Instruments and Equipment for Tooth Preparation - PowerPoint Presentation

Slide1

Instruments and Equipment for Tooth Preparation

By:

Dr. Syed Mukhtar-un- Nisar Andrabi

Assistant Professor,

Conservative Dentistry & Endodontics,

Dr. Z. A. Dental College, A. M. U. Aligarh

Slide2

Lecture outline

I. Hand instruments for cutting

Terminology and classification

Cutting instrument applications

Hand instrument techniques

Sharpening hand instruments

Sterilization and storage

II. Rotary cutting instruments

Common design characteristics

Dental burs

Diamond abrasive instruments

Other abrasive instruments

III. Cutting mechanisms

IV. Cutting Hazards

Slide3

Introduction

The removal and shaping of tooth structure are essential aspects of restorative dentistry

Initially this was a difficult process accomplished entirely by the use of hand instruments.

The early hand-operated instruments were ineffective and cumbersome to use because of the :

Large handles

Inferior metal

Non uniformity of manufacture

Lack of standardization and nomenclature

Slide4

Hand instruments

G.V. Black is credited with the first acceptable

nomenclature and classification of hand instruments

Modern hand instruments, when properly used, produce beneficial results for both the operator and the patient.

Use of hand instruments today is dictated by mainly:

Preparation form

Accessibility

Slide5

Hand instruments

Hand cutting instruments are manufactured from:

carbon steel

stainless steel

stainless steel

with

carbide inserts to

provide more durable cutting edges.

Carbon steel is harder than stainless steel, but corrodes easily.

Stainless steel loses a keen edge during use much more quickly than does carbon steel.

Carbide, although hard and wear resistant, is brittle and cannot be used in all designs.

Slide6

Slide7

Historical development

Dr. G.V. Black

- Credited with the first acceptable nomenclature for and classification of hand instruments.

Dr. Arthur D. Black

- Developed many of the instruments and techniques.

Dr. Charles E. Wood Bury

- First to modify blacks instrumentation. Designed 39 sets of Hand instruments for Class III cavity preparations & condensing points for building gold foil restorations.

Dr. Wedelstaedt-

Developed Wedelstaedt chisel now referred to as “Curved Chisel”.

Dr.

Waldon

I. Ferrier

– Developed a new set of instruments called

ferrier

set which were more refined and had uniform thickness on the cutting edge.

Dr. George

Hollenback

– Invented pneumatic condenser.

Slide8

Instrument Design

composed of three parts

handle,

shank,

Blade / nib

Slide9

Instrument Design

Most hand instruments are composed of three parts:

1.      Shaft

- it’s the part grasped by the operator hand

- available in various sizes & shapes

2.      Shank

- connect the shaft to the working end of the instrument

- may be straight, single, double or triple angled

3.      Blade/nib

For many non cutting instruments, the part corresponding to the blade is termed Nib. Some instruments have a blade on both ends of the handle & termed Double ended instruments.

Slide10

Cutting edge

Most hand cutting instruments have on the end of the blade a

single bevel that

forms the

primary cutting edge.

Beveled

:

Single

beveled

-

Bibeveled

- Triple

beveled

(1 primary and 2 secondary bevels). 

Regular bevel: distal to shaft

Reverse bevel: Mesial to shaft

Slide11

 Heat Treatment

HARDENING TREATMENT

The steel is heated to 1500 to 1600

0

F (815

0

C) and then quenched in oil to harden the working edge.

Not more than 1 - 2mm of the tip is heated for hardening purpose, otherwise the instrument will lose its balance after sharpening.

Hardens the alloy, but it also makes it brittle, especially when the carbon content is high.

TEMPERING TREATMENT

Cutting edges are usually tempered to produce additional hardness and to remove some of the brittle properties.

To accomplish this, the tip is reheated at a lower temperature.

Quenched in solutions of oil, acid or mercury at 200-

450

0

C

for 10 min.

