Page 41 - My FlipBook

USE OF THE DENTAL ENGINE. 6i
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.
Now, by repetitions of these movements cut as deeply to the
gingival as may be required, keeping close against the dento-
enamel junction. This undermines the enamel, which is now
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 is then 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 useful. In mesial and distal
cavities in nearly all positions, starling points in the axio-linguo-
gingival angle and the axio-gingivo-buccal (or laljial; 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 lead-
ing away from the pit first formed to give strength to the gold
when placed. The pit itself shtjuld not be directed into the