dental burs
DESCRIPTION
Bur designs and cutting bladesTRANSCRIPT
1
DEPARTMENT OF CONSERVATIVE DENTISTRY &
ENDODONTICS
2
Seminar on
DENTAL BURSBUR DESIGN,SHAPES,SIZES,
BURS FOR AMALGAM AND COMPOSITE
3
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
4
BUR:
Rotary cutting instrument with bladed cutting head
PARTS OF A BUR:
Shank
Neck
Head
5
HISTORICAL DEVELOPMENT: Steel bur 1891 Carbide bur 1947
PURPOSE: Tooth preparation Finishing a restoration Surgical removal of bone
6
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
7
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.
8
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”
9
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
10
IV. According to length of their head
Long
Short
Regular
V. According to their shapes
Round
Straight fissure
Tapered fissure
Inverted cone
11
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.
12
INVERTED CONE BURS: Numbered from 33 ¼, 33 ½, 34, 35, to 39. Cavity extension and occasionally for establishing wall
angulations and retention forms.
13
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.
14
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.
15
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.
16
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
17
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
18
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
19
BUR BLADE DESIGN:
20
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.
21
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
22
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
23
Additional features in head design: Head length Taper angle Neck diameter Spiral angle Cross cut
24
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
25
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
26
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
27
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
28
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
29
30
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
31
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
32
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
33
No. 700, 701 or 271 tapered fissure carbide bur - Class V
34
Inverted cone bur - class I No. 330 or 245 - class II
35
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
36
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
37
Abrasives: Coarse Medium Fine Ultra fine
Finishing of cervical areas - fine water resistant strips in to and fro motion
38
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
39
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
40
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
41
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
42Alumina disks
Felt disksSilicone polishers
43
44
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.