Page 81 - My FlipBook

Ileal the foil, then force it into the model of the cavity with ball burnish-
ers. After the foil has been irregularly forced into the model it should
be swaged gently with the velum rubber plunger. Remove the matrix
from the model and trim to proper size ; dust the model with soapstone,
applying it with a camel's hair brush, and blowing away the surplus. The

Img. 91.

matrix is placed into position and given the final swaging. The most
delicate step of the operation is removmg the matrix from the model, as
this must be done in such manner as to prevent distortion.
The method of swaging matrices over impres-
sions of cavities has some followers, and the advo-
Swasina ITlatrices
cates of this method claim that they can construct
ooer Tmpressions.
more accurately fitting inlays. However, experi-
ments show that the thinnest film to which a layer
of cement can be squeezed, under pressure equivalent to that applied in
setting inlays, is not much less than 1/2000 of an inch in thickness, so that
the inlay, when set with cement, will not absolutely fit the cavity. If sim-
ple approximal, approximo-incisal or approximo-occlusal cavities are pre-

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