This treatment relieves strains and increases toughness

.

Slide12

Nomenclature

Black's classification systems by instrument name categorized instruments by

(1)

function

(e.g., scaler, excavator), ORDER: 

(2)

manner of use

(e.g. hand condenser), SUBORDER:

(3)

design of the working end

(e.g. spoon excavator, sickle scaler), CLASS: 

(4)

shape of the shank

(e.g., mon-angle, bin-angle, contra-angle). SUB CLASS

These names were combined to form the complete description of the instrument

(e.g.,

Bin-angle

Spoon

Excavator

).

Slide13

Classification

(According To MarzouK)

Exploring or diagnostic instruments

: -

Mouth mirror - Explorer or probe - Straight probe - Right angled probe - Arch shaped (Shepherds hook) -

Interproximal

(Back action) - Tweezers -

Seperators

- Cheek retractors - Air syringe

Isolating instruments: -

Cotton roll holder - Rubber dam - Saliva ejector - Suction apparatus

Hand cutting instruments: -

Excavators

- Spoon excavator -

Cleiod

- Discoid - Hatchet excavator - Hoe –

Chisels

-

Straight chisel - Mono angle chisel - Bin angle chisel - Triple angle chisel –

Special types of chisels or modified chisels

-

Wedelsteadt

chisel - Enamel hatchet - Gingival marginal trimmer - Angle former

Slide14

Classification

(According To MarzouK)

 

Restoring instruments:

-

Mixing instruments

- Cement spatula - Agate spatula - Plastic carrying/ filling instruments –

Packing instruments

- Amalgam carrier

Condensing instruments

- Round condenser - Parallelogram condenser

Burnishing instruments

- Ball shaped - Egg shaped - Conical shaped-

Carving instruments

-

Hollenback

carver - Diamond carver - Wards carver

Miscellaneous instruments:

- Matrices and retainers - Scissors

Slide15

 

Instrument formula

(

Given By G.V.Black)

3 unit instrument formula: Cutting edge of the instrument is at a right angle to the blade.

a.

First unit

– Width of the blade in tenths of a

millimeter

.

b.

Second unit

– Length of the blade in

millimeter

c.

Third unit

– Angle the blade forms with the axis of the handle in centigrade

.

Slide16

 

Instrument formula

(

Given By G.V.Black)

 4 unit instrument formula: Cutting edge of the instrument is at an angle other than a right angle to the blade.

a. First unit

– Width of the blade in tenths of a

millimeter

.

b. Second unit

- Angle the cutting edge forms with the axis of the handle in centigrade.

c. Third unit –

Length of the blade in

millimeter

.

d. Fourth unit

– Angle the blade forms with the axis of the handle in

centigrade.Example

:- Gingival marginal trimmer & angle former

.

Slide17

The complete instrument formula (four numbers) is expressed

as

(1)

the

blade width in 0.1-mm increments,

(2)

cutting edge angle in

centigrades

,

(3) blade length in

millimeters

, and

(4)

blade angle in

centigrades

Slide18

Bibeveled

ordinary

hatchet

(3-2-28).

Hoe

(4 1/2 -1 1/2-22).

Angle former

(12-85-5-8).

Slide19

Straight chisel

(12-7-0).

Bin angle chisel

(10-7-8).

Wedelstaedt chisel

(11'/2-15-3)

Slide20

Binangle

spoon (13-7-14).

Triple-angle spoon (13-7-14)

Spoon (15-7-14).

Slide21

Cutting Instrument Applications

The cutting instruments are used to cut hard or soft tissues of the mouth.

Excavators

are used for removal of caries and refinement of the internal parts of the preparation.

Chisels

are used primarily for cutting enamel.

Slide22

Excavators

The four subdivisions of excavators are:

(1) ordinary hatchets,

(2) hoes,

(3) angle formers, and

(4) spoons

Slide23

Excavators

Ordinary hatchet excavator

has the cutting edge of the blade directed in the same plane as that of the long axis of the handle and is

bibeveled

.

