Oper.i 08

College of DentistryCollege of Dentistry
Operative Dentistry IOperative Dentistry I
Instruments & Instrumentation -1-Instruments & Instrumentation -1-
Dr. Hazem El AjramiDr. Hazem El Ajrami

• Operative procedures should be performed withOperative procedures should be performed with
exactness and refinement because of the heroicexactness and refinement because of the heroic
clinical oral conditions to which the restorationsclinical oral conditions to which the restorations
are subjected, the extreme inaccessibility thatare subjected, the extreme inaccessibility that
often exists and the obligation of avoiding tissueoften exists and the obligation of avoiding tissue
damage. The operator, therefore, should developdamage. The operator, therefore, should develop
a special degree of skill in using the differenta special degree of skill in using the different
instruments. He must also be familiar with theinstruments. He must also be familiar with the
various types of instruments, their design,various types of instruments, their design,
material characteristics, sterilization, sharpening,material characteristics, sterilization, sharpening,
and ordering on the instrument table.and ordering on the instrument table.

 General classification of instruments:General classification of instruments:
The termThe term instrumentinstrument refers to a tool,refers to a tool,
device, or implement used for a specificdevice, or implement used for a specific
purpose or type of work. Instruments may bepurpose or type of work. Instruments may be
classifiedclassified into:into:
I.I. Instruments used for isolation of theInstruments used for isolation of the
operative field.operative field.
II.II. Instruments used for exploring theInstruments used for exploring the
operative field.operative field.
III.III. Instruments used for removal of toothInstruments used for removal of tooth
substance.substance.

IV.IV. Instruments used for finishing and polishingInstruments used for finishing and polishing
purposes.purposes.
V.V. Instruments used for manipulation andInstruments used for manipulation and
packing of restoratives.packing of restoratives.
• Each will be discussed individually withEach will be discussed individually with
special emphasis on instruments used forspecial emphasis on instruments used for
removal of tooth structure (cuttingremoval of tooth structure (cutting
instruments).instruments).

I.I. Instruments used for isolation of theInstruments used for isolation of the
operative field:operative field:
It is used to keep the working field dry,It is used to keep the working field dry,
for example, cotton roll holders, rubber damfor example, cotton roll holders, rubber dam
equipment (such as punch, holder, clamps),equipment (such as punch, holder, clamps),
saliva ejectors and evacuating tips.saliva ejectors and evacuating tips.

Saliva EjectorsSaliva Ejectors

II.II. Instruments used for exploring theInstruments used for exploring the
operative field:operative field:
Instruments such as mouth mirrors,Instruments such as mouth mirrors,
probes (explorers) and magnifying loupes areprobes (explorers) and magnifying loupes are
used for the physical exploration of the dentalused for the physical exploration of the dental
lesions.lesions.

 Mouth mirrors:Mouth mirrors: available in sizes rangingavailable in sizes ranging
from (1.9 to 4 cm). The face of the mirror isfrom (1.9 to 4 cm). The face of the mirror is
available with a magnifying surface or a plainavailable with a magnifying surface or a plain
front surface. They serve to establish distinctfront surface. They serve to establish distinct
visualizationvisualization of obscure areas of the mouth,of obscure areas of the mouth,
serve asserve as soft tissue retractorsoft tissue retractor and help inand help in
reflecting lightreflecting light onto the desired area. Theyonto the desired area. They
allow the operator to maintain a body positionallow the operator to maintain a body position
that will reduce health problems associatedthat will reduce health problems associated
with posture.with posture.

Explorers:Explorers: are used to examine the tooth andare used to examine the tooth and
detect anomalies through the sense of touch.detect anomalies through the sense of touch.
Any explorer is formed of three parts: handleAny explorer is formed of three parts: handle
which is straight with serrations, shank which iswhich is straight with serrations, shank which is
smooth and may carry curvature or one or moresmooth and may carry curvature or one or more
angles and exploring tip which is the terminalangles and exploring tip which is the terminal
portion of the explorer.portion of the explorer.

• Types:Types: a variety of explorers are available; thea variety of explorers are available; the
operator's choice is often determined by theoperator's choice is often determined by the
need to gain access. These include:need to gain access. These include: straightstraight
explorer,explorer, right-angledright-angled explorer,explorer, arch (curved)arch (curved)
explorer, pig tailexplorer, pig tail (cow horn)(cow horn) explorer andexplorer and
inter-proximalinter-proximal explorer.explorer.

