Dental burs / dental implant courses

DENTAL BURS ANDDENTAL BURS AND
OTHEROTHER MODALITIES OFMODALITIES OF
TOOTH PREPERATIONTOOTH PREPERATION
INDIAN DENTAL ACADEMY
Leader in continuing Dental
Education
www.indiandentalacademy.com

INTRODUCTIONINTRODUCTION
DEFINATION
The term bur is a applied to all rotary cutting instruments
intended for such purposes as finishing metal restorations
and surgical removal of bone, as well as those primarily
intended for tooth preparation.

Historical Development Of Burs
The earliest burs were handmade. Early burs were made of
steel. Carbide burs were introduced in 1947, have largely
replaced steel burs for tooth preparation. Steel burs perform
well , cutting human dentine at low speeds, but dull rapidly at
higher speeds or when cutting enamel. Once dulled the
reduced cutting effectiveness creates increased heat and
vibration.
Carbide burs were introduced in 1947, have largely replaced
steel burs for tooth preparation. Steel burs are now mainly
used for finishing procedures.

Indian Dental academy
• www.indiandentalacademy.com
• Leader continuing dental education
• Offer both online and offline dental courses

Bur Classification Systems
In United States, dental burs traditionally have been
described in terms of an arbitrary numerical code for head
size and shape ( eg 2 = 1mm diameter round bur; 57 = 1mm
diameter straight fissure bur; 34 = 0.8mm diameter inverted
cone bur. Newer classification systems such as developed by
the International Standards Organization ( ISOI) tend to use
separate designations for shape ( usually shape name and
size) usually a number giving the head diameter in tenths of
a millimeter. ( eg round 010; straight fissure plain010;
inverted cone 008.

Bur Shapes:
The term bur refers to the contour or silhoutte of the head. the basic
shapes are round, inverted cone. pear, straight fissure and tapered
fissure.
A round bur is spherical.
Uses:
1. Initial entry into the tooth.
2. Extension of the preparation.
3.Preparation of retention features.
4. Caries removal.
A pear shaped bur is a portion of a slightly tapered cone with the
small end of the cone directed towards the bur shank.

Uses:
1. Class 1 tooth preparation for gold foil.
2. Tooth preparations for amalgam.
An Inverted cone bur is a portion of a rather rapidly tapered cone with the
apex of the cone directed towards the shank. Head length is approximately
the same as the diameter.
Uses: Providing undercuts in tooth preparations.
A Straight Fissure bur is an elongated cylinder. Some advocate this shape
for amalgam tooth preparations. Modified burs of this design with slightly
curved tip angles are available.
A Tapered Fissure bur is a portion of a slightly tapered cone with the small
end of the cone directed away from the bur shank.
Uses: Tooth preparations for indirect restorations for which freedom from
undercuts is essential for successful withdrawal of patterns and final seating
of the restorations. www.indiandentalacademy.com

Variations in bur shapes:
Fissure and Inverted Cone Burs have half round or domed
ends.

Bur Sizes
The original numbering system grouped burs by nine shapes and
eleven sizes . The half and ¼ designations were added later when
small instruments were included in the system. A number 57 with
cross cut was designated number 577 . Similarly a nine hundred
prefix was used to indicate a head design intended for end cutting
only.

Modifications in bur design
Three major trends in bur design are discernible:
1. Reduced use of crosscuts.
2. Extended heads on fissure burs.
3. Rounding of sharp tip angles.
Crosscuts are needed on fissure burs to obtain adequate
cutting effectiveness at low speeds but at high speeds they
are not needed. Carbide fissure burs with extended head
lengths 2 to 3 times those of the normal tapered fissure burs
of small diameter have been introduced.www.indiandentalacademy.com

Additional Features In Bur
Design
1. Head Length : Bur originally designed for use at low
speeds in preparing teeth for cast restorations.
2. Neck Diameter: A neck that is to small will result in a
weak instrument unable to resist lateral forces.
3. Concentricity: Direct measurement of the symmetry of
the bur head itself.
4. Run out: A dynamic test measuring the accuracy with
which all the blade tips pass through a single point when
the instrument is rotated.

Bur Blade Design
Each blade has 2 sides: the rake face, clearance face, the rake
angle, the edge angle and the clearance angle.
Rake angle is the most important design characteristic of the
bur blade. A rake angle is said to be negative when the rake
face is ahead of the radius.

