technique 4 The acid recovery was expressed in terms of extinction referring to absorption at the wavelength of 580 nm 4 The recovery curve for formaldehyde standards in nitrogen atmosphere served as reference Asbestos The release of asbestos fibers to breathing air during dismantling a mold containing a Pennwald liner Jelenko New Rochelle NY U.S.A. was Results and discussion The contents of formaldehyde and methylmethacrylate vapors in breathing air in a dental workroom following finishing and polishing a 1000 [ 100F METHYLMETHACRYLATE METHYLMETHACRYLATE THRESHOLD VALLON VALLON EXPOSUREEXPOSURE THRESHOLD LIMIT VALUE SH EXPOSURE IS WORK POSITION WITHOUT OUTLET a WORK POSITION WITH OUTLET GENERAL tH}GENERAL WORKROOM AIR measured in laboratory which was not equipped with local ventilation Asbestos fibers were collected on a membrane filter installed about 30 cm away from the twhoerkpmioelcde Saasmpwleelsl wearse collected during dismantling during two periods after terminating the procedure The asbestos fibers were counted using light Omsilcrooscopy at the Institute of Occupational Health a Fig 2. Levels of methylmethacrylate in breathing air close to workpiece as well as general workroom aiorf a dental laboratory during finishing and polishing denture base resin _ METHYLMETHACRYLATE FORMALDEHYDE AND ASBESTOS 115 a EXTINCO * HCHO IN NITROGEN MCHO IN AIR MCHO STANDARD gen atmosphere whereas anomalies appear when the gas is present in air However when formaldehyde was present in air at low levels a quantitative uptake was also demonstrated Fig 3 a. A1 02 13 eB VAN HOCHO Fig 3. Recovery of formaldehyde in sodium bisulfite solution in air and nitrogen atmosphere Recovery is expressed in terms of extinction referring to the chromotropic acid technique 4 denture base resin are presented in Figs 1 and 2 respectively Hygienic threshold limit values referring to 15 min and h daily exposure 8 are included on the illustrations According the present findings neither methylmethacrylate nor formaldehyde were found to exceed the respective hygienic threshold limit values even in cases with no ventilation Local ventilation resulted in a strong decrease of the levels of these vapors Figs 1 and 2 Fig 3 presents the recovery of formaldehyde from nitrogen or air atmosphere accomplished through fixation in sodium bisulfite solution followed with the chromotropic acid colorimetric measurement 4 According to Fig 3 formaldehyde is quantitatively retained in nitro- FIBERS 20 } 24 20 The present study involves the analysis of formaldehyde at low concentrations in air in the dental laboratory The linear relationship of the yield curve in Fig 3 was consequently used in the quantitative assay of formaldehyde Fig 4 presents the number of asbestos fibers in breathing air released during dismantling molds In two experiments values of 21 and 27 fibers were measured during the dismantling procedure According to Norwegian regulations concerning limits of pollutant levels in the working environment asbestos should not exceed two fibers 7 According to American threshold limit values for chemical substances in workroom air the asbestos fiber content should not exceed 5 fibers 8 Consequently the asbestos levels in dental laboratories could exceed threshold limit requirements up to 12 times in short intervals The dismantling procedure may account for a time of about 5 min However about 10 min after terminating the procedure the asbestos fiber content had declined to levels lower than 2 fibers In the present laboratory no access to local ventilation was available With a good local ventilation system the asbestos fiber content would most likely be reduced to levels lower than two fibers even during the dismantling procedure Efficiencies of local ventilation for " purifying polluted dental workroom air may attain values close to % 3 12 id t LIMIT R~e~f 44 . LIMIT Raf.7 ry 7 9 t < s 2 s n 26 " MIN Fig 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 Institute of Industrial Research Oslo and Mr.J. R. PEDERSEN at Institute of Occupational Health for analysis of methylmethacrylate and asbestos fibers respectively References 1. BERG .: Central Institute of Industrial Research Oslo Personal communication 116 BRUNE AND BELTESBREKKE BRUNE D. & BELTESBREKKE .: Levels of 6. . mercury and silver in dust from the trimming of amalgam dies Scand J. Dent Res 1979 87 462 465 RUYTER I. E. & SVENDSEN S. A Flexural properties of denture base polymers J. Prostk Dent 1980 43 95 104 BRUNE D. & BELTESBREKKE H Dust in dental laboratories J. Prosth Dent 1980 44 211 215 Direktoratet for Arbeidstilsynet Administrative normer for forurensninger 1978 No. 361 forurensninger i arbeidsatmosf^Oslroe SKAKE I. & DAHLNER .: Best^/mning av aldehyder i luft Arbete H^/lsa1973 6 1 91 Ruyter I. .: Release of formaldehyde from denture base polymers Acta Odontol Scand 1980 . 38 17-27 Threshold limit values for chemical substances in workroom air 1976 The American Conference of Governmental Industrial Hygienists Cincinnati USA .