This document discusses rotary instruments used in operative dentistry. It begins by introducing rotary instruments which include handpieces and cutting burs. It then describes different types of handpieces and their uses. The document outlines speed ranges for rotary instruments and discusses factors that influence the efficiency of cutting burs such as design, shape, material. It also summarizes diamond abrasive instruments and other abrasives used for shaping, finishing and polishing restorations. In summary, the document provides an overview of rotary instruments and burs used in restorative dentistry and factors affecting their cutting efficiency.

1. Rotary Instruments
in Operative Dentistry DR ASHWINI M PATIL
Reader
Navodaya dental college
Raichur

2. Introduction
• Removal and shaping of tooth structure is an essential part of restorative dentistry.
• Initially this was a difficult process accomplished entirely by the use of hand
instruments.
• In order to perform the intricate and detailed procedures associated with operative
dentistry, the dentist must have a complete knowledge of the purpose, availability
and application of the many instruments required.
2

3. • Rotary instruments includes:
•Hand Pieces
•Burs
•Polishing instruments
3

4. Type of Handpiece
•STRAIGHT handpiece
• Long axis of bur lies in same plane as long axis of handpiece
• Used in oral surgery and lab procedures.
•CONTRA-ANGLED handpiece
• Head of the handpiece is first angled away from and then back towards
the long axis of the handle
• Because of this design, bur head lies close to long axis of the handle of
handpiece which improve accessibility, visibility and stability of
handpiece while working.
4

5. •CONTRA-ANGLED handpiece
i. Air-Rotor Contra-angle handpiece
• Gets power from compressed air
supplied by the compressed
• Handpiece has high speed and low
torque
ii. Micromotor handpiece
• Gets power from electric motor or air-
motor
• Has high torque and low speed
5

6. Speed Ranges in Rotary Instruments
6
• Rotational speed of an instrument is measured in revolutions per
minute
• According to Sturdevant:
•Low speed
•Medium/Intermediate
speed
•High / Ultra high
speed
: < 12,000 rpm
: 12,000 –
2,00,000 rpm
: > 2,00,000 rpm

7. • According to
Marzouk:
•Ultra low
•Low
•Medium high
•High
•Ultra high
7
: 300 – 3,000 rpm
: 3,000 – 6,000 rpm
: 20,000 – 45,000 rpm
: 45,000 – 1,00,000
rpm
: > 1,00,000 rpm

8. • Low speed cutting is ineffective, time consuming and requires relatively heavy force
application.
• Results in heat production
• Heat and vibration are the main sources of patient discomfort.
• At low speeds, burs roll out of the tooth preparation.
• Carbide burs are easily broken at low speeds due to their brittle nature of the blades.
• Low speed mainly used for cleaning teeth, occasional caries excavation, finishing and
polishing procedures.
8

9. •Advantages of high speed includes:
•Diamond/carbide instruments remove tooth structure faster
with less pressure, vibration and heat generation.
•Operator has better control and greater ease of operation
•Instruments last longer.
•Patients are less apprehensive as the operating time is reduced.
9

10. •Color Coding for handpieces based on speed:
• Coding indicates the relative gear ratio of each component and are
present in the form of dots / rings :
• Blue
• Green
• Red
: No change in speed
: Speed Reduction
: Speed increase
10

11. Rotary Cutting Instruments
•These are individual instruments intended for use with
handpieces and are available in various shapes and
sizes.
•Common design characteristics
•Bur classification systems
•Modification in bur design
11

12. COMMON DESIGN
CHARACTERISTICS
•Each instrument
consists of 3 parts:
•Head
•Neck
•Shank
12

13. SHANK DESIGN
13
• Part that fits into the hand piece, accepts the rotary motion from
the handpiece
• Shank design and dimensions vary with the hand piece for which it
is intended for.
• ADA Specification No. 23 for dental excavating burs includes 5
classes

14. 1. Straight hand piece shank
• Shank portion : cylindrical, held by a metal chuck
that accepts a range of shank diameters.
• Straight handpiece are now used for finishing and
polishing completed restorations.
14

