Page 206 - My FlipBook

190 THE TREATMENT OF TEETH
not greatly depends on the extent to which the
base is broken away. A deeply undercut hole is
not necessary. It stands to reason that the forma-
tion of a good retainage cavity in the base of an
inlay depends on a sufficient depth of cavity to
admit of a reasonably thick inlay being made. In
shallow cavities where the inlay is so thin that no
retainage can be made in the porcelain, either by
means of a hollow in its base or by means of
grooving the sides, Mr. Rippon has devised another
method, which he finds most useful. He places
the piece of foil with which the matrix is made
between folds of fairly coarse sandpaper. By
means of forcibly rubbing the sandpaper, and by
striking it with a hammer, the foil is thoroughly
well roughened and indented. The matrix is
formed with the roughened foil in the usual way,
taking care to only apply a burnisher to the margins.
The inlay fused in the roughened matrix is found on
stripping off the foil to have a roughened and
indented surface which provides as satisfactory
retainage as can be secured in these shallow cases
with no weakening of the inlay.
In mixing the porcelain powder with either
alcohol or water there is no necessity to use a
spatula ; a camel-hair or sable brush is all that is
"
necessary. A spatula may be used to j ust " dab