conservative dentistry

1. Rotary cutting instruments
in conservative dentistry
BY
V.VASUNDHARA
2ND
YEAR PG

2. contents
 Introduction
 Evolution of rotary cutting instruments
 Recent developments
 Classification of rotary cutting instruments
 Classification of dental handpiece
 Adv and dis adv of speed
 Characteristics of rotary instruments
 Dental handpiece
 Dental burs
 History development of burs
 Classification of burs
 Bur blade design
 Abrasive instruments

3.  Cutting mechanism
 Evaluation of cutting
 Factors influencing cutting effectiveness and
efficiency of the bur
 Hazards of rotary cutting instruments
 references

4. introduction
 WHAT DOES ROTARY MEAN?
Instruments which turn on an axis to perform work.
Work may be :-
Cutting
Abrading
Burnishing
Finishing and polishing

5. EVOLUTION OF ROTARY EQUIPMENTS:

6. Historical Development:-
 Prehistoric man used sharp pieces of flint for trephineing holes in bones.
Hippocrates in 350 B.C. described a drill driven by a cord wound around
a shaft. Celsus (25 B.C. –50 A.D) described two kinds of drillers or
“Terebra”. One with a guard to prevent it from sinking deep into the
tissues and the other one was similar to a carpenter’s drill.

7.  In 2A.D. Cladius Galenius a celebrated physician reports of Archigenes
an eminent surgeon of Asia minor and practicing in Rome successfully
treated tooth ache by opening the tooth with a trephine.
 Galen (130 –200 A.D) modified Celsus’s “Terbra” and called it
“Terebraabatista” or “Modiolus”. Lubrication was done with olive oil
or milk or by dipping in cold water.

8.  Abulcasis (936 – 1013 A.D) described a boring instrument “Incisura”.
Perre Fauchard “Father of Dentistry” 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 300rpm and
was later on modified into the “Scranton’s drill” which could cut by
rotating in either direction.

9.  In 1831 dental chair was introduced.
 In 1838 John Levis made a hand held drill.
 Dr. West Cott in 1846 used “Fingerings” with drills. Taft called them
“Bur Drills”.

10.  drill stocks, bur chucks or bit holders – forerunner of the present dental
handpiece.
 eg: -Cheavlier drill stock
 -Merry’s drill stock
 ‘Chevalier drill stock” was hand
powered like an egg-beater.

11.  Tomes in 1859 described three types of burs.
1. Rose head: a short shank bur inserted in a crutch rotated between
thumb and index finger supported at the base of the thumb.
2. Long hand bur: teeth are cut for same distance along the shaft and it
is mounted in a handle.
3. Long steel shaft with too cutting blades.

12. Charles Merry in 1862 used a “Drill Stock” which had a flexible cable
drive. This also was a type of angle handpiece
George Fellows Harrington in 1865 used “Clock work drill” or
“Harrington’s Erado” which is the first motor driven drill. At first burs were
hand cut and ground and were expensive.

13. America in 1860s began mass production of burs from carbon
steel. The earliest burs had limited lateral and end cutting action. The
diameter varied form 1/32” to 1/5”. These were particularly used for
small and medium sized varieties. These carbon steel burs were called
“Small milling cutters”.

14.  In 1871 Morison’s foot engine was introduced. Morrison modified and
adapted the dental foot engine from the singer sewing machine.
 Cutting procedure was carried out with a power source
 A speed of 700 rpm was obtained.

15. In 1873 Coxeter used an electric engine with a speed of 1000
rpm. This is the predecessor of the modern micromotor. This was
held in hand and connected to a coil. The motor was open and the
spindle of the motor was connected with the hand piece.
In 1874 the electric motor hand piece was invented by S.S white
and later he also pioneered the invention of various carbon steel burs
and hand pieces.