15. 2. Latch-type handpiece shank
• Complicated shape of this shank reflects the mechanism by which
these are held in the hand piece.
• Shorter overall dimensions – permits easy access to posterior
regions in mouth.
• Handpiece has a metal tube within which the instrument fits
15

16. • Posterior portion of shank is flattened on one side, end fits
into a D-shaped socket at the bottom of the bur tube.
• Retained by a latch that slides into D-shaped socket
• Used in slow and medium speed.
16

17. 3. Friction-grip shank design
• Developed for its use in high speeds.
• Overall dimensions are smaller thus increasing access in
posterior teeth.
• Simple cylinder manufactured very close to
dimensional tolerances.
• Designed to be held in handpiece by friction between the
metal chuck.
17

18. NECK DESIGN
• Portion that connects the head to the shank.
• Neck normally tapers from the shank to the head.
• Main function - transmit rotational and transitional force to head.
• Also provides visibility and ease of operation.
• For this reason neck diameter is a compromise between strength and improved
access and visibility.
18

19. HEAD DESIGN
• It is the working part of the instrument - cutting edges or points.
• Shape and material are closely related to its intended application and technique
of use.
• Head design forms the basis of instrument classification, such as; bladed
instrument or abrasive instrument.
19

20. MATERIALS used in Manufacture of burs
•Steel Burs
• First developed burs
• Designed for slow speed <5,000 rpm, dull rapidly at high speeds.
• Once they are dulled, cutting efficiency is reduced, increasing heat and
vibration.
20

21. • Tungsten Carbide Burs
21
• Harder than steel, so does not dull rapidly.
• Carbide is more brittle and more susceptible to fracture when
subjected to sudden blow.
• Most carbide heads are welded or brazed to a steel shank and neck.

22. BUR CLASSIFICATION
SYSTEMS
Classification systems developed by FDI & ISO to use separate
designations for shape head and head diameter, measured in tenths of a mm.
SHAPES:
Round:
• Spherical
• Used for initial tooth entry, extension of
preparation, preparation of retention features and
caries removal.
22

23. Inverted cone:
•Portion of a rapidly tapered cone with apex
towards the neck.
•For providing undercuts in tooth preparation.
Pear shaped:
•Portion of a slightly tapered cone with small
end of the cone directed towards the bur shape.
•For providing undercuts in tooth preparation.
23

24. Straight Fissure:
•Elongated cylinder
•Used for amalgam preparations.
Tapered Fissure:
•Head tapered away from the shank
•Used for indirect restorations
24

25. CLASSIFICATION
25
• According to Mode Of Attachment to handpiece
• Latch type
• Friction type
• According to Composition
• Stainless steel
• Tungsten carbide
• Combination of both
• According to their Motion
• Right bur : clockwise
• Left bur : anti-clockwise

26. • According to their Length
•Long
•Short
•Regular
26
• According to their Use
•Cutting
•Finishing
•Polishing
• According to their Shape
• Round
• Inverted cone
• Pear shaped
• Wheel
• Tapering fissure
• Straight fissure
• End cutting bur

27. BUR DESIGN
• Bur head consists of uniformly spaced
blades with concave areas between
them.
• Normally a cutting bur has 6, 8 or 10
blades and a finishing bur has 12-40
blades.
• Concave areas are called the chip/flute
spaces.
• Actual cutting of the bur takes place at
the edge of the blade.
27

28. Parts of a Bur head
includes :
Bur Blade
• Blade is a projection on the bur head which forms a cutting
edge.
• Each blade has 2 sides:
• Rake face / blade face (surface of blade on leading edge)
• Clearance face (surface of blade on trailing edge)
• 3 important angles:
• Rake angle
• Edge angle
• Clearance angle
40

29. Rake Angle
• Most important design characteristic of a
blade.
• Angle between the rake face and the radial
line.
• Positive rake angle: when rake face trails the
radial line
• Negative rake angle: when rake face is ahead
of radial line
• Zero rake angle: when rake face and radial line
coincide
41

30. Blade Angle / Edge Angle
• Angle between the rake face and the clearance
face.
• Increasing the edge angle, reinforces the
cutting edge and reduces the likelihood of the
edge of the blade to fracture.
30

