Copper amalgam is still used today as a fillingmaterial for deciduous teeth. Good retentive properties
backed by the bacteriocidal properties of the copper are
claimed to reduce the incidence of secondary caries. The
main disadvantages are green discolouration of the teeth
restored by copper amalgam and unsustained reports
of toxicity to the pulp.
The aim of this study was to investigate some of
the mechanical properties of copper amalgam and carry out
some biological experiments. Silver amalgam was used
as a control material.
All the available data on the rather obscure
metallurgy of copper amalgam has been presented. Only
one intermediate phase, with a narrow band of homogeneity
has been identified. It is an intermetallic or electron
compound. Chemically such compounds are of closely
controlled composition, usually involving small, simple
ratios of the combining elements where laws of valency
are not observed. Various formulae have been suggested.
Physically such compounds are brittle and of variable
hardness. It is thus distinguished chemically and
structurally from the various types of dental silver
Remarkably little data exists on physical
properties; compressive strength (11 specimens),
tensile strength (32), dimensional change (not known) and
hardness (10). In this study over 100 specimens were
subjected to mechanical tests. Xt was found that copper
amalgam exhibits approximately half to one third of the
value for compressive strength and tensile strength of the
values for dental silver amalgams used for comparison.
Tests for these properties gave very variable results
despite considerable efforts to standardise specimen pro¬
duction. These two properties do not appear to be
related to residual mercury content. Dimensional change
on setting was more consistent showing an overall average
setting contraction of 0.13 per cent. The Yickers hard¬
ness of copper amalgams was similar to that of the silver
amalgam the hardness value was significantly higher. The
setting time of copper amalgam was undesirably slow.
The adaptability of copper amalgam was studied
and compared with 5 different types of silver amalgam.
(Only one previous worker has carried out such a study.)
Copper amalgam adapted to the cavity wall better than the
silver amalgams used for comparison. Scanning Electron
Micrographs are included in this study and further
The effects of copper amalgam restorations and
silver amalgam restorations on the dental pulps of rats
were studied. Over 80 restorations of each amalgam were
placed in the first maxillary molar teeth of rats, copper
amalgam on one side of the maxilla and silver amalgam on
the opposite side. There was no detectable difference
between the effects of unlined copper amalgams and unlined
silver amalgams on rat molar pulps over periods of 1 month
to k months even when the pulp had been surgically exposed.
Copper amalgam restorations suffered more severe attrition
than silver amalgams and were, therefore, less likely to
be lost by accidental trauma. This finding explained the
apparent good retentive properties of copper amalgam.
Retention of the restoration was found to be a key factor
in survival of the pulp
Tissue culture studies demonstrated that in a
controlled medium copper amalgam was a very much more
effective source of copper and mercury ions (predominantly copper) than the pure metals themselves.
A model of the tooth/amalgam interface was
designed to study the movement of bacteria in this area.
By comparison with previous studies of this type the
number of variables was reduced. It was found from 71
experiments using this model that a significantly higher
number of experiments incorporating silver amalgam
permitted bacteria to pass through the interface than the
number with copper amalgam.