Page 351 - My FlipBook

CEMENT AND AMALGAM. 349

into the cavity, by drawing a narrow strip of it between two pieces of
stationer's rubber (ink erasers). Place one piece of the rubber on a
table, then the strip of metal held with pliers in one hand is placed on
the cake of rubber, while with the other hand another piece of rubber
is held firndy down on the metal, which is drawn between the two until
sufficiently bright.
For ordinary cases, a piece is cut from the German silver, as shown
in Fig. 325, A, wide enough to extend from the top of the tooth to a
little beyond the cervical wall of the cavity, and long enough to a little
more than cover the cavity laterally when tied in place. Sometimes it
is necessary to make the matrix with a lip to extend under the gum, as
shown in Fig. 325, B, or in some other irregular form, so that it can be

Fig. 325.

A, Matrix and ligature; B, lipped matrix.
made to properly fit the cavity. Special cases may require a very wide
or a very narrow one. The operator's ingenuity must devise the right
shape.
For tying the matrix to the tooth, coarse, well-waxed floss silk is the
best. It is passed through the holes punched in the metal, as shown
in Fig. 325, A and B. When these holes are made, the edges must be
finished smooth, or the silk will be cut when drawn tightly around the
tooth. The operator must use tact as to
Fig. 326. how and where to make his knots in
tying on the matrix. Usually, a good
way is to place one end of the ligature, a,
between the teeth, then to make a sur-
geon's knot, as shown in Fig. 326. The
other end of the ligature, b, is then forced
between the teeth, and the knot tightened.
Manner of ligating the matrix.
This will bring the knot between the
teeth and opposite the matrix and will hold the latter until it can be
shaped and bent into place with a burnisher or other suitable instru-
ment. The knot is again tightened, and the two ends of the ligature
carried to the back of the matrix and a similar knot tied there. The
second knot, when drawn tightly against the back of the matrix, forces
it closely up to the cervical border of the cavity, and makes a firm
resistance when the filling is being condensed. The silk is then wound