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THE USE OF CEMENTS IN FILLING TEETH 147

teeth with closely approached vital pulp, or as a root filling, on ac-
count of its irritating properties.
Sulphate of Zinc, Avhen pure, is the least irritating of all cements
and is one of the best materials for pulp protection. A pulp cap-
ping of this material is of most universal application.
Oxyphosphate of Copper is especially indicated in remote cav-
ities on the necks of teeth occasioned by gum recession. Cavities
which are so ill-defined that the use of amalgam or gutta-percha is
difficult, may be successfully filled with this preparation of copper.
It can be made to adhere very tenaciously to the walls of a cavity,
thus obviating much cutting. Oxyphosphate of copper is also in-
dicated in the small cavities in the deciduous teeth.
It is claimed that this material exerts a therapeutic influence up-
on the tooth substance, thus preventing further decay.
Manipulation of Oxyphosphate of Zinc Cement. The method of
mixing this cement is not in the least difficult, yet certain details
are essential. The slab, preferably of smooth glass, should be clean.
The spatula should be flat with the side slightly convex.
Agate is the best material as it is not acted upon by the liquid.
The liquid and powder should be placed upon the slab separately, the
drop of liquid being carried there by the use of a small glass rod.
The spatula should never be immersed in the bottle to obtain more
fluid as this would destroy the efficiency of the liquid. Crystallized
portions should be carefully wiped off the mouth of the bottle as
soon as detected.
Plan of Spatulating. The powder should be added to the liquid
a little at a time and each portion thoroughly rubbed by a swinging
circular movement of the spatula upon the slab. This rubbing should
not be rapid or vigorous. For lining cavities, where thin layers are
desired which are very adhesive, the cement will prove correctly
mixed when it shows slight stringiness and when the first stickiness
appears, as shown by the slight resistance offered the spatula in its
movement over the slab. Where the entire filling is to be of cement,
more powder should be added and the spatulation continued till the
cement materially resists spatulation and the mass is the consistency
of freshly made putty. When cement is of the consistency desired
no time should be lost in placing it in position, and it should be
allowed to harden undisturbed. If the cement is to form the en-
tire filling and permanency is desired, it should be crowded to place
with some force and rapidly shaped up. As soon as crystallization
begins it should not be disturbed by manipulation till it has fully
hardened, when it should be polished with fine strips and disks.