Letters to the Editor Dear Dr. Dawes: The recent daily dose estimates of mercury from dental amalgams (Berglund, 1990) and previous estimates of some others (Mackert, 1987; Berglund et al., 1988; Snapp et al., 1989) range from 1.2 to 1.7 ,ug Hg/day. These estimates at first glance may appear comforting; however, they are too low to account for the average levels of amalgam mercury that actually accumulate in the human brain (Nylander et al., 1987; Eggleston and Nylander, 1987). Moreover, these authors (Berglund, 1990; Mackert, 1987; Berglund et al., 1988) fail to correct for the factors of serial dilution during open-mouth sampling and mercury accumulation in the closed mouth between oral respiratory cycles of normal breathing (Vimy and Lorscheider, 1990). Other recent estimates of amalgam mercury daily dose of approximately 10 jig/day (Aronsson et al., 1989) are probably closer to the truth, because it would require a dose at least this large to produce tissue levels of amalgam mercury, established in human autopsy studies, which could be explained by standard first-order pharmacokinetic equations (Vimy and Lorscheider, 1990). In any event, this debate has become irrelevant now that experimental evidence in primates shows that at four weeks (Hahn et al., 1990) and one year (Danscher et al., 1990) after amalgam placement, the body tissue levels of mercury are much higher than any of us had anticipated. Considering the numerous advances in human health care resulting from animal research, most medical scientists would view the recent statement from the American Dental Association, that animal studies are irrelevant to humans, to be totally without merit (Begley and King, 1990). - F.L. Lorscheider Professor of Medical Physiology and - M.J. Vimy Clinical Asst. Professor of Medicine The University of Calgary Calgary, Alberta, Canada T2N 4N1 REFERENCES ARONSSON, A.M.; LIND, B.; NYLANDER, M.; and NORDBERG, M. (1989): Dental Amalgam and Mercury, Biol Metals 2:25-30. BEGLEY, S. and KING, P. (1990): Drilling for Danger? A Debate over the Safety of "Silver" Fillings, Newsweek, Oct. 15, p. 80. BERGLUND, A. (1990): Estimation by a 24-hour Study of the Daily Dose of Intra-oral Mercury Vapor Inhaled after Release from Dental Amalgam, J Dent Res 69:1646-1651. BERGLUND, A.; POHL, L.; OLSSON, S.; and BERGMAN, M. (1988): Determination of the Rate of Release of Intra-oral Mercury Vapor from Amalgam, J Dent Res 67:1235-1242. DANSCHER, G.; H0RSTED-BINDSLEV, P.; and RUNGBY, J. (1990): Traces of Mercury in Organs from Primates with Amalgam Fillings, Exp Mol Pathol 52:291-299. EGGLESTON, D.W. and NYLANDER, M. (1987): Correlation of Dental Amalgam with Mercury in Brain Tissue, J Prosthet Dent 58:704-707. HAHN, L.J.; KLOIBER, R.; LEININGER, R.W.; VIMY, M.J.; and LORSCHEIDER, F.L. (1990): Whole-body Imaging of the Distribution of Mercury Released from Dental Fillings into Monkey Tissues, FASEB J 4:3256-3260. MACKERT, J.R. (1987): Factors Affecting Estimation of Dental Amalgam Mercury Exposure from Measurements of Mercury Va-
por Levels in Intra-oral and Expired Air, J Dent Res 66:17751780. NYLANDER, M.; FRIBERG, L.; and LIND, B. (1987): Mercury Concentration in the Human Brain and Kidneys in Relation to Exposure from Dental Amalgam Fillings, Swed Dent J 11:179187. SNAPP, K.R.; BOYER, D.B.; PETERSON, L.C.; and SVARE, C.W. (1989): The Contribution of Dental Amalgam to Mercury in Blood, J Dent Res 68:780-785. VIMY, M.J. and LORSCHEIDER, F.L. (1990): Dental Amalgam Mercury Daily Dose Estimated from Intra-oral Vapor Measurements: A Predictor of Mercury Accumulation in Human Tissues, J Trace Elem Exp Med 3:111-123.
