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MATERIALS FOR FILLING. 85 ;

stroy its applicability. Good fillings may be made
of well prepared platinum sponge, recently annealed.
It requires skillful manipulation, however; for the
least moisture destroys its cohesive property entirely.
It is a good conductor of heat, and on this account
objectionable. In the respect of color, too, it is undesi-
rable. Platinum should never be placed in close prox-

imity to tin fillings, or to gold plate or clasps of low
carat. It is not now, however, used in filling at all,
except experimentally.
Gold.—Of all the metals that have as yet been
used 'for filling teeth, gold possesses more of the
requisite properties than any other, except platinum,
and sufficiently so for all practical purposes. Twenty-
carat gold is very seldom affected by any agencies

with which it is brought in contact in the mouth
pure gold never. In the filling of teeth, there are
two objects to be aimed at : one, a sufficient hardness
to withstand the wear of mastication ; the other, a
thorough protection to the cavity against all foreign
substances. For the attainment of the first of these,
gold is not all that could be desired yet it is, per-
;
haps, as efficient in this respect as any other metal
that can be employed. But the second object, gold

when well manipulated, accomplishes very effectually
;
that is, so long as the filling maintains its integrity :
after it is partially worn out, it thus far fails, of course.