Page 418 - My FlipBook

186 THE TECHNICAL PEOCEDTJEES IN FILLING TEETH.

curved, the convexity is to the incisal as shown in Figure 257.
There sliould be no pits and no grooves whatever in the gingival
wall. The convenience points are not cut into the gingival wall,
but into the labial and lingual walls. The cavity. Figure 252,
will be used to illustrate filling with gold in incisor proximal
cavities.
Eecueeence of decay. The recurrence of decay so often
seen at the linguo-gingival and labio-gingival angles of well-
made fillings is shown in the whitened enamel and penetration
beside the filling in Figure 258. It is very exactly this recurrence
of decay that the form of cavity prepared under the rules of
extension for prevention is made to cover. The labio-lingual
breadth is spread out toward the gingival. Otherwise the cavity
is not essentially broader than had been made before. This
recurrence of decay is a rebeginning on the perfect surface of
the enamel and is entirely different from that shown in Figure
259, which is a rebeginning of decay from leakage. The filling
was imperfect. That may, and does, occur occasionally with the
best possible cavity preparation. If the recurrence of decay
is not observed in its incipiency, one will be unable, in most cases,
to tell with certainty the nature of the fault which has caused
it, except as the form of the filling may show that it had not been
sufficiently extended. This is clearly shown in the photograph,
Figure 260.
Desceiption of case 3. In the series of illustrations, Fig-
ures 261-264, the cavity of decay in the distal surface of a lateral
incisor. Figure 261, is much more extensive than those illus-
trated before. In this, one may do the first chipping of enamel
in opening the cavity with hoe 12-5-6 used as a chisel ; later the
15, or even the 20 chisel, may be used and the weakened enamel
rapidly trimmed away. The lingual surface is found consider-
ably undermined, so that much of the disto-lingual angle of the
tooth must be removed, as shown in Figure 262. The labial wall
of the cavity must also be cut farther onto the labial surface
than is necessary for extension for prevention. But even in this,
some extension into sound tissue is necessary at the labio-
gingival angle. The outline form of the cavity may be roughly
completed ready for the finishing of the walls by this cutting
before the rubber dam and separator have been placed, since
separation is not necessary to the excavation. The decay is so
extensive that there is serious danger of exposure of the pul]i
of the tooth, and the rubl)er dam must be placed and the tooth
cleaned and dried and made sufficiently retentive, before the