Rotary cutting instruments in dentistry /certified fixed orthodontic courses by Indian dental academy

Seminar on
ROTARY CUTTING
INSTRUMENTS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


INDEX
1. Definitions
2. Introduction
3. Dental Hand pieces
4. Improved Cutting Instruments
5. An era of increased speeds and various associated techniques
6. Care and maintenance of Rotary equipment
7. Water air cooling
8. Dental cutting burs
(a) Composition and manufacture
(b) General design of dental burs
© Parts of a bur
(d) Classification
9. Diamond Abrasive Instruments
(a) Color coding
(b) Manufacturing
© Classification
(d) Diamond/bur dual instrumentation
10. Effects of high speed cutting
11. Advantages of high speed cutting
12. Disadvantages of high speed cutting
13. Abrasion and Polishing Agents
14. Review of literature
15. Summary
16. References

The term “Rotary” is applied to tooth cutting
instruments
That turn on axis to perform work, these are the
units actually responsible for the removal of
tooth structure, and may be one of two types:
Burs; which are cutting tools, and, Stones, which
are abrading tools.
SPEED: Speed is the rate of change of position
with time (MOSBY‟s Dictionary)
Speed is the magnitude of velocity without regard
to direction. (Stedman‟s Dictionary)

Classification of Speed
According to Sturdevant
Low Speed-Below 12,000 rpm.
Medium or Intermediate speed- 12,000 to 2lakh rpm.
High or ultra high speed- Above 2lakh rpm.
According to Charbenau
Conventional or low speed below 10,000 rpm.
1. Increased or high speed- 10,000 to 1, 50,000 rpm.
2. Ultra speed- Above 1, 50,000 rpm.
According to MARZOUK
Ultra low speed- 300 to 3000 rpm.
Low speed- 3,000 to 6,000 rpm.
Medium high speed- 20,000 to 45,000 rpm.
High speed- 45,000 to 1, 00,000 rpm.
Ultra high speed- Above 1, 00,000 rpm.
According to Clearence L. Sock well (DCNA-1971)
Low or conventional speed- Below 6,000 rpm.
High or intermediate speed- 6,000 to 1, 00,000 rpm.
Ultra or super speed- Above 1, 00,000 rpm.

Dental Bur- The term bur is applied to all rotary cutting
instruments that have bladed cutting heads. This includes
instruments intended for such purposes or finishing metal
restorations and surgical removal of bone as well as those
primarily intended for tooth preparation.
Introduction
Before considering the tooth preparation, Prosthodontist must
be aware of the instruments at his disposal so that the most
suitable one can be used.
Teeth are vital organs; therefore they must be treated with
consideration. The objectives of the treatment given to the
patient are to provide oral function, esthetics, health by
restoring teeth and the adjacent structures. Frequently, the
efforts of restorations may themselves transform a
comfortable tooth intowww.indiandentalacademy.com
one that is sensitive or pathologic

Dental Hand pieces
By the middle of 17th century hand instruments
were supplemented with steel burs of various
shapes and sizes. These were rotated with
thumb and finger because many areas of the
teeth could not be reached with this design; the
angle hand piece and short shanked bur were
developed. From this beginning, two basic
designs of hand pieces and cutting instruments,
straight and angle have become standard
equipment in the dental office.

FOOT ENGINE
The old spinning wheel and sewing machine probably inspired the
development of a dental foot engine as a source of power around
1871. Rotation of a cutting instrument was made possible by a long
belt running over a series of pulleys to the back of a straight hand
piece. When the angle hand piece was needed, it could be attached to
the shaft of the straight hand piece.
ELECTRIC ENGINE
One of the most significant advances in the early history of hand
piece adoption was the adoption of the electric motor as a power
source in 1874.It was incorporated into a dental unit in 1914. Hand
piece equipment and operating speeds and maximum of 5000
revolutions per minute remained virtually unchanged until 1946.
Based on use, there are 3 hand piece designs Straight
 Angle
 Prophylaxis
These standardized shapes have continued over the years.

Rotary power from an electric engine is
transferred to the straight hand piece by a belt
that runs over a series of pulleys and a three
piece extension cord arm. A variable rheostat
sits on the floor and is operated by the foot to
control the speed of the hand piece. Rotary
cutting instruments are inserted into a chucking
mechanism at the front of the hand piece. The
electric engine is seldom used as a source of
power in a modern dental operatory but is often
used in dental laboratories where low speed and
high torque are desirable.

IMPROVED CUTTING INSTRUMENTS
Progress in dental cutting procedures was delayed by a lack of
instruments that could effectively remove hard tooth structures. The
steel burs that were used at that time could not cut enamel effectively
even with the application of great force. Silicon carbide points,
sometimes called carborundum stones, were not hard enough and lost
their shape rapidly. Diamond cutting instruments were developed in
Germany around 1935, but with the outbreak of World War II and
the accompanying scarcity of labor and materials, very few of these
instruments were produced for the duration of the war. It was during
this period, when large numbers of men had to be treated in a limited
amount of time that the need of better and more effective cutting
instruments and procedures was dramatized.
In a 10 year period, which started in the latter part of 1946, cutting
techniques were revolutionized. Diamond instruments were produced
commercially and were joined a year later by tungsten carbide burs.
For the first time in dental history, instruments became available that
could effectively remove hard tooth structure.

INCREASED SPEEDS
It was immediately evident that diamond and carbide instruments
performed best at the highest speeds available and that increased
speeds were available for more effective cutting.
Obtaining speeds of 10,000 to 15,000 rpm was a relatively simple
matter. The small pulley on the motor drive shaft was replaced
with a larger one, while the pulley at the hand piece was reduced in
size. Motor resistors were disconnected so that armature could
receive the full line current and revolve at maximum speeds. In
1949, it was reported that speeds of 60,000 rpm and above were
more effective for cutting tooth structure and were also above the
human threshold of vibration perception.
Equipment manufactures continued to make improvements in
conventional rotary hand pieces, but heat, vibration and wear were
major problems, especially in the gear mechanism of angle hand
pieces. In the mean time two non-rotary industrial cutting
methods, air abrasive technique and ultrasonics were applied in
dentistry.

