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358 THE TECHNICAL, PKOCEDmiES IN FILLING TEETH.

fillings can be made with it; second, it is mueh more easily
removed from the cavity in opening it for changes of the appli-
cations. 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 a heated burnisher 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 soimd tooth structure, and the walls and
margins 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 overfull.
Then a few moments should be allowed for the cement to stiffen
a little more, after which the filling may be 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 that it can be cut smoothly without drag-
ging. After trimming, it may be burnished lightly, and, if nec-
essary, smoothed with polishing strips. The oxyphosphate of
copper cement makes a harder mass and is not subject to the
great shrinkage that occurs in the harder qualities of oxyphos-
phate of zinc. It is therefore much better for filling the occlusal
surfaces of the teeth of children or any other fillings for children
where its jet black color is not particularly objectionable. It
becomes hard enough to wear quite well in occlusal surfaces.
It, therefore, serves an excellent purpose in these positions at a
time of life when it is especially difficult to make fillings of metal.
After the filling is completed, if the softer or more pene-
trable cements have been used, it should be protected from
moisture for some minutes, the longer the better, as the cement
will become harder. It seems that when moisture is admitted
early, a part of the phosphoric acid is dissolved out of the cement,