Used for preparing retentive areas and sharpening internal line angles, particularly in preparations for direct gold restorations.

Hoe excavator

has the primary cutting edge of the blade perpendicular to the axis of the handle.

used for planing tooth preparation walls and forming line angles.

Angle former

is mon-angled and has the primary cutting edge at an angle (other than 90 degrees) to the blade.

used primarily for sharpening line angles and creating retentive features in dentin in preparation for gold restorations.

Slide24

Chisels

Chisels are intended primarily for cutting

enamel and may be grouped as:

(a) straight, slightly curved, or bin-angle;

(b) enamel hatchets; and

(c) gingival margin trimmers.

Slide25

Chisels

Straight chisel

has a straight shank and blade, with the bevel on only one side. Its primary edge is perpendicular to the axis of the handle.

The

bin-angle

and

Wedelstaedt chisels

have the primary cutting edges in a plane perpendicular to the axis of the handle and may have either a distal bevel or a mesial (reverse) bevel.

Enamel hatchet

is a chisel similar in design to the ordinary hatchet except that the blade is larger, heavier and is bevelled on only one side.

cutting edge is parallel with the axis of the handle.

It is used for cutting enamel.

Gingival margin trimmer

is designed to produce a proper bevel on gingival enamel margins of

proximo-occlusal

preparations.

similar in design to the enamel hatchet, except the blade is curved.

primary cutting edge is at an angle to the axis of the blade.

Slide26

Instrument Grasps

Slide27

Instrument Grasps

There are Four (4) Methods for Holding an instrument:

Modified Pen grasp

Inverted pen grasp

Palm and Thumb grasp

Modified palm and thumb grasp

Slide28

the instrument, while

Pads of the thumb, index, and middle fingers contact the instrument, while the tip of the ring finger is placed on a nearby tooth surface of the same arch as a

rest.

It allows a light or a heavy touch and finely controlled movements over a wide range

Modified Pen Grasp

Slide29

Is the most effective and the most universally used grasp.

B

ecause it can be used equally well with all instruments whether the applied force is in a direction of the handle axis; or at an angle to the axis but in the same plane of the shank or in a lateral direction

.

Modified Pen

Grasp

Why?

Prof. A. Elsahn

Slide30

the instrument, while

This

is similar to the pen grasp, but the hand is rotated

(inverted)

so that the palm is facing upwards

I

t is usually used when working on upper teeth

T

he third

(ring)

finger or preferably the third and fourth fingers are held firmly

“rest”

against the adjacent teeth as teeth of the same jaw.

Inverted Modified Pen Grasp

Slide31

The handle is placed in the palm of the hand and grasped by all the fingers, while the thumb is free of the instrument and the

rest is provided

by supporting the tip of the thumb on a nearby tooth of the same arch or on a firm, stable structure

Palm and Thumb Grasp

Slide32

The modified palm-and-thumb grasp may be used when it is feasible to rest the thumb on the tooth being prepared or the adjacent tooth

The hand is only about half closed, instead of being fully closed. The end of the thumb is used for the rest

Modified Palm-and-Thumb Grasp

Slide33

Instrument Grasps

The modified pen and inverted pen grasps are used practically universally.

The modified palm-and-thumb grasp is usually used in the area of the maxillary arch and is best adopted when the dentist is operating from a rear-chair position.

Slide34

Rests and Guards

A proper

rest

is needed to steady the operator’s hand and prevent the slipping of the instruments throughout the whole procedure

Guards

are hand instruments or other items, such as inter-proximal wedges, used to protect soft tissue from contact with sharp cutting or abrasive instruments

Slide35

Care And Maintenance Of Hand Cutting Instruments

Slide36

Cutting instruments are dulled by :

1-Repeated contact with tooth tissues.

2- Frequent sterilization.

so

The frequency with which cutting instruments should be sharpened

Is determined by the extent of their use.

