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trSE OF THE DENTAL ENGIKE. 47

surface cavities, the small inverted cone burs may be used to
advantage. If, in excavating proximal cavities, we find that
after cutting the gingival wall to sound dentin it is desirable to
extend the cavity further to the gingival, place the end of an
inverted cone bur, five to eight-tenths of a millimeter in diameter,
against the gingival wall upon the dentin, close against the
dento-enamel junction, and incline the hand-piece just enough
to cause the periphery of the bur to cut, and press it toward and
into the bucco-gingival angle ; then incline the hand-piece in the
opposite direction and press the bur in the linguo-gingival angle.
By repetitions of these movements, cut as deeply to the gingi-
val as may be required, keeping close against the dento-enamel
junction. This undermines the enamel, which may be easily
removed with the enamel hatchets. In extending to the buccal
or to the lingual, the enamel hatchets generally serve best, but
occasionally the operation is facilitated by starting a small
inverted cone bur in the axio-bucco-gingival angle and drawing
it to the occlusal, cutting away the dentin of the buccal wall
just beneath the enamel, which may then be removed with the
enamel hatchet. The same operation is repeated upon the
lingual wall.
In this extension, it is important that the bur be kept close
against the enamel, so that it shall not cut into the tooth so deeply
as to endanger the pulp. There should be no attempt to cut the
enamel with the bur, for the reason, first, that it is not easily
done, and second, because it ruins the bur. Whenever it is
regarded as important that enamel should be cut with a bur,
one must expect that the bur will be ruined in the operation.
That is to say, the blades will be so dulled that it will be unfit
for further use, and a new bur must be provided for the next
operation. A good bur will cut dentin, however, for many
operations.
In making starting points for packing gold, the smaller
inverted cone bur is especially usefvd. In mesial and distal cavi-
ties in nearly all positions, starting points in the axio-gingivo-
lingual angle and the axio-gingivo-buccal (or labial) angle are
important conveniences. They are best made by placing the
end of an inverted cone bur in the angles named, and by a slight
swaying of the hand-piece cause the bur to enter just a little,
then draw the bur toward the occlusal (or incisal, if in incisor
cavities,) a short distance, making a slight groove leading away
from the pit first formed to give strength to the gold when
placed. The pit itself should not be directed into the gingival