31. Clearance Angle
• Angle between the clearance face and the work.
• Primary Clearance angle: Angle the land
makes with the work
• Secondary Clearance angle: Angle between
the back of the bur tooth and the work
• Significance:
• Clearance angle provides a stop to prevent
the bur edge from digging into the tooth
and provides adequate chip space for
clearing the debris.
31

32. Concentricty
• Direct measurement of the symmetry of the bur
• Ie. It measures whether the blades are of equal
length or not.
Runout
• Measures the accuracy with which the tip of the blades
pass through a single point when bur is moving.
• Ie it measures the maximum displacement of the bur
head from its center of rotation
32

33. Runout occurs if:
• Bur head is off center on the axis of bur
• Bur neck is bent
• Bur bur is not held straight in handpiece
chuck
Runout causes:
• Increased vibration during cutting
• Causes excessive removal of tooth
structure.
33

34. FACTORS AFFECTING CUTTING EFFICIENCY OF BUR
1. Rake Angle, Clearance Angle, Blade Angle
• More positive rake angle, greater is the cutting efficiency.
• However it has major drawback:
i. Positive rake angle produces chip, that is larger and tends to clog
the flutes
•Negative rake angle has a smaller chip and moves away from
the blade
34

35. • Increase in clearance angle reduces the blade angle, thereby decreasing the
bulk of the blade.
• Increasing the blade angle reinforces the cutting edge and reduces chance of
the blade edge to fracture.
35

36. 2. Concentricity and Runout
• It is the direct measurement of the symmetry of the bur
head.
• An indication of whether one blade is longer than the
other.
• Runout is the maximum displacement of the bur head
from the axis of rotation.
• Average clinically accepted runout is 0.023mm
36

37. 4. Heat treatment
37
• Used to harden a bur made of soft steel
• This process preserves the cutting edge and hardens the bur to improve its
life.
5. Influence of load
• Load signifies the force exerted by the dentist on the tool head and not that
pressure or stress induced in the bur during cutting.
• Load or force exerted is dependent on the speed of the handpiece.
• Slow Speed
• High Speed
: 1000 – 1500 gm (1-2 pounds)
: 60 – 120 gm (2-4 ounces)

38. 6. Influence of speed
• At a given load, rate of cutting increases with increase in speed, but this
increase is not directly proportional.
• There is also a minimum rotational speed for a given load below which
the tool will not cut.
6. Number of blades
• No. of blades are restricted to 6-8.
• Decreasing the no. of blades, increases the force on one blade and also
increases the size of the chip removed.
• Also it tends to reduce the clogging tendency since the flute space is larger.
38

39. • Major drawback of lesser no. of blades:
• Tendency of bur tooth wear is more
• Cutting life is reduced
• Increased tendency for vibration
8. Design of Flute ends
• 2 types
• Star-Cut Design : Flutes come together at a
common point on the axis of the bur
• Revelation Design : Flutes come together at
two junctions near the diametrical cutting edge.
• Revelation design is more efficient in direct cutting 39

40. MODIFICATIONS IN BUR DESIGN
40
Modifications were seen with the introduction of high speed hand
pieces.
• 3 major changes includes:
• Reduced use of crosscuts
• Extended heads on fissure burs
• Roundening of sharp tip angles

41. • Reduced use of crosscuts
• At high speeds, produce rough surface.
• Newer burs have reduced no. of crosscuts.
• Extended heads on fissure burs
• Carbide fissure burs with extended head lengths 2-3 times those of normal
tapered fissure burs of similar diameter have high efficiency at higher speed with
light pressure.
• Roundening of sharp tip angles
• Proposed by Markley & Sockwell
• Such burs will result in lower stress in restored teeth
• Burs last longer
41

42. Diamond Abrasive Instruments
• They have a greater clinical impact due to long life and effectiveness in cutting enamel and
dentin.
• Introduced in United States in 1942 and was used popularly as grinding and finishing
agents.
Terminology:
• Diamond instruments consists of 3 parts:
• Metal blank
• Powdered diamond abrasive
• Metallic bonding material
42

