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380 RESTORATION OF TEETH BY CEMENTED INLAYS.

into all the recesses with cotton ; bnt while this is undoubtedly of
advantage in some instances, the careful spinning of a piece of foil
from the edges to the cavity floor will generally give the best results.
The soft, unburnished platinum takes a beautiful impression, but when
the metal has been burnished it becomes elastic; if therefore the matrix
be moved during its formation, an accurate impression is impossible,
for the elastic platinum when distorted cannot be forced back accurately
into position until it has been rcannealed. When complaint is made

Fig. 362.

A, Posterior approximal cavity in second bicuspid ; B, edge of platinum extending over first
bicuspid to insure mobility.
against platinum by the advocates of gold matrices it probably arises
from the fact that they try to work the platinum in the same manner
as gold.
The matrix when finished should be carefully removed and heated
to redness in order to destroy all organic material, as such material will
tend to destroy the true shade of the porcelain.
In labial cavities the piece of platinum should be cut sufficiently
large to extend beyond the two adjacent teeth, and the metal should be
moulded to the three teeth by pressure with cotton and bibulous paper.
The metal is then held firmly upon the two adjacent teeth by the first
and second fingers, as in Fig. 359, when the general directions for adjust-
ing the matrix to the cavity may be readily carried out. The large
piece of platinum has two great advantages : it conduces to immobility