AIRBRASIVE TECHNIQUE
The air abrasive technique was made available to the
dental profession in 1951. The principal involves the
use of powered abrasive particles (aluminum oxide)
and kinetic energy (mass in motion). Hard tooth
structures can be reduced without perceptible
vibration, pressure or heat by a stream of abrasive
particles traveling at a high velocity. This technique
received widespread interest.
Advantages
 Patient acceptance was excellent.
 No significant pulp reaction was reported.

The air abrasive technique never became popular
with the dental profession.
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Disadvantages
Use was limited to areas of good vision because there was
no sense of touch b/n the hand-piece and the tooth to act
as a guide while cutting.
Precise angles and margins were difficult to obtain and the
operator had to return to hand or rotary instruments for
finishing procedures.
Surface of an ordinary mirror was rendered useless in a
short period by rebounding abrasive particles.
Spent dust was not effectively removed by a large noisy
suction apparatus.
Possibility of lung damage by inhalation of the abrasive
particles was investigated but not found to be a major health
hazard.

Ultrasonics
Another non-rotary (instrument) industrial cutting method known
as ultrasonics was adapted for dental use around 1952. Hard tooth
structure can be removed by vibrating a slurry of abrasive particles
(aluminum oxide) against the surface to be reduced with various
sizes and shapes of preformed instrument tips. Principle involves
the conversion of alternating current into high frequency
mechanical vibrations in a phenomenon of magnetostriction. The
movements of the working tip, back and forth approximately 29,
000 times per second with a thrust of 0.0016” can not be detected
by the operator or the patient.
Advantages
1. Precise smooth cuts of predetermined shapes and sizes can be
made without the annoyance factor
of heat, vibration, noise or pressure.
2. Patient acceptance was excellent.
3. Tactile control of the instrument is somewhat improved over the
air abrasive technique.

Disadvantages
 Use of preshaped working point is limiting because
anatomy and carious areas of
 individual teeth vary greatly.
 Interchanging the points was a relatively time
consuming process.
 Cutting rate was slow especially in a lateral direction.
 Visibility was obscured because of the accumulation
of slurry.
 Caries and resilient filing materials such as gold
could not be removed effectively.
 Maintenance problems resulted from complicated
mechanism of operation.

BELT DRIVEN HANDPIECES
A belt driven angle hand piece called the page chayres
became available in 1955. It was the first angle hand piece to
operate successfully at speeds of 1, 00, 000 rpm and was
attached to a conventional dental unit with an electric motor
as a source of power. It was a very popular angle hand piece
and several versions of this design were marketed
commercially.
Advantages

Free of maintenance problems.
Disadvantages
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Many moving parts.
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Objectionable high pitched noise during operation.

WATER TURBINE HANDPIECES

A major break through in the development of rotary equipment
for increased speeds came with the elimination of the gear and
the belt driven sections of the angle hand piece. In 1933 a
hydraulic driven turbine angle hand piece was reported to
operate satisfactorily at 60, 000 rpm and was marketed 2 years
later. The Turbo-Jet was designed as a compact mobile unit that
required no outside plumbing or air connections. Only a source
of electricity was needed to operate the unit.
Improved models had both straight and angle hand pieces
that could operate at speeds up to 1, 00,000 rpm.
ADVANTAGE
1. Rotary instruments had a threshold shank to ensure
concentricity when attached to shaft of the turbine.
DISADVANTAGE
1. Changing the instruments was time consuming and carbide burs
did not perform well with water turbine hand piece.

AIR TURBINE HAND PIECES

In the later part of 1956 the first clinically successful air driven turbine
hand pieces became available with free running speeds of approximately
3,00,000 rpm.
Early models were attached to a conventional dental unit and consisted
of a hand piece, control box, foot control, various connector hoses and a
source of compressed air. When the foot control was activated,
compressed air flowed to the control box and was carried by a flexible
hose to the back of the hand piece. From there the air was directed to
the head of the hand piece through a metal tube and was blown against
the blades of a small turbine to produce rotation. Some of the spent air
was expelled at the head of the hand piece, while the greater part was
exhausted at the back of the hand piece or returned to the control box.
Cutting instruments were inserted into the shaft of the turbine and held
by friction grip.
Although most air turbine angle hand pieces have free running speeds of
approximately 3, 00, 000 rpm, it should be noted that this speed drops to
approximately 1, 60, 000 rpm with a lateral work load of two ounces.

The reason for this is that air turbines have low torque and will stall at
lateral work loads of approximately 4 to 6 ounces. This is an excellent
safety feature, since excessive pressure can not be applied easily to the
cutting instrument.
The application of the turbine principle to the straight hand piece
eliminated the necessity of having an electric engine as part of a standard
dental unit. This greatly simplified the design and construction of
present day dental units. The design of the straight hand piece turbine
provided the desirable high torque for low speed operation.
Air bearings have been used instead of ball bearings to support the
turbine shaft in some air turbine angle hand pieces. By having the
turbine suspended in air and rotated by air, practically all friction is
eliminated and speeds may be increased to over 8, 00, 000rpm. It is not
worthy that hand pieces using this design operated only at full speed and
at this speed the dentist was handicapped by virtually no sense of touch.
Thus desirable control was reduced, and over cutting often resulted. The
hand piece was very quiet in operation. High costs, maintenance
problems and the lack of variable speed kept this design from becoming
widely used.
Air driven hand pieces have been and continue to be the most popular
type of hand piece equipment because of the over all simplicity of
design, ease of control, versatility and patient acceptance.

CARE AND MAINTENANCE OF
ROTARY EQUIPMENT
Rotary cutting or polishing instruments should never
be left in the hand piece between patients or over
night. Some of these instruments have steel shanks
that may corrode in the metal chucking system of the
hand piece. When cutting instruments become worn,
dull, bent or broken, they should be discarded. Such
instruments do not operate efficiently and cause added
trauma to the tissue.
Dental hand pieces are expensive and must receive
the utmost care to ensure peak performance, to
prolong their life and to reduce overhead costs.