• TheThe periodontal probeperiodontal probe cannot be used forcannot be used for
exploring, it is designed to detect and measureexploring, it is designed to detect and measure
the depth of periodontal pockets. It is also usedthe depth of periodontal pockets. It is also used
to measure the dimensions of instruments andto measure the dimensions of instruments and
various features of preparations andvarious features of preparations and
restorations.restorations.

Magnification:Magnification: using magnifying loupesusing magnifying loupes
significantly enhances the dentist's ability tosignificantly enhances the dentist's ability to
detect pathology and perform restorativedetect pathology and perform restorative
dentistry. Improved vision not only increasesdentistry. Improved vision not only increases
productivity but also enhances work quality. Twoproductivity but also enhances work quality. Two
times magnification is helpful in avoidingtimes magnification is helpful in avoiding
eyestrain; 3.5 times magnification is ideal foreyestrain; 3.5 times magnification is ideal for
routine operative work. Higher magnificationsroutine operative work. Higher magnifications
have the drawback of a limited depth of fieldhave the drawback of a limited depth of field
under normal operatory lighting.under normal operatory lighting.

III.III. Instruments used for removal of toothInstruments used for removal of tooth
substance:substance:
To restore a tooth, it first must beTo restore a tooth, it first must be
prepared, which involves the removal ofprepared, which involves the removal of
mostly diseased along with some sound toothmostly diseased along with some sound tooth
structure. Currently there are five sets ofstructure. Currently there are five sets of
instruments for tooth structure removal:instruments for tooth structure removal:

Hand cutting instruments: Chisels andHand cutting instruments: Chisels and
excavators.excavators.
Rotary tools: Burs, abrasives in the form ofRotary tools: Burs, abrasives in the form of
stones, discs, and others.stones, discs, and others.
Ultrasonic instruments.Ultrasonic instruments.
Air abrasion technique.Air abrasion technique.
Optical drills “Laser”.Optical drills “Laser”.

Hand Cutting InstrumentsHand Cutting Instruments
These include instruments whichThese include instruments which only utilizeonly utilize
forces exerted by the operator.forces exerted by the operator. These instrumentsThese instruments
used to cut, plane, scrape, or cleave tooth structureused to cut, plane, scrape, or cleave tooth structure
during the preparation of a cavity to receive aduring the preparation of a cavity to receive a
restoration or other treatment. The introduction ofrestoration or other treatment. The introduction of
rotary-powered cutting equipment was one of trulyrotary-powered cutting equipment was one of truly
major advances in dentistry. Modem high-speedmajor advances in dentistry. Modem high-speed
equipment has eliminated the need for many handequipment has eliminated the need for many hand
cutting instruments. However, hand instrumentscutting instruments. However, hand instruments
remain an essential part of armamentarium forremain an essential part of armamentarium for
high quality restorative dentistry.high quality restorative dentistry.

Instrument materials:Instrument materials:
Hand cutting instruments are manufacturedHand cutting instruments are manufactured
from two main materials:from two main materials: carbon steelcarbon steel andand
stainless steelstainless steel or blades ofor blades of tungsten carbidetungsten carbide areare
soldered to steel handles. In addition, somesoldered to steel handles. In addition, some
instrument handles are made frominstrument handles are made from ceramicceramic withwith
separable working ends. Carbon steel is able toseparable working ends. Carbon steel is able to
keep a cutting edge better than stainless steel, butkeep a cutting edge better than stainless steel, but
when unprotected it will rust and corrode.when unprotected it will rust and corrode.
Carbide blades however, are most efficient inCarbide blades however, are most efficient in
cutting, even though they are somewhat brittle.cutting, even though they are somewhat brittle.

Instrument parts:Instrument parts:
Most hand instruments, regardless of use,Most hand instruments, regardless of use,
are composed of three parts:are composed of three parts: shaft, shank,shaft, shank, andand
bladeblade oror nipnip..

Blade (a), shank (b), and handle (cBlade (a), shank (b), and handle (c))

A.A. Handle (Shaft):Handle (Shaft):
It is the part grasped in the operator's hand. ItIt is the part grasped in the operator's hand. It
is perfectly straight and usually withoutis perfectly straight and usually without
variations in size. It may be smooth or six-sidedvariations in size. It may be smooth or six-sided
and serrated to allow for better instrumentand serrated to allow for better instrument
control and providing friction for hand gripping.control and providing friction for hand gripping.
It could be stainless steel or padded to increaseIt could be stainless steel or padded to increase
grip and comfort during use. Most handles aregrip and comfort during use. Most handles are
in continuation with the shank but some arein continuation with the shank but some are
separable.separable.

