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CHAPTER XIII.
LARGE PROXIMAL CAVITIES ENDANGERING THE PULP.
(CLASS TWO, CONTINUED.)

Description. This class of cavities when presented shoAV exten-
sive loss of dentine in the proximal Avail. The marginal ridge may
be standing or it may have been broken through stress of mastica-
tion. In some cases there may be an occlusal decay in the central
fossa.
Danger of Pulp Exposure. There is ahvays great danger of pulp
exposure in these cases and this fact must be continually borne in
mind, during the procedure of preparation. The liability is in-
creased -when the patient is young or the cusps of the tooth are
high, particularly -when there exists a deep pit cavity -in the oc-
clusal surface necessitating a low pulpal wall. With young pa-
tients the pulps are large and the horns of the pulp generally ex-
tend well toward the cusps. Teeth Avith high, prominent cusps us-
ually have long pulp horns, Avhich should be considered in making
resistance, retention and convenience forms.
Outline Form. The first cuts in this class of cavities should be
Avith the chisel, using hand pressure, being sure that adequate hand
and finger guard has been obtained. This precaution is essential
as the chisel must be prcA^ented from reaching the sensiti\'e soft-
ened dentine Avithin the cavity. Place the chisel so as to throAv
the chips into the cavity. The chisel should be made to engage
only a small portion of enamel at each cut. Should the enamel
prove resistant the aid of the mallet may be resorted to, still main-
taining a firm finger rest.
Extension for Prevention is frequently not necessary as the ex-
tension necessary for proper resistance form Avill carrj' the caA'ity
the required distance into both buccal and lingual embrasures.
However, in many cases the decay Avill be found to have progressed
more toAvard one embrasure than the other Avhich necessitates ad-
ditional cutting for prevention, in the direction of the embrasure
least approached by decay. This should be done to the fulfillment
of the rule for ''extension for prevention."
Gingival Outline. The gingival outline in these cases Avill gen-
erally be under the free margin of the gum. At this stage it should
be planed Avith the enamel hatchets until the overhanging enamel
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