INSTRUMENTS in operative dentistry.pptx

INSTRUMENTS
IN
OPERATIVE DENTISTRY

Classification
Instrument formulas
Instrument design
Instruments
Hand instrument techniques
Powered cutting equipments
Sharpening of hand instruments
Introduction

Medical/surgical instrument
A tool, especially if used for delicate scientific or medical
work.
The removal and shaping of tooth structure are important
aspects of restorative dentistry, so it is essential to have an
adequate knowledge of types and use of the instruments
used in Operative dentistry.

Black not only organized the classification of cavity but the naming and
the numbering of hand instruments.
For many years, Carbon Steel was the primary material used in hand
instruments because they were harder and maintained sharpness better
than stainless steel.
But Stainless Steel is now the preferred material.
In addition, some instruments are made with Carbide.

Designs of some
early hand
instruments. These
instruments
were individually
handmade, variable
in design,
and cumbersome to
use. Because of
nature of the
handles, effective
sterilization was a
problem.

Hand
instruments
Rotary, powered
cutting instruments
Cutting
instruments
Non cutting
instruments
Handpieces Burs
Classification

Classification
Cutting
Non-cutting
Excavators Chisels Others
Amalgam
Condensers
Mirrors Explorers Probes
Ordinary Hatchets
Hoes
Angle Formers
Spoons
Straight,
Slightly curved,
Or Bin-angle
Enamel Hatchets
G M T
Knives
Files
Scalers
Carvers
Sturdevant’s

Instrument Names
These names were combined to form the complete description of the
instrument (e.g., bin-angle hatchet push, excavator).
Dr. G. V. Black classified all instruments by name :
(1) ORDER - Function (e.g., scaler, excavator)
(2) SUBORDER - Manner of use (e.g., push, pull)
(3) CLASS - Design of the working end (e.g., spoon excavator, sickle
scaler)
(4) SUBCLASS - Shape of the shank (e.g., mon-angle, bin-angle, contra-
angle)
Classification

Instrument Design
Handle: • Straight and octagonal in cross-section, may be
serrated to increase friction for hand gripping .
• When shank and blade are separate from the handle
and intended to be screwed into it, it is called as cone-
socket instrument.

Bladenib: Working end of a cutting instrument- blade
Working end of a non-cutting instrument-nib
Working surface or end of nib- face
Instrument Design
Shank: It connects the shaft with the blade or the working point.
Any angulations in the instrument can be placed at the
junction of the shaft and shank.

Blade angle:
It is defined as the angle between the long
axis of the blade and the long axis of the
shaft.
Cutting edge
angle:
It is defined as an angle between the margins
of the cutting edge and the long axis of the
shaft.
Instrument Design
Cutting edge:
It is the working part of the instrument. It is
usually in the form of a bevel with different
shapes.

Since substantial forces are required to cut enamel and dentin
the hand instruments must be balanced and sharp .
For optimal anti-rotational design, the blade edge must not be off
axis by more than 1 to 2 mm.
Balancing of the instrument is necessary so as to prevent the
rotation of the instrument while using the instrument.
Instrument Design
Instrument balance:
The cutting edge of the blade lies within the projected diameter
of the handle.

Instruments with complex orientations may require two or three
angles in the shank to bring the cutting edge near to the long
axis of the handle to prevent rotation when force is applied.
Such shanks are termed contra-angled.
Instrument Design
Contra- angling

Shank Angles
Straight
Mon-angle
(with one angle),
Bin-angle
(with two angles)
Triple-angle
(three angles)

Instrument Formulas
The first number indicates the width of the blade or primary cutting edge
in tenths of a millimeter (0.1 mm) (e.g., 10 = 1 mm).
These three measurements are sufficient for describing a great percentage
of instruments with cutting edge perpendicular to the blade axis.
The second number indicates the blade length in millimeters (e.g., 8 = 8
mm).
The third number indicates the blade angle, relative to the long axis of the
handle in centigrade (e.g., 14 = 50 degrees).
Three unit formula

Instrument Formulas
The second number indicates the primary cutting edge angle in
centigrade(100th of circle).
The first number indicates the width of the blade.
The third number indicates the blade length .
The fourth number indicates the blade angle.
Four unit formula
This is used to describe the instruments which have their cutting
edges at an angle other than right angle to the long axis of the
blade.