• The separable type is known as aThe separable type is known as a cone-socketcone-socket
handlehandle and allows for replacement of severaland allows for replacement of several
working ends. The cone-socket instruments areworking ends. The cone-socket instruments are
cheaper to replace but are less stable. They arecheaper to replace but are less stable. They are
limited mostly to mirrors and condensers.limited mostly to mirrors and condensers.

B.B. Shank:Shank:
It begins with the first twisted portion ofIt begins with the first twisted portion of
the shaft and ends where the blade or nibthe shaft and ends where the blade or nib
begins. It may be straight, single, double orbegins. It may be straight, single, double or
triple angled. It tapers smoothly from thetriple angled. It tapers smoothly from the
shaft to the blade.shaft to the blade.

C.C. Blade or Nib:Blade or Nib:
This is the actual working part of theThis is the actual working part of the
instrument. It begins at the angle whichinstrument. It begins at the angle which
terminates the shank (at the last angle if there isterminates the shank (at the last angle if there is
more than one angle) or at the point whichmore than one angle) or at the point which
terminates the shank. Cutting instruments haveterminates the shank. Cutting instruments have
cutting edgecutting edge which iswhich is the working part of thethe working part of the
instrument.instrument. It is usually in the form ofIt is usually in the form of bevelbevel withwith
different shapes that results in an acute angle thatdifferent shapes that results in an acute angle that
cuts into the tooth structure.cuts into the tooth structure.
On non cutting instruments such asOn non cutting instruments such as
condensers, the part corresponding to the blade iscondensers, the part corresponding to the blade is
called thecalled the nibnib oror faceface..

Instrument nomenclature:Instrument nomenclature:
G.V. Black described a way to name andG.V. Black described a way to name and
classify dental instruments according to:classify dental instruments according to:
The purpose of their useThe purpose of their use (order name)(order name) asas
excavator, scaler.excavator, scaler.
The position or manner of their useThe position or manner of their use (suborder(suborder
name)name) as gingival margin trimmer, angle former.as gingival margin trimmer, angle former.

The form of its working partThe form of its working part (class name)(class name) as hoe,as hoe,
hatchet.hatchet.
TheThe angles on the shank:angles on the shank: straight (no angles),straight (no angles),
monangle (one angle), binangle (2 angles), triple-monangle (one angle), binangle (2 angles), triple-
angle (3 angles), etc.angle (3 angles), etc.
Thus, the full name of the instrument must beThus, the full name of the instrument must be
used to identify it, e.g., spoon excavator, binangleused to identify it, e.g., spoon excavator, binangle
chisel.chisel.

Instrument formula (Black's formula):Instrument formula (Black's formula):
Furthermore, the dimensions and design ofFurthermore, the dimensions and design of
instruments must also be specified. Accordingly,instruments must also be specified. Accordingly,
the instrument formula is of importance.the instrument formula is of importance. BlackBlack
developed a system of assigning numericdeveloped a system of assigning numeric
formulas to instruments. The formulas make useformulas to instruments. The formulas make use
of theof the metric system.metric system. For designating the degreeFor designating the degree
of angulations,of angulations, centigradecentigrade is used. Centigradeis used. Centigrade
are based on a circle divided into 100 units asare based on a circle divided into 100 units as
opposed to the 360 degree circle ordinarily usedopposed to the 360 degree circle ordinarily used
to measure angles. In a centigrade circle, a rightto measure angles. In a centigrade circle, a right
angle has 25.0 centigrade.angle has 25.0 centigrade.

• The hand cutting instruments may haveThe hand cutting instruments may have three- orthree- or
four-number formula,four-number formula, carved on the shaft,carved on the shaft,
describing the dimensions and angles of thedescribing the dimensions and angles of the
working end.working end.
• Using a code of three or four numbers separatedUsing a code of three or four numbers separated
by dashes or spaces (e.g., 10 - 95 - 8 - 14).by dashes or spaces (e.g., 10 - 95 - 8 - 14). ThisThis
formula is used to specify instruments for use andformula is used to specify instruments for use and
duplication.duplication.

