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82 GENERAL REMARKS ON FILLING.

wrought into foil, and in that condition is readily
adapted to the purpose, by reason of its softness and
pliability. Fillings can be made with it in all cases
in which non-adhesive gold foil can be used, to much
of which, indeed, it can, by skillful manipulation, be
made superior in adhesive property. Its quality,

however, is greatly dependent on the manner of its
manufacture. It is harder than lead, and in many
cases hard enough for permanent fillings : we have
known it retained in crown cavities of the molars,
effectually preserving the teeth, for fifteen years. In
favorable conditions of the mouth, it is not materially
changed, not oxydizing easily, and not readily uniting
with any substances liable to be brought in contact
with it. But in an unhealthy mouth, with the secre-
tions in an abnormal condition, and the teeth neg-
lected, tin fillings are very rapidly destroyed, chiefly
by the action of the soluble chlorides. Such a

change may take place in the mouth, as will in a little
time destroy tin fillings that had long remained in.
good preservation ; and hence this material is not en-
tirely reliable in any case, since such change may at
any time occur. Some cases seemingly favorable to
its use, are found, on examination, to be otherwise
and in almost any mouth in which there is a large
proportion of mucus secreted, it cannot be depended
upon for permanency. Its color renders it unfit for