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306 PLASTIC FILLING MATERIALS.
worthy that Dr. Evans himself was the first to discover and make
public the deficiencies of his amalgam.
In America amalgam remained under a ban until Dr. Elisha Towns-
end of Philadelphia, a practitioner of such great skill as to be safe from
any imputation of lack of manipulative ability, introduced in 1855 an
alkjy of 44^ silver, 55| tin. The amalgam of this alloy received an
endorsement and application based more upon the eminence of its
author than upon the results of actual clinical tests, and a reaction
occurred which brought amalgam again under general condemnation.
What was known as the " new-departure corps " had its birth shortly
after this time. This was composed of a limited number of practi-
tioners and metallurgists, who were impressed by the fact that gold as a
filling material was not the panacea of dental caries, and that by inves-
tigation alone could the proper place of amalgam be found in the dental
armamentarium. It is due to this group of investigators to state that
the history of the rational employment of plastics is the history of the
" new-departure corps." It was undoubtedly due to it that plastics
have come to be regarded as substances having definite physical and
chemical properties which fit them for application as restorati\'e and
therapeutic agents for the relief of clearly defined physical and patho-
logical states. As the properties of these agents become better under-
stood, their employment more closely follows what is known as rational
therapeutics.
The use of any or of all of these several materials is founded so
entirely upon their individual properties that a discussion of these
properties must precede and govern that of their methods of manipula-
tion.
Natuee and Properties of Amalgam.
Ad amalgam is a combination of one or more metals with mercury ; it
is therefore any alloy into which mercury enters as a constituent. The
word amalgam (Fr. amalgame) is derived from Gr. cifia, together, yaiieco,
I marry ; or from cLfia and ndlay[xa, from iiaXdaaco, I soften—because
of the softness and fusibility which mercury confers upon alloys.
It is to be understood that amalgams are classified as alloys, and may
be therefore members ofany of Matthiessen's groups as follows A chemi-
:
cal compound in which the affinities are exactly satisfied ; one in which
there is unstable chemical equilibrium ; a sub-chemical compound, or
a mechanical mixture—although this latter is rare, as mercury exhibits
some degree of affinity for all metals.
There are two possible ways in which mercury brings about the
solution of other metals : First, by a chemical affinity for the metals
second, by lowering the melting-point of the solid metal, forming an
306 PLASTIC FILLING MATERIALS.
worthy that Dr. Evans himself was the first to discover and make
public the deficiencies of his amalgam.
In America amalgam remained under a ban until Dr. Elisha Towns-
end of Philadelphia, a practitioner of such great skill as to be safe from
any imputation of lack of manipulative ability, introduced in 1855 an
alkjy of 44^ silver, 55| tin. The amalgam of this alloy received an
endorsement and application based more upon the eminence of its
author than upon the results of actual clinical tests, and a reaction
occurred which brought amalgam again under general condemnation.
What was known as the " new-departure corps " had its birth shortly
after this time. This was composed of a limited number of practi-
tioners and metallurgists, who were impressed by the fact that gold as a
filling material was not the panacea of dental caries, and that by inves-
tigation alone could the proper place of amalgam be found in the dental
armamentarium. It is due to this group of investigators to state that
the history of the rational employment of plastics is the history of the
" new-departure corps." It was undoubtedly due to it that plastics
have come to be regarded as substances having definite physical and
chemical properties which fit them for application as restorati\'e and
therapeutic agents for the relief of clearly defined physical and patho-
logical states. As the properties of these agents become better under-
stood, their employment more closely follows what is known as rational
therapeutics.
The use of any or of all of these several materials is founded so
entirely upon their individual properties that a discussion of these
properties must precede and govern that of their methods of manipula-
tion.
Natuee and Properties of Amalgam.
Ad amalgam is a combination of one or more metals with mercury ; it
is therefore any alloy into which mercury enters as a constituent. The
word amalgam (Fr. amalgame) is derived from Gr. cifia, together, yaiieco,
I marry ; or from cLfia and ndlay[xa, from iiaXdaaco, I soften—because
of the softness and fusibility which mercury confers upon alloys.
It is to be understood that amalgams are classified as alloys, and may
be therefore members ofany of Matthiessen's groups as follows A chemi-
:
cal compound in which the affinities are exactly satisfied ; one in which
there is unstable chemical equilibrium ; a sub-chemical compound, or
a mechanical mixture—although this latter is rare, as mercury exhibits
some degree of affinity for all metals.
There are two possible ways in which mercury brings about the
solution of other metals : First, by a chemical affinity for the metals
second, by lowering the melting-point of the solid metal, forming an
