This document provides an overview of the history and development of rotary dental instruments. It discusses the evolution from early hand-rotated instruments to modern electric and air-driven devices. It also classifies rotary instruments according to design, speed, and cutting bur shape/size. Advantages of rotary instruments include reduced time/operator fatigue and improved precision compared to hand tools. Factors like speed, pressure, heat production, and vibration are also examined.

2. ContentsIntroduction
Historical development
Classification
Advantages
Maintenance of instruments
Cutting points
 Burs
 Types
 Design
 Factors influencing cutting
 Dental abrasive stones
 Types
 Factors influencing cutting
Limitations of rotary instruments
Conclusion

3. Introduction
The removal and shaping of tooth structure is
essential aspect of dentistry
The term “rotary” applied to tooth cutting
instruments, describe group of instruments that
turn on its own axis to perform work
Introduction of rotary powered cutting
equipment was a truly major advance in dentistry

4. Practical application of rotary instruments can be:
 Penetration
 Extension
 Excavation
 Refinement
 Today cavity preparation made with rotary
instruments is 90% and only 10% tooth preparation
accounts for hand instruments
 This seminar will guide us the application and types
of rotary equipment and instruments used

5. History
There is evidence that Maya (250 AD – 900 AD)
and other ancient cultures used primitive “bow
drills” and other devices
Used to prepare round ornamental cavities

6. First rotary instruments – drill or bur heads,
twisted into fingers for crude cutting or abrading
action
Dr. Taft (1728) – “bur drills”
Ranged in diameters – 1/32 " – 1/5 "
Simple rotary instrument, twisted in fingers –
very limited cutting

7. One of refinements – Scranton’s drill
Could be rotated in either direction to achieve cutting
Next modification – drill-ring
(1800)
Ring – adapted to middle or
ring finger with a socket
fitted against palm, providing
seat for blunt end of drill
Front end rotated with
thumb and forefinger

8. In 1850s another type of hand drill – developed by
Angle for indirect access preparations
Consists of handle and spring loaded bur
Bur activated- squeezing spring loaded handle

9. During 1870s efforts were made to make designs
to bring the bur to bear in various directions and
was hand powdered
Merry’s drill stock is example of this modification
This was a type of Angle handpeice

10. Techniques were
improved significantly
when Morrison modified
and adapted the dental
foot engine from singer
sewing machine in 1878
For the first time cutting
procedures were carried
out with a power source
other than operators
hand

11. 12 years later in 1883, the
electric dental engine linked
to the handpeice by flexible
cable arm was introduced
This was first time, cutting
made possible – power source
other than human hands or
feet
Consists of – foot control
with rheostst (w), belt driven
straight handpeice (x), three
piece adjustable extension
arm (y), and electric motor
(z)

12. Dental foot engine was incorporated into dental
unit in 1914
In early 1950s, the ball bearing handpeice was
introduced
In 1953, following the work of Nelson, the first
fluid turbine type of handpeice was developed
Initially it was capable of rotational speed – 50,000
rpm, was operated at one speed only
Soon after in 1954- air driven handpeices were
developed

13. A continuous belt – driven contra-angle handpiece
was introduced in an attempt to increase rotational
speeds upto 1,50,000 rpm
By introduction of air-driven handpiece , by 1957
many dentists capable of using rotational speeds
upto 3,00,000 rpm
The major breakthrough – development of
handpiece with internal turbine drives
By 1960s – possible to use greater rotational speed
– 5,00,000 rpm

14. Evolution of rotary cutting equipment in
dentistry
Date Instrument Speed(rpm)
1728 Hand rotated instrument 300
1871 Foot engine 700
1874 Electric engine 1000
1914 Dental unit 5000
1942 Diamond cutting inst 5000
1946 Old units converted to increase speed 10,000
1947 Tungsten carbide burs 12,000
1953 Ball bearing handpieces 25,000
1955 Water turbine handpiece 50,000
1955 Belt-driven handpiece (Page-Chayes) 1,50,000
1957 Air turbine handpiece 2,50,000
1962 Experimental air bearing handpiece 8,00,000
1994 Contemporary air turbine handpiece 3,00,000

15. ClassificationAccording to design:
 Straight
 Contrangle
Straight handpiece:
Long axis of bur – same as long axis of handpiece
More frequently used- lab , less frequently clinically
Contra-angled handpiece:
Primary hand piece in oral procedures
Head angled – first away from and back towards long axis
Ensures- working point within 2-3 mm of long axis, balance

