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62 OPERATIVE DENTISTRY

Resistance and Retention Forms. To reach the maximum of
these forms it is necessary that the gingival wall be flat and laid
in a plane at right angles to the stress of mastication. The gingival
Avail should meet the axial wall at an angle slightly acute.
The grooving of the gingival Avail is condemned.
The Buccal and Lingual Walls should be flat, parallel, meet the
gingival Avail at least at right angles, and meet the axial Avail at
definite and acute angles.
The Axial Wall should be convex to the proximal and meet the
pulpal Avail in a rounded pulpo-axial line angle.
The Pulpal Wall should be laid parallel to the same plane as
the gingival Avail and slightly broader at the portion most dis-
tant from the cavity proper. This gives a pulpo-distal or pulpo-

A B
Fig. 25.—Class Two filled. Cavities shown in Fig. 24.
mesial line angle of a little greater length than that of the pulpo-
axial line angle, resulting in a doA'etailed effect that is most ef-
ficient.
Line Angles. The line angles should be squared out and made
definite by the use of small hatchets and hoes of suitable shapes
to reach the desired localities.
The gingivo-buccal and gingivo-lingual line angles should ex-
tend from their corresponding point angles to the dento-enamel
junction. The axio-buccal and axio-lingual line angles AA^hich arise
in the same point angles should travel occlusally one-third to one-
half the height of the axial Avail. In some rare cases AA^here the
pulpal Avail is Ioav from decay these line angles may meet the axio-