WATER AIR COOLING:
With high speed instrumentation, the problem of over heating the
tooth during preparation is critical. Cutting dry at high speeds will
produce nearly three times as much dentinal burning as cutting with a
water spray, and thermal changes can result in pulpal inflammation or
necrosis.Brown et al calculated the temperature of dentin at a distance
of 0.5mm from a high speed bur cutting dry to be 245 degrees F. In
light of this, Zach‟s contention that a temperature rise of only 20
degrees F will lead to pulpal death in 60% of teeth is most serious
indeed. Even in non vital teeth, dry cutting at high speeds should be
avoided, since the thermal stresses will cause micro fractures in
enamel. This could contribute to marginal factor of the restoration at
some future time. The use of air alone as a coolant is harmful to the
pulp and is therefore not an acceptable substitute for a water air
spray. Prolonged dehydration of freshly cut dentin will increase pulpal
damage producing odontoblastic displacement. To minimize pulpal
trauma, a water spray should always be used when cutting a tooth
preparation at high speeds.

The use of water spray does not in itself guarantee that the pulp will be
protected from damage. A low quantity of water, poorly directed, will
result in a weak spray that can permit localized dentinal scorching. A
small orifice that produces a higher water velocity is more likely to
allow penetration of the air vortex around the instrument tip.
A water spray also increases the efficiency of high speed rotary
instruments by cutting the cutting edges washed clean of debris.
Eames et al. found that a greater flow of water coolant is required to
prevent clogging when diamonds are used under increased pressure.
Diamond stones used under high pressure (150 gm) became more
effective as the water flow rate increased from 3 to 21 ml/min. If
light pressure was used (50 gm), there was still an increase in
effectiveness, but it leveled off after the flow rate reached 7 ml/min.
The spray enhances visibility in many instances by flushing away
blood and debris. Even indirect vision can be utilized while cutting
wet, if the mirror is first coated with a film of detergent. This allows
the water to form a smooth transparent film on the surface of the
mirror with only a moderate decrease in visibility.

DENTAL CUTTING BURS
1. Composition and manufacture: Dental Burs can be
classified by their composition into two types:
(a). Steel burs: Steel burs are cut from blank steel stock by
means of a rotary cutter that cuts parallel to the long axis
of the bur. The bur is then hardened and tempered until
its Vicker‟s hardness number is approximately 800.
(b).Tungsten carbide burs: Tungsten carbide burs are best
for making precise preparation features and smooth
surfaces in enamel or dentin. A logical application of their
planning capability is the production of smooth finish
lines. Carbide burs can also be used to cut through metal,
while both carbide burs and diamonds can be used to cut
sound dentin.

The metal in the head of the carbide bur is formed by sintering, or pressure
molding, tungsten carbide powder and cobalt powder under heat and vacuum.
The tungsten carbide is cut into small cylinders and then attached to steel rods
by soldering or welding to form blanks. The tungsten carbide head is machined
with large diamond disks to create the specific head for the type of bur being
formed. The attachment of the carbide bur is quite secure, and loss of the
carbide portion of the bur is rare. Only when the process has been completed
is the shank of the instrument shortened, notched, or diminished in diameter to
make a straight hand piece, latch, or friction grip bur.
Most burs intended primarily for cutting are made with six and occasionally
eight blades. Those burs made for finishing usually have 12 blades, but they can
have 20, or even as many as 40.
Several carbide burs of specific shapes are included in the standard
armamentarium. These include at least 2 tapered fissured burs, long and
standard length, an end cutting bur and a friction grip no. 4 round bur. For
removal of deep caries a low speed hand piece no. 6 round bur is used so that
sound dentin can be distinguished from softer carious dentin by its greater
resistance to cutting.
Tapered fissure burs have a number of uses in preparing teeth for cast metal
and porcelain restorations. In addition to the placement of grooves, box forms,
and isthmuses, they are especially useful for planning vertical axial surfaces.
There are a number of tapered finishing burs whose greater length and
diameter make them suited better for this task, the commonly used sizes are
shown in the figure below: www.indiandentalacademy.com

2. General design of Dental Burs:
The dental bur is a small
milling (cutting)
instrument. A common
design is displayed in the
figure underneath:


Bur tooth:
This terminates in the cutting edge, or
blade. It has two surfaces, the tooth face,
which is the side of the tooth on the
leading edge; and the back or flank of the
tooth, which is the side of the tooth on
the trailing edge.


Rake angle: The rake angle is the angle that the face of the bur
tooth makes with the radial line from the centre of the bur
to the blade. This angle can be negative if the face is beyond
or leading the radial line (referring to the direction of
rotation). It can be 0 if the radial line and the tooth face
coincide with each other (radial rake angle). The angle can
also be positive if the radial line leads the face, so that the
rake angle is on the inside of the radial line. The more
positive the rake angle the more acute the edge of the blade,
and more effective the cutting action. A positive rake angle,
unfortunately, also has a weaker edge. Therefore, the blades
are usually made with either negative or neutral (radial) rake
angles, and wider bases. These are slightly less efficient for
cutting, but because of their greater bulk they are less likely
to chip.

Land: The plane surface
following the cutting edge.


immediately

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Clearance angle: The angle between the back of the
tooth and the work. If a land is present on the bur,
the clearance angle is divided into: primary clearance
which is the angle the land will make with work, and
secondary clearance, which is the angle between the
back of the bur tooth and work. When the back
surface of the tooth is curved, the clearance is called
radial clearance. There is an optimum clearance
angle for each diameter of bur, and the larger the
diameter, the smaller the clearance angle that is
required. The smaller the clearance angle, the
stronger the cutting blade. However, if the angle
becomes too small, the back of the blade may rub
against the cut surface, generating heat and
decreasing efficiency.

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Tooth angle: This is measured between the face and
back. If a land is present, it is measured between the
face and land.
Flute or chip space: The space between successive
teeth, which are the grooves between the blades the
amount of spiral, or helical angle, of the blades
affects the cutting characteristics of the bur. A
greater helical angle produces a smoother surface on
the preparation, and reduces the “chatter,” or
vibration of the bur on the tooth surface. This also
reduces chipping of the tungsten carbide during use
on a tooth, and it prevents debris from clogging the
flutes between the blades.
The number of teeth in dental cutting burs is usually
6-8.

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Every bur will have three
parts: The head –The
portion carrying the cutting
blades.
The shank-The portion
connecting the head to the
attachment part, and the
Shaft or the attachment
part- The portion which will
be engaged within the hand
piece.


