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1. INTRODUCTION:
The removal and shaping of tooth structure is an
essential part of restorative dentistry. Initially this was a
difficult process accomplished entirely by the use of hand
instruments. The introduction of rotary, powered cutting
equipment was one of the truly major advances in
dentistry.
In order to perform the intricate and detailed
procedures associated with operative dentistry, the dentist
must have a complete knowledge of the purpose,
availability and application of the many instruments
required.
CLASSIFICATION:
According to Marzouk:
Instruments for operative dentistry procedures can
be generally classified as
1) Those used for exploration
2) Those used for removal of tooth structure.
3) Those used for restoration of teeth.
Those used for exploration
A) Dry the area on the tooth:
- This necessitates the use of an
a) Air syringe.
b) Pair of tweezers (pliers)
c) Cotton pellets to dry the tooth.
d) Cotton rolls – to isolate the area around
the tooth.
1

2. B) Illuminate the area:
A source of light could be either an overhead fixture
supplying non-reflecting light or an intra-canal light.
They can be
- Battery operated lights.
- Built in lights attached to dental unit.
- Light attached to mirror or hand piece.
Light can be introduced directly or indirectly by
reflecting it on the filed via a mirror.
C) To retract the soft tissues:
The hand mirror is used to move the tongue and
cheek away.
- Blunt plastic instruments may help in
retraction.
- Tongue depressor or retractors are sometimes
helpful for this procedure.
D) To probe the potential lesion:
Explorers are used for this purpose.
These are 4 types of explorers.
1) Straight explorer.
2) Right angled explorer
3) Arch explorer
4) Interproximal explorer.
I) Those used for tooth structure removal:
- Hand cutting instruments.
- Rotary cutting and abrasive instruments.
- Ultrasonic instruments
2

3. II) Those used for restoring:
- Mixing instruments
- Spatulas
- Plastic instruments
- Condensing instruments
- Burnishing instruments
- Carvers
- Files
- Kives
- Finishing and polishing instruments.
According to charbenaeu:
Operative instruments can be conveniently classified
into 6 categories.
1) Cutting instruments
Hand
Hatchets
Chisels
Excavators
Others
Rotary
Burs
Stones
Disks
Others
2) Condensing instruments
Pluggers
Hand
Mechanical
3) Plastic instruments
Spatulas
Carvers
Burnishers
Packing instruments
3

4. 4) Finishing and polishing instruments
Hand
Orange wood sticks
Polishing points
Finishing strips
Rotary
Finishing burs
Mounted brushes
Mounted stones
Rubber cups
Impregnated disks and wheels
5) Isolation instruments
Rubber dam frame
Clamps, forceps, punch
Saliva ejector
Cotton roll holder
Evacuating tips and equipment
6) Miscellaneous instruments
Mouth mirrors
Explorers
Probes
Scissors
Pliers
Others
HAND CUTTING INSTRUMENTS:
Modern hand instruments, when properly used,
produce beneficial results for both the operator and the
patient.
Materials:
Hand cutting instruments
They are manufacture from two main materials.
4

5. - Carbon steel
- Stainless steel
- Some are made with carbide inserts to provide
more durable cutting edges.
- Carbon steel is harder than stainless steel but
when unprotected it will corrode.
- Stainless steel remains bright under most
conditions but loses a keen edge during carbide, while
hard and weak resistance, is brittle and cannot be used
in all designs.
- Other alloys of nickel, cobalt, chromium are
used in the manufacture of hand instruments, but they
are usually restricted to instruments other than those
used for cutting tooth structures.
Hardening and tempering heat treatments:
To gain maximal benefits from carbon or stainless
steel, the manufacturer must submit them to two heat
treatments.
- Hardening and tempering
- The hardening heat treatment hardness the
alloy, but also makes it brittle, especially when the
carbon content is high.
The tempering heat treatment relieves stains and
increases toughness.
Effects sterilization:
Sterilizing carbon steel instruments by using
- Sporicidal cold disinfection.
- Boiling water
- Steam under pressure (autoclave)
- Causes discolouration.
Rust
Corrosion
5

