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PROXIMAL CAVITIES IN BICUSPIDS AND MOLARS 59

edge rests at forty-five degrees to the position of first impact and
again apply the mallet. Repeat several times and this will gen-
erally break away the enamel rods in a small V-shaped space. This
may be continued until the cavity is completelj^ uncovered. In
comparatively resistant cases the bi-bevel drill may be applied to
break in the enamel.
The Second Method of procedure is to use the bi-bevel drill in
the mesial or distal pit, giving the hand piece that slant Avhich
will cause the drill to enter the area of decay, when sufficient depth
has been reached. The chisel is then applied and the occlusal sur-
face enamel cleaved away either by hand pressure or the mallet.
This method is more liable to cause pain than the first given and
should be used with caution.
The Third Method is to adjust the mechanical separator and at-
tack the enamel with a small chisel from the buccal direction, grad-
ually shifting more and more to the occlusal surface until finally
the enamel ridge gives way to the force of the chisel.
Preliminary Separation should in most cases be resorted to for
proper access for the many reasons set forth in Chapter IV.
This is Best Accomplished by packing the cavity at this stage
with gutta-percha for a few days or weeks. When case returns we
should be ready to consider outline form.
Outline Form. Outline form in Class Two involves the outlin-
ing of the cavity proper, as well as the outlining of the occlusal
step which is generally necessary because of the more secure seat-
ing and rigidity it gives a filling in all proximo-occlusal cavities in
molars and bicuspids when the marginal ridge has been broken.
Step May be Omitted. First: In cases which are to remain
permanently disarticulated, as when opposing tooth has been lost.
Second: When the proximating tooth is to be absent permanently
thus obviating much cutting buccally and lingually in extension
for prevention, as the remaining walls are sometimes strong enough
to give sufficient resistance form without the added step.
Third: In proximal decays in the gingival third following ex-
cessive gum recession (so-called senile decay).
Fourth: When for any reason the patient should be shielded from
long operations, or the life expectancy of either the patient or the
individual tooth is short.
Fifth: In that form of lower bicuspids with a well defined and
perfect transverse ridge. (Fig. 23.)
Outline of Cavity Proper. The outline should be carried into