16. According to speed ranges:
 Strudavent:
Low or slow speed <12,000 rpm
Medium or intermediate 12,000 – 2,00,000 rpm
High or ultra-high > 2,00,0000 rpm
 Marzouk:
Ultra-low speed 300 – 3000 rpm
Low speed 3000 – 6000 rpm
Medium high speed 20,000 – 45,000 rpm
High speed 45,000 – 1,00,000 rpm
Ultra-high speed 1,00,000 rpm and more

17. AdvantagesTime: because of high speed time required very less
Energy: compared to early rotary instruments –
make use of energy other than manual energy
Mainly reduces operator fatigue
Pressure: in case of hand instruments- pressure or
force applied for removal of tooth substance –
unwanted
High speed of rotary- no pressure or negligible pressure
Precision: by attaning good control over these
instruments- tooth structure removed and shaped
precisely

18. Characteristics of rotary instruments
Speed:
Refers to not only revolutions pre minute, but also
surface feet per unit time of contact that tooth has
with work to be cut
Maximum cutting efficiency of a cutting tool of
uniform width ranges- 5000-6000 surface feet pre
minute
Surface feet per minute – controlled mainly by rpm
and surface feet per minute

19. Important to consider size of rotating tool in
relation to speed of operation
Rotary tool – used with low speed – should be
larger in diameter to approach optimum surface
feet per unit time
Ultra-high speed range – diameter of tool reduced
to limit cutting efficiency

20.  Pressure:
 Resultant of 2 factors under control of dentist
1. Force (F) – gripping of handpiece in position and
application to tooth
2. Area (A) – amount of surface area of cutting tool in contact
with tooth surface in operation
P F
A
 Same force F, smaller tools – apply more pressure
to point of contact than larger tools
 To have cut both smaller and larger tools at same
pressure – necessary to reduce force applied with
smaller ones
= -

21. Larger tools remove more tooth structure –
increase surface per minute contact of smaller
tools by increasing rpm
Clinically low speed- 2-5 pounds of force, high
speed 1 pound, ultrs high sped 1-4 ounce for
efficient cutting
More desirable features of higher speed – better
control , less fatigue, greater patient comfort

22. Heat production:
Heat is directly proportional to:
Pressure
RPM
Area of tooth in contact with tool
Cause pulps of teeth permanently damaged if temp
of 130°F is reached
Absolute necessity – coolants may be employed to
eliminate pulpal damage
 various methods – flowinf water, water air spray, or
air
Pressure – resultant of applied force, reduction of
force will minimize heat production

23. Vibration:
It is product of equipment used and speed of
rotation
Delirious effects of vibration two-fold in origin
 Amplitude
 Undesirable modulating frequencies
Amplitude:
Wave of vibration – frequency and amplitude
Low speed – amplitude larger, frequency smaller
High speed – amplitude small, frequency large
Greater harm - amplitude

24. It is factor most destructive to
instrument , causes apprension
in patient and greatest fatigue
for dentist
Increasing operating speed –
amplitude and effects are
reduced
Vibrational waves – measured
in cycles
6000 rpm – 100 cycles per sec
As vibration increases, cycles
per sec of vibrational waves are
increased

25. A wave of vibration over 1300 cycles /sec –
vibrations practically imperceptible to patient
Higher speed – less amplitude and greater
frequency
As a result – perception will be lost in ultra high
speed of >1,00,000 rpm

26. Undesirable modulating frequency:
Are series of vibrations in all directions perceived
by patient and dentist
End result – apprehension in patient, fatigue for
dentist and accelerated wear of cutting
instrument
Fundamental vibrational wave – set up when
handpeice turbine is runing

27. Each piece of remaining attachment will vibrate
Each will set up modulating frequency or
‘overtone’ accompanying the fundamental wave
Patient and dentist – subjected to basic wave and
other accompanying waves
Objective of operator – eliminate these effects by
having equipment free from any defects

28. Friction:
Will occur in many parts of handpeice, in turbine
Critically important – high speed or above
Friction between moving parts – less reduce
damage to instrument and obstruction in free
running tool
To reduce this – bearings incorporated
Different bearings – ball bearings, needle bearings,
glass in resin bearings have been uesd by different
manufacturers

29. Torque:
It is ability of handpeice to withstand lateral
pressure on revolving tool without decreasing its
speed or reducing cutting efficiency
It is dependent on type of bearing used and
amount of energy supplied to handpiece