43. • Metal blank resembles a bur without blades
• 3 parts: Head, Neck & Shank
• Head of blank is slightly smaller than the final dimension of
the instrument head to accommodate for the thickness of
abrasive layer.
• Neck gradually tapers from the shank to the head.
• For large disk/abrasives, it may not be reduced below the
shank.
• Diamonds maybe either natural or synthetic; that are crushed
to a powder of desired particles in size and shape.
HEAD
43
NECK
SHANK

44. • These are held against the blank while it is being electroplated
with a metal.
• Done in multiple layers to provide a continuous regeneration of
cutting surface as wear occurs.
Classification
Classified based on average particle size of the abrasive:
• Coarse grit
• Medium grit
• Fine grit
• Very fine
: 125 – 150 μm
: 88 – 125 μm
: 60 – 74 μm
: 38 – 44 μm
44

45. Head shapes and sizes
• Available in wide variety of shapes and sizes.
• Because of their design which an abrasive layer over an underlying blank, the smallest
diamond instrument cannot be as small in diameter as the smallest of burs, but a wide
range of sizes are available for each shape.
45

46. FACTORS INFLUENCING THE ABRASIVE EFFECIENCY AND EFFECTIVENESS
1. Size of the abrasive particle
• Larger the particle size, more deeper is the penetration on the surface of the work,
hence rapid removal of the material occurs.
2. Shape of the particle
• Should be irregular in shape for greater efficiency.
• Irregular particles – sharp edge
• So cuts better than round smooth or cuboidal particles which have a flat edge.
46

47. 3. Density of abrasive particles
• Refers to the no. of abrasive particles per unit area.
• High density : closely spaced
• Low density : widely spaced
• Therefore, greater force will be exerted on each particle with low density when
the particles are widely spaced increasing grinding efficiency.
• Coarse grit have low density compared to fine grit.
47

48. 4. Hardness of abrasive particles
• To be effective, hardness of abrasive particle should be greater than that of the
work.
5. Clogging of the abrasive surface
• Clogging of debris between the spaces of the abrasive particles affects grinding
because this partially blocks the penetration of the abrasive particles into the
surface.
• Clogging is enhanced when particles are close together.
• Use of coolant washes away the debris and prevent clogging.
48

49. 4. Speed and Pressure
49
• Usual cause of failure of abrasive instruments is when excessive pressure is
applied onto them to increase cutting efficiency at inadequate speeds.
• This results in loss of diamonds decreasing their cutting efficiency.

50. Other Abrasives
50
Many types of abrasive were used in addition to diamond instruments. Now
they are restricted to shaping, finishing and polishing restorations.
Classification
In these instruments, the head is composed of abrasive particles, held in a continuous
matrix of softer material.
Broadly divided as:
• Molded instruments
• Coated instruments

51. MOLDED ABRASIVE INSTRUMENTS
• Have heads that are manufactured by molding or pressing a
uniform mixture of abrasive around a roughened shank or by
cementing a pre-molded head.
• Have much softer matrix and tends to wear with use thus
exposing fresh abrasive particles.
• Rigid molded materials have rigid polymer or ceramic as their
matrix.
• Mainly used for grinding and shaping procedures.
51

52. • Soft molded instruments use flexible matrix materials like
rubber, which are used for finishing and polishing procedures.
• Mounted head are termed as points / stones.
• Unmounted discs / wheel stones are available which can be
attached to a mandrel.
52

53. COATED ABRASIVE INSTRUMENTS
• Mostly discs that have a thin layer of abrasive cemented to a
flexible base.
• Allows the instrument to conform to the surface contour of
the tooth or restoration.
• Unlike molded instruments, coated instruments have to be
discarded when they wear off.
• Used in finishing certain enamel margins/walls for indirect
restorations.
• Most often for finishing procedures for restorations
53

54. Materials Used
54
• Matrix materials used are phenolic resins or rubber.
• Some molded abrasives may be sintered or may be resin bonded.
• A rubber matrix is flexible and allows ease of polishing.
• Non- flexible rubber matrix is used for molded SiC discs.
Silicon Carbide ( Carborundum)
• Molded in forms of rounds, bud-shapes, wheels and cylinders of various sizes.
• Gray-green in color suited for fast cutting except on enamel.
• Produce moderately smooth surface.

