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i6: MECHANICAL DENTISTRY AND METALLURGY,

the immediate paralysis induced renders it comparatively-
painless.
This operation, in the light of " Pressure Anresthesia "
referred to ahove, seems unnecessarily severe and cannot,
therefore, be g"enerally recommended.
Preparation of the Pulp Canal.—After the removal of
the pulp the apical foramen should be thor-
Fig. 124.
oughly closed by any method usually employed
in root filling. A neglect of this important
measure will greatly endanger the success of
the operation.
The proper treatment and preparation of
the root having been thus far accomplished,
the canal of the latter should next be enlarged
for the reception of a dowel-pin. This is
effected with an ordinary fissure drill or the
Ottolengui root reamers (Fig. 124).
The natural opening in the root should be enlarged to the
depth of two or more lines, according to the length of the
root and the orifice should be made large enough to admit
;
a support of sufficient size to secure the crown firmly in
position. The direction of the drill in cutting should fol-
low closely that of the natural canal in the root, since but a
slight deviation in this respect may endanger the integrity
of the latter by too great a thinning, or actual perforation,
of its walls. The face of the root should then be given a
suitable shape for the reception of the form of crown to be
attached, the methods of fitting and inserting which will
now be considered ; the simple or all-porcelain system being
first taken up.
Porcelain Crowns.—The porcelain crown is especially
useful where an inexpensive and cjuickly adjusted crown
is necessary; or wdiere some pathological condition would
seem to limit the probable permanency of an operation, or,