16. In 1883 rotary power from an electric engine was transferred to the
straight hand piece by a belt that ran over a series of pulleys and a three-piece
extension cord arm. A variable rheostat was used as a foot control.
Rotary cutting instruments were inserted into the chucking mechanism
at the front of the handpiece.
The desired angle handpiece is attached to the front of the straight
hand piece and a shaft and gears inside the angle section produce rotation of
the working instrument.

17. GEAR DRIVEN HANDPIECE

18. In 1891 Edward G. Acheson an American invented and produced
carborundum and carborundum tools were introduced.
 In 1901 hand piece with forward (clockwise) and reverse
(anticlockwise) direction of rotation and burs for each type movement were
brought into use.

19. In 1910 Emile Huet a Belgian perfected an electric engine to give a
speed of 10,000 rpm.
In 1935 diamond abrasives were introduced and W.H Drendel
introduced the process of galvanized bonding of diamond powder to copper
blanks and used at a speed of 5,000 rpm.

20. In 1947 Tungsten carbide was introduced and
S.S White in 1948 made tungsten carbide burs which were
used at a speed of 12,000 rpm.

21. In 1949 Walsh and Symons used diamond points at a speed
of 70,000 rpm.

22.  In 1950 ball bearings were used in contra angel handpieces.
 In 1951 air abrasive technique was introduced.
 In 1953 Nelson produced a Hydraulic driven turbine angle handpiece
of speed, 60,000 rpm.

23.  In 1955 Page-chayes introduced first belt-driven angle handpiece to operate
successfully at speeds over 100,000 rpm.
 All gears were eliminated by having a small belt run inside the handpiece
sheath over ball bearing pulleys in the angle sections.
 Improved models -Page-Chayes 909 and the Twin 909

24. In 1955 Turbo-jet was designed as a compact mobile unit that
required no outside plumbing or air connections.
Only a source of electricity was need.
A sound proof cabinet contained a motor, water pump, water
reservoirs and necessary plumbing for water circulation. Water was
conveyed to and from the hand piece by co-axial type plastic tubing

25. . The small inner tube carried water under high pressure to rotate
a turbine in the handpiece head and the larger outer tube returned the
water to the reservoir for re circulation.

26. In 1960 ultrasonics were used for hard tooth structure removal.
In 1961 air turbine straight handpiece was introduced.
In 1962 air turbine angle handpiece with air bearings were
introduced.

27.  A small compact unit consists of a handpiece, control box, foot control
and various connector hoses.
 When the foot control is activated, compressed air flows through the
control box and is carried by a flexible hose to the back of the handpiece.
 From here the air is directed to the head
of the handpiece and is blown against the
blades of a small turbine to produce
Rotation,
while the greater part is
exhausted at the back of the handpiece or
returned to the control box.

28. Most modern angled handpieces also include fireoptic lighting of the
cutting site.

30.  - earlier units were water driven and later came the air driven units.
 - have free running speed of 300,00 rpm but lateral loads
during cutting can reduce it to 200,00 rpm.
 ( excellent safety feature )
 - ADV: simple, ease of control, patient acceptance,
versatility.
 - DISADV: low torque & power output makes them
unsuitable for finishing & polishing purposes.
 - SOLUTION: Straight handpieces which provided high
torque & low speed operation.

31. RECENT DEVELOPMENTS:
 Allow repeated sterilization
 Smaller head size
 More Torque
 Lower noise
 Better chucking mechanism
 Fiber-optic lighting of the cutting site.
 (contemporary air turbine handpiece)

32. CLASSIFICATION OF ROTATING INSTRUMENTS:
According to speed :
( According to Sturdevant )
High speed range or ultra- 100,000 to 300,000
rpm
Intermediate speed range- 12000 to 100,000
rpm
Low speed range- Below 12000 rpm

33. (Acc. to Marzuok)
 Ultra low speed : 300-3000 rpm
 Low speed : 3000-6000 rpm
 Medium high speed : 20,000-45,000 rpm
 High speed : 45,000-100,000 rpm
 Ultra high speed : 1000,000 and above

34. (Acc. to Charbonneau)
Conventional or low speed : below 10,000 rpm
Increased or high speed : 10,000-150,000 rpm
 Ultra speed : Above 150,000 rpm

35. (Gilmore- 3 Edition )
Regular speed Ultra speed
500-6000 rpm 200,000 rpm

36. SO MANY SPEEDS – WHICH IS THE
RIGHT ONE TO USE ???

37.  Low speeds:
 cleaning teeth
 caries excavation
 finishing & polishing
 ADV:
 better tactile sensation
 less chances of overheating cut surfaces.

