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DEPARTMENT OF CONSERVATIVE DENTISTRY &

ENDODONTICS

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Seminar on

DENTAL BURSBUR DESIGN,SHAPES,SIZES,

BURS FOR AMALGAM AND COMPOSITE

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CONTENTSo Definitiono Parts of buro Purposeo Bur classification systemso Classification of burso Bur shapeso Bur blade designo Factors influencing cutting efficiency of burso Care with rotary instrumentso Burs for amalgam o Burs for compositeo Finishing and polishing – Amalgam, Composite

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BUR:

Rotary cutting instrument with bladed cutting head

PARTS OF A BUR:

Shank

Neck

Head

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HISTORICAL DEVELOPMENT: Steel bur 1891 Carbide bur 1947

PURPOSE: Tooth preparation Finishing a restoration Surgical removal of bone

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BUR CLASSIFICATION SYSTEMS:

A. SHORT HAND DESIGNATION

B. FDI, ISO SYSTEM

C. SIMPLIFIED NUMBERING SYSTEM

A. Short hand designation : Arbitrary numerical codes for head size and shape

E.g. : No.2 - 1mm round bur

No. 57 - 1mm straight fissure bur

No. 34 - 0.8mm inverted cone bur

B. FDI, ISO : Head diameter in tenth of mm

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C. Simplified Numbering System for dental burs: First two alphabets - 'the shape of the bur'

rd - round bur

bd - bud-shaped bur,

pr -pear-shaped bur,

sf - straight fissure bur,

tf - tapering fissure bur,

ts - torpedo-shaped bur,

Second parameter - 'maximum head diameter'.

Diameter (in mm) is being multiplied by 10 to make it a whole number. 0.5 as 5, 0.6 as 6

fs – flame-shaped bur

ic -inverted cone bur, wl - wheel-shaped bur,

fs - football-shaped bur, ec - end-cutting bur, andeb - endo bur.

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Third parameter - 'maximum length of the bur head'

This value is converted into a whole number by multiplying it by 10 and is included next to the previous number followed by a space to indicate separation.

E.g. : 1.2 as 12, 3 as 30, etc. Fourth parameter - 'material of the cutting head'.

D (diamond), C (carbide), or S (steel) .

Regular friction grip bur - 'FG'

Short-shank friction grip bur - 'SS’

“Straight fissure diamond point with head diameter of 1.2 mm, head length 3.0 mm with a normal friction grip shank will have the designation 'SF 12 30 DFG”

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CLASSIFICATION OF BURS:

I. According to their mode of attachment

Latch type

Frictional grip type

II. According their composition

Stainless steel

Tungsten carbide

Diamond

III. According to head

Bladed

Abrasive

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IV. According to length of their head

Long

Short

Regular

V. According to their shapes

Round

Straight fissure

Tapered fissure

Inverted cone

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ROUND BURS: ¼, ½, 1, 2, to 10 - Used for initial entry into the tooth,

extension of the preparation, preparation of retention features, and caries removal.

No. 2, 4, and 6 and two lengths, regular and surgical, are used for endodontic access opening.

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INVERTED CONE BURS: Numbered from 33 ¼, 33 ½, 34, 35, to 39. Cavity extension and occasionally for establishing wall

angulations and retention forms.

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PLAIN CYLINDRICAL FISSURE BUR: They are numbered from 55 to 59. The bur teeth –straight, spiral

CROSS CUT CYLINDRICAL FISSURE BUR: 555, 556 to 560. Teeth - straight ,spiral. Cylindrical fissure burs- Gross

cutting, cavity extension and creation

of walls.

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PLAIN TAPERED FISSURE BUR: 168, 169, to 172. Have a tapered cylindrical head Teeth -straight or spiral

CROSS-CUT TAPERED FISSURE BUR: 699, 700 to 703. Straight or spiral.

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PEAR-SHAPED BURS: 229 to 333 A normal-length pear bur (length slightly greater than the

width) - class I tooth preparations for gold foil. A long-length pear bur (length three times the width) Tooth preparations for amalgam.

