Dental Burs

DEPARTMENT OF

DEPARTMENT OF

CONSERVATIVE DENTISTRY &

CONSERVATIVE DENTISTRY &

ENDODONTICS

Seminar on

Seminar on

DENTAL

DENTAL

BURS

BURS

 BUR DESIGN,SHAPES,SIZES,

 BURS FOR AMALGAM AND COMPOSITE

Seminar on

Seminar on

DENTAL

DENTAL

BURS

BURS

 BUR DESIGN,SHAPES,SIZES,

 BURS FOR AMALGAM AND COMPOSITE

CONTENTS

CONTENTS

o

o  Definition Definition o

o  Parts of bur Parts of bur o

o  Purpose Purpose o

o  Bur classification  Bur classification systemssystems o

o Classification of bursClassification of burs o

o  Bur shapes Bur shapes o

o  Bur blade design Bur blade design o

o  Factors influencing  Factors influencing cutting efficicutting efficiency of bursency of burs o

o Care with rotary instrumentsCare with rotary instruments o

o  Burs for amalgam Burs for amalgam o

o  Burs for composite Burs for composite

3 3

BUR:

BUR:

Rotary cutting instrument with bladed cutting head

Rotary cutting instrument with bladed cutting head

PARTS OF A BUR: PARTS OF A BUR: Shank Shank  Neck  Neck Head Head

HISTORICAL DEVELOPMENT:  Steel bur 1891  Carbide bur 1947 PURPOSE:   Tooth preparation   Finishing a restoration   Surgical removal of bone

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

C. S impli fied Number ing System f or dental bur s:  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, and eb - endo bur.

 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'

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

IV. According to length of their head

Long Short Regular

V. According to their shapes

Round

Straight fissure Tapered fissure Inverted cone

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

INVERTED CONE BURS:

 Numbered from 33 ¼, 33 ½, 34, 35, to 39.

 Cavity extension and occasionally for establishing wall

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.

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.

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.

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

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

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

 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

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

 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

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

FACTORS INFLUENCING THE CUTTING EFFICIENCY OF BURS

1. Rake angl e:

  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

2. Clearance angl e:

3. Number of teeth or blades and their distr ibuti on:

- 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

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

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

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

BURS FOR AMALGAM

 No. 245 carbide bur - punch cut

 No 169L or No. 329 pear shaped carbide bur - extension

into fissures

 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

 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

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

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

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

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

Abrasives:

 Coarse  Medium  Fine

  Ultra fine

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

Restoration moist during polishing

Low speeds, light intermittent pressure Polishing agents :

 Tin oxide  Zinc oxide  Chalk

 Pumice

 Extra fine silex

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

Abrasives :

 Aluminium oxide   Cuttle fish

 Silicon dioxide coated disks and strips

Class V –  _{finishing bur of adequate shape}

Final lustre - polishing pastes

 Pumice  Silica

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

Felt disks Silicone polishers