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EXCAVATION OF CAVITIES BY CLASSES. 123

The outline of the cavity should now be reexamined, and if
irregularities ocour that would iirevcnt a smooth finish, the eav-
ity must be sufficiently extended to obtain conditions that will
allow a good, smooth finish of all parts of the margin to be made.
Resistance form and retention form. An inverted cone
bur 10, held with its square end against the pulpal wall, should be
carried entirely around the pulpal wall, making a sharp angle
along the line of junction of the pulpal wall with the four sur-
rounding walls. The pulpal wall is at the same time made flat,
giving the proper resistance form. In doing this, the cavity is
not to be cut deeper, but is made broader. All cavities should
be made as shallow as the removal of all decay will pennit, pro-
vided good anchorage in dentin can be had.
Convenience form. No convenience form is usually neces-
sary in a cavity so small. However, a convenience point in which
to place the first piece of gold may be made, if desired. These
points will be described later.
Removal, of remaining carious dentin. All of the carious
dentin will generally have been removed in obtaining resistance
and retention form. If any remains, it should now be removed
with spoons 10-6-12.
Finish of enamel wall. The enamel wall should be finished
by careful paring or planing with a sharp chisel. So far as pos-
sible the movement of the edge of the chisel should be in the
direction of the length of the margin or around the cavity. In
such a cavity as this, both the dentin and enamel walls may be
perpendicular and the opposing walls parallel. The enamel rods
will be inclined toward the cavity in every part, and no outward
inclination of the enamel walls is necessary. The cavo-surface
angle of the entire margin should be slightly beveled to diminish
the danger of fracture in placing the filling material. The toilet
of the cavity should then be made, as will be described in the
preparation of the larger pit cavity. Figure 124 represents
the cavity filled.
In some cases in which there is no more decay present in
the central pit than in the case shown in Figures 123, 124, the
grooves will be poorly closed, as shown in Figure 125 and begin-
ning decay will be found at a number of points along the lines
of the grooves of the occlusal surface, or in the disto-lingiial
groove of upper molars where it passes to the lingual surface.
In such cases, the grooves should be cut out as far as they may
be open, even to their ends, when that is necessary to obtain a
smooth finish for the filling. The outline form in this case is