Instrument shank and
blade design (with
primary cutting
edge positioned close
to handle axis to
produce balance).
The complete
instrument formula
(four numbers) is
expressed
as the
(1) blade width in 0.1-
mm increments,
(2) cutting edge angle
in centigrades,
(3) blade length in
millimeters, and
(4) blade angle in
centigrades.
Instrument Formulas

Cutting Instrument Bevels.
Single bevel
Bibeveled

Distal bevel: When the bevel is directed away from the shaft.
Mesial or reverse bevel: when the bevel is directed towards the
shaft.
Distal Bevel Mesial or Reverse
Bevel

Circumferentially –
beveled instruments:
Double- planed instruments where the blade is
beveled at all peripheries e.g. spoon
excavators.
Movements: Right- left & Mesial- distal instruments.
Vertical
Push
Pull
Right or left

Mirrors:
1) On the basis of
size
No. 2 – 5/8”
No.4 – 7/8”
No.5 – 15/16”
Plane mirrors
Concave mirrors
2) On the basis of mirrors
3) On the basis of
reflecting surface
Front surface reflecting
Rare surface reflecting

4) On the basis of material
Plastic
Metal
5) On the basis of joint
Cone- socket
One piece
6) On the basis of no of surfaces
One sided
Two-sided

8) Micro mirrors
9) On the basis of shaft design
Bendable shaft
Non – bendable shaft
7) Fogging mirrors & Anti – fogging mirrors

Probes: Various types of probes are available .
These can be straight ,curved or graduated(for periodontal
use).
Straight
probe
Curved
probe
Explorer Graduated
probe

Probes the potential lesion
Straight explorer
Interproximal explorer #17
Arch explorer #23
Right-angled explorer

Ordinary Hatchets:
 An ordinary hatchet excavator has the cutting edge of the blade
directed in the same plane as that of the long axis of the handle and is
bibeveled.
 Available in right and left pair.
 Indented ring on shank of right sided .
Application: On anterior teeth for preparing retentive areas and
sharpening internal line angles.
Particularly in preparations for direct gold
restorations.

Bibeveled ordinary
hatchet (3-2-28)
Ordinary Hatchets:

Hoes:
 The hoe has the primary cutting edge of the blade perpendicular to
the axis of the handle.
 Mesially or distally beveled.
 Used with pull motion.
Application: These instruments are used for cutting mesial and
distal walls of molars and premolars.
Remove harder variety of caries as well as to give
form to the internal part of the cavity.

Angle Formers
 It may be described as a combination of a chisel and gingival
margin
trimmer.
 It is available in pairs (right and left).
 Beveled on sides forming three cutting edges.
Sharpening line angles and creating retentive features
in dentin for gold restorations.
It also may be used in placing a bevel on enamel
margins.
Application:

Spoons:
The blades are slightly curved and the cutting edges may be circular
or
claw-like.
The circular edge is known as a discoid, whereas the clawlike blade
is
termed a cleoid.
Spoon excavators are used for removing caries and
carving amalgam or direct wax patterns.
Application:

Triple-angle discoid
spoon
Spoon
Cleoid blade
Spoons

Chisels
The straight chisel has a straight shank and blade, with the bevel on
only one side. Its primary edge is perpendicular to the axis of the
handle. It is similar in design to a Carpenter's chisel.
The shank and blade of the chisel also may be slightly curved
(Wedelstaedt design).
Application: Cleaving undermined enamel & shaping walls.

Straight (12-7-0)
Carpenter's chisel
Wedelstaedt
(11'/2-15-3)

Enamel Hatchets
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
preparation where it is not possible to use a
chisel.
Application:

The gingival margin trimmer is designed to produce a proper bevel
on
gingival enamel margins of proximoocclusal preparations.
It is similar in design to the enamel hatchet, except the blade is
curved
and the primary cutting edge is at an angle (other than
perpendicular)
to the axis of the blade.
Available in a right and left pair is either a mesial pair or a distal pair.
Gingival margin trimmer

The 100 and 75 pairs are for inlay/onlay preparations with steep
gingival bevels. The 90 and 85 pairs are for amalgam preparations
with gingival enamel bevels that decline gingivally only slightly.
End view of gingival
margin trimmers, paired
(a) Right cutting
(b) Left cutting.
Gingival margin trimmer

(a) Gingival marginal
trimmer being
used in a proximal
box of a class II
preparation with a
horizontal (right or
left) stroke to
plane a gingival
wall and margin;
(b) Gingival marginal
trimmer being
used with a
vertical, or
chopping stroke to
plane a facial or
lingual wall and
margin

Carvers
HOLLENBACK CARVER
INTER PROXIMAL CARVER
Carve the inter proximal
areas
WARDS CARVER
Carving amalgam
and wax patterns
Contour &carve occlusal &
interproximal anatomy in
amalgam restorations

Discoid-Cleoid
Used principally for carving occlusal anatomy in unset
amalgam restorations.
May also be used to trim or burnish inlay-0nlay margins.
This instrument is different form the discoid and cleoid
excavator as the working ends of this instrument are larger.

Hollenback
amalgam
condenser
Black
amalgam
condenser
Condensers
Round
Rectangular
Parallelogram
Diamond
Triangular

Burnishers
Football Burnisher
Smoothening Amalgam
after condensing, to contour
matrix band, to burnish
amalgam
Acorn Burnisher
used to create
occlusal anatomy

Ball Burnisher
smooth amalgam
after condensing
Beavertail Burnisher
burnish the lingual,
facial amalgam walls of
a restoration
T-Ball Burnisher
initiate carving and
occlusal anatomy

Knives
 Known as finishing knives, amalgam knives, or gold knives, are
designed with a thin, knifelike blade that is made in various sizes
and shapes .
 Knives are used for trimming excess restorative material on the
gingival, facial, or lingual margins of a proximal restoration or
trimming and contouring the surface of a Class V restoration.
Sharp secondary edges on the heel aspect of the blade are very
useful
in a scrape-pull mode.

