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FILLING WITH AMALGAM. 129

proceeded with, for if the alloy is just what it should be, the
mass will begin to stiffen very quickly, and possibly become unfit
to work before the packing is completed.

Packing Amalgam Filling.
The importance of the best form of instrument for packing
amalgam can hardly be overestimated. Until I had examined
this over and over again, experimentally, under conditions which
enabled me to determine results, I had no idea of the importance
of the instrument forms for this purpose. The one thing need-
ful in packing amalgam is to grasp the mass as a whole as nearly
as possible, and compress it into the cavity. The whole prin-
ciple of making perfect work is contained in the one word,
compression. Therefore, the cavity must be a simple one with
complete surrounding walls, or must be converted into a simple
cavity by supplying any missing walls with the matrix. Then
the instrument point should be flat and as large as the cavity
will conveniently admit, and, when practicable, its form should
be such as to as nearly fit the cavity as possible. With it and
the walls of the cavity the mass of amalgam should be grasped
as perfectly as possible and powerfully compressed, so as to force
the amalgam into all parts of the cavity. About all the force the
hand is capable of should be brought upon it and maintained for
an instant. Then more of the mass is added and again pressure
applied. This should be done as rapidly as perfect work will
admit, until the cavity is full and much more than full. Indeed,
more of the mass should be added and compressed as long as
compression of the mass in the cavity can be made by adding to
the surface, for the time comes when the m.ass added simply
spreads out over the cavity walls. If, during the packing, there
are narrow parts of the cavity or irregularity of walls into which
the instruments do not go well, a smaller instrument should be
used to pack the amalgam into them. These should not be used
with such force as to crush into the mass and chop it up, but
only with such force as will compress. When the cavity is full
it should be allowed to rest undisturbed for a few minutes to give
it time to stiffen a little before attempting to remove any of the
surplus.