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158 OPERATIVE DENTISTRY

seems to be as low as can be borne by the patient when placing a
filling in a vital tooth. It is therefore quite practical to use a
bottle slab wherein the thermometer reaches 55 to 60 degrees, as no
doubt the temperature of the filling is about 68 Avhen placed in the
tooth. It is quite possible to use a bottle that contains iced water
when the filling is to be placed in a non-vital tooth. At such times
when the atmosphere is close to the dew point, as is evidenced by
the condensation on the fountain cuspidor, there Avill be trouble
about the formation of moisture on the cold bottle. When this is
only slight, it does not seem to damage the filling. However, when
the condensation is sufficient to be noticed, or is excessive, the den-
tist has to either content himself with manipulation at a higher
temperature or postpone the operation to a time when the atmos-
phere is above the dew point. The spatula must be of some ma-
terial which will give off: none of its substance during the process
of mixing. For this reason the agate is the best and most popular.

Fig. 97.—Illustrating the circular motion which should be given the spatula in mixing a
silicate filling. Note that the spatula should be moved first in one direction and then in the
other as indicated by the arrows. Also that the spatula describes segments of small circles
and that the material is not spread over any considerable surface of the slab.
Begin the mixing only when the cavity is prepared and dried, and
the filling instruments are laid out and ready for immediate use.
While there is no great haste as long as the material lays oq the
cold slab, there are left but a few seconds to make the filling after
the material has been removed from the slab, on account of the
rising temperature hastening chemical action.
Preparing Materials. First pour out near the end of the slab to
the right, the amount of powder the mix is liable to require, and
then place stopper in the bottle. With the dropper place the
proper quantity of liquid near and to the left of the poAvder. Im-
mediately return the dropper to the bottle and secure the cap to
prevent evaporation. The best results are obtained when no less
than three drops of liquid are used for the mix. Do not shake the
liquid bottle. Make the mix promptly, for if there is any consider-
able delay, the chemical formula of the liquid may be changed, due