55. • Unmounted discs, popularly called as carborundum discs, are black or dark in colour.
• They have a soft matrix and wear easily.
• They produce moderately rough surface.
55
Aluminium Oxide
• Used for the same instrument design as SiC.
• Points are white, rigid, fine textured and less porous.
• They produce smoother surface than SiC.

56. Garnet (reddish) and Quartz (white)
• Used for coated discs
• Available in a series of particle sizes ranging from coarse to medium-fine.
• Used for initial finishing.
• Hard enough to cut tooth and other restorative materials except some porcelain.
56
Pumice
• Powdered abrasive produced by crushing foamed volcanic glass into thin glass flakes.
• Cuts effectively but breaksdown rapidly.
• Used for initial polishing procedure.

57. Cuttlebone
• Derived from cuttlefish
• A soft white abrasive.
• Used only in coated discs for final finishing and polishing.
• It is so soft that it reduces the potential for tooth damage due to its abrasive action.
57

58. Cutting Mechanisms
58
For cutting, it is necessary to apply some pressure so that the cutting tool will dig into
the surface.
The process of rotary cutting is complex and not completely understood.
1. Evaluation of Cutting
• Cutting can be measured in both effectiveness and efficiency.
• Cutting effectiveness is the rate of tooth structure removal (mm/min or mg/min).
• Cutting efficiency is the percentage of energy actually producing the cutting.
• It is reduced when energy is wasted as noise or heat.

59. • It is possible to increase effectiveness while decreasing the efficiency.
• Ie. In general both effectiveness and efficiency can be increased by increasing the speed.
2. Bladed Cutting
• Tooth structure similar to other materials undergoes
brittle and ductile fracture.
• Brittle fracture is associated with crack propagation,
usually by tensile loading.
• Ductile fracture involves plastic deformation of the
material proceeding shear.
59

60. Speed
• Low speed – plastic deformation before tooth structure fracture
• High speed – produces brittle fracture
Strain Rate
• Faster the rate of loading, greater will be the strength, hardness, modulus of elasticity
and brittleness of the material.
• For the blade to initiate the cutting action, it must be sharp, harder with high modulus of
elasticity than the material being cut.
• This helps in exceeding the shear strength of the material being cut.
60

61. 3. AbrasiveCutting
• Similar to bladed cutting in many ways, but key differences result from the properties,
size and distribution of the abrasive.
• Hardness of diamond provides superior resistance to wear and these particles tend to
have a very high negative rake angle.
• When diamond particle cuts through a
ductile material, material will flow
laterally around the cutting point and
be left as a ridge of deformed material
on the surface.
61

62. • Repeated deformation work hardens the distorted material until irregular portion become
brittle and breaks off.
• This is less efficient than bladed cutting; therefore bur are preferred to cut through ductile
material like dentin.
62

63. • When diamond cuts through brittle material, most cutting results from tensile fractures
that produces subsurface cracks.
• Hence they are most efficient to remove enamel than burs.
• Also preferred for use in tooth preparations for bonded restoration, since they increase the
surface area.
63

64. Cutting Recommendations
64
• Requirements for effective and efficient cutting include using
• Contra-angle handpiece
• High operating speed
• Air water spray for cooling
• Light pressure
• Carbide or diamond instrument
• Carbide burs are better for end cutting, produce lower heat and have more blade edges per
diameter for cutting.
• Effective for punch cuts to enter tooth structure, intra-coronal tooth preparation, amalgam
removal, small preparations and secondary retentive features.

65. • Diamonds are more effective than burs for both intra and extra coronal tooth preparation,
bevelling enamel margins and enameloplasty.
65

66. Hazards with Rotary Instruments
Pulpal Precautions
• Injury to the pulp caused by:
• Mechanical vibration
• Heat generation
• Desiccation of the dentin
• Transection of the odontoblastic process.
• The Pulpal sequelae, take 2 weeks to 6 months, depending on degree of trauma.
• The remaining tissue is effective in protecting the pulp in proportion to the square of its
thickness.
66

67. • Heat is produced by:
• Steel burs than carbide burs
• Toolsplugged with debris
• When used without a coolant, diamond abrasives > carbide burs.
• Air-water spray must be used as
• Acts as a coolant
• Moisten the tissues, lubricates
• Cleans and cools the cutting tool thus increasing tool life
• Clear the operating site
67

