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184 THE TECHNICAL, PEOCEDURES IN FILLING TEETH.

how sharp the angles of the dentin walls ; sometimes it is diffi-
cult to plane the whole length of the gingival wall smoothly with
a hoe or chisel, especially where it joins the curve at the linguo-
gingival angle. Here enamel hatchets 10-6-12 may be used, one
from the labial direction, the other from the lingual, or hatchet
12-5-6 or 12-5-12. These instruments will also smooth the lingual
portion of the curve at the incisal angle in many cases. At the
incisal angle, the inclination of the enamel wall must generally
be strongly toward the incisal, especially in distal cavities, in
order to follow the length of the enamel rods. When the trim-
ming is done, note carefully whether the retentive form has been
injured at any important point by trimming too deeply, and make
such corrections as may be required.
Bevel the cavo-surfaee angle in all parts of the enamel mar-
gin, using the same instruments as were used in planing the
enamel walls. The toilet of the cavitj- should then be made.
The foregoing description is to be taken as the general type
of the instrumentation and the formation of cavities in proxi-
mal surfaces of the incisors. It must be understood, however,
that other instruments than those set apart for this work in the
illustration given in Figure 246 may often be conveniently used
and that many variations in the detail of cavity forms may be
substituted or become actually necessary. Some of these will be
given in the additional series of illustrations which follow. In
cutting the incisal retention it will often be well to cut the axial
wall deeper, sloping it deeper into the tooth for a space toward
the incisal in order to place the incisal anchorage deeper in the
dentin than that shown in Figure 255.
Description of case 2. In Figure 251, the distal surface of
a central incisor is shown with an almost round whitened area
of caries of enamel, the incisal margin of which is slightly to the
gingival of the contact point. In the central part of this, the
enamel rods are beginning to fall away. If every cavity of decay
could be discovered and filled at this stage, before more serious
injury is done to the dentin, it would be much better for the teeth.
After placing the rul^ber dam, separating and drying the teeth,
hoe excavator 6-2-6 is forced in near the center of the decayed
area and the dentin is found considerably softened. A few
strokes easily remove the greater part of the decayed area; and
the decay along the dento-enamel junction is found to be already
greater in extent than the decay on the surface of the enamel.
TToe 8-3-6 is su1)stitutcd for the smaller one and the enamel
chipped away until it is found supported by perfectly sound den-