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170 MECHANICAL DENTISTRY AND METALLURGY.

every point. The surplus of the base plate material should,
with shears and corundum or carborundum-stone, be
trimmed off flush with the band, the two now forming- a
complete cap for the face and sides of the root.
Fitting the Pin.—The next step is the preparation and
adjustment of a pin through the cap into the root canal.
The canal should be enlarged toward tJic palatal side of the
root ; this will give more room when we come to grind the
tooth, and at the same time secure the greatest attainable
strength when the crown is completed.
The base plate of the cap is perforated at a point directl}^
over the opening in the canal. This may be done \\ith a
plate punch and enlarged to suit the case with a burr on the
dental engine. A pin of platinum wire, number 16 or 17,
standard gauge, should now be slightly tapered at the end
and passed through the aperture made in the cap and up
into the root canal. The end of the pin projecting below
the cap may be marked, withdrawn, and bent at a right
angle, so that it will point away from the tooth, that is,
toward the palatal surface; it may then be waxed in, in-
vested, and soldered with the tooth, or invested and soldered
at this stage, and the surplus of pin and solder brought
down flush with a file or stone.
Grinding and Fitting the Tooth.—The cap and pin
should be readjusted to the root. A plain-plate tooth,* of
suitable form and color, is now ground and fitted to the
cap. The labio-cervical edge of the tooth (a, Fig. 136)
should be so ground that it will be flush with the edge of
* Many writers advise using cross-pin teeth is self evident, how-
; it
ever, that in this work straight-pin teeth should be employed and the
cross-pins avoided wherever possible, for the same reasons as given
under plate work: (i) The position of the pins weakens the body of
the tooth. (2) Their position makes the strain upon the tooth greater,
as it gives increased leverage between the pins and the cutting edge.
(3) There is more liability of cracking the teeth in soldering, on ac-
count of so much metal being brought at one point.