68. Soft Tissue Precautions
• Injury to lips, tongue and cheek.
• Rubber dam used to isolate soft tissues
• Use good accessibility and visibility to the operative field
• Patient instructed not to make sudden movements.
• If accident occurs, control haemorrhage with pressure pack
• Chance of mechanical pulp involvement during caries excavation is more with hand
instruments than with rotary instruments.
• Residual caries can be removed using a bur at low speed and light intermittent forces.
68

69. Eye Precautions
• Use of protective eye wear
• Eye damage from airborne particles
• High volume evacuation is advised
Ear Precautions
• High pitched sound by some air-turbine handpieces at high speeds.
• Potential damage to hearing depends on:
• Intensity or loudness (decibels- db)
• Frequency (cps)
• Duration of the noise
• Susceptibility of the individual
69

70. • Increased age, existing ear damage disease and medications are other factors that can
accelerate hearing loss.
• Air turbine handpieces at 30 pounds : 70 – 94 db at high frequency.
• Noise levels > 75 db @ of 1000 – 8000 cps : hearing damage.
• Protective measures are recommended for 85 db @ 300 – 4800 cps.
• Protection is mandatory at 95 db.
• Earplugs, sound proof rooms with absorbing materials on walls and floor
• Anti-noise devices can be used to cancel the unwanted sounds as well.
70

71. Inhalational Precautions
• Aerosols are fine dispersion in air of water, tooth debris, micro-organisms and / or
restorative materials.
• Cutting amalgams or composite resin produce both sub-micron particles and vapours.
• Vapours from cutting amalgam - mercury & that from composite resins -monomers.
• Inhalation can produce alveolar irritation & tissue reactions.
• A face mask filters out bacteria and fine particulate matter
but not mercury or monomer vapours.
71

72. Infection Control
72
• Latch angles, burs and rotary stones must be cleaned & sterilized.
• Handpieces are semicritical instruments requiring sterilization
• Motor-end of micro-motor must be covered with a single used disposable plastic bag.
• Scrub and disinfection of the end may also be performed

73. Sterilization of Burs
• Presoak: burs placed in soap water to loosen debris
• Cleaning: Stainless brush under water or ultrasonic systems
• Sterilization by:
• Dry-clave - 160°C for 30min
• Autoclave – 121°C for 15min @ 15 lbs.
• Tendency of corrosion at the neck region, hence soak in 2% Sodium nitrite prior to
autoclaving.
• Chemiclave – chemical vapour under pressure: 131°C @ 20 pounds pressure.
• Best suited for corrosion prone instruments.
73

74. Sterilization of Handpiece
• With metal bearing:
• Scrub the metal bearing with water and soap.
• Lubricate and place in sterilization bag & autoclaved.
• Lube-free ceramic bearing
• Must not be chemically sterilized – damage to internal parts.
• Chemical vapor pressure sterilization
• Ethylene oxide gas
• Provides both internal & external sterilization due to penetrating capacity.
• Takes long time for sterilization.
• Dry heat for handpiece is generally not recommended
74

75. Recent Advances
75
Single patient use burs:
• Developed by CDC & ADA to minimise cross- contamination & prolonged sterilization
protocol
Turbo diamond:
• Have diamond free zone or continual spiral of blank space.
• The diamond free zone breaks surface contact with the tooth, thus allowing cooler &
cleaner cutting.
• The continual spiral design leaves a smooth wall.

76. Fiber-optic handpieces:
• Provide light at the working site.
• Shut off delay – allows illumination even after release at foot control
Cellular optic handpiece:
• Handpiece can be repeatedly sterilized without light degradation.
Lube free ceramic bearing handpiece:
• Do not require lubrication
• Care should be taken against chemicals
76

77. Fissureotomy burs (carbide):
• Tip of the bur is smaller than no. ¼ round bur.
• Helpful in conservative preparations
Smart Prep burs:
• Aka Polymer bur / smart bur
• Made from polymer
• Self limiting
• Effectively remove decayed dentin without affecting
the healthy dentin
77