Finishing knife
Alternative
finishing knife
design
emphasizing
secondary cutting
edges
Knives

Amalgam knives Gold knife
Knives

Wilson’s Knife:
Interproximal use
Stien’s Knife: Trapezoidal nib
Used mainly for direct gold
restorations for contouring and
margination
Knives

Files
Files also can be used to trim excess restorative material.
They are particularly useful at gingival margins.
Files are manufactured in various shapes and angles to allow
access
to restorations.
 If the serations are directed away from the handle, it is a push file
and if the serations are directed towards the handle, it is a pull

Hand instrument techniques
There are four grasps used with hand instruments:
(1) Modified pen
(2) Inverted pen
(3) Palm-and-thumb
(4) Modified palm-and-thumb
The pen grasp is not an acceptable instrument grasp.

Modified Pen Grasp The grasp that permits the
greatest delicacy of touch is the
modified pen grasp.
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 fingers) is placed on
a nearby tooth surface of the
same arch as a rest.

Inverted Pen Grasp The finger positions of the inverted
pen grasp are the same as for the
modified pen grasp.
The hand is rotated so that the palm
faces more toward the operator .
This grasp is used mostly for tooth
preparations utilizing the lingual
approach on anterior teeth.

Palm-and-Thumb Grasp The palm-and-thumb grasp is similar
to that used for holding a knife while
pealing the skin from an apple.
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 rest is provided by supporting the tip
of the thumb on a nearby tooth of the
same arch or on a firm, stable structure.

Modified Palm-
and-Thumb
Grasp
Used when it is feasible to rest the thumb on
the
tooth being prepared or the adjacent tooth .
The handle of the instrument is held by all four
fingers whose pads press the handle against
the
distal area of the palm, as well as the pad and
first joint of the thumb.
 Grasping the handle under the first joint of the
ring and little fingers acts as a stabilizer.

Modified palm-and-thumb
grasp:

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.
Conventional: immediately adjacent to the working surface.
Cross-arch: other side of the same arch.
Opposite arch: rest on opposite arch.
Finger on finger: on index finger or thumb of non operating arm.

Guards are the finger positions of the hand opposite
the
one using the instrument, to steady the parts being
operated on and to protect them from injury in case
the
instrument accidentally slips off the working surface.
These should be used particularly when adjacent teeth
are not available as rests or when rests must be
obtained on soft tissue or on the opposite arch.
Guards

SHARPENING HAND INSTRUMENTS
 Instruments with dull cutting edges cause more pain,
prolong operating time, are less controllable, and reduce
quality and precision in tooth preparation and also make
control difficult.
 Sharpening is done by reducing the bulk of the metal at
the cutting edge, following the original configuration of the
bevel.

The most frequently used sharpening equipment consists
of a block or stick of abrasive material called a "stone."
Stationary stones are often called oilstones because of the
common practice of applying a coating of oil to them as an
aid to the sharpening process.
Four types of materials are in common use for sharpening
stones:
Arkansas stone
Silicon carbide
Aluminum oxide
Diamond
Stationary stone technique

Arkansas stone
 Naturally occurring mineral containing microcrystalline quartz.
Hard enough to sharpen steel, but not carbide instruments.
The hard stone, although it may cut slower, is preferred because
the
soft stone scratches and grooves easily, rendering it useless.

Silicon carbide
Widely used as an industrial
abrasive.
It is the most commonly used material for grinding
wheels and "sandpapers," as well as for sharpening
stones.
It is hard enough to cut steel effectively, but
not hard enough to sharpen carbide
instruments.
SiC stones are available in many shapes in
coarse and medium grits, but not in fine grits.

Aluminum oxide
Increasingly used to manufacture sharpening stones.
Coarse and medium grit stones are brownish in color and fine grit
stones are usually white.
Have superior properties, and are less porous so that they require
less
lubrication during use.

Diamond
Hardest and most effective for cutting and shaping hard materials.
Only material routinely capable of sharpening
both carbide and steel instruments
Diamond hones are small blocks of metal with
fine diamond particles impregnated in the
surface.
Most hones include grooved and rounded
surfaces, as well as a straight surface, and are
adaptable for sharpening instruments with curved
blades.

While using mechanical sharpener the blade should be placed against
the steady rest and the proper angle of the cutting edge to the blade
should be established before activating the motor.
Mechanical technique
Rx Honing Machine

Handpiece Sharpening Stones
Mounted SiC and aluminum oxide stones for use with straight and
angle handpieces are available in various sizes and shapes .
For straight handpieces particularly the cylindrical instruments
and smaller points for the angle handpieces.

