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AMALGAM IN THE MAKING OF A FILLING 143
of the hand and made into a pellet and then transferred to the thumb
finger grasp and rolled between the fingers with sufficient force to
produce a decided squeaking noise, sometimes spoken of as the "cry
of tin," Either too little or too much mercury will destroy this
sound which should be sought. This kneading should be continued
till the maximum plasticitj^ has been secured, and the tendency to
stiffen has just appeared.
Wringing Out Excess Mercury. All surplus mercury should be
expressed as soon as detected. With small masses this is thoroughly
and quickly done by grasping the mass between the ball of the thumb
and the tip of the first or second finger. The flesh of the fingers
should entirely cover the mass from view. Then by a rocking mo-
tion in which the mass is kept entirely covered the mercury will
appear from between the fingers and not carry with it any appreci-
able amount of the alloy.
If the mass is too large to keep entirely covered during the proc-
ess, it may be placed in a chamois skin and wrung to dryness, or di-
vided into piefees sufficiently small to be manipulated with the fingers.
As soon as the excess mercury has been expressed the whole mass
should be again kneaded, as it should not be allowed to stand in this
compressed condition. The mass should be rolled between the thumb
and finger into a loose rope, broken into pieces, and laid in a posi-
tion convenient to carry to the mouth. The rope or ball of amal-
gam should never be cut with instruments, as that part close to the
instrument is compressed and rapid setting facilitated.
Amalgam Pluggers. The packing instruments should be as large
as can be well used in the cavity, that the whole mass may receive
the force of compression at each effort. The face of the plugger
should be serrated to prevent slipping. A ball burnisher should
not be used in packing amalgam, but is intended for finishing after
the amalgam has set.
Making the Filling. The cavity should be in complete readiness
to receive the amalgam immediately after it has been prepared. The
size of the portions will depend upon the orifice of the cavity, and
should be as large as can be easily crowded into the opening. This
should be immediately compressed upon the seat of the cavity with
as large a plugger as possible, with a rocking motion and as much
weight as the circumstances wall permit. When using a point that
is much smaller than the cavity, the same wedging principle used in
packing gold should be employed; that is, compress the central por-
tion of the mass first and against the walls last. A burnisher should
not be used ; neither should the burnishing nor wiping motion be used,