Burs in dentisty ashish

DENTAL BURS

Guided By:Dr Sandeep Metgud

Dr Deepali Aggerwal

Presented by:Dr Ashish chhajlani

Content Introduction and Definition

History

Parts of the Dental Bur

Classification of Dental Bur

Design Of Dental Bur

Significance Of Bur Design

Modification in Bur Design

Cutting Mechanism of Dental Bur

Factor Influencing Dental Bur

DEFINITION:

“The term Bur is applied to all rotary cutting instrument that have bladed cutting heads.”

Strudevants 5th edition

or

A bur is revolving cutting instrument which has a cutting blades on head.

History

Early around 1728 Hand rotated drills were used

First machine made burs introduced in1891 made up of steel.

In 1940s Diamond abrasive points were introduced

In 1947 carbide burs were introduced

Parts of dental bur

The dental bur has 3 basic parts :

Shank

Neck

Head

Shank design : 3 types of designs are commonly seen

1. Straight Hand piece Shank : simple cylindrical held in straight hand piece by a metal chuck that closes to the shank diameter

2. Latch type angle hand piece shank : it is also in cylindrical in shape but the posterior portion of the bur shank is flattened on one side.

3. Friction grip angle hand-piece : The shank is simple cylinder and even smaller in dimension .

Classification of Burs

According to the Shank Design:

1. Straight hand piece shank

2. Latch type angle hand piece shank

3. Friction grip angle hand-piece

According to Material Of Manufacturing

1. Stainless Steel

2. Tungsten Carbide

Stainless Steel Bur Tungsten Carbide

According to shape of the Bur Head

1. Round

2. Straight

3. inverted cone

4. Tapered fissure

5. Pear shaped

ACCORDING TO THE DIRECTION OF ROTATION

Clockwise (right)- most common

Anticlockwise (left)

ACCORDING TO THE HAND PIECE THEY ARE DESIGNED FOR

1. Contrangle bur

2. Straight hand piece bur

According to the Size of the bur head :

The original numbering system groped burs by 9 shapes and 11 sizes

The 1/2 and 1/4 designations were added later when small instruments were included in the system.

Design of Dental Bur Dental Burs have blades which are usually in even numbers.

cavity preparation burs have 6 , 8 , 10 blades

The following features we normally seen in the Dental bur :

Bur Blade : These are uniformly spaced projections on Bur head which terminate in cutting edge.

It has two surfaces :

1. Blade Face / Rake Face

2. Blade back / Clearance face

Flute / Chip Spaces: These are the depressed areas in between the bur blades.

Radial Line : This is the line connecting the centre of the bur and blades

Rake Angle : This is the angle between the rake face and the radial line . This may be

Negative

Positive

Zero

Land: This represents the plane surface immediately

following the cutting edge

Clearance angle: This is angle between the

clearance face and the work that is tooth.

Blade Angle : this is the angle between the rake

face and clearance face or the rake face of the land

Radial Clearance : If the clearance face is curved it is

known as radial clearance

Significance of Bur Design

The rake angle is most important design feature of a bur blade.

A positive angle increases the cutting efficiency but having following drawbacks :

1. It tend to clog the cut debris in flute space

2. it reduces the life of bur.

A negative rake angle reduces the fracture of cutting edge thus increases the life of bur .

Neck Design is also important feature in Bur.

Modification in Bur design

With the development of high speed ranges a new cycle of modification of bur occurred

The three major trends in bur design : -

1. Reduced use of crosscut burs

2. Extended Head Length

3. rounding of sharp tip angle

Cutting Mechanism of Dental BursFor Effective cutting tooth structure the dental bur should be used at high speed .

Adequate pressure must be applied .

Two types of fracture mechanism Brittle and Ductile fracture occurs in tooth structure

Factors influencing the cutting of the burs:

Factors that affects cutting of burs are following:

1. RAKE ANGLE

2. CONCENTRICITY

3. CLEARANCE ANGLE

4. RUN-OUT

5. NUMBER OF TEETH OR BLADE & ITS DISTRIBUTION

RAKE ANGLE

Order of cutting efficiency :

Positive rake angle > radial rake angle > Negative rake angle.

Concentricity

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 the blades of bur

CLEARANCE ANGLE:

It provides clearance between the work & the cutting edge to prevent the tooth back from rubbing on the work.

Large clearance angle may result in less rapid dulling of the bur.

Run OutRun Out is a procedure measuring the accuracy with which all blade tips pass through a single point when the instrument is rotated.

It measures concentricity as well as accuracy of the centre of rotation passes through the centre of the head .

NUMBER OF TEETH OR BLADE & ITS DISTRIBUTION

As the number of blades decreases, the magnitude of forces at each blade increases & the thickness of the chip removed by each flute correspondingly increases.

Fewer number of bur teeth has increased space between bur teeth & thus decreases the clogging tendency.

Sterlization of Burs

Some common sterilisation technique used for Burs :

Dry Heat : Temperature at 320 F for 30 min

Chemiclave : Aldehyde vapours at 270 F and 20 lb of

pressure

Autoclave : 2 % soduim nitrate solution is used ,

BIBLIOGRAPHY

•Sturdevant’s Art And Science Of Operative

Dentistry

•Charbenues Operative Dentistry

•Pickards manual of conservative dentistry

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