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.
Only very light pressure is exerted in testing for sharpness.

Basic principles for using sharpening equipment:
1. Sharpen instruments only after they have been cleaned and
sterilized.
2. Establish the proper bevel angle (usually 45 degrees) and the
desired angle of the cutting edge to the blade before placing the
instrument against the stone, and maintain these angles while
sharpening.
3. Use a 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 may be created.
7. After sharpening, re-sterilize the instrument along with other
items on the instrument tray setup.
8. Keep the sharpening stones clean and free of metal cuttings.

POWERED CUTTING EQUIPMENT
The term ‘rotary instruments’ in dentistry refers to a group of
instruments that turn on an axis to perform a work such as cutting,
abrading, burnishing, finishing or polishing tooth tissues or a
restoration.
Pierre Faucard in his book “The Chirurgien Dentiste” in 1728 described
the first dental rotary instrument of modern times .
It was known as the “Bow drill ”could be rotated at 300 rpm and was
later on modified into the “Scranton’s drill” which could cut by rotating
in either direction.
A handpiece is a device for holding rotating instruments, transmitting
power to them, and for positioning them intraorally.

Early straight hand drill for direct access preparations . Back end of bur
shank fits into a finger ring while the front end is rotated with thumb and
forefinger

Early angle hand drill for indirect access preparations . The bur
is activated by squeezing the spring-loaded handle.

Dental handpieces are classified according to the driving
mechanism:
1. Gear-Driven Handpiece :
Rotary power is transferred from the straight
handpiece by a shaft and gears inside the angle
section.
Conventional handpieces are designed to operate at
speeds under 5000rpm.
By the use of several speed increasing transmission
it is possible to obtain speeds of 10000rpm with a
gear driven angle that has an automatic lubricating
system.

2.Water-Driven Handpiece
In 1953, a hydraulic driven turbine handpiece was reported to operate
satisfactorily at 60,000rpm.
Improved units have straight and angle handpiece which will operate
at speed upto 100,000rpm.
Water is conveyed to and from the handpiece by a co-axial type
tubing(tube inside the tube). The small inner tube carries water under
high pressure to rotate a turbine in the handpiece head and the larger
outer tube returns the water to the reservoir.

Turbo-Jet portable unit .

3. Belt-Driven Handpiece
A Belt-Driven Handpiece called the Page-Chayes became available
in 1953 and was the first angle handpiece to operate successfully at
speeds above 100,000rpm.
The rotary cutting instrument has a 1/6inch shank held in the
handpiece by friction grip.
Improved models of the belt-driven designs are the Page-Chayes
909 and the Twin 909. The Twin 909 is a complete unit having two
engines and a foot control.

Page-Chayes handpiece.
Typical equipment when
an electric motor is used
as the source of power:
foot control with rheostat

4. Air-Driven Handpiece
In the last part of 1956, the first clinically successful air-driven turbine
handpiece became available with free running speeds of
approximately 300,000rpm.
A small compact unit consists of a handpiece, control box, foot
control and various connector hoses.
The rotary instrument’s 1/6 inch shank is held by friction grip.

The Borden Airotor
handpiece was the
first clinically
successful air-
turbine handpiece.
Air-turbine straight
handpiece.

Contemporary contra-angle air-turbine handpiece connected
to the air-water supply line.

Fiberoptic
lighting
4-port
spray
View of the
handpiece
showing four
spray ports for
cooling and
fiberoptic
illumination.

Electric handpieces that compete effectively with air-turbine
designs

Comparison of cutting efficiencies between electric and air-
turbine dental handpieces.
J Prosthet Dent 2010 Feb;103(2).
Choi et al
Abstract
PURPOSE:
The purpose of this study was to compare the cutting efficiency of an
electric handpiece and an air-turbine handpiece, using various
materials commonly used in dentistry.
CONCLUSIONS:
The electric handpiece is more efficient at cutting various materials
used in dentistry, especially machinable glass ceramic, silver
amalgam, and high noble alloy, than the air-turbine handpiece.

Low speed
 Excavating caries with round burs,
 Refining cavity preparations,
 Using sandpaper disks,
 Marinating gold restoration and
 Polishing procedures.

High speed
Cavity preparation but not as effectively as ultra speed a large
section
of specially shaped instrument is required.
 Many finishing procedures such as placement of retentive grooves
are
best performed at high speed.
This speed range is preferred where vision is poor or a more
positive

Ultra speed
At speed above 100000rpm smaller , more versatile cutting
instruments are used.
Bulk reduction, obtaining outline form and removing metal
restorations.
Some cavity preparation may be completed entirely at ultra
speeds, but usually the operator should use lower speeds for
finishing touches.

