Page 82 - My FlipBook

pared with proper marginal form, there will be no perceptible difference in
the fit of the inlay, whether it is constructed in a matrix, burnished into
the cavity or swaged over an impression of the cavity.
The method of constructing matrices over an impression is particu-
larly indicated for cavities on the labial or buccal surfaces of teeth, or in
any form of cavity known as a four-w^all cavity. Such forms of cavities
can not be prepared so that the matrix can be burnished into the cavity
and the inlay compensate for the space of the matrix unless it be con-
structed with frail margins of porcelain, which lack edge strength,
and are so thin that a change of color is noticeable along these margins.
The technique of constructing matrices, by swaging over an impres-
sion of the cavity, is as follows : The impression should be taken in ce-
ment, which should be mixed to a thick consistency. It should be formed
into an irregular conical shaped mass, forced into the cavity and permitted
to remain under pressure until it has hardened. To take an impression
of a labial or buccal cavity extending beneath the gum margin, mix the
cement to a thick consistency. Then with some form of retractor, crowd
the gum back and force the cement to place with the fingers, holding it in
position until it has hardened.
The impression (Fig. 90) is invested in the ring of the swaging
device. A piece of platinum foil not thinner than i/iooo of an inch is
placed over the impression and partially swaged with the velum rubber
plunger. The foil is then trimmed to proper shape and placed over the
impression and burnished, at the angle formed by the cavity margins and
the surface of the tooth, with steel burnishers (Fig. 91). The matrix
is then removed and the impression dusted with soapstone : then the matrix
is reswaged with a velum rubber plunger which has a flat face. It is
then carefully removed without changing its form.
The method of swaging the matri.x into a model
Befitting matrices. of the cavity and then burnishing it directly into the
cavity as a subsequent operation is particularly indi-
cated for those approximo-occlusal cavities where the cavity extends far be-
neath the gingival margin and involves a large portion of the occlusal sur-
face. The matrix may be swaged of gold or platinum 1/500 of an inch
in thickness. If a heavy material is used for the matrix, there is less dan-
ger of warping during the process of fusing. The matrix, however, should
become a part of the inlay. After it has been swaged to conform to the
model, the foundation of the inlay should be fused, then the matrix placed
into the cavity and burnished to conform to the cavity margins. The
matrix should be trimmed close to the margins of the cavity after the
final fusing, but the final finishing of the margins should not be accom-
plished until after it has been set.