Prof. A. Elsahn

Slide37

HOW TO KNOW THAT THE INSTRUMENT

BECOME DULL ?

1- Looking at the cutting edges in bright light; using a magnifying lenses are useful in evaluating their condition.

The presence of “glint” indicate that the edge is dull or rounded.

Slide38

2- the operator can pull the instrument across hard plastic such as a handle of a plastic mouth mirror or an evacuator tip.

A dull blade will slide across the plastic

.

A sharp blade will cut into the plastic surface.

3- A specially made, sterilizable, sharpness-testing stick is available (Dalron Test Stick, Thompson Dental).

Slide39

Sharpening hand cutting instruments must be preceded by their cleansing and sterilization and is made routinely in a definite manner to maintain their edges.

Slide40

In any sharpening technique oil should be used as a lubricant.

The stone should be kept slightly moistened with a drop or two of lubricating oil.

Too much oil should be avoided to prevent the formation of a shellac-like coating that will prevent the abrasion needed for sharpening.

Slide41

1-

Manual Sharpening

Sharpening is performed in different ways for different instruments:

A) For Chisels, Hatchets, Hoes and margin trimmers:

The cutting edge (bevel) is placed flat against the flat stone

( Arkansas)

which is placed on a stable surface.

Slide42

The instrument is pushed or pulled so that the acute cutting edge is moved forward, with a fairly heavy force on the forward stroke ,and with a little or no force on the back stroke.

Only two or three forward strokes are required.

The blade should make a 45 degree angle with the surface of the sharpening stone to

ensure

a 45 angle with the face of the blade (bevel).

Slide43

B)For spoon ,discoid

cleoid

excavators

“carver

” :

The blade of the instrument is rotated on the flat stone with the bevel at 45 degree or less.

A continuous rotation of the blade for both spoon and discoid in a clockwise from 9.o’clock position to the 3.o’clock position in one motion.

Slide44

For the cleiod excavators, the rotation begins with the shank in the 9-o’clock position and continues clockwise only until the bevel just next to point is ground.

To sharpen the other side of the cleiod, the rotation begins with the shank at 3-o’oclock position and continues counter- clockwise to the point.

Slide45

2-MECHANICAL SHARPENING

For mechanical sharpening, the following machines are available:

a) A slowly rotating soft sharpening wheel- shaped Arkansas stone is employed by one type of machine.

Slide46

B) An oscillating machine “with a back and front motions” is also useful for sharpening instruments.

Their sharpening stone is flat with different shapes and sizes for each shape and

angulation

of the instrument edge.

Slide47

Slide48

Rotary Instruments

Slide49

Rotary instruments

A group of instruments that turns on an axis to perform cutting, abrading, burnishing, finishing or polishing of dental tissues or restorations

The introduction of rotary powered cutting equipment came as a major advancement in the field of dentistry.

It involves the use of replaceable bladed or abrasive instruments held in a rotary handpiece, usually powered by electric engine and compressed air.

Slide50

Rotary instruments

A

handpiece

is a device for holding rotating instruments, transmitting power to them, and for positioning them

intraorally

.

Handpieces and associated cutting and polishing instruments developed as two basic types,

straight

and

angle handpieces

.

Slide51

Historical Development

The first rotary instruments used for cutting tooth tissue were actually drill or bur heads that could be twisted in the fingers for a crude cutting or abrading action.

Dr. Jonathan Taft, in his textbook of operative Dentistry in 1868 described them as “bur drills”. He suggested that they may be made from the best steel, forged close to their proper size & be properly /finally shaped on a lathe

Slide52

Historical Development

These simple rotary instruments, twisted with the fingers were capable of a very limited lateral & end cutting action.

They were particularly adapted to small & medium sized cavities & also were used for making “retaining points” for fillings.