LASER EQUIPMENT
Lasers are devices that produce beams of coherent and very high
intensity light.
The word laser is an acronym for "light amplification by stimulated
emission of radiation."
A crystal or gas is excited to emit light photons of a characteristic
wavelength that are amplified and filtered to make a coherent light
beam.
At the present time, CO,, Nd:YAG, and Er:YAG lasers are the most
promising.

Generally, dental lasers produce photo - thermal effects, with soft or
hard tissue being ablated by the action.
Lasers may be operated as continuous wave (CW) and pulsed (p)
lasers.
At low energy densities for short times enamel melts and
recrystallizes.
High energy densities and/or longer times produce vaporization with
drilling or cutting of the surface.
For dentin, the same effects occur at lower energy densities. Such
surfaces can be produced to seal the dentin and assist bonding of
restorative materials.

Nd:YAG laser unit Laser probe and beam
emanating from probe tip

Air abrasion unit
Its an alternative method of cutting enamel and dentin periodically
assessed in mid-1950s .
It has certain clinical problems-
The abrasive dust interfered with visibility of the site
Lack of tactile sensation
Abrasive dust inhalation

At present air abrasive equipment
is being used for-
Stain removal
Debriding pits and fissures
Micro mechanical
roughening
of surfaces to be bonded.

Common features of rotary instruments:
In spite of a great variation that is seen among rotary cutting
instruments, they have certain design features in common which are
the :
1. Shank,
2. Neck and
3. Head.

SHANK
Fits into the handpiece.
Accepts the rotary movement from the handpiece .
Controls the alignment and concentricity of the instrument.
1. Straight handpiece shank
2. Latch type handpiece shank
3. Friction type handpiece shank
( eg. Air motor handpiece straight)
( eg. Micromotor contrangle handpiece)
(eg. Airotor handpiece)
The three commonly seen instrument shanks are:

Characteristics and typical diameters (in inches) of three
common instrument shank designs.

NECK
Neck is intermediate part of the instrument that connects the
shank to the head.
It tapers from the shank diameter to the head and its size should be
so adjusted that it allows greatest possible visibility and
manipulation.
Its main function is to transmit rotational and translational forces to
the head.

Head
It is the working part of the instrument whose cutting edges perform
the desired shaping of the tooth structure.
The heads of instrument show great variations in design and
construction. Based upon their head characteristics, the
instruments can be bladed or abrasive.
Head can vary in their material of construction, size and shape.

Dental burs:
The term bur is applied to all rotary cutting instruments that have
bladed cutting heads.
It is used for various purposes such as finishing restorations,
surgical removal of bone and tooth preparation.
The earliest burs were hand-made. Machine-made burs were
introduced in 1891, which were made of steel. Later on the carbide
burs(1947) replaced the steel burs.

Composition of Dental burs:
Classified into two types:
Stainless steel burs
Tungsten carbide burs
Stainless steel burs :
Cut from steel blank parallel to long axis of the bur
Perform well only at low speeds and dull rapidly at high speeds or
when cutting enamel and then cutting effectiveness thereby
heat production and vibration.
Vickers hardness :800

Tungsten carbide burs : Vickers hardness : 1650-1700
Introduced in 1947
Perform better than steel burs at all speeds
and their superiority is greatest at high speeds.
Carbide is also more brittle and more susceptible to fracture when
subjected to sudden blow.
Harder than steel and therefore does not dull rapidly

Modern burs: combination of the above two
Carbide head Steel shank
Major drawback is that steel necks bends causing increased
vibration and over cutting .
This combines the advantages of the two, in one.

Classification of burs:
1. According to their mode of attachment to the handpiece, they
can be classified as a latch type or friction grip type.
2. According to their composition, they can be classifies as
stainless steel burs, tungsten carbide burs or a combination.
3. According to their motion, they can be classified as right or left
bur. A right bur is one which cuts when it revolves clockwise and
left bur is the one which cuts when revolving anticlockwise.

4. According to the length of their head, they can be classified as
long, short or regular.
5. According to their use, they can be classified as cutting burs
or those used to finish and polish restoration.
6. According to their shapes, they can be classified as round,
inverted cone, pear shaped, wheel shaped, tapering fissure,
straight fissure, end cutting, etc.

Bur shapes:
Round bur : a bur with a spherical head is a round bur. It
is used for initial tooth preparation, removal of caries,
extension of the preparation and for the placement of
retentive grooves.
Numbered from- ¼ , ½ , 1, 2, to 10.
Inverted cone bur: a bur with rapidly tapering cone
head whose small end of the cone is directed towards the
bur shank. It is used for establishing wall angulations and
providing undercuts in cavity preparations.
Numbered- 33 ¼ ,33 ½ ,34 , 35 to 39.

Pear-shaped bur: It is used in class I cavity
preparations for gold foils. A long length pear bur is
advocated for amalgam cavity.
Numbered – 229-333.
Straight fissure bur: a bur with the head shape of
an elongated cylinder. It is used for amalgam cavity
preparations. Numbered - 55–59.