CLASSIFICATION
1. According to their mode of attachment to the hand piece:
-Latch type
-Friction grip type
2. According to the hand piece they are designed for:
-Contrangle bur
-Straight hand piece bur
3. They can also be classified as right and left. The most common ones
are the right, which cut when they revolve clockwise.
4. According to the length of the head:
-Long
-Short
-Regular
5. According to the function:
-Cutting burs
-Finishing and polishing burs

DIAMOND ABRASIVE INSTRUMENTS
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The second major category of rotary dental cutting
instruments involve abrasives rather then blade cutting.
Abrasive instruments are generally grouped as diamond or
other instruments. Diamond instruments for dental use were
introduced in the United States in 1942.
These diamond instruments are nothing but small angular
particles of diamond held in a matrix of softer material. The
diamond employed is industrial diamonds either natural or
synthetic that have been crushed to powder and then carefully
graded for size and quality.
Diamond particle size is commonly categorized as coarse (125
to 150um) medium (88 to 125 um) fine (60 to 74um) and very
fine (38 to 44 um).

Color coding is done depending on the
particle size i.e.,
Coarse- Green (125 – 150 um )
 Medium-Blue (125 – 88 um )
 Fine- Red (60 – 74 um )
 Very fine- Yellow ( 38 – 44 um )
The particle size used by four major U.S.
dental firms is compared by both U.S. MeshStandard and equivalent metric size.
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Manufacturing of Diamond Abrasive
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Abrasive particles are held together by means of a “binder”
(base) of variable nature. A ceramic binder is used in many
cases particularly for binding diamond chips. Also, an
electroplating process providing a metallic binder may be
used. For soft grade stone, rubber or shellac may be used.
Sintered types are strongest because abrasive particles are
fused together.
The type of binder is intimately related to the life of the tool in
use with most abrasives, the binder is impregnated through
out with abrasive particles of certain grade so that as a particle
is wrenched from the binder during use; another will take its
place as binder wears. Eames et al. found that they cut tooth
structure two to three times as quickly as burs.

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They are deposited in one to three layers on the
surface of the instrument. The best diamond stones
have abrasive particles evenly spaced over the surface
of the instrument. There also should be intimate
contact between the chips and the binding material.
While there are many shapes and sizes of diamonds to
be used for special applications and to suit the taste of
every operator, there are a few diamond stones which
should be included in a basic set of instruments: the
round-end tapered, flat-end tapered, long-needle,
short-needle, and small round-edge wheel diamonds.
Two other diamonds also commonly used, the
torpedo and flame, are frequently paired with carbide
burs of matching shapes. Figures and dimensions for
these instruments are shown below:

According to their shapes and sizes
they can be classified as:
(a)Flat

ended tapered
diamond cylinder: It is
used for bulk axial and
occlusal reduction and
shoulder preparation on
PJC and PFM tooth
preparations. End cutting
burs are also used to
develop and lower
shoulder preparation.
They are kept
perpendicular to the plane
being reduced.

(b) Straight cylinder
diamond with a tapered
point: A suitable
instrument for chamfer
placement is a Tinker
diamond; a straight cylinder
with a tapered point. This
tapered point creates a
chamfer with greater
control then the round-end
tapered diamond. It is
usually indicated for
molars.

c)Twelve fluted
carbide bur: It is a
smooth cutting
instrument and gives
a highly finished
surface to a
preparation. The
greater the number of
blades on a bur, the
smoother the cut.

(d)Round-ended tapered
diamond cylinders: They
are available in various
sizes. They are used for
axial and occlusal reduction
and developing chamfer
margins. Less than half the
diameter of the tip is used
for chamfer margins.
Cutting to a depth greater
then one-half the diameter
of the tip produces a
shoulder.

(e)Round diamonds:
They facilitate
establishing depth
grooves before
reduction. They vary in
size and are measured to
determine the cut depth.
They are also used to
establish rest seats and
reduce lingual surfaces
of anterior teeth. They
are numbered from ¼,
½, 1, 2 to 10.


(f)Round

diamond
wheels (donut):
They are gross
reduction
instruments and
also used in
anterior teeth
lingual reductions.
They are numbered
as 14 and 15.

(g)Oblong
diamonds
(football):
Variously shaped
football diamonds
are available for
lingual reduction of
anterior teeth. They
are available in
sizes that uniformly
reduce the foosae.

(h)Thin

tapered
diamond cones
(needle): Thin tapered
cones are used for
proximal slices to isolate
teeth from adjacent
teeth. They tend to lose
their sharpness sooner
than coarse diamonds
and are replaced
frequently.

(i)Tapered

oblong
diamond (flame):
Small flame-shaped
diamonds are used in
bevel placement.
There are many multi
fluted flame-shaped
carbides that have
identical functions.


(j)Cross cut fissure
burs: They come in
varying sizes and are
numbered from
555,556 to 560, both
tapered and cylindrical.
The tapered burs are
used for groove
placement in three
quarter crowns, flutes,
and for seating grooves
in complete gold
crowns.


(k)Plain

fissure burs:
They cut smoothly
and come in a variety
of sizes, both tapered
and cylindrical. They
may also be used for
groove placement
and finishing of
preparations.


(l)Large carborundum

disc (laboratory):
Mounted stones, discs,
and wheels are all used
in finishing cast gold,
porcelains, acrylics, and
tooth structure. Large,
thin carborundum discs
quickly section a sprue
from a casting. Similar
diamond discs can be
used to shape bulk
porcelain.

(m)Heatless

stone
(laboratory):
Large heatless
stones will remove
the remnant of the
sprue attached to
the casting.


(n)

Mounted green and
white stones (low
speed): Various
mounted green and white
stones exist for straight
and contraangle hand
pieces. They are not for
high speeds. They can be
altered by grinding
against a coarse/heatless
stone. White stones have
a finer texture than green
stones and are preferable.

(o) Sand paper discs:
Sand paper discs of
various grits are
excellent in finishing
marginal areas of
castings while
maintaining
contours. They may
also be used in
finishing tooth
preparations.

(p) Small pin discs:
Small-pin sand paper
discs are fine for
accessible margins in
the mouth and
finishing axial walls in
inlay preparations.


(q)

Chamois wheels
(laboratory):
Chamois wheel are
used only with dental
rouge and give a
luster to the casting.


(r) Rubber burlew discs
(laboratory): Rubber
burlew discs used after
the fine sandpaper stage
of finishing provide a
smooth surface to the
casting. Smaller sulci
discs exist for smaller
ridge and groove areas
but are rarely used
intraorally.

