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CUTTING INSTRUMENTS. 33

the instrument to be fairly balanced in the hand when pressure
is made with its cutting edge. This will be better appreciated
by trying such an instrument as any of those illustrated in
Figure 15, which have been incorrectly contra-angled. At every
effort to cut with such an instrument, there is felt a tendency
to turn in the fingers, and, unless this is closely guarded in
every considerable effort, it may do damage. Under any con-
ditions such an instrument will be found lacking in usefulness
as compared with a similar length of blade properly contra-
angled as shown in Figure 16. The object of the contra-angle
is to enable one to use a long blade effectively.
In Figures 15, 16, a line has been drawn over the handle
and instrument point to show the relation of the point to the
long axis of the instrument handle. It will be noticed that
those in Figure 15 have the point far to one side of the central
line of the shaft, while those in Figure 16 have the contra-angle
so made that the working jDoint is close to the line of the central
axis of the shaft. These latter will reach into a deep cavity
just as well as the former, and will be steady under pressure in
cutting. In using those made as in Figure 15, the hand will
always be struggling to prevent the instrument from tipping or
turning. This will not be felt in the use of those made as shown
in Figure 16.
Formerly dentists used instruments with very large handles,
as has been mentioned; often as much as three-quarters of an
inch in diameter and these were used with the palm grasp. An
instrument with a blade such as the spoons in Figures 20 or 22
would need no contra-angling when used with such a handle and
such a grasp, and this contra-angling was then not thought of.
In the change to the small handles suitable to the pen grasp,
there has been much tendency to continue these old forms. Also
many persons seem to have had the thought that a very crooked
instrument with a point far off from the line of the shaft would
enable them to reach into very deep cavities better. An examina-
tion of the long blades in Figure 21 will dispel this idea. Such
instrument points not only reach into deep cavities well, but
they are also well balanced in use and much more effective
because of that fact.
Sharpening Instruments,
Nothing in the technical procedures of dental practice is
more important than the care of the cutting edges of instru-
ments. No man has ever yet become a good and efficient dentist