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138 THE TECHNICAL PROCEDURES IN FILLING TEETH.

the second and third lower molars, except that smaller cutting
instrmnents will be required.
PIT CAVITIES IN THE BUCCAL SURFACES OF THE MOLARS.
ILLUSTRATIONS: FIGURES 147-153.
These must be distinguished sharply from smooth-surface
cavities occurring in these surfaces. The pit cavities have their
beginning only in the buccal pits and are primarily in the occlu-
sal half of the buccal surface, as shown in Figures 147, 148.
Smooth-surface buccal cavities are primarily in the gingival
third of the buccal surface and begin in the smooth portion of the
enamel close to the gum margin.* They are not always very
close to the gingival margin of the buccal surface of the tooth,
because the free margin of the gimi often, particularly in young
people, considerably overlaps the gingival portion of this sur-
face.
In these pit cavities, the principles of instrumentation are
the same throughout as that described for occlusal cavities,
except as their location and the direction of approach render dif-
ferences necessary. Pits, in which decay has just begim, should
be opened with burs as described for occlusal surfaces. Where
more decay has occurred, so as to allow the use of chisels, or hoes
used as chisels, the opening should be made by chip]3iug away
the enamel. The squaring up of the axial and surrounding walls
and making the axial line angles definite, should be done in the
same way as in occlusal cavities, if done with burs or if done
with the hoes and chisels. If these are filled early, or as soon
as decay is discoverable, they are very simple cavities, requiring
no further extension than that required to fully uncover the
area of decay, as shown in the upper first molar in Figures 147,
148. Sometimes in the second molars, and generally in the third
molars, the angle of approach will be such that the straight hand-
piece of the engine can not approach the cavity at the correct
angle, and the contra-augle hand-piece. Figure 25, must be used,
or, what is usually better, the work must be done with hoes and
binangle chisels. In finishing the enamel walls, the case is dif-
ferent in that the enamel rods will generally be found inclining
toward the pit from every direction around it for a little distance,
but farther away they will l)e perpendicular to the surface upon

* Note.— Distinguish carofiilly bctwrrn the terms gum marfiin and (jingival line,
or a gingival margin of a surface of a tooth. Gum margin refers to the position of
the free edge of the gum, while the gingival line is the line of junction of the enamel
with the conientum, or the normal line of the attachment of the gums to the tooth.
The gingival margin of a surface of a tooth is at its gingival lino.