Page 294 - My FlipBook

292 THE OPERATIOX OF FTLLTNG CAVITIES.
atljoiiiing tooth and koop the matrix firmly in place and at the same
time act as a separator. If the operator feels that he has insufficient
space, as his filling progresses he can occasionally tighten the screws
and gradually gain space between the teeth, which is of value ^\•hen he
is ready to dress down and polish his tilling. Several sizes of these
should be at hand to meet the exigencies of individual cases.
It has been said that the matrix converts a comjjouud <'avitv into a
simple one. This is accomplished by making ol" metal a temporary
fourth wall to the cavity. It must be borne in mind, however, that
Fir;. 255.

Examples showing uses of matrices.
the use of the matrix does not lessen the care which should at all times
be exercised in the packing of the filling. Direct pressure against the
disto-buccal and disto-ling-ual borders of the cavitv cannot be as well
obtained when the matrix is used as when it is not, hence the importance
of having the matrix so adjusted that these walls may be accessible.
Cavities of this variety seldom require retaining pits. The cavity is
supposed to be of a retentive form. If the matrix has been made to
fit the cervical border of the cavity and is thoroughly wedged against
it, the filling may be started with mats of non-cohesive foil or Avith loosely
Fig. 256.

Woodward's screw matrices.
rolled cylinders. Two, three, or even more may be pressed thoroughly
against the cervical wall and condensed with a hand mallet or with the
automatic mallet. Similar pieces are then inserted and malleted to place
Cohesive gold may
until the upper third of the cavity has been filled.
then be substituted for the non-cohesive and each piece packed with
hand pressure or mallet force as preferred. The instruments shown in
Fig. 257 are well adapted to fillings of this description.
As there is sometimes difficulty in adjusting the matrix to the cer-
vical border of the cavitv, it is well at times to insert a cylinder or two