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MATERIALS FOR FILLING. 81

indispensable properties than any other; but the fol-
lowing have been used for filling; lead, tin, silver,
platinum, gold, and amalgam. In the preparation of the
latter, gold, silver, platinum, tin, bismuth, antimony,
cadium, zinc, and mercury, have been employed.

Lead.—This metal, in the early history of the pro-
fession, was used to some extent for filling teeth, though
it possesses but few of the requisites for that purpose.
The principal quality which recommended it, is its
adaptability ; but it is quite too soft for permanent
fillings in the masticating surfaces of the molars. It
is easily wrought into foil and welded into mass in
the cavity, but it is rapidly worn down by mastica-
tion, and its integrity readily impaired by the influ-

ence of peculiar conditions of the mouth ; much more
readily, indeed, than that of tin or silver. Acetic and
other acids act upon it with considerable energy in
the mouth. By exposure to air and moisture, it is
soon coated with carbonate or protoxyd of lead ; and
this change is effected much more readily in the
mouth. Lead is also objectionable in color—especially
for fillings in the anterior teeth—it being darker

than the other metals employed for the purpose. It
is, however, a less perfect conductor of heat than some
others that are in far more extensive use.
Tin.—This metal has been, and is even yet, much
employed as a material for filling. It is easily