The cutting edge:The cutting edge:
Is the working part of the instrument. It isIs the working part of the instrument. It is
usually in the form of bevel with differentusually in the form of bevel with different
shapes.shapes.
The blade angle:The blade angle:
It is defined as the angle between the longIt is defined as the angle between the long
axis of the blade and the long axis of the shaft.axis of the blade and the long axis of the shaft.
The cutting edge angle:The cutting edge angle:
It is defined as the angle between theIt is defined as the angle between the
margin of the cutting edge and the long axis ofmargin of the cutting edge and the long axis of
the shaft.the shaft.

 Three-number formula:Three-number formula: describes instrumentsdescribes instruments
in which the cutting edge is atin which the cutting edge is at right angleright angle toto
the long axis of the blade, for example, thethe long axis of the blade, for example, the
number would be 10 - 4 - 8:number would be 10 - 4 - 8:
1)1) The first number:The first number: indicates theindicates the width of thewidth of the
blade in tenths of mm,blade in tenths of mm, i.e. the number 10 in thei.e. the number 10 in the
example indicates 1 mm.example indicates 1 mm.
2)2) The second number:The second number: indicates theindicates the length of thelength of the
blade in mm,blade in mm, it is 4 mm in example.it is 4 mm in example.

3)3) The third number:The third number: indicates theindicates the blade angleblade angle
which iswhich is the angle between the long axis of thethe angle between the long axis of the
blade and the long axis of the handle (shaft) inblade and the long axis of the handle (shaft) in
centigrade,centigrade, it is (8 centigrade in example). Theit is (8 centigrade in example). The
instrument is designed so that this number isinstrument is designed so that this number is
always 50 or less.always 50 or less.

 Four-number formula:Four-number formula: is designed foris designed for
instruments in which the cutting edge isinstruments in which the cutting edge is not atnot at
right angleright angle to the long axis of the blade, forto the long axis of the blade, for
example, the number is 13-95-8-14.example, the number is 13-95-8-14.
1)1) The first number:The first number: indicates theindicates the width of thewidth of the
blade in tenths of mm;blade in tenths of mm; 1.3mm in the example.1.3mm in the example.

2)2) The second number:The second number: indicates theindicates the cutting edgecutting edge
angleangle which iswhich is the angle formed between thethe angle formed between the
cutting edge/working end andcutting edge/working end and a line parallel toa line parallel to
the long axis of the instrument handle inthe long axis of the instrument handle in
clockwise centigrade.clockwise centigrade.
 If the edge is locally perpendicular to the bladeIf the edge is locally perpendicular to the blade
then this number is normally omitted resultingthen this number is normally omitted resulting
in a three numbers code.in a three numbers code.
 The instrument is positioned so that this numberThe instrument is positioned so that this number
always exceeds 50.always exceeds 50.

3)3) The third number:The third number: indicates theindicates the length of thelength of the
blade in mm,blade in mm, 8mm in example.8mm in example.
4)4) The fourth number:The fourth number: indicatesindicates blade angle inblade angle in
centigrade,centigrade, 14 centigrade in the example.14 centigrade in the example.

Dental instrument gauge:Dental instrument gauge:
It is used to measure the dimensions ofIt is used to measure the dimensions of
hand instruments. The instrument is placed inhand instruments. The instrument is placed in
the center of the measuring circle with thethe center of the measuring circle with the
handle parallel to the ruler to measure thehandle parallel to the ruler to measure the
blade angle and the cutting edge angle.blade angle and the cutting edge angle.

• Angle formers and gingival margin trimmersAngle formers and gingival margin trimmers areare
the only hand cutting instruments with four-the only hand cutting instruments with four-
figure instrument formula. Other identificationfigure instrument formula. Other identification
marks may be on the shaft as well. Inmarks may be on the shaft as well. In case ofcase of
instruments which are supplied in pairs for useinstruments which are supplied in pairs for use
on both sides of cavities, a letter R or L ison both sides of cavities, a letter R or L is
engraved on the shaft denoting that theengraved on the shaft denoting that the
instrument isinstrument is right or left cutting,right or left cutting, respectively.respectively.
The last separate figure at the endThe last separate figure at the end
of the shaft is theof the shaft is the stock numberstock number for thefor the
manufacturer of the particular instrument.manufacturer of the particular instrument.

Instrument Design:Instrument Design:
Contra-angling:Contra-angling:
In order to gain access to every part of theIn order to gain access to every part of the
cavity, many instruments have the shank bent atcavity, many instruments have the shank bent at
one or more points to angle the blade relative toone or more points to angle the blade relative to
the handle. Moreover, cutting enamel and dentinthe handle. Moreover, cutting enamel and dentin
requires the application of moderate force on therequires the application of moderate force on the
instrument; therefore, the instrument must beinstrument; therefore, the instrument must be
balancedbalanced to allow for concentration of force at theto allow for concentration of force at the
blade, and at the same time to prevent theblade, and at the same time to prevent the
instrument from rotating in the fingers of theinstrument from rotating in the fingers of the
operator.operator.

