A detailed explanation of rotary cutting instruments used in operative dentistry. This is based on the Textbook of preclinical conservative dentistry by Nisha Garg and Amit Garg

1. ROTARY CUTTING
INSTRUMENTS
SARA SULTANA
II BDS

2. INTRODUCTION
 Rotary cutting instruments are those instruments which rotate on an axis to do
the work of abrading and cutting on tooth structure
 TYPES:
 1. Handpiece: power device
 2. Bur: cutting tool

3. HANDPIECES
 First rotary instruments: drill or bur heads that were twisted with the fingers for
crude cutting of the tooth tissue.
 Drilling—modification where seat for the drill was provided by a socket fitting
against the palm and the ring was adapted to the index or middle finger
 Mid 19th century- invention and development of both mechanical and pedal
powered handpieces.
 George fellow invented the clockwork drill—bur was attached to it by a shaft with
a rotating spindle inside
 The drill was wound up like a clock with a key inserted into the back.
 Drill used to spin for 2 minutes before needing to be rewound.

4. Electrically driven handpieces
 Electrically driven handpieces—advantageous over the air driven predecessors.
 Heavier and bigger than air-driven handpieces
 Maintain constant speed during cutting which doesn't decrease under load
 Ability to control the rpm rate.

5. Design for better efficiency
 Diameter and bend of handpiece should be designed such that it fits optimally
between thumb and forefinger and also has balanced center of gravity to make
the handpiece feel lighter than its actual weight.
 Head diameter of handpiece should be smaller in size so as to allow greater
visibility and maneuverability.

6. Classification of handpiece
 According to their driving mechanisms: gear driven, water driven, belt driven and air-
driven
 1. Gear driven handpiece: rotary power is transferred by a belt which runs from an
electric engine.
 Power is transferred from the straight handpiece by a shaft and gears inside the angle
section
 Wide speed range
 Work best at low speed because of so many moving parts with metal to metal contact
 2. Water driven handpiece: speed can be up to 100,000 rpm
 Small inner piece transport water under high pressure to rotate the turbine in the
handpiece and the larger outer tube returns the water to the reservoir
 Advantage: quiet, and have highest torque

7.  3. Belt-driven handpiece:
 Speed >100,000 rpm
 Excellent performance and great
 4. Air-driven handpiece:
 Speed= 300,000 rpm

8. Types of handpiece based on design
 Contra-angle handpiece
 Head is first angled away from and then backwards
towards long axis of handle
 Bur head lies close to long axis of the handle of
handpiece which improve accessibility, visibility and
stability of handpiece while working.
 a. Air-rotor contra-angle handpiece: It gets power
from the compressed air supplied by the
compressor. This handpiece has high speed and low
torque
 b. Micromotor handpiece: It gets power from
electric micromotor or airmotor. This handpiece has
high torque and low speed
 Straight handpiece:
 Long axis of bur lies in same plane as long axis of
handpiece
 Used in oral surgical and lab procedures.

10. DENTAL BURS
 “Bur is a rotary cutting instrument which has bladed cutting head.”
 Used to remove tooth surface by chipping it away or by grinding.
 Diamond burs grind away the tooth.
 Diamond particles of < 25 µm size are recommended for polishing procedures
and > 100 µm are used for cavity preparation.
 Diamond particles are attached to bur shank either by sintering or by galvanic
metal bond.

11. Materials used to make burs
 Stainless steel: slow speed (<5000rpm))
 Usually a bur has 8 blades with positive rake angle for active cutting of dentin
 This makes them fragile, therefore short life
 Used for cutting soft carious dentin and finishing procedures
 Tungsten carbide burs:
 Withstand heavy stresses and increase shelf life
 Work best beyond 300,000 rpm.
 6 blades and negative rake angle—better support for cutting edge.
 Head of cemented tungsten carbide in the matrix of cobalt or nickel
 Can cut metal and dentin very well but can produce microcracks in the enamel so weaken the
cavosurface margins
 Diamonds have good cutting efficiency in removing enamel (brittle) while carbide burs cut
dentin (elastic material) with maximum efficiency

12. CLASSIFICATION OF BURS:
 1. ACCORDING TO THEIR MODE OF ATTACHMENT TO THE HANDPIECE:
 Latch type
 Friction grip type
 2. ACCORDING TO THEIR COMPOSITION:
 Stainless steel burs.
 Tungsten carbide burs
 A combination of both

13.  3. ACCORDING TO THEIR MOTION:
 Right bur: cuts when it revolves clockwise
 Left bur: cuts when revolving anticlockwise.
 4. ACCORDING TO THE LENGTH OF THEIR HEAD:
 Long
 Short
 Regular
 5. ACCORDING TO THEIR USE::
 Cutting burs
 Finishing burs
 Polishing burs

