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168 THE TECHNICAL PROCEDrRES IX FILLING TEETH.

is liow far toward the gingival this undermining of the enamel
has gone. The cutting away of the cusp should proceed at once
and this point determined, for, if it reaches to the gingival line,
the propriety of going farther with the case with the view of
building a tilling may well be questioned. In this case, how-
ever, enamel complete in thickness and strength is found mid-
length of the crown with dentin supporting it just a little farther
to the gingival. The rubber dam is now placed and the decay
removed. The pulp is uncovered in this process. All conditions
have been made ready and the pulp is immediately anesthetized
by cocain under pressure, and removed with the broach. The
cavity may now be sealed with gutta-percha and allowed to rest
for a week with a dressing laid loosely in the root canals. At
the next sitting, the root canals are tilled, provided the condi-
tions ai'e favorable. In all such cases the rubber dam is
adjusted and the field of operation made clean before the tem-
porary filling is removed. When the root fillings are in place
and have been allowed to rest for a week, if thought desirable,
the excavation may again proceed. The mesial half of the buccal
enamel wall is trimmed flat in the horizontal jilaue to the mesio-
buccal angle of the tooth. In the distal portion, the buccal wall
and the lingual wall are found to be abundantly strong. The
distal groove is cut out to the marginal ridge and much broad-
ened, as shown in Figure 212, and is given good retention form,
but is not cut much deeper than the thickness of the enamel in
the central fossa. The lingual groove is cut out upon the same
level. The gingival wall, which must be at a lower level, is
trimmed flat in the horizontal plane and the remainder of the
mesial portion of the buccal wall rounded down to the pulp
chamber, retaining the full strength of the remaining dentin.
The outline form is now completed.
Resistance form and retention form. For the completion
of the resistance form and the retention form, the floor and walls
of the pulp chamber are squared up into a box form with fairly
definite angles.
Convenience form. No especial convenience form is re-
quired in this cavity.
Finish of enamel wall. The finishing of the enamel wall
and beveling of the cavo-surface angle should be as previously
described, the direction of the enamel rods governing the plane
of the enamel wall in every position, and the bevel of the cavo-
surface angle making the enamel margin safe. The toilet of
the cavity should then be made.