Page 192 - My FlipBook

176 THE TREATMENT OF TEETH
mass usually readily leaves the walls of the matrix
at one or more points, and does not in any way drag
the wall with it, and careful painting around the
wall and fusing in successive layers prevents the
body leaving the walls. There is, however, a warp-
ing of the porcelain that takes place if it is fused
in a certain form. If a long, fine-pointed cone is
made, and fused in a horizontal position, it will
be found that the apex of the cone turns up ; also
if an inlay is made for a fairly large approximal
cavity in an incisor that tapers in a V-shaped
manner from a broad cervical margin to a shallow
almost pointed apex at the cutting edge, it will,
if made in an uninvested gold matrix, curl up
at the cutting edge and rock in the cavity so
as to be a bad fit. The same thing may occur
if very thin platinum is used, though not to the
same extent. If, however, the cavity is practi-
cally a round hole of fair depth, with supporting
walls of equal height, the inlay, if made in an
uninvested gold matrix, will rarely show signs of
warping. The same kind of warping will take
place if the whole of the labial wall of a fairly
large incisor cavity is completely removed, leaving
only lingual, cervical, and cutting edge walls.
In this case, the matrix being entirely unsupported
at one side, will warp or shrink away from the