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104 THE TECHNICAL, PEOCEDUEES IN FILLING TEETH.

surfaces of the molar teeth. In proximal cavities the crest of
the pnlp is a frequent point of exposure by decay.
Probably the best means of studying the forms of the pulp
chamber is to obtain teeth not too much decayed from numbers
of persons of known age, from childhood to advanced life, cut
them in the horizontal plane at or near the gingival line, leaving
the greater part of the pulp chamber in the crown portion. A
suiBeieut number of such specimens, if carefully studied in series,
would give an excellent idea of the progress of shortening of the
horns of the pulp and the general reduction of its size by reason
of age.
In the preparation of cavities, the rule should be to avoid
cutting any of the recessional lines of the pulpal horns whenever
the extension of decay will allow of its complete removal without
so doing. In the preparation of proximo-occlusal cavities there
is usually room to occupy one-third of the bucco-lingual breadth
of the tooth in a step without interfering with the pulpal horns,
provided the step is not cut too deep, i. e., deeper than necessary
for substantial strength. In mesial cavities in upper molars, the
occlusal step may be rather broader than in distal ca\dties in
upper molars, or in mesial or distal cavities in lower molars,
because the lingual horn of the pulp in the upper molars is placed
farther to the distal, giving more room in the neighborhood of
the mesial surface. In all of the molar teeth there is more danger
from cutting these recessional lines in the mesial than in the dis-
tal areas because the pulpal horns are longer, giving less room
between the occlusal surface of the tooth and the probable ends
of the pulpal horns.