Replies to Drs. Lorscheider and Vimy Dear Dr. Dawes, Apparently Drs. Lorscheider and Vimy have not sufficiently considered either the observations made by Olsson and Bergman (1987) or the publications by Mackert (1987) and Berglund et al. (1988). The release of mercury vapor from amalgam restorations is a process that is time-dependent and not volumedependent, as claimed by Lorscheider and Vimy (1990). Berglund et al. (1988) measure the amount of mercury vapor release per time unit, thereby being independent of any dilution. As regards the accumulation of mercury vapor in the closed mouth between oral respiratory cycles, Nylander et al. (1990)in a preliminary report based on experimental data-stated that the accumulation during the chewing period is negligible. Furthermore, Olsson et al. (1989) have shown that tissues in an oral cavity with amalgam restorations cannot be considered a substantial source of mercury during respiration and intra-oral air sampling. This is evident, firstly, from the fact that the diffusion rate of mercury in aqueous systems such as saliva is low and, secondly, from the fact that the rate of air contact with oral tissue is zero, which means in turn that the air-flow cannot capture any other mercury than that present in the gas phase in the oral cavity. Thus, the air flow cannot influence the rate of release of mercury vapor from the amalgam restorations. The amount of mercury vapor released is inspired, expired, dissolved in oral tissue, or swallowed together with the saliva, irrespective of the breathing pattern. The relative distribution of mercury to the vicinity, the air-ways, and the gastrointestinal tract is debatable, but, except in special cases, the daily dose of inhaled mercury vapor released from amalgam restorations should not be much higher than that shown by Berglund (1990). In fact, experimental data (Berglund, 1990) seem to indicate that the major part of the released mercury vapor is swallowed together with the saliva. It is interesting to note that the inhaled daily dose obtained by Berglund (1990) (mean = 1.7 jLg Hg/day) agrees very well with the corresponding value of 1.2 ,ug Hg/day, obtained after a re-calculation of the results from an experimental study by Vimy and
Lorscheider (1985). In an attempt to confirm the higher levels of mercury exposure claimed by Vimy and Lorscheider, these authors in a recent publication (1990) do not hesitate to refer to a calculated average value based on results from nine different publications, which in turn are based on five experimental studies (Table V and page 121 in Vimy and Lorscheider, 1990), which are not directly comparable. Furthermore, Vimy and Lorscheider in their letter to the editor try to verify their mercury exposure values from amalgam restorations by referring to the consistency of these values with autopsy data (Eggleston and Nylan-
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por Levels in Intra-oral and Expired Air, J Dent Res 66:17751780. NYLANDER, M.; FRIBERG, L.; and LIND, B. (1987): Mercury Concentration in the Human Brain and Kidneys in Relation to Exposure from Dental Amalgam Fillings, Swed Dent J 11:179187. SNAPP, K.R.; BOYER, D.B.; PETERSON, L.C.; and SVARE, C.W. (1989): The Contribution of Dental Amalgam to Mercury in Blood, J Dent Res 68:780-785. VIMY, M.J. and LORSCHEIDER, F.L. (1990): Dental Amalgam Mercury Daily Dose Estimated from Intra-oral Vapor Measurements: A Predictor of Mercury Accumulation in Human Tissues, J Trace Elem Exp Med 3:111-123.
Replies to Drs. Lorscheider and Vimy Dear Dr. Dawes, Apparently Drs. Lorscheider and Vimy have not sufficiently considered either the observations made by Olsson and Bergman (1987) or the publications by Mackert (1987) and Berglund et al. (1988). The release of mercury vapor from amalgam restorations is a process that is time-dependent and not volumedependent, as claimed by Lorscheider and Vimy (1990). Berglund et al. (1988) measure the amount of mercury vapor release per time unit, thereby being independent of any dilution. As regards the accumulation of mercury vapor in the closed mouth between oral respiratory cycles, Nylander et al. (1990)in a preliminary report based on experimental data-stated that the accumulation during the chewing period is negligible. Furthermore, Olsson et al. (1989) have shown that tissues in an oral cavity with amalgam restorations cannot be considered a substantial source of mercury during respiration and intra-oral air sampling. This is evident, firstly, from the fact that the diffusion rate of mercury in aqueous systems such as saliva is low and, secondly, from the fact that the rate of air contact with oral tissue is zero, which means in turn that the air-flow cannot capture any other mercury than that present in the gas phase in the oral cavity. Thus, the air flow cannot influence the rate of release of mercury vapor from the amalgam restorations. The amount of mercury vapor released is inspired, expired, dissolved in oral tissue, or swallowed together with the saliva, irrespective of the breathing pattern. The relative distribution of mercury to the vicinity, the air-ways, and the gastrointestinal tract is debatable, but, except in special cases, the daily dose of inhaled mercury vapor released from amalgam restorations should not be much higher than that shown by Berglund (1990). In fact, experimental data (Berglund, 1990) seem to indicate that the major part of the released mercury vapor is swallowed together with the saliva. It is interesting to note that the inhaled daily dose obtained by Berglund (1990) (mean = 1.7 jLg Hg/day) agrees very well with the corresponding value of 1.2 ,ug Hg/day, obtained after a re-calculation of the results from an experimental study by Vimy and
Lorscheider (1985). In an attempt to confirm the higher levels of mercury exposure claimed by Vimy and Lorscheider, these authors in a recent publication (1990) do not hesitate to refer to a calculated average value based on results from nine different publications, which in turn are based on five experimental studies (Table V and page 121 in Vimy and Lorscheider, 1990), which are not directly comparable. Furthermore, Vimy and Lorscheider in their letter to the editor try to verify their mercury exposure values from amalgam restorations by referring to the consistency of these values with autopsy data (Eggleston and Nylan-
Downloaded from jdr.sagepub.com at Bobst Library, New York University on June 6, 2015 For personal use only. No other uses without permission.
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