(s)

Robinson brushes
(laboratory): Robinson
brushes (stiff, medium,
soft) are used with
pumice or tripoli. Slow
speed with pressure
produces greater cutting
potential; high speed
with light pressure
produces a high-lustre
finish.

(t)

End cutting burs: They are
cylindrical in shape with just the end
carrying blades. They are very efficient
in extending preparations apically
without axial reduction. They are
numbered from 900 to 904.


Diamond/bur dual instrumentation:
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Diamonds remove tooth structure more efficiently than do
burs, but they leave undesirably rough surfaces and irregular
cavosurface finish lines. Tungsten carbide burs produce
smooth finish lines and precise internal features, but they cut
more slowly. Therefore, to take advantage of the best features
of both types of instrument, diamonds should be used for the
bulk reduction and carbide burs for finishing the preparation
and placing internal features such as grooves, box forms,
isthmuses, etc.
The technique of choice in this situation utilizes diamonds and
carbide burs of matching size and configuration as described
by Lustig. These instruments are manufactured by making
both the diamond and bur from a common blank
configuration. This assumes that the shape of the instrument
and the resultant contour of the tooth will match exactly when
the diamond and carbide finishing bur are used for each step
of the preparation. www.indiandentalacademy.com

EFFECTS OF HIGH SPEED CUTTING
ENAMEL:
Enamel is composed of 92% mineral and 8% of organic
material and water. It is recognized as the hardest human
tissue. The basic structure of enamel is mushroom shaped
enamel rod, which begins at the dentinoenamel junction and
ends at enamel surface. Usually enamel originates at right
angles to the dentin surface and follows a spiral pattern
towards the surface ending at near right angles to the surface.
Eccentric burs that do not run true in the high-speed hand
piece can produce crazing of the enamel. Crazing can also be
brought about by internal stresses, such as might be induced
by thermal changes or a retentive pin i.e., angled outward and
that has been forced into enamel.

DENTIN
Dentin is composed of 65% inorganic material. The remaining
35% is organic matter and water, which allows it to be cut
more readily than enamel with a dental bur. Dentin is
organized in the form of tubules that are supported by
calcified network of collagen fibers. The tubules contain the
living extensions of the odontoblasts whose cell bodies are in
the periphery of the pulp.
Crown preparations involve the exposure of dentinal tubules,
cutting of odontoblast processes. Generation of heat,
desiccation and pressure. The deeper the dentin is cut, more
severly odontoblasts may be damaged. If the water coolant
does not reach the interface between the cutting instrument
and the tooth surface in the crown preparation a surface
“dentin burn” lesion will occur. The odontoblast destruction
will be extensive.

PULP
The pulp of a tooth is unique among other body tissues or organs. It is
very small, but it is able to fulfill sensory and nutritional functions for
a tooth. It also forms additional dentin and form provides a defense
against infection. The pulp responds very quickly to external stimuli
and the response depends on the severity of the stimuli.
The degree of pulp reaction is proptionately increased in direct
relation to the depth and particularly the extensiveness of crown
preparation.
If the odontoblasts are injured primarily by desiccation, the
disintegration products of these cells will act as an irritant and cause
an inflammatory response in the pulp in that area where cut dentinal
tubules terminate. When there is dentin burn odontoblast destruction
will be extensive.
Photo and Schenin (1958) showed if pulp temperature was raised
above 46 degree C irreversible changes such as stasis and thrombosis
could occur in the pulp. Drying the tooth with a constant air blowing
also cause irreversible pulp damage, even if the cavity is prepared
under sufficient water coolant. Therefore the preparation should be
dried with careful blasts of air at short duration and with sterile
cotton after preparation. www.indiandentalacademy.com

Advantages of high speed cutting
1. Increased cutting efficiency.
2. Faster tooth removal, hence less pressure, less vibration and
less heat generation.
3. Operator has better control and less fatigue.
4. Great ease of operation.
5. Patients less apprehensive because less vibration, less noise
and less operation time.
6. Reduced tension and fatigue for both operator and the patient
due to reduced operation time.
7. Greater ease of operation.
8. As a whole, it is possible to manage more patients in less time.

Disadvantages of high speed cutting
Desiccation of dentinal tubules.

Impaired visibility due to water spray.

Mechanical injury to soft tissues due to coarse speed. This can be
avoided by
Using rubber dams.
Taking care while removing hand piece.

Over reduction of tooth
This can be avoided by properly following the steps during
preparation and experience.

Eye damage
Due to flying tooth restorative material particles. This can be avoided
by protective eyewear for dentist, patient and assistant.

Noise
Hi pitched noise from air turbine can cause hearing damage.

Cross contamination
Use of face masks for the protection from air borne infections like
tuberculosis etc reduces the risk.


ABRASION AND POLISHING AGENTS




The finishing and polishing of restorative dental
materials are important steps in the fabrication of
clinically successful restorations. The techniques
employed for these procedures are meant not only
for removal of excess material but also to smoothen
rough surfaces.
The finishing of dental restorations prior to their
placement in the oral cavity has therefore three
benefits:




To promote oral hygiene.
Enhance oral function.
To improve esthetics.

DESIRABLE CHARACTERISTICS OF AN
ABRASIVE








It should be irregular in shape so that it presents a sharp
edge. (Jagged particles are more effective. Round sand
particles and cubicle particles of sand paper are poor
abrasives).
It should be harder than the work it abrades. If it cannot
indent the surface to be abraded then it cannot cut it and
therefore wears out.
Abrasive should posses a high impact strength or body
strength. Abrasive point should always fracture than dull out
so that always, a sharp point or edge is available. The cuts
also help in shredding debris accumulated from work for eg,
a grinding wheel against a metal.
Abrasive should posses attrition resistance so that it does
not wear.

DESIGN OF ABRASIVE
INSTRUMENTS
The abrasives employed could be one of the
three types,
 Abrasive Grits.
 Bonded Abrasives.
 Coated Abrasive Disks and Strips.


A. Abrasive Grits
Abrasive grits are derived from (abrasive)
materials that have been crushed and passed
through series of mesh screens to obtain
different particle size ranges. The grits are
classified as COARSE, MEDIUM COARSE,
MEDIUM FINE and SUPER FINE according
to the particle size ranges.


B. Bonded Abrasives









These consist of abrasive particles incorporated through a binder to
form grinding tools.
The abrasive particles are bonded by 4 general methods:

Sintering.