• If the cutting edge isIf the cutting edge is more than 2-3mmmore than 2-3mm furtherfurther
from the long axis of the handle, the instrumentfrom the long axis of the handle, the instrument
will not be balancedwill not be balanced..
• To prevent such, instrument imbalance, the shankTo prevent such, instrument imbalance, the shank
is contra-angled, i.e.,is contra-angled, i.e., given additional angle orgiven additional angle or
angles in the opposite direction of the blade toangles in the opposite direction of the blade to
bring the working end of the blade or nib withinbring the working end of the blade or nib within 22
toto 33 mm from the central axis of the handle to givemm from the central axis of the handle to give
balance and better accessibilitybalance and better accessibility. This principle of. This principle of
design is calleddesign is called contrangling.contrangling.

• The functionalThe functional orientation and length of theorientation and length of the
bladeblade determines the number of angles necessarydetermines the number of angles necessary
in the shank to balance the instrument.in the shank to balance the instrument.
Instruments with small, short blades may beInstruments with small, short blades may be
easily designed in mono-angle form, whileeasily designed in mono-angle form, while
instruments withinstruments with longer bladeslonger blades may requires twomay requires two
or three angle in the shank to bring the cuttingor three angle in the shank to bring the cutting
edge near to the long axis of the handle.edge near to the long axis of the handle.

• For the dentist, usually, theFor the dentist, usually, the depth of the cavitydepth of the cavity
determines the suitabledetermines the suitable blade lengthblade length required.required.
Similarly, theSimilarly, the degree of inaccessibilitydegree of inaccessibility willwill
determine thedetermine the anglesangles needed in the shank.needed in the shank.
Therefore, the selection of the suitable size andTherefore, the selection of the suitable size and
design of instruments depends on thedesign of instruments depends on the dimensionsdimensions
of the cavityof the cavity and theand the degree of inaccessibility.degree of inaccessibility. AsAs
mentioned before, instruments are classifiedmentioned before, instruments are classified
based on the number of shank angles, asbased on the number of shank angles, as mono-mono-
angleangle (one),(one), bin-anglebin-angle (two), or(two), or triple-angletriple-angle
(three).(three).

Shank angles:Shank angles:
A: Mon-angle, B: Bin-angle and C: Triple-angleA: Mon-angle, B: Bin-angle and C: Triple-angle

 Instrument bevels:Instrument bevels:
Thinning the cutting edge of an instrument isThinning the cutting edge of an instrument is
achieved by what is known as beveling toachieved by what is known as beveling to
provide the hand instrument with the property ofprovide the hand instrument with the property of
cutting.cutting.
Instrument could be:Instrument could be:
a)a) Single beveled instruments.Single beveled instruments.
b)b) Bibeveled instruments.Bibeveled instruments.
c)c) Triple-beveled instruments.Triple-beveled instruments.
d)d) Circumferential beveled instruments.Circumferential beveled instruments.

a)a) Single beveled instruments (right or left, mesialSingle beveled instruments (right or left, mesial
or distal):or distal):
Single bevels are made by placing a bevel onSingle bevels are made by placing a bevel on
one side of the blade. If the instrument is heldone side of the blade. If the instrument is held
with the cutting edge down and pointing awaywith the cutting edge down and pointing away
from the operator and the bevel appears on thefrom the operator and the bevel appears on the
right side of the blade, it will be theright side of the blade, it will be the rightright
instrument of the pair. The opposite holds trueinstrument of the pair. The opposite holds true
for thefor the leftleft instrument of the pair. Suchinstrument of the pair. Such
instruments are designated asinstruments are designated as rights and leftsrights and lefts andand
are indicated by the letter R or L on their shaftsare indicated by the letter R or L on their shafts
e.g. Enamel hatchet.e.g. Enamel hatchet.

• Some instruments have their cutting edgesSome instruments have their cutting edges
perpendicularperpendicular to the long axis of the handle. Ifto the long axis of the handle. If
they are beveled on the side away from the shaftthey are beveled on the side away from the shaft
(top bevel),(top bevel), they are calledthey are called distally beveled.distally beveled. IfIf
they are beveled on the side of the blade towardthey are beveled on the side of the blade toward
the shaftthe shaft (downwards bevel),(downwards bevel), they are calledthey are called
mesial beveledmesial beveled oror reversely beveledreversely beveled e.g. directe.g. direct
(distal) and reverse (mesial) beveled chisels.(distal) and reverse (mesial) beveled chisels.