30. Maintenance of instrument
Because of sensitivity of rotary equipment and
their parts , these are not sterilized as other
instruments
It is usually sterilized by using different method
suitable for the instrument
Chemical sterilizing agent through the hand piece
in an compartment

31. To reduce the friction of rotating parts of
handpeice, agents should be applied
These are usually lubricant sprays available
These are oily in nature and reduces the friction
of the components

32. Cutting points
Burs
The term bur is applied to all rotary cutting
instruments that have bladed cutting edges

33. Historical development
The earliest burs were hand made
They were variable in dimension and performance
First machine made burs introduced in 1891
Early burs – steel
Perform well – cutting human dentin at low speed
But dull rapidly – higher speeds or cutting enamel
Dulled burs – reduced cutting efficiency, increased
heat and vibration

34. Carbide burs – 1947, have largely replaced steel
burs
Steel burs - now mainly used for finishing
Carbide burs – perform better than steel burs at
all speed and superiority is greatest at high speed
Much harder than steel and less subjected to
dulling during cutting
Carbide head is attached to a steel shank and
neck by welding or brazing
Carbide is stiffer and stronger than steel, but it is
also more brittle

35. Parts:
Shank:
Part that is secured in hand piece to hold and
drive the bur
Shaft:
Connects shank to head of bur
Head:
Contains the blades that cut the tooth

36. General design
Bur tooth:
It is projections from the bur which aid in cutting
They terminate in cutting edge or blade
Has two surfaces:
 Tooth face – side of the tooth on leading edge
 Back or flank – side of the tooth on the trailing edge

37. Rake angle:
Angle that face of bur tooth makes with radial
line from the center of bur to blade
Angle can be negative if face is beyond or leading
the radial line
Can be 0 if radial line and tooth face coincide
with each other
Can also be positive if radial line leads the face

38. Land:
The plane surface immediately following the
cutting edge

39. Clearance angle:
Angle back of tooth and work
If land is present – clearance is divided into two:
 primary clearance – angle the land will make with work
 Secondary clearance – angle between back of tooth and
work
 Back surface of tooth is curved – clearance angle is
called radial angle

40. Tooth angle:
Measured between the face and blank
If land present – measured between face and land

41. Flute or chip space:
The space between successive teeth
no. teeth in dental cutting cutting burs usually-
6-8

42. Burs classification system
To facilitate description, selection and
manufacture – highly desirable to have shorthand
designation
In US – traditionally described in arbitrary
numerical code for head size and shape
eg.-2 = 1mm diameter round bur
57 = 0.8mm diameter inverted cone bur
Despite complexity – common in use
Other countries – similar arbitrary systems

43. Newer classification systems - Federation
Dentaire internationale (FDI) and international
standers organization (ISO)
Use a separate designation for shape (shape
name) and size (diameter in tenths of millimeter)
are used
Eg.- round 010, straight fissure plain 020 inverted
cone 008

44. Classification
According to mode of attachment:
Latch type
Friction grip
According to direction of motion:
Right – move clockwise
Left – anti-clockwise
According to length of shank:
Short shank
Long shank

45. According to their shape and sizes:
Round burs:
Numbered from ¼, ½, 1,2, to 10
Round in shape
Uses: - initial tooth penetration
 placement of retention grooves

46. Wheel burs:
Numbered – 14 and 15
Wheel in shape
Uses – placement of grooves
 gross removal of tooth structure
Inverted cone burs:
Numbered – 33 ¼, 33 ½, 34, 35, to 39
Have an inverted cone shape
Uses – in cavity extensions
 establishing wall angulations and retention
forms
Flatten the pulpal floors

47. Plain cylindrical fissure burs:
Numbered – 55 to 59
Bur teeth cut – parallel to long axis of teeth
– called straight
Or cut obliquely to long axis of teeth –
called spiral, have better unclogging
Cross-cut cylindrical fissure burs:
Numbered from 555 – 560
Teeth can cut parallel to long axis (straight)
or obliquely (spiral)
Uses – gross cutting
 cavity extension and creation of walls

48. Plain taper fissure:
Numbered – 168 – 172
Tapered cylindrical head
Teeth can be straight or spiral
Cross- cut tapered fissure bur:
Numbered – 699 – 703
Can also be straight or spiral
Uses – same as that as straight fissure burs
 mostly used in cutting cavities for inlays

49. Round nose- fissure burs:
All eight types of fissure burs can be
round-ended
No 1 will be added to previous
numbering to denote round nosing
Eg.- round-nose plain cylindrical burs
no- 156-159.
- round-nose tapered fissure burs
no from 1169-1172
Uses – for extension of cavities