Vitreous bonding (Glass/Ceramic)

Resin bonding (usually phenolic resin).

Rubber bonding (usually silicon rubber).
Sintering- Sintered abrasives are the strongest variety since the
abrasive particles are fused together.
Vitreous bonded- Are mixed with a glassy or ceramic matrix
material, cold pressed to the instrument shape and fired to fuse
with the binder.
Resin bonded- are cold or hot pressed and then heated to cure the
resin.
Rubber bonded- made in a manner that is similar to resin bonded.

C. Coated Abrasive Disks and Strips
These abrasives are supplied as disks and
finishing strips. They are fabricated by securing
abrasive particles to a flexible backing material
(heavy weight paper or Mylar).
 The disks are available in different diameters
with thin and very thin backings. Moisture –
resistant backings are advantageous, as the
abrasive stiffness is not reduced by water
degradation.



ABRASIVE ACTION
The mode of action of the abrasives is similar to
that of the dental burs, that is, it is meraly a
cutting action. Each fine abrasive particle thus
presents as a sharp edge, which cuts through the
surface similar to a pointed chisel. During this
cutting process, the shaving thus formed is
powdered and usually clogs the abrasive which
thus makes periodic cleaning of the abrasive
necessary.

FACTORS AFFECTING RATE OF
ABRASION
Rate of abrasion of a given material by a given
abrasive is determined primarily by three factors:
 Size of the abrasive particle – larger the size –
greater the abrasion.
 Pressure of the work against the abrasive. When
work is pressed against the abrasive, scratches are
deeper and abrasion is more rapid – so greater
chances of the abrasives to fracture.
 Speed at which the abrasive particles travels across
the work. Greater the speed, greater would be the
rate of abrasion.

FACTORS INFLUENCING
EFFICIENCY OF THE ABRASIVES
These factors are as follows:

The hardness of the abrasive particle (diamond is hardest; pumice and
garnet etc. are relatively mild).

The shape of the abrasive particle (particles with sharp edge are more
effective).

Particle size of the abrasive (longer particle size will cut deeper
grooves).

Mechanical properties of the abrasive (If the material breaks, it should
form a new cutting edge. Therefore brittleness can be an advantage).

Rate of movement of the abrasive particles (slower abrasion – deeper
scratches).

Pressure applied to the abrasive (too much pressure can fracture the
abrasive instrument and increase heat of friction that has evolved).

Properties of material that is being abraded. (a brittle material can be
rapidly abraded whereas ductile / malleable metal like pure gold will
flow instead of being removed by the abrasive).





TYPES OS ABRASIVES
According to Craig : The abrasives
used can be classified and grouped as
Finishing Abrasives.
Polishing Abrasives.
Cleaning abrasives.








Finishing Abrasives
These are hard, coarse abrasives used initially to
develop desired contours and remove off gross
irregularities.
Polishing Abrasives
These have a smaller particle size and are less hard
than abrasives used for finishing. They are used for
smoothening surfaces that are typically roughened
by finishing abrasives.
Cleaning Abrasives
These are soft abrasives with small particle size and
are intended to remove softer materials that adhere
to enamel or a restoration.

2. Skinner has grouped the abrasives
employed in dentistry as follows:
A. Natural Abrasives.
B. Manufactured Abrasives.


Under Natural Abrasives we have:
1. Arkansas stone
- Semi translucent, light gray, siliceous sedimentary rock,
mined in Arkansas.
- It contains microcrystalline quartz.
- Small pieces of this mineral is attached to metal shanks
and trued to various shapes for fine grinding of tooth
enamel and metal alloys.
2. Chalk
- Mineral form of calcite.
- Contains calcium carbonate.
- Used as mild abrasive paste to polish teeth enamel,
gold foil, amalgam and plastic materials.

3. Corundum
- Is largely replaced by alpha Aluminum oxide due to its
superior physical properties. However corundum is
primarily used for grinding metal alloys and is
available as a bonded abrasive.
4. Diamond is a transparent colorless mineral
composed of carbon called super abrasive because
of its ability to abrade any other known substance. It
is used on ceramic and resin based composite
materials.
Supplied as:
Bonded abrasive rotary instrument.
Flexible metal backed abrasive strips.
Diamond polishing pastes.

5. Emery
- This abrasive is grayish black corundum that is prepared in
a fine grain form.
- Supplied predominantly as coated abrasive disks.
- Used for finishing metal alloys or plastic materials.
6. Garnet – the term garnet includes several minerals which
possess similar physical properties like Silicates of Al, Co,
Fe, Mg and Mn.
- Garnet is dark red, extremely hard and when fractured
during abrasive abrasive activity forms sharp chisel shaped
plates – therefore making Garnet an effective abrasive.
- Garnet is available on coated disks and Arbor box.
- Used in grinding metal alloys and plastic materials.

7. Pumice
- Is produced from volcanic activity.
- Flour of pumice is an extremely fine grinded volcanic rock
derivative from Italy.
- Used in polishing teeth enamel, gold foil, dental amalgam and
acrylic resins.
8. Quartz – the particles are pulverized to form sharp angular
particles which are useful in making coated disks.
- Used to finish metal alloys and may be used to grind dental
enamel.
9. Sand
- Is a mixture of small mineral particles predominantly silica.
- Particles have rounded to angular shape.
- Used to remove refractory investment material from base metal
castings.
- It is coated on paper disks for grinding of metal alloys and
plastic materials.

10. Tripoli
- Derived from a light weight, siliceous sedimentary
rock.
- Could be white, gray, pink, red or yellow.
- Gray and red are most frequently used.
- Used for finishing metal alloys and some plastic
materials.
11. Zirconium silicate
- Off white mineral, ground to various sizes used to
make coated disks and strips.
- Also used as a component of dental prophylaxis
pastes.

Under Manufactured Abrasives we have:
1. Silicon Carbide
- This is the first of the synthetic abrasive to be developed.
- Two types were manufactured 1. Green form and 2. Blue
form. Both are having similar physical properties.
- However, the green variety is preferred because substrates
are more visible against the green color.
- The cutting efficiency of silicon carbide abrasives is higher
as the particles are sharp and break to form new sharp
particles.
- Supplied as air abrasive in coated disks and vitreous and
rubber bonded instruments.
- Used in cutting metal alloys, ceramics and plastic materials.

