"Chewing releases mercury from fillings" [letter]. THE LANCET

Gay DD, et al.  "Chewing releases mercury from fillings" [letter].  THE LANCET, (8123):985-6 (5/5/79).

CHEWING RELEASES MERCURY FROM FILLINGS

SIR, -- While examining the exposure of dental patients to elemental mercury via dental restorations [3], we noticed that chewing, after teeth had been filled with a silver-mercury amalgam, was accompanied by an increase in the amount of elemental mercury breathed out by the patient.

  In our studies the patient breathes out ten times through a 'Drierite'  tube into a 'Vycor' tube packed with 1 g of silver wool mesh.  This silver trap is wrapped with nichrome heating wire.  After collection, the trap is connected to a continuous-flow, long-tube absorption apparatus monitoring the 254 nm absorbance wavelength of mercury.  Heating the silver wool via the nichrome wire with an activated charcoal purified air stream sweeping through the trap releases the mercury adsorbed onto the silver and carries it into the monitor.  The instrument is calibrated with standard concen- trations of mercury injected onto the silver wool.  After determination of the background level the patient chews a piece of gum for 15 min and then repeats the ten expirations into the trap.

         

EFFECT OF CHEWING ON MERCURY IN EXPIRED BREATH

                  Age of                    Expired Hg (ng/10 breaths)
  Patient      recent filling    Smoker    Before chewing   After chewing

     1             1 wk           Yes           14              244
     2             2 wk           No            22              172
     3             7 mo           Yes           19              101
     4             1 yr           No            16               76
     5             2 yr           No            17               64
     6             None           Yes            1                1
     7             None           No             6                6


We found that the level of elemental mercury in the expired breath of patients with silver-mercury amalgams up to 2 years old increased almost four times after a 15 min period of chewing (see table).  The patients with no silver-mercury fillings had lower levels of mercury before chewing than did patients with fillings, and their mercury levels were not affected by chewing.  One patient with no fillings was also a heavy smoker yet no increase in mercury was observed.

Cross et al. [4] found methyl mercury in the blood of dentists at levels significantly greater than those in a control group.  However, the range of methylmercury in the control group was 1.9-13.7 ng/g dry weight of blood.  It would be interesting to know how many of the controls had silver-mercury amalgam fillings.  Such amalgams give a low level, chronic exposure to elemental mercury with the real possibility of biotransformation to the more toxic methylmercury.


Departments of Preventive Medicine
and Chemistry,
University of Iowa,
Iowa City, Iowa  52242, U.S.A.,;
DON D. GAY and College of Dentistry,
ROBERT D. COX
University of Iowa
JOHN W. REINHARDT



[3]  Reinhardt JW, Boyer DB, Gay DD, Cox RD,
Svare CW, Frank CW.  J DENT
       RES (in the press).

[4]  Cross JD, Dale IM, Goolvard L, Lenihan
JMA, Smith H.  LANCET, 1978,
       ii, 312.
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