Slide53

Early straight hand drill for direct access preparations (circa 1800). Back end of bur shank fits into a finger ring while the front end is rotated with thumb and forefinger

Early angle hand drill for indirect access preparations(Circa 1850). The bur is activated by squeezing the Spring-loaded handle.

Slide54

Historical Development

In 1871

, Morrison modified & adapted the dental foot engine from the singer-sewing machine.

In 1883

the electric dental engine with an attached handpiece & flexible cable arm was introduced

In 1914

, belt driven handpiece on a jointed engine arm became available.

The initial hand piece equipment & operating speeds remained unchanged until 1946. The steel burs were used for cutting at that time, were:

Ineffective

Weared easily

Produced a lot of heat

Slide55

Historical Development

Diamond cutting instruments were developed in Germany around 1935 but were available in USA only after World War II.

From 1946 in a 10 year period, cutting techniques were revolutionized

Diamond & carbide instruments /burs capable of cutting enamel were produced commercially

By 1950s speeds up to 60000 rpm had been attained

Slide56

Historical Development

The development of high speed contra-angled handpieces with internal turbine drives in the contra-angle head were a major breakthrough in the development of high speed rotary equipment. Early units were water driven but subsequent units were air driven.

Most current air-turbine handpieces have speeds up to 30,0000 rpm more torque, power output, smaller head size & lower noise levels.

Since

1955

angle handpieces have had an air-water spray feature to provide cooling, cleaning & improved visibility.

Most modern-angled handpieces also include fiber optic lighting of the cutting site.

Slide57

Slide58

Belt-driven Straight handpiece

Belt-driven Straight handpiece

Page-

Chayes

handpiece (circa 1955). The first belt driven Angle handpiece to operate successfully at speeds over100,000 rpm.

Gear-driven angle handpiece

Slide59

Contemporary air-turbine handpiece

Slide60

Rotary Cutting Tools (Basics)

The rotary tools for the removal of tooth structure may be one of the two types:

Burs

-

Which are cutting tools & have blades.

Stones /Abrasive points

:-

Which are abrading tools

Slide61

Common Basic Design

Shank:

Is the part that fits into handpiece & accepts the rotatory motion from handpiece. Shank can be –latch type, friction grip, & straight handpiece shank.

Neck:

Is the intermediate portion that connects the shank with the head. Its main function is to transmit rotational & translational forces to the head. Its diameter tapers from shank, for access & visibility.

Head:

Is the working part of the instrument, the cutting edges or points that perform the desired shape.

Slide62

Slide63

Dental Bur

The term bur is applied to all rotary cutting instruments that have bladed cutting heads. This includes instruments intended for such purposes as finishing metal restorations & surgical removal of bone, as well as those primarily intended for tooth preparation.

Burs are actually cutting tools. Burs can be classified by their composition into two types:

Steel Bur

Tungsten carbide Bur

Slide64

Dental Bur

STEEL BUR:

These are cut from blank steel stock by means of a rotary cutter that cuts parallel to the long axis of the bur.

The bur is then hardened & tampered until its Vickers hardness number is approximately 800.

Steel bur can cut dentin well at low speeds, but at high speeds they dull rapidly & also they are inefficient in cutting enamel.

Once dulled, their cutting efficiency is reduced & this results in increased heat production & vibration.

Steel burs are no longer popular now days.

Slide65

Dental Bur

TUNGSTEN CARBIDE BUR

: These were introduced in 1947 & have now largely replaced steel burs for tooth preparation.

Carbide burs perform better than steel burs at all speeds, & their superiority is greatest at high speeds.

Carbide is much harder than steel & less subject to dulling during cutting.

All carbide burs have heads of cemented carbide in which microscopic carbide particles, usually tungsten carbide, are held together in a matrix of cobalt or nickel.

The VHN of carbide bur is in the range of 1650-1700.