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ROUND BURS

Bur # Cutter Size FG 1 0.8 mm FG 2 1.0 mm FG 4 1.4 mm FG 6 1.8 mm FG 8 2.3 mm

PLAIN TAPERED FISSURE

Bur # Cutter Size FG 169L 0.9 x 5.2 mm FG 170L 1.0 x 5.2 mm FG 171L 1.2 x 5.2 mm

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CROSS CUT TAPERED FISSURE

Bur # Cutter Size FG 669L 0.9 x 5.2 mm FG 700L 1.0 x 5.2 mm FG 701 1.2 x 4.2 mm FG 701L 1.2 x 5.2 mm

INVERTED CONE

Bur # Cutter Size FG 35 1.0 x 0.9 mm FG 36 1.2 x 1.0 mm FG 37 1.4 x 1.2mm FG 38 1.6 x 1.4mm FG 39 1.8 x 1.5mm

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STRAIGHT FISSURE CROSS CUT

Bur # Cutter Size FG 556L 0.9 x 5.2 mm FG 557 1.0 x 4.0 mm FG 557L 1.0 x 5.2 mm FG 558L 1.2 x 5.2 mm FG 559 1.4 x 4.5 mm FG 559L 1.4 x 5.2 mm FG 560 1.6 x 4.5 mm

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BUR BLADE DESIGN:

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Bur blade Blade angle Chip space or flute Rake angle:

* Negative - if the face is leading the radial line

* Zero - if the radial line & face coincide

* Positive - if radial line leads the face.

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Land:

- The plane surface immediately following the cutting edge

Clearance angle:- The angle between the back of the bur tooth and tooth being

cut.- Eliminates rubbing friction of clearance face- Provides stop to prevent bur edge from digging into the

tooth

Carbide burs: slightly negative rake angle

90 degree edge angle

Low clearance angle

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Modifications in bur design: Reduced use of crosscuts: - Crosscuts produce unduly rough surface when used

with high speed Extended heads on fissure burs: - Light pressure needed for high speeds permits this

modification Roundening of the sharp tip angles - lower stresses - enhance strengthof tooth - facilitate adaptation of restorative materials

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Additional features in head design: Head length Taper angle Neck diameter Spiral angle Cross cut

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FACTORS INFLUENCING THE CUTTING EFFICIENCY OF BURS

1. Rake angle: Positive the rake angle - more the cutting efficiency Positive rake angle>radial rake angle>negative rake angle But negative rake angle is used because of following

reasons

- The size of bur tooth and tooth angle is more thus increasing its bulk and increased resistance to fracture

- The cut chips moves directly away from the blade

- Positive rake angle-the chips are larger and tend to clog the chip space

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2. Clearance angle:

3. Number of teeth or blades and their distribution:- For ideal cutting efficiency- 6 to 8.

- As number of blades decreases, magnitude of force at each blade increases & thickness of the chip removed by each flute increases.4. Concentricity:

- Measures how closely a single circle can be passed through tips of all the blades

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5. Run out:

- The eccentricity or maximum displacement of the bur head from its axis of rotation while the bur turns.

- Run out leads to inaccurate cutting and increased heat production

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CARE WITH ROTARY CUTTING INSTRUMENTS

1. Ensure good access & visibility by providing proper retraction, use of rubber dam, evacuation and good illumination of the working area

2. Use proper finger rests to guide the handpiece, support it & provide maximum control of the cutting instrument

3. Avoid uncontrolled or excessive removal of uninvolved tooth structure. In case of deep caries removal use slow speed round steel burs with intermittent, light pressure to protect pulp.

