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146 THE TECHNICAL PROCEDURES IN FILLING TEETH.

that the decay has progressed so far that the pulp of the tooth
is seriously endangered; and certainly much greater harm is
done. In the illustrations in Volume I, Figures 107-118, these
various conditions are shown. Still, quite a large majority of
the cavities in proximal surfaces can be successfully filled with-
out seriously endangering the pulp after the marginal ridge has
begun to break down. The opening of such cavities is much
easier for the dentist, but the operation should never be delayed
on that account.
Extensions of caries gingivally. One of the most persist-
ent and disastrous failures in the preparation of proximal cav-
ities of the second class, is in the failure to recognize extensions
of caries of the enamel to the gingival of its most common orig-
inal beginning point, just to the gingival of the contact point,
and the conditions under which these extensions occur. In a
considerable number of cases, several illustrations of which are
given in photomicrographs in the treatise on caries in the first
volume, this extension occurs because of conditions which cause
food to be so held between the teeth that the gum is forced away,
forming a pocket in which acid fermentation becomes established
farther to the gingival than the first beginning of caries.
When the enamel rods in the second beginning have not
yet broken away, these extensions of decay ai'e very difficult
of discovery in the primary examination. Greater care in noting
the condition of the interproximal gum tissue would correct
many errors in diagnosis. A case is illustrated by the photo-
micrograph in Figure 164, in which this second decay has begun
to the gingival of the first beginning, before the enamel rods
have fallen away from the first. In cases of this character in
which the penetration of the enamel at the point of original
beginning is discovered early, this extension will usually not
be discovered in the i:)rimaiy examination, unless it has been
suspected because of the discovery of absorption of some of the
central part of tlie interproximal gum tissue. If discovered
at all, it will usually be during the excavation of the cavity.
^\nien this discovery is not made, the gingival wall of the cavity
will most generally be cut to about tlie position marked d in Fig-
ure 164. The usual result is that the gingival margin of the fill-
ing is undermined by caries in a very short time. The only
preparation that will make such a case safe against recurrence
of decay, is to continue the cutting so as to lay the gingival cavity
margin at the line of c, Figure 164. After this has been done the
contact point on the finished filling must be so formed as to pre-