Slide66

Bur Classification

Mode of attachment

– latch type,

frictiongrip

type

Composition

– stainless steel, carbide burr or combination

Length of head

– long, short, regular

Use

– cutting , finishing , polishing

Shape

– round, inverted cone ,pear shaped, tapering fissure, straight fissure, endcutting

Slide67

Bur uses

Round bur:

caries removal, initial tooth preparation, extension, placing retentive grooves

Inverted cone:

wall angulations, creating undercuts, smoothening floors

Pear shaped bur:

class I cavity for gold foil

Straight fissure:

amalgam preparation

 

Tapering fissure:

inlay and crown

End cutting bur:

preparation apically without axial reduction

(finish line preparation)

Slide68

Slide69

General Design Of Dental Bur

The dental bur consists of a head, neck & shank.

Head is the cutting part of the bur & it consists of bur teeth .

There are about 6-8 bur teeth in every bur.

A

bur tooth

terminates in the cutting edge or blade. It has two surfaces,

the tooth

face,

which is the side of the tooth on the leading edge, & the back or flank of the tooth, which is the side of the tooth on the trailing edge.

Sometimes there can be a land with a plane surface immediately following the cutting edge.

Slide70

Slide71

Slide72

General Design Of Dental Bur

Rake Angle

:

It is the angle that the face of the bur tooth makes with the radial line from the center of the bur to the blade.

This angle can be:

negative

if (referring to direction of rotation) the face is beyond or leading the radial line.

‘O’

if radial line & face of bur tooth coincide with each other.

positive

if the face of the blade is behind the radial line i.e. if the radial line leads the face of bur tooth & the rake angle is on the inside of the radial line.

Slide73

Slide74

General Design Of Dental Bur

Clearance Angle

:-

It is the angle between the back of the bur tooth and the work or the surface to be cut. If a land is present on the bur, the clearance angle is divided into,

Primary clearance angle:

- Angle between the land & the work.

Secondary Clearance angle:

-Angle between the back of the bur tooth & the work.

When the back surface of the bur tooth is curved , the clearance is called as the

radial clearance.

The clearance angle:

eliminates rubbing friction of the clearance face,

provides a stop to prevent the bur edge from digging into the tooth structure excessively,

provide adequate flute space or clearance space for the chips formed ahead of the following blade.

Slide75

General Design Of Dental Bur

The Tooth Angle /Edge Angle:

-

This is the angle between the face & back .

If a land is present it is measured between the face and the land.

Increasing the edge angle reinforces the cutting edge and reduces the likelihood for the edge of the blade to fracture.

Carbide bur blades have higher hardness and are more wear resistant, but they are more brittle than steel blades and require greater edge angles to minimize fractures,

Slide76

Negative rake angles are desirable for cutting hard & brittle materials.

Negative rake angle minimizes the fracture of cutting edge, thereby increasing tool life.

Increasing the edge angle reinforces the cutting edge & reduces the likelihood for the edge of the blade to fracture.

Carbide burs require greater edge angles to minimize fracture, because carbide burs have higher hardness & are more wear resistant, but they are more brittle than steel burs.

Carbide burs have normally blades of slight negative rake angle & edge angles of approximately 90

o

.

Slide77

The three angles cannot be varied independently of each other

e.g. An increase in the clearance angle causes a decrease in the edge angle. To overcome this problem

radial clearances or two surface clearances

are used.

These provide adequate clearance space & as well as at the same time does not compromise the strength of bur tooth by excessively reducing edge angle.

Slide78

Modifications In Bur Design

With the increased availability of high speed air turbine handpieces after 1950, a new cycle of modification of bur sizes & shapes occurred. The most obvious modifications have been in the following aspects of the bur design.

Size of the bur.

(older larger diameter burs were replaced by smaller sizes.)

Reduced use of cross cuts.

(not needed at high speed)

Extended heads on fissure burs

.(applied pressure needed for cutting at very high speeds are extremely low)

Rounding of sharp tip angles.

