Page 229 - My FlipBook

SIMPLE CAVITIES ON EXPOSED SURFACES. 227
running over from the occlusal to the buccal surface between the two
buccal cusps. Oftentimes the cavity is so large as to include the greater
portion of this surface of the tooth. Its usual form and appearance are
shown in Fig. LSI.
Not infrequently this cavity is compounded with one on the occlusal
surface. In opening and preparing it a slightly undercut
form is readily given to it.
Class C.—Decay rarely occurs upon the lingual sur-
faces of molars on account of their smoothness and con-
vexity and because they are more or less constantly rubbed
gu^cai cavitv
by the tongue in speech and mastication. The evenness of i" lower sec-
this surface is, however, broken in the upper first and sec-
ond molars by a fissure extending over from the occlusal surface and
passing between the two lingual cusps. (See Chap. I., p. 39.) This fis-
sure is deeper and more pronounced in the first molar, but in each tooth
it is generally the seat of caries early or later in life. In the majority
of cases this fissure is decayed througliout its entire length, forming a
compound cavity, but occasionally only the pit at its termination on
the lingual surface is affected.
Another point on the lingual surface liable to decay is on or near the
mesio-lingual angle of the upper first molar, about midway between the
cervical and occlusal margins. At this place is often found a supple-
mental cusp, diminutive in size, and where it joins the main surface of
the tooth a small fissure exists which invites decay. This
^^' ^^^
additional cusp, when it does exist, is found only upon the
first molar. It is shown at A in Fig. 182. (See Chap.
I., p. ol>.) Neither of these cavities presents any diffi-
culties in preparation except such as occur from their slight
difficulty of access.
Oecasionall}', though very rarely, the lingual surface
of any of the molars may present a cavity of decay close
to the gingival line and partly beneath it. Such cavities are doubtless
caused by the retention of food debris beneath the free margin of the
gum, and owing to their position they are difficult to treat. They
should be opened and packed over-full with cotton and varnish or
gutta-percha for a day or two, to press the gum away, after wdiich they
may be prepared and filled in the usual manner.

INCISOKS AND CANIXES.
Class D.—Cavities upon the labial surfaces of incisors and canines
are usually found along the gingival margin, and are the result of the
direct action of acids probably formed at this point. In the beginning,
and when small, they are entirely exposed, but when of greater extent