38. DISADV:
more heat production
vibration
time consuming
inefficient for cutting
burs have tendency to roll out proximal margin or
tooth surface.
carbide burs do not last long.

39.  High speeds:
 tooth preparation
 removing old restorations
 ADV:
 faster tooth structure removal
 less heat production
 less vibration
 better control & ease of operation
 time saving
 diamond & carbide instruments stay longer

40. Characteristics of rotary instruments
Speed refers not only to revolutions per minute, but also to the surface
feet per unit time of contact that the tool has with the work to be cut.
It is important to consider the size of the working tool in relation to the
speed of operation.
A rotary tool should be large in diameter when used with low speeds
to approach the optimum surface feet per unit time.
In ultra high speed range, the diameter of cutting tool should be
reduced to approximate the limits of maximum cutting efficiency.
speedspeed

41.  Pressure is resultant effect of two factors under the control of
dentist.
1. force : the gripping of the handpiece and its positioning and
application to the tooth.
2. Area : the amount of surface area of cutting tool in contact with the
tooth surface during a cutting operation.
P=F/A
It has been observed that low speed requires 2-5 pounds force, high
speed requires less force i.e 1 pound and ultra high speed still less
force
i.E 1-4 ounces
Higher speed-less fatigue to operator-greater comfort to patient
pressure

42.  At is directly proportional to;
1. Pressure
2. RPM
3. Area of tooth in contact with the tool
At temp of 130 F tooth pulp is permanently damaged
At 113 F inflammatory responses that could result in pulpitis and
eventual pulp necrosis is seen
Higher speed call for less force and if coolants are used, heat production
could be eliminated or at least minimized
Heat production

43.  Vibration is not only a major annoying factor for the patient, but it also
causes fatigue for operator, excessive wear of instruments and most
importantly, a destructive reaction in the tooth and supporting tissue.
 Vibration is a product of the equipment used and speed of rotation.
 The equipment primarily the hand pieces and the revolving cutting
tools
 The deleterious effects of vibration are two fold in origin
1. Amplitude
2. Undesirable modulating frequencies
Vibration

44. 1. Amplitude
a wave of vibration consists of frequency and amplitude.
 at low speed, the amplitude is large but the frequency is small. At
higher speeds the reverse is true
 By increasing the operating speed the amplitude and its effects are
reduced as well as its sequelae.
 Higher RPM s produce less amplitude and greater frequency of
vibrations. As a result, perception will be lost in the ultra high speed
ranges of 1,00,000 RPM or more.

45. 2. Undesirable modulating frequency
 The second deleterious effect of vibration is caused by improperly
designed, or poorly maintained equipments.
 Improper equipment use or care allows modulating frequencies to be
established so that a series of vibrations are perceived by the patient
and the dentist. The end result is again apprehension in the patient,
fatigue for dentist and accelerated wear of cutting instruments
 To eliminate these, The operator should supply himself with true
running energy source, centrically cutting tools and handpieces that
run at high speed.

