Page 242 - My FlipBook

102 THE TECHNICAL PBOCEDTJKES IN FILLING TEETH.

a kind of step, if the enamel of this i3ortion of the lingual surface
is strong enough to remain. See Figures 225, 226.
If the mesio-buecal angle of a molar is so decayed as to
make the removal of a considerable part of it necessary, cut to
the buccal groove, for if this is not done the intervening jiortion
of the enamel is very likely to break away. The same rule
applies to the triangular grooves of the bicuspids that pass over
to the buccal surfaces to the mesial and distal of the buccal cusps.
If, in any case, the enamel of the angles of these teeth is so under-
mined by decay that the cavity lines should approach near these
grooves, cut past the grooves.
In any case in which the angle of an incisor must be removed,
cut to the labial groove, whether it be mesial or distal. This is
for the reason that the lines of the grooves are weak and the
enamel is likely to break along them.
Recessional Lines of the Pulpal Horns.

These are the lines along which the pulp has receded during
the growth of the dentin. They are also the lines in which
unusually long horns are found and often exposed when these
lines are cut. The accidental exposure of the pulp usually occurs
from the cutting of the recessional lines at too great a depth in
the tooth, or too close to the body of the pulja.
In the early growth of the tooth, the full size of the occlusal
surface of the tooth is represented when the first joining of the
enamel plates of the several lobes of the tooth has occurred. At
this time but a very thin layer of dentin has been formed on the
inner surface of the enamel ca]). The whole, practically, of the
dentin of the crown of the tooth is represented in pulp tissue.
The dentin grows from the dento-enamel junction inward. The
pulp recedes and l)ecomes smaller as the dentin is formed. This
is rapid, comparatively, during the childhood period, but under
normal conditions gradually slows down until the person is forty
years old or jjast. Under abnormal conditions of irritation from
very slowly progressive caries, erosion, abrasion, etc., this is
much hurried; and may go on to the complete obliteration of
the pulp ('liaml)er. In this normal and al)n()rnial recession of the
X)ulp, the puli)al horns become shorter and shorter. It is the track
of this recession of the horns of the pulp that we call the
recessional lines of the pulpal horns. It not infroquentlj' hap-
pens that a horn of a ]3ulp will ]iersist as a slender thread of
pulp tissue reaching far toward the point of a cusp to or past
middle age, even when the pulp chamber has become quite small.