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68 THE TECHNICAL PROCEDURES IN FILLING TEETH.

portion of the enamel close to the gum margin. They are not
always very close to the gingival margin* of the buccal sur-
face of the tooth, because the free margin of the gum often,
particularly in young people, considerably overlaps the gingival
portion of this surface.
In these 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 differences
necessary. Pits, in which decay has just begun, 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 chipping
away the enamel. The squaring up of the axial and surround-
ing 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. 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 right-angle
hand-piece 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 different, in that the enamel rods will
generally be found perpendicular to the surface upon the central
part, but inclining toward the occlusal as the occlusal
margin of the surface is approached. Therefore the incli-
nation of the enamel rods, or the direction of the cleavage, should
be closely noted while chipping away, and the occlusal enamel
wall finished in inclination to the occlusal, so as to be parallel
with the line of the cleavage. If in any case it is found that
because of close approach to the occlusal surface, the inclination
of the enamel wall to the occlusal will render the filling material
too thin at its margin to have sufficient strength, the buccal
groove should be opened over the crest of the marginal ridge
and the filling carried onto the occlusal surface in the form of a
step. Neglect of this precaution is causing the loss of many
otherwise good fillings in this position.
* Note.— Distinguish carefully between the terms gum margin and gingival 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 cementum, 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 line.