Tapering fissure bur: a bur with tapering cone head
with the small end of the cone directed away from the bur
shank. It is used for inlay and crown preparation.
Numbered – 168, 169 to 172.
End cutting bur: This bur is cylindrical in shape,
with just the end carrying the blades. It is used for
carrying the preparation apically without axial reduction.
Numbered -900-904

Twist drills
Twist drills, with cutting edges on their tips, are used for boring
small-diameter holes in tooth structure.
They are the least frequently used of the rotary instruments.
Wheel burs:
Used for placing grooves and for gross removal of tooth structure.
Numbered -14 & 15.

Brushed handpieces have 2 carbon composite brushes that bring
“DC” electricity from the control box to the armature, which is the
heart of the handpiece.
Brushless handpieces utilize sophisticated control electronics to
generate strong electro-magnetic pulses to rotate a rotor.
“Brushed” and “Brushless” Handpieces

The original numbering system for the burs was developed by SS
white dental manufacturing company in 1891.
Bur sizes
In this system the burs were grouped by 9 shapes and 11 sizes.
The ½ and ¼ designations were added later with the introduction
of smaller sized instruments .
Later for non-crosscut size no.500 was added and prefix 900 was
added to indicate end cutting head design.

There was a general uniformity in this system for about 60
years.
1891-1954

Changes gradually occurred over time without actually disrupting the
system. Certain sizes vanished and the new ones were introduced in
1955 and are still being used, though rarely .

Speed Ranges
Low/conventional speed : below 6000rpm
High/intermediate speed : 6000-100000rpm
Ultra/super speeds : Above 100000rpm
The rotational speed of an instrument is
measured in revolutions per minute (rpm).

Speed Ranges
Low or slow speeds (below 12,000 rpm),
Medium or intermediate speeds (12,000 to 200,000
rpm),
High or ultrahigh speeds (above 200,000 rpm).
Sturdevant’s

Speed Ranges
Ultra Low speed (300-3000 rpm),
Low speeds (3000-6000 rpm),
Medium high speed(20,000-45,000 rpm),
High speed(45,000-100,000 rpm)
Ultra high speed(100,000 and more).
Marzouk

Modifications in the bur design:
1. Reduced use of crosscuts
2. Extended heads on fissure burs
3. Roundening of the sharp tip angle

Crosscuts are notches present on the blade of the
instrument to obtain adequate cutting effectiveness at low
speeds.
These are needed on fissure burs to obtain adequate
cutting effectiveness at low speeds.
Reduced use of crosscuts

Carbide fissure burs with extended head lengths two to three times
those of the normal tapered fissure burs of similar diameter have been
introduced.
Extended head lengths

Roundening of the corners
Early contributions to the roundening of the sharp tip corners were
made by Markley & Sockwell.
Because teeth are relatively brittle, the sharp angles produced by
conventional burs can result in high stress concentrations and increase
the tendency of the tooth to fracture.
Bur heads with rounded corners result in lower stresses in restored
teeth, enhance the strength of the tooth by preserving vital dentin.

Design of a dental bur:
The actual cutting action of a bur takes place at the edge of the
blade present on the bur head.
The depressed area in the head are called the flute or the chip
spaces.
The blades on the cutting bur are usually 6, 8 or 10 and those on
the finishing bur are usually 12 to 40.
The projection on the bur head is known as the blade or the
tooth.

Blade has two surfaces :
Blade face / rake face
Blade back / flank / clearance face
Rake face the surface of the bur blade on the leading edge and
clearance face is the surface of the bur on the trailing end.
Three important angles:
Rake angle,
 Edge angle, and
 Clearance angle

Rake angle is the angle between the rake face and the radial
line (line connecting the center of the bur and the blade).
Positive- rake face trails the radial line
Negative - rake face is ahead of the radial line
(cutting hard, brittle materials)
Zero- rake face and the radial line coincide

A. Positive B. Zero C. Negative

Clearance angle: The angle between the clearance face and
the
work (e.g. tooth).
When the clearance face is curved, then it is known as the radial
clearance.
Blade angle/tooth angle: Is the angle between the rake face
and the clearance face.

Factors affecting the cutting effectiveness and efficiency of bur
1. Rake angle, clearance angle and blade angle
Positive rake angle also has two major drawbacks.
(1)It reduces the bulk of the bur blade, as a result the bur tooth can
easily curve, flatten or even fracture during use.
(2) A positive rake angle produces a chip that is larger and tends to
clog the flute space whereas a negative rake angle produces a
chip that is smaller and moves away from the blade.

The clearance angle eliminates friction between the cutting edge and
the work and prevents the bur from digging excessively into the tooth
structure.
An increase in clearance angle, however, reduces the blade angle,
thereby decreasing the bulk of the bur blade.

2. Neck diameter
Too small neck unable to resist lateral forces.
Large neck interface with the visibility and restrict access to
coolants.
As the head of the bur increases in length and diameter, the movement
exerted by the lateral forces also increase and the neck needs to be
larger.