14.  6. ACCORDING TO THEIR SHAPES:
 Round bur
 Inverted cone
 Pear shaped
 Wheel shaped
 Tapering fissure
 Straight fissure
 End cutting bur

15. PARTS OF A BUR
1. SHANK
2. NECK
3. HEAD

16. SHANK
 That part of the bur that fits into the handpiece, accepts the rotary movement
from the handpiece and controls the alignment and concentricity of the
instrument.
 The three commonly seen instrument shanks are:
 1. straight handpiece shank
 2. latch type handpiece shank
 3. friction grip handpiece shank

17. NECK
 Connects the shank to the hand
 Main function- to transmit the rotational and translational forces to the head

18. HEAD
 It is working part of the instrument.
 Based upon their head characteristics, the instruments can be bladed or abrasive

19. 1. SHANK DESIGN
STRAIGHT
HANDPIECE SHANK
Shank part of straight handpiece is
like a cylinder into which bur is held
with a metal chuck
LATCH TYPE ANGLE
HANDPIECE SHANK
Posterior portion of shank is made
flat on one side so that end of bur
fits into D-shaped socket at bottom
of bur tube
Instrument is not retained in
handpiece with chuck but with a latch
which fits into the grooves made in
shank of bur.
In contra angle handpiece for
finishing and polishing
FRICTION GRIP
ANGLE HANDPIECE
SHANK
Used in high speed handpiece
Shank- simple cylinder held in the
handpiece by friction between shank
and metal chuck
Smaller than latch type

20. 2. DESIGN OF NECK
 Neck connects head and shank.
 It is tapered from shank to the head. For optical visibility and efficiency of bur,
dimensions of neck should be small but at the same time it should not
compromise the strength.

21. 3. DESIGN OF BUR HEAD
1. ROUND BUR
Spherical in shape, used for removal
of caries, extension of the
preparation and for the placement of
retentive grooves
2. INVERTED CONE
BUR
: It has flat base and sides tapered
towards shank.
It is used for establishing wall
angulations and providing undercuts
in tooth preparations.
3. PEAR SHAPED BUR
Head is shaped like tapered cone
with small end of cone directed
towards shank. It is used in class I
tooth preparation for gold foil. A
long length pear bur is used for tooth
preparation for amalgam

22. 4. STRAIGHT FISSURE
BUR
It is parallel sided cylindrical bur of
different lengths and is used for
amalgam tooth preparations.
5. TAPERING FISSURE
BUR
It is tapered sided cylindrical but
sides tapering towards tip and is
used for inlay and crown
preparations.
6. END CUTTING BUR
It is used for carrying the preparation
apically without axial reduction.

24. MODIFICATIONS IN BUR DESIGN
 Larger diameter carbide burs have been replaced by small diameter burs
 Reduced number of crosscuts: Since at high speed, crosscuts tends to produce
rough surface, newer burs have reduced number of crosscuts.
 Extended head lengths: Burs with extended head length have been introduced so
as to produce effective cutting with very light pressure
 Rounding of sharp tip corners: Since, sharp tip corners of burs produce sharp
internal angles, resulting in stress concentration. Burs with round tip corners
produce rounded internal line angles and thus lower stress in restored tooth

25. SIZES OF BUR
 bur size—diameter of the bur head
 Earlier burs had a numbering system in which burs were grouped by 9 shapes and
11 sizes
 Later this numbering system was modified.

27. BUR DESIGN
 Bur head consists of
uniformly spaced blades
with concave areas in
between them.
 These concave depressed
areas are called chip or flute
spaces.
 Normally, a bur has 6, 8, or
10 numbers of blades

28. 1. BUR BLADE:
 Blade is a projection on the bur
head which forms a cutting edge.
Blade has two surfaces:
 • Blade face/Rake face: It is the
surface of bur blade on the
leading edge.
 • Clearance face: It is the surface
of bur blade on the trailing edge.

29. 2. RAKE ANGLE:
 The 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 each other

30. 3. RADIAL LINE
IT IS THE LINE CONNECTING
CENTER OF THE BUR AND THE
BLADE

31. 4. LAND
 It is the plane surface
immediately following
the cutting edge

32. 5. CLEARANCE ANGLE
 The angle between the
clearance face 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 debris.

33. 6. BLADE ANGLE
It is the angle between the rake face and the clearance face.
Significance: Among these rake angle is one of the most
important feature of bur blade design.
Negative rake angle increases the life of bur by reducing
fracture of cutting edges. Positive rake angle increases the
cutting efficiency but since it reduces the bulk of bur blade, it
becomes prone to fracture.
Positive rake angle also causes clogging of debris in the chip
space.
If blade angle is increased, it reinforces the cutting edge and
thus reduces their fracture. But clearance angle, blade angle
and rake angle cannot be varied independent of each other.
For example, increase in blade angle, decreases the clearance
angle. Usually, the carbide burs have negative rake angles and
90° of blade angle so as to reduce their chances of fracture.
For better clearance of debris, the clearance faces of carbide
burs are made curved to provide adequate flute space.

