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92 OPERATIVE DENTISTRY

Outline Form. In outlining the cavity proper most of that which
has been said about plan one should be followed here.
As to the lingual outline and that of the step particular attention
must be paid to so placing the margins as to remove them as much
as possible from the stress of articulation.
The Step. The lingual step is added to this cavity as it ma-
terially assists in retention, resistance and convenience forms.
In the laying of the walls of the step portion the particulars
are carried out much as though the lingual surface of the cuspid
were an occlusal surface, as next to an occlusal surface it receives
the greatest stress in articulation.
Axial Walls. It will be seen that this cavity has two axial walls.

Fig. 52. Fig. 53.
Fig. 52.—Cavity of Class Four, modified plan three, for cohesive gold in the distal of
the superior cuspid. This plan is sometimes used to advantage in the incisors when the
tooth is short and stocky. In such cases the lingual step is made to include the lingual pit.
Fig. S3.—Class Four, modified plan three, filled. Cavity shown in Fig. 52.
The one in cavity proper is the axial, while that in the .step is
termed the lingual axial Avail.
The Lingual Axial Wall should be placed on a plane parallel Avith
the lingual surface of the tooth. Its surrounding line angles should
be laid just below the dento-enamel junction.
Convenience Form in this cavity is pretty well secured by the ad-
dition of this lingual step, as the filling is then easily built in from
the lingual direction. Both gingival point angles in the cavity
proper should be made convenience angles as well as the axio-
gingivo-mesial point angle in the step portion.