50. Pear shaped burs:
As name indicates, shaped like pears
Numbered – 229 – 333
Uses - Mainly used in pedodontics
End cutting burs:
Cylindrical in shape
Just the end carrying blades
Numbered – 900- 904
Uses – in extending preparations apically
without axial reduction

51. Factors influencing cutting efficiency
Rake angle:
More positive – greater cutting efficiency
Burs with radial angles cut more effectively than
designs with negative rake angles

52. Negative rake angle – cut chip moves directly
away from the blade edge and often fractures into
small bits
Positive rake angle – chips are larger and tend to
clog the chip space
Positivity of rake angle – decreases size of bur
tooth and tooth angle – decreasing its bulk

53. As a result, greater possibility – bur teeth will be
curved, flattened, or even fractured during cutting
Positive rake angle – can be used with tungsten
carbide burs where there is greater hardness and
strength of the material

54. Clearance angle:
Provides clearance between the work and cutting
edge to prevent tooth back from rubbing on work
There is always a component of frictional force on
ant cutting edge as it rubs against the surface
Slight wear of cutting edge – increase the duling
perceptibility
Larger clearance angle – less rapid dulling of bur

55. No. of teeth or blades:
No. of teeth in a bur is usually limited to 6-8
The external load is distributed among the blades
As no. of blades decreased – magnitude of forces at
each blade increases and thickness of chip removed
by each flute increases
Reason for construction of burs with fewer teeth-
increased space between bur teeth - decreases the
clogging tendency

56. Each bur tooth – removing more material-
tendency of tooth wear greater and cutting life
reduced
Bur with straight flutes- less temperature than
one with spiral flutes
Formation of large chip by straight flutes- chip
then carries some heat energy
Bur with fewer flutes – cooler with operating

57. However, fewer the no. of bur teeth –
greater the tendency of vibration
If there are two or more blades in
contact with work at one time, this effect
is reduced
If bur teeth are cross-cut – tendency is
to increase no. of teeth , based on
assumption that cross-cutting reduces
friction in cutting and provides more
chip space
Burs – 10-12 or even up to 40 blades
Used only for finishing and polishing

58. Run – out:
Refers to eccentricity or displacement of bur
head from its axis of rotation while it turns
Average value of clinically acceptable- 0.023mm
Also depends on precision of handpeice
Shaft or collar, holding the bur wobbles – effect is
magnified at bur head
Efficiency in cutting is definitely affected by run-
out

59. If bur moves away from tooth periodically – all
blades will not cut equally
Operator senses lack of cutting – greater force
will be exerted on bur
Structure will be removed by shattering rather
than cutting
Such removal of tooth structure – inefficient,
inaccurate and increases heat generation

60. Finish of flutes:
Bur formed – cutting each flute into bur blank with
rotating tool
During 1st
cut or pass of cutter- flute is roughly formed
2nd
cut – places cutting edge on bur flute
Roughness will remain along the flute
Roughness removed - making subsequent passes or
cuts on the flute
Those cut 6 times- more efficient, cut 2 times- least
efficient

61. Heat treatment:
Used to harden the bur made of soft steel
Done by heating the bur according to metal used
to a temperature below its melting temperature
It is then allowed to come to room temp slowly
This operation – preserves edge placed on bur flute
by the cutter , and hardens the bur to increase the
cutting life

62. Design of flute end:
Formed with 2 different types of end flutes:
Revelation cut – flutes come together at 2
junctions near a diametrical cutting edge
Star cut – end flutes come together in common
junction at axis of bur
Revelation type shows more superiority in direct
cutting
Both show equal efficiency in lateral cuting

63. Bur diameter:
Factor on which the volume of material removed
will vary
More the diameter head, more will be amount of
material removed and vice versa
Forces on each bur tooth, linear displacement
and length of cut do not depend on diameter
It is because length is constant

64. Depth of engagement:
As depth of engagement is decreased – force
intensity on each small portion of bur tooth is
increased
The average displacement per flute revolution
should also be increased
This increase can be such that volume of material
removed by shallow cut exceeds that of deeper
cuts

65. Influnce of load:
It signifies force exerted by dentist on tool head and
not pressure or stress induced in the tooth during
cutting
Load exerted is related to speed of the bur
It is estimated that 2 pounds- for low speed and 2-4
ounces- high rotational speed
Generally – every range of speed at which bur is
rotating has a minimum force or load under which
cutting efficiency of bur used is decreased
So range do low speed- 1000-1500gm and that for
high speed- 60-120gm