34. 7. CONCENTRICITY
 It is a direct measurement of symmetry of the bur head. In
other words, concentricity measures whether blades are of
equal length or not. It is done when the bur is static.

35. 8. RUN-OUT
 It measures the accuracy with which all the
tip of blades pass through a single point
when bur is moving
 It measures the maximum displacement of
bur head from its center of rotation.
 In case, there is trembling of bur during
rotation, this effect of run-out is directly
proportional to length of bur shank
 Run-out occurs if: a. Bur head
is off center on axis of the bur. b. If
bur neck is bent. c. If bur is not
held straight in handpiece chuck.
 Run-out causes:
 a. Increase in vibration during cutting.
 b. Causes excessive removal of tooth structure.

36. “
”
FACTORS AFFECTING CUTTING
EFFICIENCY OF A BUR

37. 1. CLEARANCE ANGLE, RAKE ANGLE AND
BLADE ANGLE
 Clearance angle reduces the friction between cutting edge and the work. It also
prevents the bur from digging excessively into the tooth structure.
 But an increase in rake angle decreases the blade angle which inturn decreases the
bulk of bur blade
 Positive rake angle increases cutting efficiency of bur, but increase in rake angle
causes decrease in bulk of bur blade and clogging of flute space because of
production of larger chips

38. 2. END CUTTING OR SIDE CUTTING BUR
 According to particular task, choice of bur can be end
cutting, side cutting or combination of both. For example, it
is preferred to make entry to enamel by end cutting bur,
while for making preparation outline, use side cutting bur.

39. 3. NECK DIAMETER OF BUR:
 If neck diameter of bur is large, it may interfere with
accessibility and visibility.
 But if diameter is too short, it will make bur unable to resist
the lateral forces

40. 4. SPIRAL ANGLE
BURS WITH SMALLER SPIRAL
ANGLE HAVE SHOWN BETTER
EFFICIENCY AT HIGH SPEEDS.

41. 5. LINEAR
SURFACE SPEED
WITHIN THE LIMIT, FASTER THE
SPEED OF CUTTING
INSTRUMENT, FASTER IS THE
ABRASIVE ACTION AND MORE
EFFICIENT IS THE TOOTH
CUTTING INSTRUMENT. BUR
SPEED SHOULD BE INCREASED
IN LIMITS BECAUSE WITH
ULTRAHIGH SPEED,
CENTRIFUGAL FORCE COMES
INTO THE PLAY.

42. 6. APPLICATION OF LOAD
 : Load is force exerted by a operator on tool head.
 Normally for high speed instruments, load should range between 60 and 120 gm
and for low rotational speeds, it should range between 1000 and 1500 gm.
 Cutting efficiency decreases when load is applied, there is increase in temperature
at work face which results in greater wear and tear of handpiece bearings.

43. 7.
CONCENTRICITY
AND RUN-OUT
THE AVERAGE CLINICALLY
ACCEPTABLE RUN-OUT IS 0.023
MM. INCREASE IN RUN-OUT
CAUSES INCREASE IN
VIBRATIONS OF THE BUR AND
EXCESSIVE REMOVAL OF
TOOTH STRUCTURE.

44. 8. LUBRICATION
 Lubricant/coolant applied to tooth and bur during cutting
increases the cutting efficiency and decreases the rise in
temperature during cutting.
 Absence of coolant can result in increase in surface
temperature which may produce deleterious effects on pulp.

45. 9. HEAT
TREATMENT OF
BUR
HEAT TREATMENT OF BUR
PRESERVE THE CUTTING EDGES
AND INCREASES SHELF LIFE OF THE
BUR.

46. 10. NUMBER OF BLADES
 Usually a bur has 6-8
number of blades.
 Decrease in number of
blades reduces the
cutting efficiency but
causes faster clearance
of debris because of
larger chip space

47. 11. VISUAL
CONTACT WITH
BUR HEAD
FOR EFFICIENT TOOTH
CUTTING, IT IS MANDATORY
TO MAINTAIN VISUAL
CONTACT WITH BUR HEAD
WHILE WORKING.

48. 12. DESIGN OF FLUTE ENDS
 There are two types of flute ends:
 • Star cut design: Here the flutes
come together in a common
point at the axis of bur.
 • Revelation design: Here the
flutes come together at two
junctions near diametrical cutting
edge. It has better efficiency in
direct cutting

49. THANK YOU.....