rotary instrumentation

8/2/2019 Rotary Instrumentation

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ROTARY INSTRUMENTATION

1728 Hand rotated instruments 300 rpm

1871 Foot Engine 700

1874 Electric engine 1000

1914 Dental unit 5000

1942 Diamond Cutting instruments 5000

1947 Tungsten carbide 10000


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ROTARY INSTRUMENTATION

1953 Ball bearing hand piece 25000

1955 Water turbine H P 50000

1955 Belt driven angle HP 150000

1957 Air Turbine Angle H P 250000

1961 Air turbine St H P 250000

1962 Air bearing H P 800000

1994 Contemporary air turbine HP 300000


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OTHER IMPROVEMENTS

Smaller head size

More torque control

Low noise level

Better chucking mechanism

Better cooling system

Most modern H P have fiber optic light at the cutting tip


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LASER

OTHER DEVELOPMENTS

A crystal or gas is excited to emit light photons of

characteristic wavelength that are amplified and filtered

to make a coherent light beam.

Power of the beam and the extend to which the beam is

absorbed determines the effect


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LASER TYPES

A Infra red CO 2

Ho : YAG Long wave length

Nd : YAG

B Visible Range He & Ne Visible wave length

C Ultra violet Xe F , Xe Cl, Kr F, Ar F Short

Special U V wave length Excimers


6/31

OTHER CUTTING DEVICES

Air abrasion 1950 Arthur Black

Contemporary Air Abrasion techniques rely ontransfer of kinetic energy from a steam of powderparticles on the surface of the tooth structure tofracture the surface layer resulting in roughness .

Energy depends on the powder particles, pressureangulation, surface composition and clearance angle .

[ 60 To 90 with 3 . 5 mm distance ]


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ROTARY INSTRUMENTS

CHARACTERISTICS

SPEED

Rpm and also surface feet area of contact per unit time of the cutting tool with the work

ultra low 300 to 3000

low speed 3000 to 6000 medium high 20000 to 45000 high speed 45000 to 100000 ultra high 100000 and above


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PRESSURE

Resultant of force and the surface area of thecutting tool in contact with the tooth .

P = F / A

When pressure is constant more force required to cutSmaller area & vice versa.

Force constant small tools require more pressureAnd vice versa


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HEAT PRODUCTION

Directly proportional to

a. Pressure

b. RPM

c. Area of the tooth in contact with the tool

Increase in any one of these increases heat .

Max tolerable temperature 113 o F


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VIBRATION

Product of the equipment used and the speed

Causes fatigue for operator , wear ofInstrument, and annoyance for patient .

Amplitude & modulating frequency areresponsible for vibration

Low speed amplitude is large than frequencyHigh speed frequency larger.

Amplitude is more harmful


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VIBRATION CNTD

Vibration waves are measured in cycles

6000RPM vibrational wave 100 cycles / sec

Most annoying to patient & operator

100,000 RPM 1600 cycles

Vibrations above 1300 is not perceptible .

Vibrations are in different directions


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FORCE REQUIRED

Low speed 2 to 5 lbs

High speed 1 lb

Ultra high speed 1 to 4 ounces force


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ANNOYANCE FACTOR

Subjective reaction of the patient to

tooth preparation

pressure , vibration

noise recorded through the bone

heat , the smell generated and

finally the time taken


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OTHER FACTORS

Patient reaction

Operator fatigue

Source of power


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FACTORS RELATED

Vibration & Noise

Coarseness of the bur,speed & size

Small tool & high speed reduce vibration

Heat & Smell

Depends on the adequacy of lubrication


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INSTRUMENTS DESIGN

Discussed under 2 headings

1 Hand piece

Which holds the cutting tool

2 Cutting tool


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HAND PIECES

Holds cutting tool in 3 ways

LATCH TYPE

FRICTION GRIP

SCREW TYPE


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EVALUATION OF HANDPIECE

FRICTION

Moving parts have friction producing heatReduced by ball bearings needle bearings orResin bearings

TORQUE

On the rotating tool without reduction in Ability of the H P to resist lateral pressure

speed or cutting efficiency .

VIBRATION


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CUTTING TOOLS

Effect cutting in 2 ways

CUTTING Burs

ABRADING Stones & Diamond


20/31

BUR

BUR is a minute milling unit with

cutting edges or flutes

Available in assorted sizes & shapes

ISO has assigned a classification for

bur which is globally accepted


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I S O IDENTIFICATION SYSTEM

a. Material of working part 806

b. Type of shank 031

c.Length of bur 019

d.Shape of bur head 168

e.Color code in case of diamond 534

f.Bur head diameter 014


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a

.

a. Steel TC Diomond - 804 b. Latch, friction - 031

c. Length - 019d. Shape - 168e. Colour code - 534f. Bur head diameter - 014


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Cut from a steel blank with

rotary cutter.Tempered to a VHN of 800

T C burs are made by powder metallurgyIt is partial alloyingTC powder is mixed with powdered CobaltUnder pressure in vacuum resulting inPartial alloying or sintering

A blank is formed which is cut to shape

V H N 1650 to 1700


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DESIGN FEATURES OF BUR

Bur toothFace on the leading edge

Back on the trailing edge


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RAKE ANGLE

Angle formed by the face of the bur with the radial line

Positive

Negative

Radial rake or Zero rake


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LAND

The flat surface or plane immediately following the cutting edge

CLEARANCE ANGLE

Angle between the back and the work

Primary clearance angle the angle the land will make with the work Secondary clearance angle between the back and the work

When the back of the flute is curved the clearance angle is calledRadial ClearanceBLADE ANGLE angle between face & back

FLUTE SPACE space between back and face


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CUTTING EFFICIENCY OF BUR

RAKE ANGLE+ ve efficient cutting than - ve

Cut chips are larger in + ve smaller in - ve

Steel bur it is disadvantage . Reduce bulk of flute .So bends or fractures .

So + ve is better suited for T C burs


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CLEARANCE ANGLE

If clearance angle is less back rubs with the work

Resulting in frictional force and dulling of flutes

Large clearance reduces chance of dulling


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NUMBER OF FLUTES

Standard 6 or 8

Reduced flutes chip size removed is greater

Chances of clogging less, wear more

Fissure burs with straight flutes less heatthan spirals due to larger chip removal

Fewer flutes vibration more . Reduced byEnsuring 2 or more flutes in contact at a time


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RUN OUT

Eccentricity or maximum displacement of the bur head

from its axis of rotation while the bur turns

Average accepted value is 0 .023 mm

Run out depends on the bur & the hand piece

When run out exceeds the average value cutting is

ineffective and operator exerts more force resulting in

vibration and heat generation


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OTHER FEATURES

a. Heat treatment

b. Design of flutes Star & Revelationbetter in direct cutting

c. Bur diameterforces on the bur tooth depends on

the number of flutes and the rotational positionand not on the diameter of the bur

d. Loadlow speed 1000 gm or 2 lbs

high d 60 t 120 g 2 t 4

rotary instrumentation

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