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SniPLE APPROXIMAL CAVITIES. 229

depth of these cavities is greater than the diameter of their orifices, no
special retentive shape need be given them.
The orifice shoukl always be bevelled and enlarged, if necessary, to
include any neighboring fissures.
When these cavities are of greater extent they are prepared and
filled like others of similar size and form.
Class F,—Cavities upon and confined to the inched edge of incisors
and canines are easily prepared on account of their accessibility. This
particular surface should, and generally does, remain free from decay
on account of the attrition to which it is constantly subjected ; but
when defects in the enamel exist, caries sometimes occurs in connection
v/ith it.
This surface often needs covering with gold to check abrasion in
cases Avhere, after middle life, the crowns (especially those
of the upper teeth) have been shortened by excessive
wear. Under these conditions the surface has to be so
prepared and shaped as to retain the gold that is to cover
and protect it just as though caries had originally injured
the part. In forming the cavity in the exposed dentin
it is only necessary to cut deeply enough to aiford a lodg-
ment for the filling, but the orifice must be so enlarged and
^ross section of
excessively bevelled as to reach to the marginal edge of cavity on in-
enamel all around. This is done to protect the enamel
from chipping or fracture in mastication. To aiford the greatest
security to the filling the cavity should be undercut throughout its
whole extent. When thus prepared, the cavity in cross section will
resemble a double dove-tail as shown in Fiff. 184,

II. Simple Approximal Cavities.
INCISORS AND CANINES.
Class G.—Cavities upon the mesial and distal surfaces of the
anterior teeth present only the difficulty arising from inaccessibility.
To reach and operate upon these cavities, the teeth, if in normal contact,
will usually have to l)e }>ressed apart either by gradual wedging or by
immediate separation with a " separator." Even after this has been
accomplished the cavity cannot be operated upon in a direct way as are
cavities upon exposed surfaces, but will have to be approached from
either the labial or lingual aspect of the crown. To do this, if the
cavity be small, will generally necessitate an additional enlargement of
the cavity toward the surface from which it is to be approached. As
the lesser of two evils the enlargement is usually made toward the
lingual surface, for in this way the exposure of gold when the filling is