6. Methods of protection:
1) Electroplate the instrument and affords protection
except on the blade, where use and sharpening remove
the plating.
2) Use of rust inhibitors (soluble alkaline compounds).
3) Minimizing the effect of moisture is to remove the
instruments promptly at the end of the recommended
sterilizing period, dry them thoroughly and place them
in the instrument cabinet.
The boiling water or autoclave methods of
sterilization do not produce discolouration rust or
corrosion of stainless steel instruments.
Prolong immersion in cold disinfectant solution may
case rust.
Dry heat sterilizers do not rust and corrode carbon
steel instruments, but the high heat may reduce the
hardness of the alloy.
Instrument categories:
Hand instruments in the dental operatory may be
categorized as
1) Cutting
- Excavators, chisels and others.
2) Non cutting
- Amalgam condensers, mirrors, explorers,
probes.
Instrument design:
Most hand cutting instruments are composed of 3
parts.
- Handle, Shank and Blade.
6

7. For non-cutting instruments the parts corresponding
to the blade is termed – the nib.
The end of the nib or the working surface is known
as the – face.
The blade or nib is connected to the handle by the
shank.
Instruments which have blades on both sides of the
handle are known as double – ended instruments.
Shafts and handles are available in various shapes
and sizes. It may be serrated to increase friction grip.
Shanks serve to connect the handles to the working
ends of the instruments.
They are;
Smooth, rounded and tapered. They often have one
or more bends to avoid the instrument having a tendency
to twist in use when force is applied.
Hand instruments must be balanced to allow for the
concentration of force onto the blade without causing
rotation of the instrument in the grasp.
This balance is accomplished by designing the angles
of the shank so that the cutting edge of the blade lies
within the projected diameter of the handle and nearly
coincides with the projected axis of the handle. For
optimal anti-rotational design the blade edge must not be
off axis by more than 1 to 2 mm.
All dental instruments and equipment need the
satisfy this principle of balance.
7

8. Instrument shank angle:
The functional orientation and length of the blade
determines the number of angles necessary in the shank
to balance the instrument. G.V. Black classified
instruments based on the number of shank angles as
- Mono-angle (one)
- Bin-angle (two) or
- Triple-angle
Instruments with small, short blades may be easily
designed in mono-angle form while confining the cutting
edge within the required limit.
Instruments with longer shanks require 2 or 3 angles
in the shank to bring the cutting edge near to the long
axis of the handle such shanks are termed contra-angled.
Instrument name:
G.V. Black described a way to name dental instruments.
1) Order: The order denotes the purpose or function of
the instrument. E.g. Excavator, scaler.
2) The sub-order denotes the position or manner of use
of the instrument. E.g Push, pull.
3) The class describes the form of the blade. Eg.
Hatchets, chisel.
4) Shape of the shank – subclass. Eg. Mon-angle,
Binangle.
These names were combined to form in complete
description of the instrument (eg. Binangle spoon
excavator).
8

9. Operative cutting instrument formulas:
Cutting instruments have formulas describing the
dimensions and angles of the working end.
1st
number indicates:
Width of the blade or primary cutting edge in tenths
of a mm (0.1mm).
2nd
number of indicates:
The primary cutting edge angel (measured from a line
parallel to the long axis of the instrument handle in
clockwise centigrades). The instrument is positioned so
that this number always exceeds 50.
If the edge is located angular to the blade then this
number is normally omitted resulting in a 3 number code.
The 3rd
number indicates:
- blade length in mm.
The 4th
number indicates the:
Blade angle relative to the long axis of the handle in
clockwise direction. the angle is expressed in hundredths
of a circle or centigrade. It is always 50 or less than 50.
Cutting instrument bevels:
Most hand cutting instruments have on the end of
the blade a single bevel that forms the primary cutting
edge.
Two additional edges, called secondary cutting edges,
extend from the primary edge for the length of the blade.
Bibeveled instruments, such as ordinary hatchets,
have 2 bevels that form the cutting edge.
9

10. Certain single beveled instruments such as spoon
excavators and GMT’s are used with a scraping or lateral
cutting motion. Others as enamel hatchets may be used
with a planing or direct cutting motion for such single-
beveled designs the instruments must be made in pairs.
To determine whether the instruments has a right or
left bevel, the primary cutting edge is held down and
pointing away, and if the bevel appears on the right side
of the blade, it is the right instrument of the pair and vice
versa.
Most instruments are available with blades and
shank on both ends of the handle.
Such instruments are termed double-ended.
Instruments having cutting edges angled the axis of
the handle such as bin-angle chiles are single beveled and
not designated as right or left but have a mesial bevel or
distal bevel.
If when one observes the inside of the blade
carvature, the primary bevel is not visible, the instrument
has a distal bevel and if the bevel can be seen then the
instrument has a reverse or mesial bevel.
APPLICATIONS OF CUTTING INSTRUMENTS:
The cutting instruments are used to cut hard or soft
tissues of the mouth.
Excavators are used for removal of caries and
refinement of the internal parts of the cavity.
The four subdivisions of excavators are
1) Ordinary hatchets
10

