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48 THE TECHNIC^VX, PEOCEDUKES IN FILLING TEETH.

wall, or only slightly, but to the lingual oi- buccal (lal)ial in the
incisors and cuspids), and the groove should be close against
the axio-buccal or axio-lingual line angle. In this method of
cutting these starting points, the square end of the bur gives a
square floor to the pit at the point where the first piece of gold
is placed, which prevents any tendency of the gold to roll from
side to side in the first efforts to condense it, so that a very
shallow pit, a mere sharp angle, is all that is necessary. It
should be remembered always that in proximal cavities in bicus-
pids and molars, these convenience points are not anchorage
points for the filling, but are simply starting points for the tem-
porary anchorage of the first pieces of gold.
The drill. The use of drills should be confined to certain
especial purposes. These should be used when for any reason
it becomes necessaiy to cut into the pulp chamber of a sound
tooth, or one that has already been filled. This necessity occurs
frequently because of hyperemia or death of the pulp after a
filling has been made, or from death of the pulp from a blow
or some unknown cause. In these eases it is often necessary to
cut from the surface of the tooth to the pulp chamber, either
through a filling or through the enamel and dentin. The bur is
not suitable for this work. The flat drill, bibeveled to a point,
is the proper instrument; or the drill, followed by a round
bur to enlarge the opening. In doing this where considerable
tissue is to be cut through, it is best to use a small drill first, and
when this has penetrated some distance, enlarge the opening
with a larger drill or a round bur, then penetrate farther with
the small drill and again enlarge. Proceed in this way until the
pulp chamber is reached. In the attempt to drill deeply with a
small flat drill, the instrument does not clear itself of chips
also, it is likely to be broken by any
readily and is apt to heat ;
movement of the patient.
The drill is also the best instrument for enlarging root
canals for setting posts or pins for artificial crowns. It will be
seen that these uses of the drill are aside from cavity excavation.
The contra-angle hand-piece, Figure 25, is often useful
for doing this work in cavities in the lower second and third
molars. With it the proper position of the bur may be obtained
in those places that are not accessible to the straight hand-piece.
The right-angle hand-piece has been used much in the past for
this purpose, but it is a very awkward instrument, for the reason
that the working end of the bur is far out of the line of the
axis of the hand-piece. This renders it ineffective. The contra-