46.  The factor that cause patients apprehension are
 Heat production
 Vibrational sensation
 Length of operating time
 Number of visits
 The proper understanding of the instruments and the speed at which it
is being used,
 the use of coolants,
 intermittent application of a tool to the tooth;
 sharp instruments aid in minimizing patients discomfort and
unnecessary irritant to oral tissue
Patients reaction

47. the major cause of fatigue is
Duration of operation
Vibration produced in the handpiece
High speed rotary instrumentation minimizes fatigue by decreasing both
the vibrations and the time of the operation.
Operator fatigue

48.  Instrument design for rotary instrumentation should be evaluated in 2
parameters .
1. Handpiece
2. Cutting tool itself
Instruments design

49. Dental Handpieces:
- Device for holding rotating instruments, transmitting power to them &
for positioning them intra-orally.
Types:
a) Straight
b) Angled

50. Classification of Dental Hand Pieces
According to Speed:
Conventional <10,000 rpm
Intermediate 10,000-1,00,000 rpm
High /Ultra high >1,00,000 rpm
According to Applications: Straight
Contra angle
Prophylaxis
Type of power mechanism: Belt devices
Gear devices
Direct motor devices
Water driven
Air driven

51. The following criteria should be used in evaluating
handpieces :
a. Friction:
Friction will occur in the moving parts of
handpiece; especially the turbine.
heat from friction is prevented by
handpieces equiping with bearings:
ball bearing, needle bearings, glass and resin
bearings, etc

52. b. Torque
 Torque is the ability of the handpiece to withstand
lateral pressure on the revolving tool without
decreasing its speed or reducing its cutting efficiency.
 Torque is dependent upon the type of bearing used
and the amount of energy supplied to the handpiece.

53. C. Vibration
 While some vibration is unavoidable, care should be
taken not to introduce it unnecessarily.
 Excessive wear of the turbine bearings, will cause
eccentric running which creates substantial vibration .

54. DENTAL BURS
 All rotary cutting instruments that have-
bladed cutting heads.
 This includes instruments intended for such
purposes as finishing metal restorations and
surgical removal of bone, & tooth
preparation.

55. COMMON DESIGN CHARACTERISTICS
 three parts:
(1)shank,
(2) neck, and
(3) head.

56. Shank Design
 part that fits into the handpiece, accepts the
rotary motion from the hand-piece, and
provides a bearing surface to control the
alignment and concentricity of the
instruments .
 straight handpiece shank,
 latch-type angle handpiece shank,
 friction-grip angle handpiece shank,

57. Neck Design
 intermediate portion of an instrument that
connects the head to the shank.
 The main function of the neck is to transmit
rotational and translational forces to the
head.

58. Head Design
 working part of the instrument .
 the cutting edges or points that perform the
desired shaping of tooth structure.
 bladed instruments
 abrasive instruments

59. Historical Development of Dental Burs
earliest burs :
 expensive
 variable in dimension and
performance
• first machine made burs introduced in 1891

60.  Carbide burs
 introduced in 1947 .
 All carbide burs have heads of cemented carbide in
which microscopic carbide particles, usually tungsten
carbide, are held together in a matrix of cobalt or
nickel.
• In most burs, the carbide head is attached to a steel
shank and neck by welding or brazing.
• Although most carbide burs have the joint located in
the posterior part of the head, others are sold that have
the joint located within the shank and therefore have
carbide necks as well as heads .

61. Bur Classification Systems
BASED ON MODE OF ATTACTMENT TO THE
HANDPIECE:
 latch-type
 friction-grip

62. COMPOSITION:
o Stainless steel
o Tungsten carbide burs
o combination

63. MOTION:
o Right bur
o Left bur

64. LENGTH OF THEIR HEAD:
o Long
o Short
o regular

65. USES:
o Cutting burs
o Finishing & polishing burs

66. 1.Head shapes
o round,
o inverted cone,
o pear,
o straight fissure,
o tapered fissure ,
o Wheel shaped,
o End cutting bur

67. Round bur
 spherical .
 initial entry into the tooth ,
 extension of the preparation,
 preparation of retention features/and caries
removal.
 numbered from ¼, ½, 1, and 2 to 10 .

