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HISTORY OF DENTAL SURGERY 173

cheaper class of operations. Tlie time and labor necessar\' to fill a large
cavity with gold were much lessened by the employment of tin, for it was
softer and more pliable than even lead, and did not harden under the instru-
ment like gold. It certainly oxydized, giving the tooth an ugly black color,
and was, therefore, generally used only in the back teeth. It also wore
rapidly away under mastication, but could be then cheaply, easily, and com-
paratively quickly replaced. In brief, it possessed several negative advantages
which were opposed by few positive disadvantages, and, for many years, was
voi'y extensively employed by the best dentists, with hardly a dissentient voice.
"But the growing influence of gold at length made itself felt in opposition
to the huml)ler metal. The introduction of various plastic fillings, too, operated
against it, and its employment was finally very much reduced in extent, al-
though it has never been entirely rejected, but is even now considerably used,
in the less expensive class of cases."
Amalgam is responsible for the almost entire displacement of tin as a
filling material. The only class of cases in which tin is the most suitable
filling material is in enamel defects and slightly decayed cavities in occlusal
surfaces in first and second molars of children who cannot be required to
endure sufficient thoroughness in the operations to make gold fillings that
can be permanently depended on. The tin fillings are expected to be temporary,
liut will almost always preserve the teeth perfectly till the children are old
enough to have gold fillings made without difficulty.
Many operators use a combination of tin and gold, laying a sheet of each
together, or one of tin with two of gold, or two of tin with one of gold ; making
the foundation of large fillings with this and finishing with gold. These opera-
tions, if made thoroughly and with good judgment, are very satisfactory.

PLASTIC FILLINGS.'
"The first of these * * * were simple etherial or alcoholic solutions
of some of the gums, as mastic, sandurac, etc-
"TriTo-metallic Ccmrnt.—This was composed of a mixture of sulphate of
lime and oxide of iron. The celebrated anodyne cement was similar to it, with
the addition of morphia. These cements served only a temporary purpose,
the last also having as part of its object the relief of pain. Robinson savs
tliat a 'few hours' after their introduction, 'they dry, crumble, and fall out.'

' History of Dental and Oral Science.
iii.
- Kobinson on the Teetli, p.