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132 THE TECHNICAL PROCEDURES IN FILLING TEETH.

together with a spatula. This spatulation should be continued
until a very smooth, creamy mass has been formed. The mix-
ture of the oxy-phosphate should be much thicker and stififer
than the mixture of the oxy-chloride to obtain the best results
with the respective cements. Indeed, the oxy-chloride may be
mixed so thin and soft as almost to flow and yet become very
hard and firm; while the oxy-phosphate, to produce the best mass,
should be rather stiff, yet it may be quite plastic.
As yet, there has been very little careful examination of the
physical properties of these cements. We do not know accu-
rately the proportions of powder and fluid required to produce
the best results. It is probable that these vary with the different
makes of these cements, and also with the age, for the fluids
seem to be inconstant in their properties. It has been the con-
stant habit of dentists to mix them without any rule, simply
observing the plasticity of the mass produced, being governed
entirely by the eye and the observation of the results. This
must be regarded as a very inaccurate method of using this
material, but so long as we are without more accurate knowledge
of it than this gives, we can only follow it. Very recently some
work has been done on the physical properties of the cements by
Doctor Wedelstaedt, of St. Paul, and by Doctor Ames, of Chi-
cago. In this work it has been shown that most of the cements
are readily permeated by moisture, while some are not, and also
that some of the cements will shrink badly while hardening.
In mixing the oxy-phosphate it seems to be best to draw the
powder into the fluid and incorporate it little by little until the
required stiffness of the mass has been acquired. Just what this
should be can not, in the absence of carefully conducted experi-
ments, be definitely stated. In practice it is varied with the
particular use to be made of the particular mix. If for filling
and setting crowns, in which case great plasticity is required,
the consistency of very thick cream is usually acquired, and this
very thoroughly spatulated and used quickly, or before it has
begun to stiffen. If for filling cavities in teeth, more of the
powder is added and the mix made stiffer, and the spatulation
continued somewhat longer, so that the mass assumes a putty-
like consistence. It seems to be the general notion that when
mixed in this way a much stronger mass is formed. This idea
is strongly supported by some recent physical experiments, yet