Page 127 - My FlipBook

FINISHING FILLINGS. 123

passed over the surface of the gold in some regular order, being
careful not to cut too deeply in some parts, or cutting down
irregularly. In occlusal cavities, when the bulk of the trim-
ming has been done in this way, overlaps will remain in the
grooves and irregularities of the surface. These are best re-
moved with the discoid excavator, or spoons 20-9-12. These
instruments should be very sharp.
In buccal and labial cavities the finishing of the gin-
gival margin is the difficult point. Generally no attempt
should be made to cut these fully down to the enamel margin
with the bur or stone, but after the first part of the cutting has
been done, the gingival margin should be trimmed with the files
or with the finishing knives. In some positions this will be
done easiest with the knives ; in others it will be done easiest
with the files. Generally the knives should do the last part
of the trimming, for the reason that the sharp edge (and it
must be very sharp to be of use) will catch under the least over-
lap, find the exact enamel margin, and cut to it with certainty.
In using the finishing knives no effort should be made to cut
away a thick mass at a single stroke, but rather so catch it as to
remove thin shavings and pare down the gold litde by little.
Used in this way they will, in positions suited to their use, cut
faster than any other instrument used for this purpose. Great
care should be taken not to overtrim the gingival margin,
cutting away part of the thin enamel, or all of it, leaving
a depression. This is very liable to be done by the careless
use of the stone, and forms a depression in which debris will
lodge, setting up fermentation which will insure the recurrence
of decay at that point. This error is a very common one. All
parts of the margin of the filling should be trimmed exacdy to
the cavity margins. This should be so perfect that a sharp
edge or a sharp point will slide from the enamel onto the filling,
or from the filling onto the enamel, without the least catch or
interference with the perfectly smooth movement. All parts of
the surface of the filling should harmonize with the surface of
the tooth ; or, in other words, should reproduce the tooth form
with accuracy. Then the whole surface should be evenly
polished. This is best done by using a rubber disk of triangular
form with a sharp outer edge armed with pulverized pumice,
rotating rapidly in the engine. Or, on axial surface fillings, the