Page 37 - My FlipBook

INSTRUMENTS AND INSTRUMENTATION. 33

Student who can not, or will not, learn to keep the edges of his
cutting instruments in good condition had better quit and go
home, for he will not succeed as a dentist. A good stone is a
necessity. It is of first importance that the stone be very hard.
Our instruments are small, and if we attempt to use a soft stone
the point will catch and ruin both the edge of the instrument
and the surface of the stone. The stone should never be smaller
than I ^2 by 5 inches. A stone somewhat larger is much better,
but a smaller stone is a nuisance. A hard Arkansas stone is
best. The hardness should be especially looked to in selecting
a stone. The care of the stone is very important. It should be
thoroughly oil-soaked and then wiped off. It may then be used
dry or with oil, but however used it should be wiped off clean
with oil upon a cloth after using. If this be not done the stone
will soon fill up with the steel cuttings and it will fail to cut when
the effort is made to grind with it. These steel cuttings are
removed from the stone by the oil and the cloth. If the face of
the stone becomes marred or unlevel from use, it may be refaced
by rubbing it on a sheet of emery paper laid flat upon a smooth,
level table or board. The facing should be finished on the finest
grade of emery paper. A good stone should last a lifetime if
well taken care of
The cutting edges of the excavators should be ground care-
fully, observing that the correct bevel of the edge be maintained
and that the edge is kept straight. To this end instruments
should be carefully applied to the stone and the correct position
maintained throughout the back and forth motions of grinding.
The spoons and discoids are ground by placing them on the
stone so that the motion in grinding will be parallel with the
length of the cutting edge, and during each stroke the instru-
ment is rotated upon its edge in such a way that every part of
the semi-circular edge will come against the stone in some part
of each motion. This is easily done after a little practice.
Care as to heating the instrument points while grinding is
very important. If heavy pressure is made and the instrument
moved rapidly upon the stone, enough heat will be quickly
developed to draw the temper of the steel and ruin the instru-
ment. It is well for the beginner to place one finger upon the
point of the instrument while grinding, that he may feel the heat
develop, until he has learned to judge accurately of this danger,
3