Page 158 - My FlipBook

154 OPERATIVE DENTISTRY

Convenience Form. This step in cavity preparation for the
silicate filling, as with other plastics, comes in for only a minimum
consideration, as it is seldom necessary in the use of this material
to make any changes to facilitate the making of the filling, for when
other rules have been followed we find ample convenience for its in-
troduction.
Removal of Remaining Decay. There is one major reason why
all softened dentine should be removed from the cavity walls. The
decalcified portion of tooth substance is always saturated with the
—
acid of tooth decay, ^lactic acid. Experience has proved that the
crystallizing silicate will absorb this acid, resulting in a filling of
weak structure. It would therefore follow that no softened dentine
be allowed to remain in the cavity.
Finishing of Enamel Walls. With other fillings it has been found

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Fig. 91.—A small set of instruments for mani[)ulating silicate.
advisable to bevel the enamel margins from 6 to 10 degrees centi-
grade. With all silicate fillings, this beveling seems to make an ad-
ditional weakness and should be avoided as it will cause the filling
to break at the margin, even though the procedure results in an im-
perfect cavity, from a scientific standpoint. We should determine
that Ave have full-length rods and that we have found their direc-
tion by complete cleavage and then omit the beveling.
Toilet of the Cavity. To the ordinary toilet given for other fill-
ings should be added the varnishing of the dentine walls, as a pre-
caution against the material absorbing either acid or moisture from
the walls or the absorption by drying dentinal walls of the fluid
part of the filling, due to excessively desiccated dentine.
Rubber Dam. The application of the rubber dam, or other means
equally as efficient, should have taken place following partial outline