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CAVITY PREPARATION FOR GOLD INLAYS 105
All exception may be made in those Avhich are large and have
through decay lost their entire lingual wall.
Access. It is of a necessity from the lingual as Class Three
cavities receive their stress from that direction.
The Outline is the same as though a cohesive filling Avere to be
made. Care should be taken that the labial level is laid on the
same plane as the travel of the Avax pattern to exit, else this por-
tion of the model will be distorted in removal.
The Gingival Wall Should Meet the axial Avail at an acute an-

Fig. 59.—Cavity of Class Three for Fig. 60.—Inlay shown in Fig. 59 partly
gold inlay, lingual approach. Cavity side in place.
of inlay shown.
gle and the cavity should have a line angle Avhich might be termed
axio-incisal. The labio-axial line angle should be slightly shorter
than the outline of the cavity Avhere the axial Avail meets the lin-
gual surface. This Avill result in alloAving the pattern exit to the
lingual. As the labial Avail, Avhich is the seat of the cavity, is frail,
care should be taken that it is Avell supported by sound dentine,
else the seating of the inlay Avill cause fracture of this Avail.
Preparation of Cavities of Class Four.
The use of the inlay should be largely restricted to non-vital
cases and a pin in the pulp canal used for the major portion of
retention.
If the Inlay is used in Class Four plans one and three, the case