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186 METHODS OF FILLING TEETH.

to work too rapidly, which, by throwing back a great amount of de-
bris, renders it difficult to withdraw the drill. It is compelled to cut
its and so leaves within the canal some of the chips, which
way through,
at the next entrance of the drill are pushed forward and packed into
The
the extremity. proper method is to avoid this, first by frequently
withdrawing the drill, cutting only a little at a time, and secondly by
using a clean broach every time the drill is removed, with which the
debris is easily loosened so that it is withdrawn or may be blown out
with the air syringe. The continued use of a drill of the Gates-Glidden
type cannot open a hole by forward cutting, since it has a safe
end. It could make an aperture by lateral cutting, however, if used
where the canal has flattened sides and thin walls. This is most com-
mon in lower incisors and in first bicuspids, so that these canals
should be most carefully scrutinized before the risk of using a drill
is taken. Even where it is deemed safe to use it, by every pre-
caution we should be upon the alert to avoid the disaster. The
should most a of before the
patient certainly give sign pain opening
could be actually formed, for the heat from the friction would be con-
veyed through the thinning wall, causing a response. Thus it is a
safe rule to withdraw a drill upon the slightest evidence that it causes
pain.
In Diagram 234 we have the canal partly prepared ; but as the curve
at the extremity prevented the further use of the drill, what are we to
do ? What has been gained, since it is after all this very part of the
root which we should most certainly fill ? The reply is, first, we have
lost for it were as some claim, to this curved
nothing, if possible, Jill
part without enlargement of the rest of the canal, -we assuredly can do
so now with greater access. In fact, we can more certainly accomplish
it. The use of broaches will indicate the nature of the curve, for as
it is withdrawn now, the curve at its extremity, where it followed the
bend of the root, will not be bent back, the enlarged canal allowing it
to be freely removed. The upper part of the canal being made as clean
as with broaches, further is with the Evans root-
possible procedure
canal drier. This instrument, having a point of soft platinum or
silver connected with a copper bulb, may be inserted hot and pliable.
The instrument is seen in position in the canal of Fig. 234, and it is
observed that the fine silver is forced almost to the foramen.
point
In many cases it may even pass to the very end. This is accom-
plished because the heated point destroys impediments in the way of
its progress, and being pliable it readily follows curves.
Thus by the judicious use of canal-drills we may enlarge the open-
more
ings of canals, gaining such access as will render further cleansing
possible, whilst in many instances curves may be entirely eradicated.
Consequently, in all cases it is necessary to open a tooth so that a drill