68. Inverted cone bur
 providing undercuts in tooth preparations .
 numbered from 33¼, 33½, 34, 35 to 39.

69. Pear-shaped bur
 A normal-length pear bur (length slightly
greater than the width) is advocated for use
in Class I tooth preparations for gold foil .
 long-length pear bur (length three times the
width) is advocated for tooth preparations
for amalgam.
 They are numbered from 229 to 333 and
mainly used in pedodontics.

70. Straight fissure bur
 Elongated cylinder.
 amalgam tooth preparation.
 They are numbered from 555, 556 to 560 .

71. Tapered fissure bur
 slightly tapered cone with the small end of
the cone directed away from the bur shank.
 Tooth preparations for indirect restorations.
 They are numbered from 168, 169 to 172.

72. Wheel burs
 They are numbered as 14 and 15.
 They are wheel shape and are used to place
grooves and for gross removal of tooth
structure.

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

74. Modifications in Bur Design
 Reduced use of crosscut ,
 extended heads on fissure burs ,
 rounding of sharp tip angles.

75. Bur Blade Design
 The actual cutting action of a bur (or a diamond) takes
place in a very small region at the edge of the blade (or
at the point of a diamond chip). In the high-speed
range, this effective portion of the individual blade is
limited to no more than a few thousands of a
centimeter adjacent to the blade edge
 The optimal angles are dependent on such factors as
the mechanical properties of the blade material, the
mechanical properties of the material being cut, the
rotational speed and diameter of the bur
 force applied by the operator to the handpiece, and
thus to the bur.

78. ABRASIVE
INSTRUMENTS

79. Abrasive instruments
Head consists of small angular particles of hard
substance embedded in a softbinder(ceramic, metal,
shellac, rubber)
1.Diamond abrasive
2.Other abrasives – boron carbide,pumice,silicon, garnet

80.  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.
 Cutting occurs at a large number of points where
individual hard particles protrude from the matrix,
rather than along a continuous blade edge

81.  ADV:
 Effective in cutting enamel & dentin
 Long life of instruments.

82. Diamond particle size is commonly categorized
as:
 Coarse (125- 150 um);
 Medium (88- 125um);
 Fine ( 60- 74um);
 Very fine (38- 44um).

83.  Factors influencing the abrasive efficiency
and effectiveness
 Size of the particle
 Shape of the particle
 Density of the particle
 Hardness of the particle
 Clogging of abrasive surface

84.  Other abrasive instruments
 Moulded abrasive instrument – heads that manufactured
by pressing a uniform mixture of abrasive and matrix
around roughened end of shank; points and stones;
finishing &polishing
 Coated abrasive instrument – disks that have a thin
layer of abrasive cemented to a flexible backing ;surface
contour, finishing

85.  Diamond bur preferred over tungsten carbide because-
{Sharon Siegel 1996;JADA vol.127 }
* Greater resistance to abrasion
* Lower heat generation
* Longer life
Disadvantages :
Heterogeneity of grain shapes
Difficulty of automation during fabrication.
The decrease of cutting effectiveness due to
repeated sterilization
Short lifetime
Potential release of nickel ions from the metallic
binder into the body fluids.

86. 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. Local fracture occurs more easily if the
strain rate is high (high rotary instrument surface speed)
because the surface being cut responds in a brittle
fashion.
 When the bur is used a compressive stress is first
induced as the blade forces its way into the work. If
cutting results, the blade shears the surface it gradually
becomes parallel with the surface of work and it pushes
the material ahead along the tooth face to form the chip.
The chip is subjected to compressive stress.

87.  On the other hand , if the force exerted by the blade is
insufficient to induce stress to exceed the elastic limit of
the material, it cause’s only elastic deformation of the
surface , without chip formation.