11. 2) Hoes
3) Angle formers
4) Spoon
Ordinary hatchet excavator (3-2-28)
Has the cutting edge of the blade directed in the
same plane as that of the long axis of the handle and is
bibeveled. These instruments are used primarily on
anterior teeth for preparing retentive areas and
sharpening internal line angles, particularly in
preparations for direct gold restoration.
The hoe excavator (4½ - 1½ -22) has the primary
cutting edge of the blade angle to the axis of the handle.
Used for planing cavity walls and forming line angles.
Used in Class III and V preparations for direct gold
restoration.
Some sets contain hoes with longer and heavier
blades with shanks contra-angled. They are intended for
use on enamel or posterior teeth.
Angle former (12-85-5-8) (Monangled):
It is primarily used for sharpening line angles and
creating retentive feature in dentin in preparations for
gold restoration.
May be used for placing bevels on enamel margins. It
is described as a combination of a chisel and GMT. It is
available in pairs (right and left).
Spoon excavator (15-8-14):
Used for removing caries and carving amalgam or
direct wax patterns.
The blades are curved and cutting edges are either
circular (discoid) or claw like – cleoid.
11

12. The shanks may be binangled (13-7-14) or triple
angled, to facilitate accessibility.
Chisels:
Are intended primarily for cutting enamel and may
be grouped as
- Straight, slightly curved or binangle.
- Enamel hatchets
- Gingival margin trimmers.
Straight chisel (12-7-0):
The straight chisel has a shank and blade with the
bevel on only one side. The shank and blade of the chisel
may be slightly curved (Wedelstaedt design) or may be
bin-angled.
The force used with all these chisels is essentially a
straight thrust.
Enamel hatchet (10-7-14):
Is a chisel similar in design to the ordinary hatchet
except that the blade is larger, heavier and is beveled on
only one side.
It is used for cutting enamel and comes as right or
left types for use on opposite sides of the cavity.
Offset hatchets: The offset is like the regular hatchet or
backward except the whole blade is rotated a ¼ turn from
the long axis.
Gingival marginal trimmer (12 ½ -100 – 8-14) (12 ½
-75-8-14)
12

13. It is similar in design to the enamel hatchet, except
the blade is curved, and the primary cutting edge is at an
angle to the axis of the blade.
It is made as right and left types. When the second
number in the formula is 90 to 100 the pair is used on the
distal gingival margin.
When this number is 85 to 75 the pair is used to
bevel, the mesial margin.
The GMT is designed to produce a proper bevel on
the gingival enamel margins of proximal occlusal
preparations.
The 100 and 75 pairs are for inlay / onlay
preparation with steep gingival bevels.
The 90 and 85 pairs are for amalgam preparation
with gingival enamel bevels that decline gingivally only
slightly.
Among other uses is the rounding or beveling of the
axiopulpal line angle of the 2-surface preparations.
Other cutting instruments:
Other hand cutting instruments include
Knife: used for trimming excess filling material on the
gingival facial or lingual margins of proximal restoration
or trimming and contouring the surface of class-V
restoration.
Files: can be used to trim excess filling material. They are
particularly useful at the gingival margins.
13

14. The discoid-cleiod instrument may be used to trim or
burnish inlay- onlay margins. (It is principally used for
carving occlusal anatomy).
HAND INSTRUMENT TECHNIQUE:
There are 4 grasps used with hand instruments.
1) Modified pen.
2) Inverted pen.
3) Palm and thumb.
4) Modified palm and thumb.
Modified pen grasps:
It is similar to that used in holding a pen but not
identical.
Pads of the thumb, index and middle fingers contact
the instrument, while the tip of the ring finger or tips of
the ring and little finger is placed on a nearly tooth
surface of the same arch as a restoration. The palm of the
hand generally is facing away from the operator. The pad
of the middle finger is placed near the top side of the
instrument.
Inverted pen grasps:
The finger position of the inverted pen grasp are the
same as for the modified pen grasp, but the hand is
rotated so that the palm faces more towards the operator.
This grasp is used mostly for cavity preparations
utilizing the lingual approach on anterior teeth.
The modified pen and inverted pen grasps are
practically universal.
14