2. Aluminium Oxide
- This is the second synthetic abrasive to be manufactured.
- This form of alumina is much harder than its natural
counterpart (CORUNDUM) because of its purity.
- The forms usually prepared are:
a. White stones – made of sintered aluminium oxide are
used for contouring of enamel and finishing metal and
ceramic materials.
b. Variations of aluminium oxide include those with
chromium compound additions, these obtained in pink
and ruby colours are obtained as vitreous bonded noncontaminating mounted stones – used for preparation of
metal ceramic alloys to receive porcelain.

3. Synthetic Diamond – developed in 1955.
- Synthetic or manufactured for of diamond is
produced at 5 times the level of the natural
diamond abrasive.
- This synthetic diamond is used for the
manufacture of diamond saws, wheels and burs
and also diamond locks employed for truing of
bonded abrasives.
- Synthetic diamond abrasives are used primarily
on tooth structure, ceramic materials and resin
based components.

4. Rouge
- Principle component is iron oxide blended with
various binders.
- Used to polish high noble metal alloys.
- May be impregnated in paper or fabric known as
CROCUS CLOTH.
5. Tin Oxide
- Is composed of very fine abrasive particles.
- May be employed in an abrasive paste form along with
water, alcohol or glycerin.
- Used as a polishing agent for teeth and metallic
restorations.

REVIEW OF LITERATURE
1. In 1952, Lawrence H. Clayman described the modern
techniques for the full crown and plastic faced gold
veneer crown preparations using diamond instruments.
The introduction of diamond cutting instruments into
dentistry has been a great aid for crown and bridge
prosthesis. Diamond instruments have enabled us to
prepare teeth faster and have also reduced trauma incident
to operative dentistry procedures by cutting more
efficiently, more quickly, and with less friction and
resulting heat.
For maximum cutting efficiency, diamond instruments
should be used at high speed with light pressure and
should be well lubricated by a continuous stream of water.

2. In 1953, Edwin S. Smyd mentions the importance
of diamond tools in dentistry; diamond tools are
distinct from burs or cutting tools in that they work
by a scoring action, that is, each diamond particle
scrapes off the surface of the object it is abrading to
the depth of the diamond protruding from the tool.
Light pressure minimizes frictional heat.
Experimental studies in Germany indicates that
diamond tools are best used wet or dry in a moist
loose slurry of the abraded material- both too much
water and dryness should be avoided.
Diamond tools are not selective in their grinding
action. They will grind enamel, dentin and
cementum at equal rate.

3. In 1957, Rex Ingraham, did an evaluation of recent
progress in the field of increased speeds and modern
instrument design. Increased speeds for the rotary
instruments is one of the newest fields in dental
science and one involving the most rapid and dramatic
changes in the history of the profession. The ultra
high speeds (above the threshold of vibration
perception) produce a favorable response. Operating
at about 10,000 rpm and above requires only a light
„feather like‟ touch which reduces digital fatigue for
the operator. However, it becomes necessary to
operate with much more exactness and a keen visual
sense must be employed to safeguard against overcutting and inadvertent damage to adjacent tooth
surfaces.

4. In 1958, Allison G. James, discussed the subject of high
speeds and concluded that unless steps are taken to bring
adequate instruction to the vast majority of dentists who are
influenced to use high speed rotary instruments, it may be
anticipated that an era of slovenly tooth preparations will
plague dentistry for some time to come.
5. In 1959, Edmund V. Street, did a critical evaluation of
ultrasonics in dentistry and concluded that pulps of vital
permanent teeth appear to be unaffected, but operations on
children‟s teeth should not be attempted until future
research indicates no ill effects. The ultrasonic method of
cutting instruments carious or sound enamel, carious or
sound dentin and certain types of restorative materials does
not approach the effectiveness that can be demonstrated
with the ultra high speed rotational instruments.

6. In 1960, Alexander Leff, did an evaluation of high speed in
full coverage preparations. From a practical point of view,
high speed can be defined as rotational speeds starting at 1,
00,000 rpm. This is the beginning range of speed at which
tools can be used efficiently with light pressure.
7. In 1965, Schuchard and Watkins, compared the efficiency
of rotary cutting instruments.
a. Any of the high or low torque rotary cutting equipment will
operate efficiently in its useful range, if properly used.
b. The various low torque ultrahigh speed contra angle
instruments are comparable, and are most efficient at the
higher operating air pressures.
c. Simplicity of design and size of equipment are significant in
evaluation.
d. High torque air driven straight hand pieces are not as efficient
as comparable electric www.indiandentalacademy.com
driven equipment.

8. In 1970, Charles Watkins, elaborated on the cutting
effectiveness of rotary instruments in a turbine hand piece and
concluded that in enamel, diamond cutting instruments
compare favorably with TC burs. The carbide burs remove
dentin more rapidly than do the diamond points. The
„lubricating‟ effect of water to enhance the cutting
effectiveness of diamonds in not documented in this study.
9. In 1988, Robert Cooley et al, did a study on the effect of air
powder abrasive instrument on porcelain. The effects of an air
powder abrasive instrument on porcelain were evaluated.
Sample disks made from two commercial porcelains and three
porcelain strains were treated for 80 seconds with this
instrument.
It was recommended that the air powder abrasive instrument
be used cautiously or not at all on porcelain restorations,
especially those with staining and / or specific
characterizations.

10. In 1988, Price and Sutow, conducted a
micrographic and profilometric evaluation of the
finish produced by diamond and TC finishing burs
on enamel and dentin and concluded thata. Minimal marginal chipping combined with low
surface roughness suggests that a superfine
diamond is indicated for producing clinically
acceptable margins on all surfaces of the teeth.
b. Where the rotation of the bur was away from the
margin, multifluted tungsten carbide burs
frequently produced chipping of the enamel
margin.

11. In 1988, Prattern and Johnson, did an evaluation
of finishing instruments for an anterior and a
posterior composite. The same finishing instruments
and techniques revealed no significant differences in
the surface roughness of the anterior and posterior
composites. The smoothest surface was achieved with
Mylar strips; the smoothest instrumented surface was
achieved with a series of abrasive disks, but a fine
diamond bur with 25 um particles produced the
roughest surface. However an X-fine diamond with 15
um particles produced a surface smoothness superior
to that produced with a white stone and similar to the
smoothness produced with a carbide bur and rubber
point. Diamond finishing with slow speed produced a
somewhat smooth finish than with high speed.