66. Influence of speed:
Rate of cutting increases with rotational speed,
but this increase is not directly proportional
Rate of cutting is increased at a rotational speed
above 30,000 than below this
The time required for removal of same weight of
tooth structure at a speed 0f 1,50,000 and above is
nearly the same
Conclusion – no time is saved by dentist when
rotational speeds are employed higher than
1,50,000 rpm

67. Dental abrasives
Designs:
The shape used for burs
are similar used of
abrasives
Only difference is bur
contains cutting edges
where as this contains
abrasive particles

68. Abrasive particle are held together by means of
“binder” (base)
Different binders are usually used
Ceramic binder – diamond chips
Metallic binder is used in electro plating of
particles
Rubber or shellac – soft grade stones
Type of binder – related to life of tool
Later types wear rapidly, useful only in delicate
cutting

69. With most abrasives – binder is impregnated
throughout with abrasive particles of certain
grade
Abrasive distributed evenly - the surface of tool
wears evenly
Wide spacing between particles – room for
resultant debris less chance of packing or clogging
Some abrasives glued to paper that can be
attached to handpeice through mounting tools

70. Parts

71. According to composition of abrasive particles,
are of following types
Diamond stones:
Hardest and most efficient abrasive stones for
removing tooth enamel
Diamond chips are bind together with either
ceramic binder or more efficient metallic binder

72. Carbides:
May be silicon or boron carbides
Manufactured by heating silicon or boron at high
temperature to affect union with carbon
Carbides are sintered or pressed with binder into
grinding wheels, disks or stones
Sand:
Sand and other forms of quartz can be bound
together with adhesives
Mounted into different shapes of discs stone and
strips

73. Aluminum oxide:
Natural or extracted pure aluminum – most
efficient abrasive in fine cutting
Particles are sintered on the surface
Garnet:
These particles contain a no. of different minerals
with similar physical properties and crystalline
form
Stones made from these used for finishing and
polishing of dental appliances

74. Factors influencing abrasive efficiency
Irregularity in shape of partices:
Irregular in shape – a sharp edge
Smooth particle – poor abrasive property
Cubical particles- flat face and not efficient
More irregular particles – greater abrasive
efficiency

75. Hardness of abrasive material:
If abrasive cannot indent the surface, it cannot
remove any of that material
Abrasive will dull in such a case
Harder abrasive relative to hardness of material –
more abrasive efficiency

76. Impact strength of abrasive material:
During rotation – abrasive particles strike work
suddenly
If it engages and doesn't fracture – become dull
The abrasive should fracture rather than dull so
sharp edges are always present
Fracture of abrasive – shedding of debris
Diamond stones do not fracture but loose
substance
Because of their hardness – most efficient in
removal of very hard and brittle tooth enamel

77. Size of abrasive particles:
Larger particles – deeper scratches on
surface – faster the material will be
removed
Pressure and rpm:
Same factors are involved as discussed in rotary
instruments
Both factors are proportional to the abrasive
efficiency

78. Limitations
Tactile sensitivity: it is sensation while cutting to
which control is necessary
For rotary instruments it is less, especially at higher
speeds
Heat production: it is a major factor in rotary
instrument application
Due to high speed and friction heat production is more
If not controlled may lead to damage to pukp tissue

79. Source of power: at present source of power
applied to rotary instruments is other than human
power
Any deficiency or variation in power will affect the
continuity of work
Control of cutting: due to rotary nature of cutting
there needs to be more control of instrument for
the amount of removal to be controlled
Sterilization: because of sensitivity of these
instruments these equipments cannot be
efficiently sterilized by regular methods

80. Conclusion
In present operative procedures majority of the
work is carried out with rotary instruments
Although other alternatives have been evolving
for removal of tooth structure, rotary cutting is
most practically used
For better dentistry it is then necessary to have a
knowledge about these instruments and their
applications

81. References
Art & science of operative dentistry
Strudavent ..5th
ed
Operative dentistry
M.A.Marzouk ..1st
ed
Principles & practice of operative dentidtry
G.T.Charbenau ..3rd
ed
Fundamentals of operative dentistry
James B. Sumitt ..3rd
ed
Operative dentistry
Gillmore ..4th
ed
Pickards manual of operative dentistry
E.M.A.Kidd ..8th
ed