15. Palm and thumb grasp:
The handle is placed in the palm of the hand and
grasped by all the fingers, while the thumb is free of the
instrument and the restoration is provided by supporting
the tip of the thumb on a nearby tooth of the same arch or
on a firm, stable structure. It may be useful on maxillary
teeth especially the right side when working from the right
rear position.
This form of grasp is usually necessary where the
rest support for the thumb is at some distance from the
point of operation, so that the thumb itself must be
extended and hence cannot be used for gripping.
Modified palm and thumb grasp:
In this, the handle of the instrument is in contact
with the tips of the 4 fingers on one side, opposed to
which are contacts with the mesial end of the 1st
phalanx
of the thumb. The hand is only half closed instead of
being fully closed. The end of the thumb is used as a rest.
Rests:
A proper instrument grasp must include a firm rest
to steady the hand during operating procedures.
The closer the rest areas are to the operating area,
the more reliable they are.
In cases where it is impossible to establish a rest on
tooth structure then soft tissue may be used.
Occasionally, it is impossible to establish normal
finger rests with the hand holding the instrument, then
instrument control may be gained using the forefinger of
the opposite hand on the shank of the instrument or using
an indirect rest (i.e. operating hand rests on the opposite
side which rests on a stable oral structure).
15

16. Guards- are hand instruments or other items such
as interproximal wedges, used to protect soft tissue from
contact with sharp cutting or abrasive instruments.
SHARPENING HAND INSTRUMENTS:
Instruments with dull cutting edges cause more pain,
prolong operating time, are less controllable and reduce
quality and precision in cavity preparation. It is essential
therefore that all cutting edges be sharp. Resharpening
requires little time and is very rewarding.
The sharpening equipments include
1) Stationary sharpening stones.
2) Mechanical sharpeners.
3) Stones that are used in hand piece.
Stationary sharpening stones:
The most frequently used sharpening equipment
consists of a block or stick of abrasive material called a
stone.
They are sometimes called as oil stones (because of
the common practice of applying a coating of oil to them
as an aid to the sharpening process).
The oil stones are available in coarse, medium, or
fine grit. They can be obtained in a variety of shapes like.
- Flat
- Grooved
- Cylindrical
- Tapered
16

17. 4. Types of materials are in common use for sharpening
stones
- Arkansas stone
- Silicon carbide
- Aluminium oxide
- Diamond
Mechanical sharpeners:
One type of mechanical sharpener is represented by
the treatment honing machine. Basically this instrument
moves hone in a reciprocating motion at a slow speed
while the instrument is held at an appropriate angulation
and supported by a rest. This type of sharpener is very
versatile.
Handpiece sharpening stones:
Mounted silicon carbide and aluminium oxide stones
for use with both straight and angle handpieces are
available in a variety of sizes and shapes.
These stones may produce inconsistent results
because of the speed variables and the usual lack of a rest
or guide for the instrument.
Principles of sharpening:
In use of any equipment there are several basic
principles of sharpening that should be followed.
1) Sharpen instruments after they have been cleaned
and sterilized.
2) Establish the proper bevel angel (usually 45°) and
the desired angle of the cutting edge to the blade
17

18. before placing the instrument against the stone and
maintain these angles while sharpening.
3) Use light stroke or pressure against the stone to
minimize frictional heat.
4) Use a rest or guide whenever possible.
5) Remove as little metal from the blade as possible.
6) Lightly hone the unbeveled side of the blade after
sharpening to remove the fine bur that might be
created.
7) After sharpening, resterilize the instrument along
with other instruments on the tray setup.
8) Keep sharpening stones clean and free of metal
cuttings.
Sharpness test:
Sharpness of an instrument can be tested by lightly
resting the cutting edge on a hard plastic surface. If the
cutting edge digs in during an attempt to slide the
instrument forward over the surface, the instrument is
sharp. If it slides the instrument is dull.
STERILIZATION AND STORAGE:
Sterilization in dental office can be accomplished by
- Autoclaving
- Dry heat procedure
- Ethylene oxide equipment
- Chemical vapour sterilizers.
Boiling and chemical solution will not sterilize and
should be considered only as a disinfection procedure.
18

