Page 59 - My FlipBook

MA TRICES.
45
after which it will not be to The dam can be removed
wedge, apt slip.
by first cutting the septum of rubber between the teeth.
Where it can be used, I like the wooden wedge better than any
other. To apply it, first cut a thin wedge, soap it, and slip it between
the teeth next to the gum. Next trim the wedge proper with a long
taper, soap it, and force between the teeth, driving it into place with,
After off the ends, withdraw the
gentle taps. cutting wedge which
was first placed, thus relieving the pressure against the gum.
Whenever there is sufficient space above the gingival margin of the
cavity to permit it, a wedge should be forced between the teeth during
of This not
the operation only supports the teeth, lessening
filling.
the shock from the mallet blows, but it protects the dam when the
disk is used. This wedge should be made thin and
shaped as seen in Fig. 59. The grooves at each side FlG * 59>
make it more firm, and prevent it from riding up.
As the wooden wedge is not always entirely satisfac-
tory, owing to the fact that if proper grooves be cut
it sometimes becomes difficult or impossible to force
it into place, I have devised a steel wedge which
serves admirably in most cases. This is shown in
Fig. 60. It is similar in general shape to the wooden wedge, but a
V-shaped cut forms the sides into two arms which can be sprung
together, and so forced into place, where it is retained by the strength
It will be noticed that this has a to further
of the spring. tendency
separate the teeth ; this is slight, and no disadvantage.
The Uses and Dangers of Matrices. If separators have worked
evil, matrices have proved even a more disastrous delusion. It seems
so easy to prove that a tooth which has been encircled by a matrix
cannot be properly filled with gold, that it is astonishing that so many
skillful men use them.
really
The argument is this : What is the principle upon which a matrix
is used ? It is made to supply a lost wall, and thus to produce a
cavity which is practically similar to one which has all walls standing,
which latter is admittedly the least difficult to fill. This the matrix
does, and since the cavity which it simplifies is usually most difficult,
at a casual glance it would appear that the matrix is a most valuable
instrument. The fallacy lies in this, that while (perhaps) it renders
the actual filling- process more simple, it forms the gold so that it be-
To
comes impossible to properly polish it. explain this the illustra-
tion (Fig. 61) will serve. The matrix is seen drawn tightly around
The teeth have not been wedged, since no
the bicuspid. space is
can be crowded between
needed save for the matrix, which usually
the teeth in their normal position : indeed, it is usually preferred that
It seems to me that the
the teeth should be close together. logic