(to produce preparations with rounded internal angles)

Slide79

Concentricity & Run Out

Concentricity

is a direct measurement of the symmetry of the bur head itself.

It measures how closely a single circle can be passed through the tips of all of the blades.

It is an indication of whether one blade is longer or shorter than the others.

It is a static measurement & not directly related to function.

Slide80

Concentricity & Run Out

Runout

is a dynamic test measuring the accuracy with which all blade tips pass through a single point when the instrument is rotated.

Runout refers to the eccentricity or maximum displacement of the bur head form its axis of rotation.

A bur will exhibit substantial

runout

if:

the head is off center on the axis of the bur

the bur neck is bent

the bur is not held straight in the handpiece chuck

the chuck is eccentric relative to the handpiece bearings

Slide81

Concentricity & Run Out

Runout will depend not only on the eccentricity of the bur itself but also on the precision of the dental handpiece

Runout is the primary cause of vibration during

cutting

and is the factor that determines the minimum diameter

of the hole that can be prepared by a given bur.

Clinically acceptable average

runout

value is 0.023 mm.

Slide82

Diamond Abrasive Instruments

Slide83

Diamond Abrasive Instruments

The second major category of rotary cutting instruments which involve abrasive rather than bladed cutting

Abrasive instruments are based on small angular particles of a hard substance held in a matrix of softer material.

Cutting occurs at a large number of points where individual hard particles protrude from the matrix rather than along a continuous blade edge.

Slide84

Diamond Abrasive Instruments

Abrasive instruments are generally grouped as:

Diamond abrasive instruments.

Other abrasive instruments. 

Molded abrasive Instruments

Silicon carbide (

carborandum

)

Aluminum oxide.

Coated abrasive Instruments.

Garnet

Quartz

Pumice

Slide85

History of development

Before the 1890s, silicon carbide discs & stones were used to cut enamel because carbon steel burs were inefficient at cutting enamel

In

1897 William & Schroeder

from the University of Berlin, Germany, made first diamond bur.

The 1899 catalog of

Claudius Ash & Sons Ltd

listed “ diamond burs for trimming & polishing enamel margins” & advised lubricating the burs well with water & running them at high speed.

Slide86

History of development

The

1913

catalog of the S.S white Dental manufacturing Co.

described “ a diamond starting point” as a narrow diamond wheel for removing enamel when excavating natural teeth.

The modern diamond bur was created in 1932 by

W.H.

Drendel

, a German industrialist, who developed a process for bonding diamond points to stainless steel shapes or blanks.

Widespread acceptance of diamond bur was limited form 1939 through 1946 because of expense & impractical shapes & sizes then available.

The introduction & subsequent mass production of the high speed air- turbine hand piece in 1957 was the stimulus for universal acceptance of diamond burs by the profession. (Siegel &

Fraunhofer

).

Slide87

Schematic Diagram Of A Dental Diamond Bur.

Slide88

Slide89

Classification

For Diamond Preparation Instruments:

Coarse (125 to 150 µm)

Medium (88 to 125 µm),

Fine (60 to 74 µm),

Very Fine (38 to 44 µm)

For Diamond Finishing Instruments:

Extra Fine (10 to 38 µm)

Slide90

Slide91

Molded abrasive instruments

Coated abrasive instruments

Slide92

CUTTING MECHANISMS

Slide93

Cutting Mechanisms

The process by which rotary instruments cut tooth structure is complex and not fully understood.

Tooth structure, like other materials, undergoes

brittle

and

ductile

fracture.

Brittle fracture

is associated

with crack production, usually by tensile loading.

Ductile fracture

involves plastic deformation of material, usually

proceeding by shear.

Slide94

Ductile fracture

Brittle fracture

Slide95

HAZARDS WITH

CUTTING INSTRUMENTS

PULPAL PRECAUTIONS

SOFT TISSUE PRECAUTIONS

EYE PRECAUTIONS

EAR PRECAUTIONS

I NHALATION PRECAUTIONS