4. Always use sharp burs of small dimensions, avoid use of dull or clogged burs

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5. Use air-water spray to cool, moisten & clear the operating site. The spray lubricates, cleans & cools the cutting instrument, thus increasing its cutting efficiency & life

6. Care for the adjacent teeth and gingiva. Use retraction, wedge & rubber dam isolation. Use safe-ended burs while operating near the gingiva

7. Wear protective glasses for protecting the eyes. Use of face shields are valuable in preventing aerosol spatter

8. Ear plugs, anti-noise devices can be used to minimize unwanted sounds

9. Disposable masks filter out bacteria. Use of rubber dam & high volume evacuation near the tooth may minimize inhalation of vapors.

BURS FOR AMALGAM No. 245 carbide bur - punch cut No 169L or No. 329 pear shaped carbide bur - extension

into fissures No. 169L or No. 330 - small lesions

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No ¼ or No. 33 ½ - retention grooves No. ¼ round bur or No. 169 - Retention locks No. 33 ½ or no. ¼ - retention coves in facio pulpal line

angle No. 169 - sharpen line angles ,class VI tooth preparation No. 2 or no. 4 bur - slot preparation

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No. 2 or no ½ or no. 1 – entry cut for class III No. ½ - accentuate axio gingival line angle No. 2 or No. 4 round bur - infected dentin No. ¼ - incisal retention cove at axiofacioincisal point

angle of class III No. 2 or No. 4 round carbide bur or suitable tapered

fissure bur - class V

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BURS FOR COMPOSITE No. ½ ,1 or 2 round bur – outline form for class III No. ¼ - retention groove and cove Flame shaped or round diamond instrument – bevel Appropriate size round bur - class IV

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No. 700, 701 or 271 tapered fissure carbide bur - Class V

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Inverted cone bur - class I No. 330 or 245 - class II

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FINISHING AND POLISHING:

FOR AMALGAM

Additional appointment

Use: Reduce plaque accumulation

Decrease gingival inflammation

Secondary caries

Better marginal adaptation

Minimizes tarnish and corrosion

Esthetically acceptable

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Procedure:

Wait for 24 hr

Finish with steel bur or stones

High point - reduced with carborundum stones or finishing burs

Overhangs reduced by rhein trimmers, bard parker knives, periodontal knives or gold foil knives

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Abrasives: Coarse Medium Fine Ultra fine

Finishing of cervical areas - fine water resistant strips in to and fro motion

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Restoration moist during polishing

Low speeds, light intermittent pressure

Polishing agents : Tin oxide Zinc oxide Chalk Pumice Extra fine silex

Used with Polishing strips, brushes, rubber cups

Hazards: Aerosols High temperature

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FOR COMPOSITE:

*Contour unpolymerized composite with hand instruments

Excess at cavosurface margins - scraped with scalpel or sharp gold knife

Gross contouring and finishing : Alpine stone Diamond points fluted carbide burs

Use Low speed,

Water stream,

Little pressure,

Lubricant

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Abrasives : Aluminium oxide Cuttle fish Silicon dioxide coated disks and strips

Class V – finishing bur of adequate shape

Final lustre - polishing pastes Pumice Silica Alumina Tin oxide Silicon carbide Zirconium silicate

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Mix abrasive with water or glycerin

Carried with brushes, rubber cups,

linen strips, dental tapes

Low speed, light pressure

Dental floss to inspect proximal surfaces

Etch restoration and adjoining enamel

Apply thin layer of glaze

Glaze : film of unfilled polymers with a composition similar to resin matrix

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Felt disksSilicone polishers

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REFERENCES: STURDEVANT’S ART & SCIENCE OF OPERATIVE

DENTISTRY –-5TH EDITION OPERATIVE DENTISTRY- MODERN THEORY AND

PRACTICE- M.A. MARZOUK, A.L.SIMONTON, R.D. GROSS

PRINCIPLES AND PRACTICE OF OPERATIVE DENTISTRY- GERALD T. CHARBENEAU- THIRD EDITION

TEXT BOOK OF OPERATIVE DENTISTRY-VIMAL SIKRI

Hemamalathi,SK, Abarajithan M, Kandaswamy D Indian J Dent Res. 2008 Oct-Dec;19(4):284-7.