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CAVITY PREPARATION FOR GOLD INLAYS 107
Retention Form. This step in cavity procedure will vary ac-
cording to -which plan of Class Four is used. In plan one, which
as before stated should be used only in non-vital cases, a pin
should be placed in the pulp canal and depended upon almost en-

Fig. 63.—Cavity of Class Four, plan two, for gold inlay. Cavity side of inlay shown. Black
wax has been used to temporarily remove undercuts caused by decay.

Fig. 64.—Class Four, plan two, gold inlay in position. Cavity shown in Fig. 63.

tirely for the retention. In plan two, largely used in vital cases,
a short, 20-gauge pin of iridio-platinuiii or tungsten should be
placed in the step portion of the cavity lying parallel to the long
axis of the tooth. This small pin had best be from one to three