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INSTRUMENTOLOGY ' 47

small handles, while some others are used for heavier work and
should have larger handles. The rule in selecting handles
is, the more delicate the work intended to be performed
the smaller the handle and vice versa. Handles, whenever

possible, should be of steel on account of convenience in
sterilizing (Fig. 51).
Angles in Shanks.—The shank of an instrument may be
straight or bent at various angles for better balancing of the
instrument and to carry the blade or working part into

inaccessible places. Dr. Black has classified instruments
into (i) Mon-angle, (2) Bin-angle, (3) Triple-angle, and (4)
Quadrangle, depending on whether they have one, two, three,
or four angles in the shank.
Centra-angles.—For better balancing and in order to

bring the blade as nearly as possible in a direct line with the
long axis of the shaft, the shanks of instruments are also
contra-angled. This form of instrument has a less tend-
ency to turn in the hand when being used, and consequently
will do better work with less strain on the operator. Contra-

angle instruments are divided into (i) Bin-angle Contra-
angles, (2) Triple-angle Contra-angles, and (3) Quadrangle
Contra-angles, depending on whether there are two, three or
four bends in the shank of the instrument. A well-balanced

instrument should be so contra-angled as to bring its working
point within 2 millimeters of the long axis of its shaft. For
example of angles in instrument shanks see Fig. 60.
Instrument Grasps.—As soon as one begins to handle
instruments, he should learn the proper grasps. Proper

instrument grasps lead to proficiency in the performance of
dental operations, and should be thoroughly studied and
practised, if the best results are to be obtained. Carelessness
in this respect will lead to bad habits which may cling through-

out life. The three principal grasps are (i) The Pen Grasp,