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TIN AS A FILLING MATERIAL 167

ductor of heat as gold, hence, indicated under gold fillings in deep-
seated caries with vital pulp.
Indicated in Rapid Caries. In caries of a light or white color
indicating the most rapid form of decay, tin is of peculiar advan-
tage, particularly in regions removed from view and protected
from the wear of mastication.
Tin in the Teeth of Children. There is no better material for fill-
, ing the teeth of children than tin. The principle of mechanical ex-
clusion depended upon with other filling materials to prevent re-
current decay does not seem to be sufficient in the rapid form of
decay met with in both temporary and permanent teeth in the
mouths of children particularly during the age of rapid develop-
ment as found before the age of fifteen or sixteen. The additional
advantage of the therapeutic influences of tin seems to be sufficient
to check this rapid progress of decay till a period is reached when
the process of tooth destruction is less apparent, due to more hy-
gienic conditions in the oral cavity.
Cavity Preparation for Tin. The cavity preparation for the use
of tin is not unlike that given in the chapters on cavity prepara-
tion by classes for cohesive gold. It will be of advantage if the
convenience angles are a little more distinct, and the general re-
tentive form throughout should be emphasized. The bevel angle
should be a little more deeply buried as the edge strength is not
as good as hammered gold. However the edge strength is better
than amalgam. Tin has no tendencj^ to spheroid like amalgam.
Its flow is similar to that of gold but greater with the same given
load and like gold it is capable of being so condensed that it will
stand repeated stress of a given load within a limited range and
show no flow.
Forms of Tin. Formerly the only form of tin to be had for this
purpose was the sheet tin. This was manipulated in much the
same way as cohesive gold except that it required no annealing.
It was then, and is yet, sometimes combined Avith gold by rolling
a sheet of pure tin with a sheet of annealed cohesive gold into
rolls, the gold on the outside and condensed in the usual manner
using a large proportion of hand pressure.
At present there is on the market a form of tin prepared in the
shreds, which appears like a mass of coarse silver-colored hair.
This is removed from the tube and shaped into pellets of suitable
size and placed in the cavity in the manner one would place pellets
of gold.
Methods of Introduction. The rubber dam or other efficient