19. POWERED CUTTING EQUIPMENT:
Development of rotary equipment:
Much of the subsequent history leading to present
powered cutting equipment can be seen as a search for
improved sources of energy and means for holding and
controlling the cutting instrument. This has culminated in
the use of replaceable bladed or abrasive instruments held
in a rotary handpiece usually powered by compressed air.
A handpiece is a device for holding rotating
instruments, transmitting power to them and for
positioning them intraorally.
Handpiece and associated cutting and polishing
instruments developed as 2 basic types straight and
angle.
One of the most significant advancement was the
introduction of the electric motor as a power source in
1874. It was incorporated into a dental unit in 1914.
Steel burs that were used that time were not able to
cut the enamel effectively even when applied with great
force.
It only resulted in increased heat and instrument
wear.
Diamond cutting instrument were developed in
Germany around 1935.
In 1946 diamond instruments and tungsten carbide
burs capable of cutting enamel were produced
commercially.
By 1950 speeds of 60,000 rpm and above have been
attained.
19

20. The major break through came with the introduction
of contra-angled handpieces with internal turbine drives
in contra angle heads.
Air driven hand pieces continue to be the most
popular type of hand piece equipment because of the
overall simplicity of design ease of control, versatility and
patient acceptance.
Rotary sped ranges:
The rotational speed of an instrument is measured in
revolution pr minute (rpm).
3 speed ranges are generally recognized.
1) Low or slow speeds (below 12,000 rpm)
2) Medium or intermediate speed 12,000 to
2,00,000rpm.
3) High or ultra-high speeds above 2,00,000rpm.
According to Marzouk:
Speeds are classified as
a) Ultra low speed (300-3000rpm)
b) Low speed (3000-6000rpm)
c) High sped (20,000-45,000rpm)
d) Ultra-high speed (1,00,000rpm)
Some dental equipment can actually produce upto
5,00,000.
The crucial factor for some purpose is the surface
speed of the instrument (i.e.) the velocity at which the
edges of the cutting instrument pass across the surface
being cut. This is proportional to both the rotational
speed and diameter of the instrument.
20

21. Low-speed cutting is ineffective, time consuming and
requires relatively heavy force application. This results in
heat production at the operating site and produces
vibrations of low frequency and high amplitude.
The low speed range is used for cleaning teeth,
occasional caries excavation and finishing and polishing
procedures.
At high speed, the surface speed needed for efficient
cutting can be attained with smaller and versatile cutting
instruments.
This speed is used for
1) Tooth preparation
2) Removal of old restoration
Other advantages are
1) Diamond and carbide cutting instruments remove
tooth structure faster with less pressure vibration
and heat generation.
2) The number of rotary cutting instruments need is
reduced because smaller sizes are more universal in
application.
3) The operator has better control and greater ease of
operation.
4) Instruments last longer
5) Patients are generally less apprehensive because
annoying vibrations and operating time are
decreased.
6) Several teeth in the same arch can and should be
treated all teeth same appointment.
21

22. LASER EQUIPMENT:
The word laser is an acronym for “Light amplification
by stimulated emission of radiation”.
They are devices, which produce beams of very high
intensity light.
The lasers range from
Long wavelengths (infrared)
Visible wavelengths
Short wavelengths (Ultraviolet)
Excimers are special ultraviolet lasers. At present
time CO2 and Nd:YAG lasers have shown the most
promises.
Lasers are regulated by food and drug administration
(FDA) for safety and efficacy. They have been approved for
soft tissue surgery but not for tooth preparation.
Other equipment:
In the mid 1950’s air abrasive cutting was tested but
there were several clinical problems.
There was no tactile sense associated with air
abrasive cutting of tooth structure. At present air abrasive
equipment is being promoted for stain removal, debriding
pit and fissures prior to sealing and micromechanical
roughening of surfaces to be bonded (enamel, porcelain).
ROTARY CUTTING INSTRUMENTS:
The individual instruments intended for use with
dental hand pieces are manufactured in hundreds of sizes,
shapes and types.
22

