Page 228 - My FlipBook

226 PREPARATION OF CAVVriES.
Extreme care should bo exorcised in ])roparing cavities of this
character to insure that the fissures running between the buccal cusps
are fully opened and cleared of every particle of decay and discolora-
tion. Too often this is overlooked and caries supervenes.
The lower second molar with its four cusps has two sulci inter-
secting each other at a right angle. Decay usually begins at the inter-
section and extends along the radiating arms of the fissures. If the
cavitv wore jireparcd by cutting out the fissures only it would yield a
crucial-shaped cavity with four sharj) or nearly sharp angles at the
intersection, as shown in Fig. 179. Owing to those angles of dentin

Fig. 178. Fig. 179. Fk;. 180.

Lower first molar with stel- Lower second molar with Prepared cavity in lower
late cavity. Prepared. crucial cavity. Not pro- second molar.
perly prepared.

and enamel the perfect filling of the cavity would be exceedingly
difficult.
The case may be simplified and better results in every way obtained
by rounding these angles and giving the cavity a form like the one
shown in Fig. 180.
Class B. — Buccal cavities are seldom met with in the bicuspids
except at the cervix. In this location they possess the same features as
the similar class of cavities occurrino; on the labial surfaces of the
incisors. Their treatment will be described under class I).
The upper molars also are seldom found decayed on the buccal sur-
face except at the cervical border. Cavities occurring at this point are
usually narrow and long, following the outline of the gum. They can
best be prepared with an engine bur of suitable form, and if occurring
on the second and third molars a right-angle attachment may have to
be employed to reach them conveniently. Decay at this point is often
of the white variety, and as it so nearly resembles the natural color
of the tooth extreme care will have to be exercised to include all of
the decalcified portion within the limits of the cavity. A retentive
form is most conveniently given to these cavities by slightly undercut-
ting them in the direction of their length. In the third molars it is
sometimes advisable to make an undercut or starting-pit at the distal
end for the beginning of the filling.
Sometimes a small cavity will be found at about the centre of the
buccal surface of the upper molars, but far more frequently a cavity
of greater extent will be found upon the same surface of the lower
second molar. It originates in a pit at the termination of the fissure