Diamond Abrasive Instruments
Abrasive instruments are based on small, angular particles of
a hard substance held in a matrix of softer material.
Diamond instruments have a greater clinical impact because
of their long life and greater cutting effectiveness in cutting
enamel and dentine.
TERMINOLOGY: Diamond instruments consist of 3 parts: a
metal blank, the powdered diamond abrasive and a metallic
bonding material that holds the diamond powder onto the
blank.
The blank resembles a bur without blades. It has the same
essential parts: head, neck and shank.

Head Shapes and Sizes
Round, Football, Barrel, Flat and cylinder, Beveled and
cylinder, Inverted cone, Flat and taper, Round and taper,
Flame, Needle, Interproximal, Pear, Donut and Wheel.

Diamond Particle Factors
The clinical performance of diamond abrasive instruments
depends on the size, spacing, uniformity, exposure and
bonding of the diamond particles. Increased pressure causes
the particles to dig into the surface more deeply, leaving
deeper scratches and removing more tooth structure.
Diamond particle size is is commonly characterised as
coarse(125 – 150micrometer) medium( 88 – 125micrometer),
fine( 160 –74 micrometer) and very fine ( 38 – 44
micrometer) for diamond preparation instruments.

Other Abrasive Instruments
CLASSIFICATION:
1. Molded Abrasive Instruments.
2. Molded Unmounted Discs or Wheel stones.
3. Coated Abrasive Instruments.
USES: They were at one time extensively used for tooth
preparation, but their use is now primarily restricted
to shaping, finishing and polishing restorations both in
laboratory and clinic.

Materials
Matrix materials usually are phenolic resins or rubber.
Rubber matrix is used primarily to obtain a flexible head
on instruments to be used for polishing.
Synthetic or natural abrasives may be used e.g.
1. Aluminum Oxide.
2 . Garnet.
3. Pumice.
4. Cuttlebone.

Cutting Mechanisms
For cutting it is necessary to apply sufficient pressure to
make the cutting edge of the blade or abrasive particle dig
into the surface. Local fracture occurs more easily if the
strain rate is high( high rotary instrument surface being cut
responds in a brittle fashion).

Evaluation Of Cutting
1. CUTTING EFFECTIVENESS: It is defined as the rate of
tooth structure removal ( mm/ min or mg/sec).
2. CUTTING EFFICIENCY: It is defined as the % of energy
actually producing cutting.

Bladed Cutting
In order for the blade to initiate the cutting action it must be
sharp, must have a higher hardness and modulus of elasticity
than the material being cut and must be pressed against the
surface with sufficient force.
Brittle fracture is associated with crack production, usually
by tensile loading.
Ductile fracture involves plastic deformation of material
usually proceeding with shear.

Abrasive Cutting
When diamond instruments are used to cut ductile
materials, some material will be removed as chips, but
much material will flow laterally around the cutting point
and be left as a ridge of deformed material on the surface.
Irregular portions become brittle, break off and are
recovered.
In case of brittle materials most cutting results from tensile
fractures that produce a series of subsurface cracks.
USES: 1.Tooth preparation for bonded restorations.
2. Milling in CAD/CAM or copy-milling
applications.

Cutting Recommendations
1. Contra angle Handpiece.
2. Air water spray for cooling.
3. High Operating Speed.( above 200,000 rpm).
4. Light Pressure.
5. Carbide Bur.
6. Diamond Instrument.
Carbide burs are better for end cutting, produce less heat
and have more blade edges per diameter for cutting.
Diamonds are more effective than burs for both
intracoronal and extracoronal preparations, beveling
enamel margins on tooth preparations and
enameloplasty.

Hazards With Cutting
Instruments
1. PULPAL PRECAUTIONS.
2. SOFT TISSUE PRECAUTIONS.
3. EYE PRECAUTIONS.
4. EAR PRECAUTIONS.
5. INHALATION PRECAUTIONS.

References
1. Dental Burs: Sturdevant’s Art and Science Of
Operative Dentistry, 4th
Edition, Published by Elsevier.
2. Hazards With Cutting Instruments : Art and Science Of
Operative Dentistry, 4TH
Edition, 2004, Published by
Elsevier.
3. Morrant GA: Burs and Rotary Cutting Instruments:
Introduction of a New Standard Numbering System.
4. Nuckles DB: Status Report On Rotary Diamond
Instruments. J, AM Dent Asso97(2) :233- 235, 1978.
5. Hartley J L , Hudson DC : Modern Rotating
Instruments: burs and diamond points, Dent Clinic
North America 737, November 1958.www.indiandentalacademy.com

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