23. Common design characteristics:
Inspite of the great variation that exists among
rotary cutting instruments, they have certain design
features in common.
Each instrument consists of 3 parts
(i) Shank
(ii) Neck
(iii) Head
Shank design:
The shank is the part
- That fits into the hand piece
- Accepts rotary motion from the hand piece.
- Provides a bearing surface to control the
alignment and concentricity of the instrument.
The shank design and dimensions vary from the
hand piece for which it is intended. The ADA specification
no. 23 for dental excavating burs include 5 classes.
Three of these
- Straight hand piece shank.
- Latch type angle hand piece shank.
- Friction grip angle hand piece shank. Are
commonly encountered.
Neck design:
The neck is the intermediate portion of an
instrument that connects the head to the shank.
23

24. The main function of the neck is to transmit
rotational and translation forces to the head. At the same
time it is desirable for operator to have the greatest
possible visibility of the cutting head and greatest
manipulative freedom.
Head design:
The head is the working part of the instrument, the
cutting edges or points of which perform the derived
shaping of tooth structure. The heads of instruments show
great variation in design and construction than either of
the other main portions. For this reason the
characteristics of the head for the basis on which rotary
instruments are classified.
Dental burs:
The term bur is applied to all rotary cutting
instruments that have bladed cutting heads.
This includes instruments intended for such
purposes as finishing metal restorations and surgical
removal of bone, as well as those primarily intended for
tooth preparation.
HISTORICAL DEVELOPMENT OF DENTAL BURS:
The earliest burs were hand made. They were both
expensive and variable in dimension and performance.
The shapes and dimensions of modern burs are
directly related to those of the machine made burs
introduced in 1891.
Steel burs:
They perform well, cutting human dentin at low
speeds, but dull rapidly at higher speeds or when cutting
enamel. Once dulled the reduced cutting efficiency creates
heat and vibration.
24

25. Carbide burs – Introduced in 1947, have largely replaced
steel burs for cavity preparation. Steel burs now are used
mainly for finishing procedures. They perform better than
steel burs at all speeds and their superiority is greatest at
high speeds.
All carbide burs have heads of cemented carbide in
which microscopic carbide particles, usually of tungsten
carbide are held together in a matrix of cobalt or nickel.
Carbide is stiffer and stronger than steel but it is
also more brittle.
Bur classification systems:
In the United States dental burs traditionally have
been described in terms of an arbitrary numerical code for
head size and shape.
2 = 1mm diameter round bur.
57 = 1mm diameter straight fissure bur.
34 = 0.8mm diameter inverted cone bur.
Newer classification systems like the FDI and ISO
tend to use separate designations for shape, usually a
shape name and size usually a number giving the head
diameter in tenths of a mm. Eg. Round 010; inverted cone
008.
Shapes:
The term bur shape refers to the contour or
silhouette the head. The basic head shapes are
Round bur – is spherical. The shape has been used for
1) Initial entry into the tooth.
2) Extension of the preparation
3) Preparation of retention potholes.
4) Caries removal.
25

26. Inverted cone bur:
It is a portion of a rather rapidly tapered cone with
the apex of the cone directed towards the bur shank.
It is particularly suitable for providing undercuts in
cavity preparation.
Pear-shaped bur:
It is a portion of a slightly tapered cone with the
small of the cone directed towards the bur shank. (Normal
length)
It is advocated for use in Class I cavity preparation
for gold foil. Long length pear bur is advocated for cavity
preparations for amalgam.
Straight fissure:
A straight fissure bur is an elongated cylinder. This
shape is advocating some for amalgam cavity preparation.
Tapered fissure bur:
Is a portion of a slightly tapered cone with the small
end of the cone directed away from the bur shank. This
shape is useful for
1) Inlay and crown preparations where freedom from
undercuts is essential for successful withdrawal of
patterns and final seating of cast restoration.
Among these basic shapes, variations are possible.
Sizes:
In the United States the number designating bur size
also has traditionally served as a code for head design.
The original numbering system grouped burs by 9
shapes and parallel sizes.
26

27. Modifications in bur design:
There has been a reduction in the number of
standard sizes that have continued in use. As
effectiveness of small burs has increased they have
replaced larger burs in many procedure.
3 other major tends in bur design are used
- Reduced use of crosscuts.
- Extended heads on fissure burs.
- Rounding of sharp tip angles.
Crosscuts are needed on fissure burs to obtain
adequate cutting effectiveness at low speeds but at high
speeds they are not needed.
Because crosscut burs used at high speeds tend to
produce unduly rough surfaces many of the cross cut
sizes originally developed for low speed use have been
replaced by non-crosscut instrument of the same
dimensions for high-speed use.
Carbide fissure burs have been introduced that have
extended head lengths 2 or 3 times those of the normal
tapered fissure burs of similar diameter.
The third major trend in bur design has been toward
rounding of the sharp tip corner. Because teeth are
relatively brittle, the sharp angles produced by
conventional burs can result in high stress cone and
include the tendency of the tooth to fracture.
Additional features in head design:
A large number of factors other than head size and
shape are involved in determining the clinical
effectiveness of a bur design.
27