88.  There is general agreement that increased rotational
speed results in increased effectiveness and
efficiency.
 Adverse effects associated with
increased speeds are heat, vibration, and noise

89. EVALUATION OF CUTTING
 Cutting can be measured in terms of both 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. It is possible to
increase effectiveness while decreasing efficiency

90. Factors influencing the cutting effectiveness and
efficiency of the bur :
 Rake angle,
 Clearance angle and
 Blade angle

91.  Neck diameter
 Heat treatment
 Influence of load
 Number of teeth

92.  Concentricity is a direct measurement of the symmetry
of the bur head itself. It measures how closely a single
circle can be passed through the tips of all of the blades.
Thus, concentricity is an indication of whether one blade
is longer or shorter than the others. It is a static
measurement not directly related to function.

93.  Runout, on the other hand, is a dynamic test
measuring the accuracy with which all blade tips pass
through a single point when the instrument is rotated.
It measures not only the concentricity of the head, but
also the accuracy with which the center of rotation
passes through the center of the head

94.  The runout is the more significant term clinically,
because it is the primary cause of vibration during
cutting and is the factor that determines the
minimum diameter of the hole that can be prepared
by a given bur. The average acceptable run out is
0.023mm.

95. BLADED CUTTING
 Brittle fracture is associated with crack
production, usually by tensile loading.
 Ductile fracture involves plastic deformation of
material, usually proceeding by shear.
 Extensive plastic deformation also may produce
local work hardening and encourage brittle
fracture as well.

96.  The rate of stress application (or strain rate) affects the
resultant properties of materials. In general, the faster
the rate of loading, the greater will be the strength,
hardness, modulus of elasticity, and brittleness of a
material.
 A cutting instrument with a large diameter and high
rotational speed produces a high surface speed, and
thus a high stress (or strain) rate.

97.  Many factors interact to determine which cutting
mechanism is active in a particular situation. The
mechanical properties of tooth structure, the design of
the cutting edge or point, the linear speed of the
instrument‘s surface, the contact force applied, and the
power output characteristics of the handpiece influence
the cutting process in various ways.

98.  In order for the blade to initiate the cutting action, it
must be sharp, must have a higher hardness and
modulus of elasticity than the material being cut, and
must be pressed against the surface with sufficient
force. 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

99.  Heat thus produced is dissipated-
1. By conduction through the tool
2. By conduction through the work
3. By the chip itself
4. By the coolant

100. HAZARDS WITH ROTARY CUTTING
INSTRUMRENTS:

101. classified into:
Pulpal dangers
Soft tissue dangers
Eye, ear, inhalational dangers.

102. Pulpal precautions:
Steel burs produce more heat than carbide
burs
Burs/diamond points clogged with debris
produce more heat.
When used without coolant, diamond
instruments are more damaging than carbide
burs.
Prevention: use of air-water coolant.
Use of air alone is not advised as it can cause
desiccation of the dentinal tubules.

103.  Soft tissue precautions:
 Lip, tongue, cheeks most common areas of injury.
 Prevention: use rubber dam, cotton rolls, mouth
mirrors, evacuator tips etc.

104.  Eye precautions:
 Patient, operator, dental assistant ALL should wear
protective eye glasses.

105.  Ear precautions:
 Noise levels more than 75db may cause hearing
damage.
 Prevention:
o Use ear plugs
o Sound proofing of rooms

106.  Inhalational precautions:
 Aerosols & vapors produced while cutting with
rotary instruments all hazardous.
 May cause alveolar irritation & tissue reactions.
 Prevention:
o Use rubber dams,
o Mouth masks etc.

107. References
 Art And Science Of Operative Dentistry, Sturdevent..5th Edition
 Principles and practice of operative dentistry second edition Gerald T. Charbencau.
 Operative dentistry, modern theory and practice. 1st
edition Marzouk.
 Textbook of operative dentistry. 3rd
edition vimal k sikri.
 Text Book of operative Dentistry. Second edition Baum Philips hand.
 CUTTING EFFICIENCY OF THREE DIAMOND BUR GRIT SIZES.
SHARON CRANE SIEGEL, D.D.S., M.S.; J. ANTHONY VON
FRAUNHOFER, M.SC., PH.D 1996;JADA vol.127

108. Thank You
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