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.