28. They include
- Neck diameter
- Head diameter
- Head length
- Taper angle
- Blade spiral angle
- Crosscut size and spacing
Bur blade design:
The actual cutting action of a bur takes place in a
very small region at the edge of the blade.
Each blade has 2 sides
- The rake face (towards the direction of cutting)
- Clearance face and
Three important angles:
- Rake angle (angle made between the rake force
and the line connecting the edge to the axis of the bur)
- Edge angle (is the internal angle at the edges
followed by the forces of the bur blade).
- Clearance angle (is the angle between the
clearance face immune behind the edge and a tangent
to the path of rotation).
The rake angle is the most important design
characteristic of a bur blade.
For cutting hard, brittle materials a negative rake
angle minimizes fractures of a cutting edge, thereby
include the tool life extreme positive rake angles are used.
When relatively soft and weak materials are cut.
A rake angle is said to be negative when the rake
face is ahead of the reduce (from cutting edge to axis of
bur).
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29. Increasing the edge angel reinforces the cutting edge
and reduces the likelihood for the edge of the blade to
fracture.
The 3 angles cannot be varied independently of each
other.
At high speeds a radial rake angle that is either
negative or positive may be equally effective.
(An increase in the clearance angle causes a decrease
in the edge angle. The clearance angle eliminates rubbing
friction of the clearance face, provides a stop to prevent
the bur edge from digging into tooth structure extensively
and reduces the radius of the blade back of the cutting
edge to provide adequate flute space for the chips formed
ahead of the following blade).
Carbide burs normally have blades with slight
negative rake angles and edge angles of about 90 degrees.
DIAMOND ABRASIVE INSTRUMENTS:
The second major category of rotary dental cutting
instruments involves abrasive rather than blade cutting.
Abrasive instruments are based on small angular
particles of a hard substances held in a matrix of softer
material.
Cutting occurs at a large number of points where
individual hard particle protrude from the matrix rather
than along a continuous blade edge.
Abrasive instruments are generally grouped as
diamond or other instruments. Diamond instruments have
a great clinical impact because of their long life and great
effectiveness in cutting enamel and dentin.
Diamond instruments for dental use were introduced
in the United States in 1942.
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30. Terminology:
Diamond instruments consist of 3 parts.
A metal blank, powered diamond abrasive, Metallic
bonding material that hold the diamond powder onto the
blank.
The blank has the same parts
- Head
- Neck
- Shank
The diamonds employed are industrial diamonds
either natural or synthetic that have been crushed to
powder and then carefully graded for size and quality.
Method of manufacture:
The diamonds are attached to the blank by
electroplating a layer of metal on the blank while holding
the diamonds in place against it.
Head shapes and sizes:
Diamond instruments are available in a wide variety
of shapes and in sizes, which corresponded to all except
the smallest diameter burs.
Diamond particle factors:
The clinical performance of diamond abrasive
instruments depend on the
- Size
- Spacing
- Uniformity
- Exposure and
- Bonding of diamond particles
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31. Diamond particle size is commonly categorized as
coarse (125 to 150m), medium (88 to 125m) fine (60 to
74m) and very fine (38 to 44m) for diamond excavating
instruments.
When using large particle size, the number of
abrasive particles that can be placed on a given area of
the head is decreased.
Almost of only cause of failure of diamond
instruments is the loss of diamonds from the critical area.
Other abrasive instruments:
Many types of abrasives instruments are used in
dentistry in addition to diamond instruments. They may
be divided into 2 distinct groups
- Moulded instruments
- Coated instruments
Moulded abrasive instruments:
They have heads that are manufactured by moulding
or pressing a uniform mixture of abrasive and matrix
around the roughening end of the shank or cementing a
pre-moulded head to the shank.
In contrast to diamond instruments, moulded
instruments have a much softer matrix and are expected
to wear during use. The mounted heads are often termed
as points or stones.
Coated abrasive instruments:
They are mostly discs that have a thin layer of
abrasives cemented to a flexible backing.
They are used in finishing / smoothening procedure
of certain enamel walls of cavity preparations for indirect
restoration as well as in finishing procedures for
restoration.
