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26 THE TECHNICAL PROCEDURES IN FILLING TEETH.

mon-angle hatchet excavator, bin-angle spoon excavator, etc.
In these combinations each name is descriptive of some part of
the instrument, or of its uses.^
In addition to these we have adopted formula names -for the
cutting instruments that describe each individual instrument so
accurately that when learned each one will be known when its
formula name is spoken. This is necessary in order that a
teacher may be understood when speaking of the uses of par-
ticular instruments in lectures, or that students may understand
the directions of demonstrators in the infirmary.
These formula names are made upon the same principle as
that used by the carpenter in naming his chisels or augers, as
half-inch chisel, one-inch chisel,^ three-quarter-inch auger, etc.
But for us to sufficiently describe the point of an excavator so
that we will know the particular instrument at sight, it is neces-
sary that we give three measurements. We give first the class
name, as hatchet, hoe, spoon, etc. , and then give the formula of
the point, or working part. This formula consists of the meas-
urement, first, of the width of the blade in tenths of a milli-
meter ; second, of the length of the blade in millimeters ; third,
the angle of the blade with its shaft or handle, in centigrades,
or hundredths of the circle. Note particularly that the width
and length make up the size of the blade. Also, in order that
the individual instruments of the set may be easily learned and
remembered we confine the set to a regular order of sizes and
angles of blade that will give a sufficient variety of forms.
The set of cutting ihstrurnents consists of two lists of
formulae. One of these we call ordinaries, and the other
specials. Aside from the regular formula lists we have four
instruments that are not made upon these formula lines. These
we call side instruments.
Dental Instrument Gauge.
This gauge for dental instruments is used especially in the
measurement of excavators, pluggers and burs. It is in the
metric system. It is used as follows
:
Measure the width of the blade in the slot numbered from
I.
o to 50, which gives the width in tenths of a millimeter. This is
the first figure of the formula.
* Only the nomenclature and the uses of instruments will be given here. The phi-
losophy of instrument forms has been well presented in the freshman year.