3. Spiral angle and crosscuts
Burs with small spiral angles are preferred at high speeds as
small angles produce more efficient cutting.
The greater the length of a blade, greater is the force required to
initiate cutting.

4. Concentricity and run-out
Concentricity is a direct measurement of the symmetry of the bur head.
It measures how closely a single circle can be passed through the tips
of all the blades.
Run-out, on the other hand, is a dynamic measurement of the
maximum displacement of the bur head from its axis of rotation while
the bur runs. The average clinically acceptable run-out is 0.023 mm.
Run-out tends to increase the vibrations of the bur and also removes
excessive amount of tooth structure.

6. Influence of load
Load is the force exerted by the operator on the tool head and not
the pressure. The cutting effectiveness of the bur is reduced when
the load applied is below the minimum required and also is
reduced when the load applied is above the maximum required.
5. Heat treatment
Heat treatment is used to harden a bur made of soft steel not for
carbide burs.

Polymer burs
The SS White (USA) introduced polymer bur (Smart Prep) which has
a
unique flute design, constructed from a medical grade polyether-
ketone-ketone (PEKK) with particular hardness and wear resistance.
Removes only soft caries-infected dentine, leaving the caries
&affected
dentin intact.
The bur usually works in slow speed (500-800 rpm) and quickly dulls
when encounters the highly calcified caries affected dentin.

Comparison of dentin caries excavation with polymer
and conventional tungsten carbide burs.
Quintessence Int 2007;38(7).Meller C et al
Abstract
OBJECTIVE:
To compare the effectiveness of polymer burs (SmartPrep, SS
White) and conventional carbide burs in removing dentin caries.
CONCLUSION:
Polymer burs and tungsten carbide burs were similarly effective
for caries removal.

Diamond abrasive instruments
Introduced in United States in 1942
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 substance held in a matrix of softer material(binder).
Cutting occurs at numerous points where individual hard particles
protrude from the matrix, rather than along a continuous blade edge.

Their preference over tungsten carbide burs is based on their greater
resistance to abrasion, lower heat generation and longer life.
Diamond instruments consists of three parts :
 Metal blank,
Powdered diamond abrasive and
Bonding material.
Diamond abrasive instruments

Classification of diamond abrasive
According to the shape of the head.
According to the diameter of the head.
According to the size of the head.
According to the size of the particles.

Head, shapes & sizes
Diamond instruments are available in a wide variety of shapes
and in sizes that correspond to all except the smallest-diameter
burs.
More than 200 shapes and sizes of diamonds are currently
marketed.
The smallest diamond instruments cannot be as small in
diameter as the smallest burs because of their design.

Diamond particle factors
The clinical performance of diamond abrasive instruments
depends on the-
Size
Spacing
Uniformity
Exposure
Bonding of the diamond particles.

Classification of diamond abrasive
Coarse grit diamond burs(125-150 µ particle
size)
Medium grit diamond burs(88-125 µ particle
size)
Fine grit diamond burs(60-74 µ particle size)
Very fine grit diamond burs(38-44 µ particle size)

Colour coding of diamond abrasive
Super coarse grit – Black
Coarse grit- Green
Medium grit - White
Fine grit- Red
Super fine grit - Yellow

Cause of failure
Almost the only cause of failure of diamond instruments is
loss of the diamonds from critical areas.
This loss results from the use of excess pressure in an
attempt to increase the cutting rate at inadequate speeds.

Disposable diamond abrasives
The “single patient use” or the disposable diamond bur is a recent
introduction that minimizes the risk of cross contamination of the blood
borne pathogens at an equal cost.
Some of the disposable diamond burs are marketed as Cobra, Monosteryl,
Neo, Patriot, SS White and Spring.
Siegel et al (1997)17 in their study measured the cutting experiences of 15
types of conventional and disposable round and tapered diamond burs. The
results showed comparable cutting efficiencies between the two; and hence
the use of disposable burs could reduce the risk of clinical cross-infection.

Other abrasive instruments
May be natural or synthetic including silicon carbide, aluminium
oxide, garnet, quartz, pumice, cuttle bone etc.
Primarily used to shaping, finishing, and polishing restorations,
both in the clinic and in the laboratory.

These instruments have heads that are manufactured by molding or
pressing a uniform mixture of abrasive and matrix around the roughened
end of the shank or cementing a premolded head to the shank.
Molded instruments
These type of instruments are mainly used in denture finishing.
Other than diamonds and carbides, there are two groups of instruments,
divided as-
Molded instruments
Coated instruments.

Coated abrasives
Are mostly disks that have a thin layer of abrasive cemented to a
flexible backing.
This construction allows the instruments to conform to the surface
contour of a tooth or restoration.
These type of abrasives may be used in the finishing/ smoothing
procedures of certain enamel walls (and margins) of tooth preparations
for indirect restorations, but most often in finishing procedures for
restorations.

