Page 60 - My FlipBook

24 THE TECHNICAL PROCEDURES IN FILLING TEETH.

2. Measure the length of the blade in the gradations on the
principal bar, which gives the length of the blade in millimeters.
This is the second figure of the formula.
3. Measure the angle of the blade with its shaft. Lay the
handle of the instrument on the main bar of the gauge, parallel
with the lengthwise lines, and, while keeping it so, bring the
blade (turned toward the small numbers to the right) parallel
with one of the gradations of the circular head. This will give
the angle of the blade with the shaft in centigrades or hundredths
of the circle. This gives the third figure of the formula and com-
pletes it.
Whenever it is necessary to designate the angle of the cut-
ting edge of a blade with its shaft, it is done by sliding the instru-
ment, without rotating it, to the left, keeping its shaft parallel
with the longitudinal lines on the gauge, until the angle of the cut-
ting edge corresponds with one of the lines of the larger numbers
to the left. This number is then entered in brackets following
the width number. (See gingival margin trimmers. Figure 23.)
When not so designated, the cutting edge is at right angles with
the length of the blade. Note particularly that all angles are
made from the line of the long axis of the handle or shaft of the
instrument and express the deviation of the blade from that line.
These formulas are stamped on the handles of the excava-
tors. Plugger points may be measured and designated in a sim-
ilar manner.
The diameters of burs and drills, and the dimensions of
plugger points may be obtained by measurement in the slot. The
instrument gauge here described is necessarily a rather expen-
sive instrument, designed more especially for the use of instru-
ment makers and others where great exactness is required. The
Boley gauge described later, and which every dentist and dental
student should have, though less convenient, will answer for all
instrument measurements except the measurement of angles.
The measurement of angles may be done as well on the illustra-
tion of instrument here published ; other measurements can also
be made, but less perfectly.
The CENTIGRADE CIRCLE, Figure 17, was adopted for the meas-
urement of the angles of instrument blades with shafts or han-
dles after much inquiry and trial of the divisions of the circle in
general use. The astronomical divisions of the circle (360
degrees) would be very cuniI)ersome because of its excessive
number. The division of tlie mariner's comi)ass (32 points) was
not found well suited to this work. After much measurement