12. In 1988, Jeffrey Norlandes and Dennis wies and
Warren Stoffer, studied the taper of clinical
preparations for fixed prosthodontics and concluded
thata. The ideal convergence angle of 4-10 degrees is seldom
achieved in clinical practice.
b. Mean convergence angles for mandibular preparations
were greater than mean maxillary convergence angles.
c. No significant differences were found between the
mean convergence angles of crowns and FPD
retainers.
d. Auxiliary retention should be used in the molar region
because these preparations were found to have large
convergence angles.

13. In 1990, Robert W. Schutt, did a procedure to
sterilize dental burs with dry heat.
a. After dental treatment, debride the bur and wipe dry
with gauze. Both short and long shank burs can be
used.
b. Place the burs in screw-cap 13 x 100 mm glass test
tubes with a maximum of 10 burs per tube.
c. Place the tubes in wire racks and insert in a dry heat
even at a monitored temperature of 170 degree C for a
minimum period of 60 minutes.
d. After the sterilization period, remove the wire racks
and allow the tubes to cool. The glass tubes
containing the sterile burs may be stored and
indefinitely and will maintain the sterility of the burs.

14. In 1991, Kevin M. Gureckis et al, conducted a study on
the cutting effectiveness of diamond instruments subjected
to cyclic sterilization methods and concluded thata. The cutting effectiveness of rotary dental diamond
instruments was not influenced by the sterilization method.
b. There are considerable differences in the cutting efficiency
of new individual diamond instruments.
15. In 1999, a study was done which investigated a new
diamond rotary instrument made of a continuous diamond
film obtained by chemical vapor deposition (CVD). This
bur characterized by a pure diamond cutting surface without
metallic binder between crystals was compared with a
conventional diamond bur and they came down to a
conclusion that the new CVD bur not only proves to be
more efficient in its cutting ability and longevity, but also
excludes the risk of metal contamination.

16. In 2001, Katoh Y and Sunico M, did a study on
the newly developed diamond points and said that
the rapid decrease in size of dental restorations has
increased the demand for the smallest rotary
cutting instrument possible. The width of cavities
prepared with two experimental diamond points
and the smallest commercial diamond point were
compared and significant differences found. SEM
observation of the head surfaces of the three
diamond points revealed that the experimental
points had comparable cutting characteristics with
the commercial diamond point.

17. In 2002, Bruno Neves Cavalcanti, Choyu
Otani and Sigmourmello Rode, did a study and
evaluated the efficiency of 3 different water flows
for 2 different tooth preparation techniques to
determine which one is safe for use. Cavity and
tooth preparations generate heat because the use of
rotary cutting instruments on dental tissues creates
friction. Dental pulps cannot survive temperature
increases greater than 5.5 degree C. The results of
this study confirms that thenecessity of using a
low-load technique and water coolants during
cavity and tooth preparation procedures.

SUMMARY AND CONCLUSION
Tooth preparations for cast restorations have
been influenced at least in part, by the
technology of instrumentation. This is seen in
the development of hand pieces and power
sources as well as in the evolution of abrasives
and cutting instruments. This seminar considers
all the aspects of instrumentation in fixed
prosthodontics and is based on the current
available literature.

REFRENCES












M A Marzouk- Operative Dentistry, modern theory and
practice.
Herbert T Shillingburg- Fundamentals of fixed
prosthodontics- third edition.
Tylman’s- Theory and practice of fixed prosthodonticseight edition.
Stephen F Rosenstiel- Contemporary fixed
prosthodontics.
Gerald T Charbeneau- Principles and practice of
operative dentistry.
Sturdewant’s- Art and science of operative dentistryfourth edition.












Bruno Neves Cavalcanti, Choyu otani, Sigmar mello
rode- High speed cavity cutting preparation techniques
with different water flows.JPD 87(2) 158-161, FEB 2002.
Katoh Y, Sunico M- Newly developed diamond points
for conservative operative procedures.Oper Dent 2001
Jan 26(1)76-80.
Dental diamond burs made with a new technology.JPD
1999 July, 82(1), 73-79.
Kevin Guruckes- Cutting effectiveness of diamond
instruments subjected cyclic sterilization. JPD 1991, 56
300-306.
Robert Schutt- Sterilization of dental burs with dry heat.
JPD 1990,42 22-26.
Pratten and Johnson- Evaluation of finishing
instruments for an anterior and a posterior
composite.JPD 1988, 38, 362-365.













Price and Sutow- Micrographic and profilometric evaluation
of the finish produced by diamond and tungsten carbide
finishing burs on enamel and dentin. JPD 1988; Vol39,30-35.
Robert Colley- Effect of air powder abrasive instrument on
porcelain.JPD1988,vol39,88-92.
Jeffrey Norchlander & Dennis Wies & Warren ClofferTips of clinical preparation for fixed prosthodontia.JPD
1988;Vol38,42-46.
Charles Watkins- Cutting effectiveness of rotary instruments
in a turbine hand piece. JPD 1970; Vol 19; 88-105.
Schuchard & Watkins- Comparison of cutting efficiency of
tungsten carbide burs and diamond points at ultra high
rotational speeds. JPD 1967; Vol 20; 362-366.
Schuchard & Watkins- Comparison of efficiency of rotary
cutting instruments. JP 1965; Vol 18; 25-28.











Alexander Leff- Evaluation of high speed in full
coverage preparations. JPD 1960; Vol 10; 220-224.
Allison G. James- High speeds. JPD 1958; Vol 8;
168-172.
Rex Ingraham- Evaluation of recent progress in
the field of increased speeds and modern
instrument design. JPD 1957; Vol 7; 112-118.
Edwin Smyd- Importance of diamond tools in
dentistry. JPD 1953; Vol 3; 361-364.
Lawrence Claywan- Modern techniques for full
crown and plastic faced gold veneer crown
preparations using diamond instruments. JPD 1952;
Vol 2; 272-276.











Griscome- History of dentistry-Weinburg.
Robert Arthur- History of dentistryWeinburg
Archigenes- History of dentistryWeinburg; „Instrumentation‟.
Dendel & Zweiling- History of dentistryWeinburg; „Instrumentation‟.
Brown et al- Operative dentistry by
Sturdevant; Cutting instruments.

THANK YOU


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