Cutting mechanisms
For cutting, it is necessary to apply sufficient pressure to
make the cutting edge of a blade or abrasive particle dig into
the surface.
The cutting mechanism can be discussed as follows:
Cutting evaluation.
Bladed cutting.
Abrasive cutting

Evaluation of cutting
Cutting can be measured in terms of effectiveness and
efficiency.
Cutting effectiveness is the rate of tooth structure removal
(mm/min or mg/sec). Effectiveness does not consider
potential side effects such as heat or noise.
Cutting efficiency is the percentage of energy actually
producing cutting. Cutting efficiency is reduced when energy
is wasted as heat or noise.

Bladed cutting
Tooth structure, similarly to other materials, undergoes brittle and
ductile fracture.
Brittle fracture-is associated with crack production, usually by tensile
loading.
Ductile fracture-involves plastic deformation of material, usually
proceeding by shear.
Low-speed cutting tends to proceed by plastic deformation before tooth
structure fracture.
High-speed cutting, especially of enamel, proceeds by brittle fracture.

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.
The high hardness and modulus of elasticity are essential to
concentrate the applied force on a small enough area to exceed
the shear strength of the material being cut.

Sheared segments accumulate in a
distorted layer that slides up along
the rake face of the blade until it
brakes or until the blade
disengages from the surface as it
rotates.
These chips accumulate in the
clearance space between blades
until washed out or thrown out by
centrifugal force.
Schematic representation of
bur blade (end view) cutting a
ductile material by shearing
mechanism.

Abrasive cutting
As diamond prepares a rougher tooth surface, they may be
preferred for use in tooth prep. for bonded restoration, as
roughened prep. surface increases the surface area and the
bonding potential.
When diamond instruments are used to cut ductile materials, some
material will be removed as chips, but much material will flow
laterally around the cutting point and be left as a ridge of deformed
material on the surface.

Schematic representation of an abrasive particle cutting ductile material.
A, Lateral view. B, Cross-sectional view.
Material is displaced laterally by passage of an abrasive particle, work
hardened, and subsequently removed by other particles.

Schematic representation of abrasive particle cutting brittle material.
A, Lateral view.B, Cross-sectional view.
Subsurface cracks caused by the passage of abrasive particles
intersect,
undermining small pieces of material, which are then easily removed
by following abrasive particles.

Diamonds are more effective than burs for both intracoronal and
extracoronal tooth preparations, beveling enamel margins on
tooth preparations, and enameloplasty.

Hazards/pollution caused by cutting instruments
Almost everything done in a dental office involves some risk
to the patient, dentist, or auxiliaries.
For eg. pulpal dangers, soft tissue dangers, eye, ear &
inhalational dangers etc.

Pulpal precautions
The use of cutting instruments can harm the pulp by
exposure to mechanical vibrations, heat generation,
desiccation and loss of dentinal tubule fluid, or transaction
of odontoblastic processes.

Soft tissue precautions
The lips, tongue and cheeks of the patient are the most frequent
areas of soft tissue injuries.
The handpiece should never be operated unless there is good
access and vision to the cutting site.
A rubber dam is helpful in isolating the operative site.
The dentist and the assistant always must be aware of the
patient’s response during cutting.

Eyes precautions
The operator, assistant and patient should wear glasses with side
shields to prevent eye damage from air-borne particles during
operative procedures using rotary instruments.

Ears precautions
Normal ears require that the intensity of sound reach a certain
minimal level before the ear can detect it. This is known as the
auditory threshold.
Turbine handpieces with ball bearings, free running at 30lb air
pressure, may have noise levels of 70 to 94db at high frequencies.
Noise levels greater than 75 db in freq. ranges of 1000 to 8000 cps
may cause hearing damage.

Inhalation precautions
Aerosols and vapors are created by cutting tooth structure
and restorative materials, and these are health hazards to
all present.
Aerosols-are fine dispersions in air or water, tooth debris,
microorganisms, or restorative materials

References
Sturdevant, Roberson, Heymann. Sturdevant’s Art and Science of
Operative Dentistry. Ed5th. Elsiever pub.
V Gopikrishna .Preclinical manual of Conservative dentistry. Ed
1st. Elsiever pub
Sumei mai . Dental instrument packet . University of California,
San Diego Pre-Dental Society.
Operative Dentistry: Hand Instruments. 2007 Columbia University
Marzouk, Simonton,Gross. Operative Dentistry:mordern theory
and practice.

References
Fraunhofer , Smith, Marshall. The effect of multiple uses of disposable
diamond burs on restoration leakage. J Am Dent Assoc. 2005;136(1).
Meller , Welk , Zeligowski , Splieth. Comparison of dentin caries
excavation with polymer and conventional tungsten carbide burs.
Quintessence Int. 2007 ;38(7).
Choi , Driscoll ,Romberg . Comparison of cutting efficiencies between
electric and air-turbine dental handpieces. J Prosthet Dent. 2010;103(2).

INSTRUMENTS in operative dentistry.pptx

INSTRUMENTS in operative dentistry.pptx

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