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90 THE TECHNICAL PROCEDURES IN FILLING TEETH.

points and will retain the filling while the building of this part is
in progress.
Variations due to position.—The variations of procedure
due to position of the teeth in the mouth and the different
degrees of exposure of the parts to view and to approach, relate
mostly to the second and third molars and to the lower bicuspids.
The upper first bicuspids are usually so well exposed that both
the mesial and distal cavities are easily reached, and except that
the smaller cutting instruments, as the 15-8-12 and 10-6-12
enamel hatchets and corresponding chisels and spoons, are neces-
sary, the instruments and the instrumentation will be the same.
Neither is it often necessary to make any variation in distal cavi-
ties in the first molar or mesial cavities in the second molar,
above or below.
In distal cavities in the second molar and mesial cavities in
the third molar it frequently happens that the inverted cone bur
can not be made to approach the cavity at the proper angle to
square out and extend the bucco- and linguo-gingival angles. In
these cases the bur in the right-angle hand-piece may be substi-
tuted, or the cutting may be done entirely with the hand instru-
ments. However, in the greater number of cases in which distal
cavities in the second molar are excavated at the same time with
mesial cavities in the third, the straight hand-piece may be used
for both. This is facilitated by cutting the step in the second
molar first and carrying it well to the mesial. This gives addi-
tional room for the application of instruments to the distal portion
of the cavity and also to the mesial cavity in the third molar.
Occasionally there is difficulty in so placing the inverted cone
bur as to begin cutting the step in the occlusal portion from the
distal cavity of a second molar. The approach is such that the
shaft of the instrument is inclined so much to the distal that the
bur cuts the enamel from the surface inward, instead of cutting
the enamel from within outward, and for this reason will not cut
well. The proper position of the bur may be obtained with the
right-angle hand-piece, but if the enamel proves very hard this
instrument does not work well. It is better in such cases to
enter the occlusal surface through the pit in the central fossa in
the usual way of opening pits, or with a drill, if the pit is fully
closed, and then enter the inverted cone bur at this point and
cut to the distal along the line of the distal groove until the