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158 THE TECHNICAL PKOCEDUEES IN FILLING TEETH.

better appreciated by a careful examination of Figure 181. In
this the mesial portion of the cavity is cut narrow. Very many
times it must be broader bucco-lingually. In my own work for
children these have pulled away a little occasionally from the
margins, causing a leak by the stretching of the narrow part of
the filling between the two mesial cusps. Through fear of pulp
exposure, this part was not made strong enough to resist the
stress of mastication. In mature persons there is generally
room for sufficient depth of step over these horns, when this
becomes so imperative as to call for greater risk of pulp expos-
ure. In doing this, one will occasionally be surprised by the
exposure of an extra long pulpal horn. At this age, root fillings
may be made that are good and the exposure of the pulp is not
so serious, but we are not justified in taking the chance of an
exposure in the tooth of the child. The general rule is that when
the decay may all be removed without cutting the recessional
lines of the pulpal horns, the strength of the tooth will be ample.
It is only after the removal of the pulp and cutting out these
recessional lines that breakage of the tooth is feared. In all
of this, it must be remembered that the object should be to keep
the cavities as shallow in all parts as the penetration of decay
will allow, and to make them no deeper than is essential for suf-
ficient anchorage. Broad cutting is often necessary in proximal
cavities to prevent recurrence of decay, but this does not neces-
sitate deep cutting.
DANGER OF PULP EXPOSURE IN CAVITY PREPARATION.
ILLUSTRATIONS: FIGURES 187-196.
In the excavation of proximal cavities, there is always
danger of pulp exposure when the decay in the dentin is deep.
This danger is much increased when there is also a deep pit
cavity, which seems to include the requirement of a deep step
in order to obtain a flat pulpal wall. Figure 187, an upper first
molar split mesio-distally for tlie purpose of showing the decayed
areas together with the buccal half of the tooth, is the first in
a series of ten illustrations designed to illustrate more definitely
the positions of instruments, the steps in the progress of exca-
vating and plans of avoiding pulp exposure in the preparation
of cavities of this class.
Description of case. The case chosen is in a young person.
There is a decay in the occlusal surface and a decay in the mesial
sui'face. The extent of these is shown in Figure 187. The
pulp chamber is large and the horns of the pulp are long.