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EHC 226: Palladium
60
Table 16. Total average mean and 97.5th percentile dietary intake estimates
of palladium and platinum
Element
Total dietary intake (µg/day)
Population average
a
Mean
b
97.5th percentile
b
Palladium
1
1
2
Platinum
0.2
0.2
0.3
a
 
Population  average  intakes  have  been  estimated  from  th e  mean concen-
trations  of  each of these elements in 20 food groups and the average
consumption of each food group from the National Food Survey.
b
 
Mean and upper range (97.5th percentile) total intakes have been estimated
from the mean concentrations of each  element in 20 food groups and data
on consumption of each food group from the Dietary and Nutritional Survey
of British Adults.
(0.024  µg/litre)  (J ohnson  et  al.,  1976).  Tap  water  in  one  city  in  the
People’s Republic of China contained 0.3 µg palladium/litre  (Zhou &
Liu, 1997). Detailed information on this single value is not available.
5.2.4
Iatrogenic exposure
5.2.4.1
In vitro studies
For economic  reasons, a large number of palladium alternatives  to
dental casting gold  alloys have been introduced on the market. The
physical and chemical properties  of these alternative alloys have been
questioned by some researchers.
Wataha et al. (1991a) showed that palladium release into cell
culture  medium from a variety of dental casting alloys was  not propor-
tional to the atomic  percentage of palladium in the alloys. Palladium
was  non-labile  in any tested alloy environment. Palladium was present
at levels  below 17 µg/litre  in the cell culture  medium at 72 h for nine
different commercial alloys. For one multiphase alloy (Au52, Ni28,
Ga13,  Pd4,  In4;   atomic   per  cent),  the  palladium  concentration in
solution after 72 h was 29 µg/litre (0.003 µg palladium/cm
2
 per day), but
the  gallium  and  nic kel concentrations were 8.7 mg/litre (0.97 µg
gallium/cm
2
 per day) and 14.4 mg/litre  (1.46 µg nickel/cm
2
 per day),
respectively.  It  appeared  that  multiphase microstructure was more
critical to release than was the overall content of noble metals. An
initial cleaning (brushing) did  not change the pattern of release but did

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Environmental Levels and Human Exposure
61
generally decrease the quantities of elements released (Wataha et al.,
1992).
High-noble  (Au50, Cu32, Ag12, Pd3, Zn3;  atomic  per cent) and
noble  alloys (Au36, Ag30, Cu24, Pd6, Zn3; atomic per cent) do not
release detectable levels of palladium (AAS detection limit 20 µg/litre).
A  silver-based metal alloy (Ag55, Pd23, Cu18, Zn3;  atomic per cent)
released palladium at a level of 30 µg/litre (0.003 µg palladium/cm
2
 per
day) between 1 and 96 h (Wataha et al., 1995a).
The corrosion of a palladium alloy (Pd73, Cu14, In5; probably
weight per cent) was  examined after insertion in a lactic acid–saline
solution by AAS and potentiodynamic measurements. This alloy had
a low corrosion resistance, with a release of 0.3 µg palladium/cm
2
 per
day. No corresponding clinical findings in 72 patients  who had partial
dentures of this alloy in their mouths for up to 48 months were found
(Augthun & Spiekermann, 1994).
Pfeiffer  &  Schwickerath  (1995)  determined the ion release of
palladium-based dental alloys by AAS. The palladium specimens were
immersed in an electrolyte (artificial saliva consisting of 0.1 mol lactic
acid/litre and 0.1 mol sodium chloride/litre; pH 2.3; 37 °C) for 42 days.
Ion release (µg/cm
2
 per day) of the dental materials was determined as
the average of the periods 1st day, 2nd to 4th day, 5th to 7th day, and
40th to 42nd day. The t e s t solution was  replaced at 3-day intervals.
The examinations showed that the tested palladium–copper fusions
(0.2–6 µg palladium/ c m
2
 per day) were  less corrosion-resistant than
palladium fusions with low (<3% by weight) copper contents (<0.2 µg
palladium/cm
2
  per  day).  Copper–palladium–tin fusions showed the
highest palladium solubility (6–22.5 µg palladium/cm
2
 per day).
The long-term corrosion behaviour of two palladium dental cast-
ing alloys was  studied by Strietzel & Viohl (1992). The alloys were
subjected  to five simulated ceramic firings. For each alloy, three
specimens were  tested for 1 year (53 weeks). In weekly  intervals, the
artificial saliva (pH not given) was  exchanged and analysed by AAS.
The total palladium release after 1 year (2000 µg/cm
2
 
.
 5.5 µg/cm
2
 per
day) from the first alloy (Pd80, Sn6.5, Ga6.5, Cu5; weight per cent) was
markedly higher than that from the second palladium–silver alloy
(Pd58, Ag30, Sn6, In4;  weight per cent), which released about 18 µg
palladium/cm
2
 (~0.05 µg/cm
2
 per day).

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EHC 226: Palladium
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The release of elements  from several palladium-containing dental
alloys into cell culture  medium over 10 months was evaluated with
flame A A S (detection limit 54 µg/litre). The cell culture medium was
changed every  month. A  palladium–gold alloy (Pd48, Au35, Ga15, In2;
atomic weight per cent) released an average of 0.003 µg palladium/cm
2
per day. A palladium–copper–gallium alloy (Pd74, Cu11, Ga8, In4, Sn2,
Au1;   atomic   weight  per  cent) released an average of 0.005 µg
palladium/cm
2
 per day. A  palladium–silver alloy (Pd62, Ag24, Sn9, Zn3,
In2; atomic  weight per cent) released 0.003 µg palladium/cm
2
 per day
(Wataha & Luckwood, 1998).
A n  in vitro study has  measure d the release of palladium from a
palladium–copper–gallium alloy (Pd79.7, Ga6.0, Sn6.5, Cu5.0, A u1.0,
Ru0.8;   weight  per  cent)  and  gold–palladium alloy (Au51.1, Pd38.5,
In9.0, Ga1.2, Ir0.2; weight per cent) with and without toothbrushing for
30  min  at 200 g force. Brushing without toothpaste increased the
palladium  release  from  the  silver–palladium alloy from <0.06 to
0.10 µg/cm
2
 and from the palladium–copper–gallium alloy from <0.06 to
0.15  µg/cm
2
.  W h e n  brushing with toothpaste was done, palladium
release from the gold–palladium alloy increased to 0.5 µg/cm
2
 and from
the paladium–copper–gallium alloy to 0.9 µg/cm
2
. The alloys had a
surface area of 9.08 cm
2
 (Wataha et al., 1999).
Other studies by Marx (1987), Kobayashi (1989), Drápal &
Pomajbík  (1993), Wataha et al. (1994a), Schultz et al. (1997) and
Begerow et al. (1999a) reported similar results.
5.2.4.2
Clinical studies
Salivary   fluid  was   colle cted  from  97  persons  of  both  sexes   in
Switzerland. The palladium content in saliva was determined by AAS.
Six-millilitre samples of morning saliva were collected before breakfast
and  before   toothbrushing  (Wirz  et  al.,  1993). Three groups were
formed: a control group (A) consisting of 33 healthy subjects with
intact teeth, group B consisting of 32 persons with amalgam fillings
and  group  C  consisting  of  32  persons  with  amalgam  fillings  and
metallic dental appliances. The palladium content in  saliva was higher
in group B (2.8 ± 2.7 µg/litre) and significantly  higher in group C (10.6 ±
7.4 µg/litre) than in control group A (1.5 ± 1.5 µg/litre).

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