Page 247 - My FlipBook

THE HISTOLOGICAL STRUCTURE OF THE TEETH. 103

Careful observation sliows that fully ninety per cent of tli(i
accidental exposures of the i)nlp in the preparation of cavities
of medium and moderately deep decays occurring in either occlu-
sal pits or proximal surfaces in molar teeth, are exposures of
the horns of the pulp, '^riiese exposures are all made by cutting
across the recessional lines of the pulpal horns. These lines are,
therefore, especially dangerous.
The recessional lines lead from the axio-occlusal mai'gin or
crest of the pulp on one of its angles, toward the point of eacli
of the cusps of the tooth. This line is usually nearly straight,
but a little bent in the form of the concavity of the occlusal sur-
face of the tooth. In Figure 105, the recessional lines of the
pulpal horns are indicated by dotted lines. The anatomy and
histology of the tooth in respect to these lines should be very
closely studied for the advantage it will give in locating and
avoiding these lines in the excavation of cavities. If the reader
will review the forms of occlusal and occluso-proximal cavities
in molar teeth illustrated in this book, he will find that in all but
a single one, of those with living pulps, the recessional line of
the mesio-buccal horn of the pulp has been avoided in their prepa-
ration. Wlien the decay is such that this can not be done, the
pulji is in imminent danger of exposure. This one cavity making
the exception, is the cavity prepared for the illustration of the
packing of gold. This cavity was cut as broad as would be per-
missible in the tooth of a person forty or tifty years old. It was
cut broad for the purpose of giving the best view of the progress
of building a gold filling. While there are frequently conditions
that justify the formation of such a cavitj'' in persons of advanced
age, this one should not be taken as typical of the usual prepara-
tion of cavities in the molar teeth. For young people such lines
of cavity preparation would expose many pulps for the reason
that the recessional line of the mesio-buccal horn of the tooth
would be cut.
While the mesio-buccal horn of the pulp is the most danger-
ous of the horns of the pulp in the molar teeth in regard to expo-
sure, counting very much the larger number of accidents, the
mesio-lingual horn of the lower molar is also very dangerous.
Indeed, all horns of the pulp have their recessional lines, and all
of these are to be shown due respect in cavity preparation.
The recessional lines of the crests of pulps may also be
traced in histological specimens. While these are much lower
than the horns, they are responsible for a minority of the expo-
sures by accident in the preparation of cavities in the proximal