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all About Burs in dentistry
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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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