Page 297 - My FlipBook

EXCAVATION OP CAVITIES BY CLASSES. 133
of the horns of the pulp, than to run imminent risk of exposing
them. But always sufficient ledges should be obtained to furnish
ample seating area to prevent the possibility of a filling tipping
and moving on a rounded surface like that shown in Figure 133.
Such a cavity is the most difficult of all forms to fill satisfactorily
and should not 1)e attempted. Filling the rounded portion with
cement does not help matters. In such cases ledges of firm den-
tin should be had to receive the stress to prevent the possibility
of movement, both in the packing of gold or amalgam, and also
in the after stress of usage in mastication. When this has been
done, the deeper rounded portion may be filled to the level of the
ledges with cement to act as a non-conductor of thermal changes
when that is thought desirable.
Convenience eoem. The cavity should be carefully exam-
ined with reference to convenience form for insertion of the fill-
ing. For filling with amalgam, the rule will be that nothing more
is required; but for filling with gold in a cavity of such depth,
one should be careful to have the approach for plugging instru-
ments such that the filling can be easily packed against every
part of every wall of the cavity by direct mallet force. In upper
first molars this is generally easily done when the walls are
parallel with the long axis of the tooth. But in upper second and
third molars and in any of the lower molars, the mesial wall or
the mesial and part of the buccal wall or both should be sloped
more toward the marginal ridge, cut to its crest, or even cut
slightly over the marginal ridge, to give convenience and cer-
tainty in packing gold against them. Therefore, such modifica-
tions should be made as this may demand, completing the con-
venience form.
Finish of enamel wall and toilet of cavity. Finally the
enamel walls must be finished and the cavo-surface angle slightly
beveled, and the toilet of the cavity made by sweeping out the
last of the cuttings not removable with the air syringe.
Vaeiations. In very deep cavities of this class, and espe-
cially when it is suspected that the pulp is near exposure, it is
well to fill the deeper portion as far as the ledge cut around the
margin with cement and allow this to harden before placing gold
or amalgam. The best way to do this is to cut a bit of stiff paper
or light cardboard to fit the cavity loosely, and, having mixed
the cement and worked it until it begins to stiffen, form a globule
of suitable size and take this on the paper and place both in the
cavity, forcing the cement into the concavity in the dentin by