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32. Materials:
The matrix materials usually are phenolic resins or
rubber. A rubber matrix is used primarily to obtain a
flexible head on instruments to be used for polishing.
A harder, non-flexible rubber matrix is often used for
moulded silicon carbide discs. Synthetic or natural
abrasives may be used including.
- Silicon carbide (carborundum)
- Aluminium oxide
- Garnet
- Quartz
- Pumice
- Cuttlebone
Cutting mechanism:
For cutting it is necessary to apply sufficient
pressure to make the cutting edge of a blade or abrasive
particle dig into the surface.
Evaluation of cutting:
Cutting can be measured both in terms of
effectiveness and efficiency.
Cutting effectiveness is the rate of tooth structure
removal (mm/min or mg/sec).
It does not consider the potential side effects such as
heat or noise.
Cutting efficiency is the percentage of energy
actually producing cutting.
Bladed cutting:
Tooth structure, like other materials, undergoes both
brittle and ductile fracture.
Brittle fracture is associated with crack production,
usually by tensile loading.
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33. Ductile fracture involves plastic deformation of
material, usually proceeding by shear. In order for the
blade to initiate the cutting action, it must be sharp, must
have a higher hardness and modulus of elasticity than the
material being cut and must be pressed against the
surface with sufficient force.
Abrasive cutting:
The cutting action of diamond abrasive instruments
is similar in many ways to that of bladed instruments but
the key differences result from the properties size and
distribution of the abrasive.
The very high hardness of diamonds provides
superior resistance to wear.
Diamonds are more efficient when used to cut brittle
materials and are superior to burs for the removal of
dental enamel.
Diamond abrasives are commonly used for milling
disks or instruments of CAD / CAM or copy milling
applications.
Cutting recommendations:
The requirements for effectiveness and efficient
cutting include using a contra-angle handpiece, air-water
spray for cooling, high operating speeds, light pressure,
and a carbide or diamond instrument.
Carbide burs are better for
- End cutting
- Produce lower heat
- Have more blade edges per diameter for cutting.
- For punch cuts to enter tooth structure
- Intercoronal cavity preparation
- Amalgam removal
- Small preparations
- Secondary retention features
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34. Diamond instruments have higher hardness and
coarse diamonds have very high cutting efficiency.
They are better for
- Extra-coronal cavity preparation
- Beveling enamel margins on cavity preparation
- Enameloplasty
HAZARDS WITH CUTTING INSTRUMENTS:
Almost everything done in a dental office involves
some risk to the patient, dentist and / or auxiliaries.
The patient has pulpal dangers from the cavity
preparation and restoration procedure. There are also soft
tissue dangers. Everyone is potentially susceptibility to
eye, ear and inhalation dangers.
PULPAL PRECAUTIONS:
As the thickness of the remaining dentin decreases,
the pulpal insult from heat or desiccation increases.
Steel burs produce more heat than carbide burs
because of in sufficient cutting. Burs and diamond
instruments that are dull or plugged with debris do not
cut efficiently, resulting in heat production. When used
without coolants, diamond instruments generate more
damaging heat than carbide burs.
The most common instrument coolants are air or air
water spray.
Air alone as a coolant is not effective in preventing
pulpal damage since it needle by desiccates the dentin
and damages the odontoblasts.
The use of a water spray and its removal by an
effective high volume evacuator are especially important
when old amalgam restorations are removed in order to
decrease mercury vapour release and include visibility.
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35. Soft tissue precautions:
A rubber dam is very helpful in isolating the
operating site. If not used then a mouth mirror, cotton roll
or evacuator tip may be used to retract the tissues.
Eye precautions:
Protective glasses are always indicated. If an eye is
injured it must be covered by a clean gauze pad until
medical attention can be obtained. Precautions from
unusual light sources (VLC, laser) should be taken.
Ear precautions must be taken.
Inhalation precautions:
Both aerosols and vapours are a health hazard to all
present. Rubber dam should be used, Disposable masks
should be worn.
REFERENCES:
 Operative dentistry: Modern theory and practice – MA
Marzouk, I Edition.
 The art and science of operative dentistry – Sturdevent,
III Edition.
 Principles and practice of Operative Dentistry –
Charbenaeu.
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