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FILLING TEETH 67

working properties, depending on the kind that is
used, and great familiarity with an instrument has
much to do with the quaUty of the work produced.
The nearest approach to the hand mallet is a certain
make of pneumatic mallet. If it is so constructed
that the plugger is screwed into the hand-piece, so
that they form one rigid plugger, and the plunger
strikes the end of the hand-piece above the part
that is grasped by the hand, the operator feels
exactly what he is doing, and can regulate and vary
the force of the impact far better than when he has
to hold a hand-piece inside which the plunger works.
Preparation of Cavities for Gold Fillinys.—To
prepare a cavity for the reception of gold it is
necessary, in nearly all cases, to cut away part of
the tooth, to enable the instruments to be freely
used in the removal of the decay, the cutting of the
retainage, and the insertion and packing of the gold.
A certain amount of " opening the cavity," as it
is called, is necessary, no matter what material is
selected; but the cutting must usually be much
more freely done if gold is to be used, for every
piece must be placed at once just where it is
wanted, and condensed by the direct action of the
plugger. There is no possibility of pressing the
gold round a corner and squeezing it into position.
This cutting away of part of the tooth does no