A: Distal beveled (direct);A: Distal beveled (direct);
B: mesial beveled (reverse) bin-angle chisel.B: mesial beveled (reverse) bin-angle chisel.

b)b) Bibeveled instruments:Bibeveled instruments: have the cutting edgehave the cutting edge
formed by equal bevels on both sides of theformed by equal bevels on both sides of the
blade, and they cut by pushing them in theblade, and they cut by pushing them in the
direction of the long axis of the blade e.g.direction of the long axis of the blade e.g.
bibeveled hatchet.bibeveled hatchet.

c)c) Triple-beveled instruments:Triple-beveled instruments: Instruments whichInstruments which
have on the end of the blade a single bevel thathave on the end of the blade a single bevel that
forms theforms the primary cutting edgeprimary cutting edge (direct bevel),(direct bevel),
might as well be beveled at both sides of theirmight as well be beveled at both sides of their
blades. Thus, forming two additional edgesblades. Thus, forming two additional edges
calledcalled secondary cutting edges,secondary cutting edges, which extendwhich extend
from the primary cutting edge for the length offrom the primary cutting edge for the length of
the blade. These allow cutting in threethe blade. These allow cutting in three
directions as the need presents e.g. angledirections as the need presents e.g. angle
former.former.

d)d) Circumferential beveled instruments:Circumferential beveled instruments: AA
circumferential bevel occurs where the bladecircumferential bevel occurs where the blade
is beveled at all its peripheries such as spoonis beveled at all its peripheries such as spoon
excavators.excavators.

Spoon ExcavatorSpoon Excavator

Direct and lateral cutting instruments:Direct and lateral cutting instruments:
A direct cutting instrumentA direct cutting instrument is one in which theis one in which the
force is applied in theforce is applied in the same planesame plane as that of theas that of the
blade and handle. It is called ablade and handle. It is called a "single-planed""single-planed"
instrument (e.g., Enamel hatchet, chisels). Theinstrument (e.g., Enamel hatchet, chisels). The
single-planed instruments, although they maysingle-planed instruments, although they may
have two or more angles in their shanks, allhave two or more angles in their shanks, all
are in the same plane as the handleare in the same plane as the handle (If the(If the
instrument is placed on flat surface, all of itsinstrument is placed on flat surface, all of its
parts will be laid in the same plane).parts will be laid in the same plane).

Direct (A) and lateral (B) cutting instruments.Direct (A) and lateral (B) cutting instruments.

 Lateral cutting instrumentsLateral cutting instruments are those in which theare those in which the
force is applied at aforce is applied at a right angleright angle to the plane of theto the plane of the
blade and handle. These usually have ablade and handle. These usually have a curvedcurved
bladeblade and are calledand are called "double-planed""double-planed" instrumentsinstruments
(e.g., spoon excavators and gingival marginal(e.g., spoon excavators and gingival marginal
trimmers). Thus, double-planed instruments havetrimmers). Thus, double-planed instruments have
an angle or curve in a plane at a right angle to thatan angle or curve in a plane at a right angle to that
of the handle.of the handle.
 Single-planed instruments can be used inSingle-planed instruments can be used in directdirect
and lateral cutting (provided that they areand lateral cutting (provided that they are
contrangled).contrangled). However double planed instrumentsHowever double planed instruments
cancan only be used in lateral cutting (all should beonly be used in lateral cutting (all should be
contrangled).contrangled).

Single-ended and double-ended instruments:Single-ended and double-ended instruments:
Most instruments are available with bladesMost instruments are available with blades
and shanks on both ends of the handle. Suchand shanks on both ends of the handle. Such
instruments are termedinstruments are termed double-endeddouble-ended instruments.instruments.
In many cases, the right instrument of the pair isIn many cases, the right instrument of the pair is
on one end of the handle, and the left instrumenton one end of the handle, and the left instrument
is on the other end. Single-ended instruments mayis on the other end. Single-ended instruments may
be safer to use (reduces operator injury), butbe safer to use (reduces operator injury), but
double-ended instruments are more efficientdouble-ended instruments are more efficient
because they reduce instrument exchange.because they reduce instrument exchange.

Oper.i 08

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