The document discusses rotary instruments used in dentistry, categorizing them by operating speed and detailing their components, such as the bur, shank, and head. It explains different types of burs and their specific functions in procedures like cavity excavation and finishing. The text also addresses design factors affecting cutting efficiency, including clearance angle and rake angle, which influence how effectively the instrument removes tooth structure.

1. Rotary
instruments

2. Operating Speed ranges and uses:
1. Regular, low or conventional
speed: (2.000 to 10000 rpm).
2. Higher or intermediate speed
(10.000 to 100.000 rpm).
3. Ultra or super speed (above
100.000 rpm) is accomplished
with the air turbine.
Rotary instruments

3. Cutting Points:
The smallest unit and the one actually removing
tooth structures, may be one of two:
1. Bur 2. Stone.
Rotary instruments

4. Bur parts:
Shank:
The shank is secured to the hand piece for the purpose
of driving the bur.
Rotary instruments

5. Shaft:
The Shaft connects the head of the bur with the
shank.
Head:
This part of the bur does the cutting by the means of
the small blades located on the metal.
Rotary instruments
shaft

6. Burs are classified according to their shanks
into:
Rotary instruments
1. The friction-grip bur is
used for the ultra-
speed air turbine.
2. The latch type: are
used for regular and
medium-speed
instruments.

7. Round bur
1.Gainig access.
2.Excavation of caries.
Rotary instruments

8. Inverted cone bur
1. Extension of cavity outline form
2. Flattening of pulpal floor
Rotary instruments

9. 1. May be used instead of the
inverted cone bur in making
extension of cavity walls to
obtain outline form.
2. Finishing of cavity walls and
margins to form sweeping
curves.
Fissure Bur
Rotary instruments

10. 1. Tapered a few
degrees in order to
place wall inclinations
for the cast gold inlay.
2. The burs are selected
to produce grooves for
retention of the proximal
amalgam and inlay
restorations.
Rotary instruments
Tapered Fissure
Bur

11. The blades are shorter and closer
together than in other burs.
They are used for finishing and
polishing of metallic restorations.
Rotary instruments
Finishing bur

12. Design of dental bur:
The bur head may be
divided into 6 or 8 blades
(also called teeth, flutes).
Each flute or blade has a
leading side “Face”, and a
trailing side “Back” with
an angle in between, called
the “flute Angle” or blade
angle.
Bur Design
Clearance
angle

13. Clearance Angle:
It is the angle between the
back of the blade and the
“work”
It acts to decrease the
friction between the back
of bur blade and the work
or tooth tissues during
cutting, and therefore,
decrease heat generation.
Bur Design
Clearance
angle

14. Clearance or Chip Space:.
The space between each two
successive blades
A space where the chips
formed during the cutting
procedures collect and get
eliminated.
Too small, the formed chips
will remain in-between the
bur blades, causing its
clogging generation of more
heat and loss of
effectiveness.
Bur Design
Clearance
angle

15. Bur Design

16. Rake Angle:
An angle created between the face of the blade with the
radius of the bur .
The rake angle may be positive, Zero (radial), and
negative, depending on whether the radial line is ahead,
over-lying. Or tailing the face of the blade respectively.
Bur Design

17. Radius
where the radial line is ahead to the
face of the blade.
A positive rake angle enables the blade
to cut more effectively.
making the rake angle more positive
can only be attained by thinning out the
blade.
This will cause the blade to become
weak and to turn and lose its
effectiveness quite more rapidly.
Bur Design

18. Bur Design
Zero Rake Angle: where the
radial line is over-lying the face
of the blade.
A positive rake angle enables
the blade to cut more effectively
than a zero one.

19. Bur Design
Radius
Negative rake angle: where the
radial line is tailing the face of
the blade.
A positive rake angle enables
the blade to cut more effectively
than a negative one.

21. Cutting efficiency:
It is the ability of the instrument to remove a
maximum amount of tooth tissues with a minimum of
effort and time involved.
Cutting efficiency
Factors influencing the cutting efficiency of burs:
1. Bur design.
2. Composition of the bur.
3. Tissues to be cut.

22. 1. Bur design:
The number of blades.
Cutting efficiency
The more positive the rake angle the more
effective is the bur in cutting.