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134 THE TECHNICAL PROCEDURES IN FILLING TEETH.

They may also be used for temporary fillings in cases of very
sensitive dentin for the purpose of allaying the extreme sensitive-
ness, which is generally found to disappear, in large part at
least, within a few weeks or months. They may also be used
for temporary fillings in cases of hyperaemia of the dental pulp
with marked advantage, for the reason that their conductivity of
thermal impressions is less than that of the metals, though in this
respect gutta-percha is much better than the cements ; also they
may be used in capping exposed pulps.
The cements are also much used for sealing treatments in
pulp-chambers and root-canals. This last use of the cements is
not good practice. They do not perfectly exclude moisture.
Gutta-percha is much better for this purpose for the reasons, first,
that gutta-percha is impermeable to fluids, and moisture-tight
fillings can be made with it; second, gutta-percha is much more
easily removed from the cavity in opening it for changes of the
applications. It is very painful to cut out a cement filling when
the peridental membrane of the tooth is sore, while gutta-percha
may be softened by heat and removed with very little pain.
Filling with Cement.

In filling cavities with cement the preparation should be well
made, all of the walls being cleaned by perfectly removing all
carious dentin to sound tooth structure, and the walls and mar-
gins trimmed smooth. Some degree of retention should also be
given to the cavity form, but this is not so imperative as with
metal fillings.
-The cavity should be perfectly dry at every part, for in this
case we may expect that the cement will adhere strongly to the
cavity walls and in part sustain the filling in position. The
cement should be mixed with as much of the powder as will
work into a plastic mass and spatulated vigorously until it has
begun to stiffen, and, when at the consistence of putty, should
be packed into the cavity in moderately small masses, using as
much force as the consistence will allow, adding piece after piece,
until all parts of the cavity are full and over-full. Then a few
moments should be allowed for the cement to stiffen a little more,
after which the filling is trimmed to form with the finishing
knives. In this trimming the cement should be so stiff that the
stickiness shall have disappeared, for it is only just at this time