Abrasives , Classification , Applications in Dentistry, Working principles, Armentarium.

1. ABRASIVES
PRESENTED BY:
DR. HASHMAT GUL
DEMONSTRATOR ,
DENTAL MATERIALS ,
AMC, NUST.

2. SOME IMPORTANT DEFINITIONS
ABRASIVE A hard substance used for grinding, finishing, or polishing a less-hard surface.
CUTTING Process of removing material from the substrate by use of a bladed bur or an abrasive embedded
in a binding matrix on a bur or disk.
GRINDING Process of removing material from a substrate by abrasion with relatively coarse Particles.
CONTOURING Process of producing a desired anatomical form by cutting or grinding away excess material.
FINISHING Process of removing surface defects or scratches created during the contouring process through the
use of cutting or grinding instruments or both.
POLISHING Process of providing luster or gloss on a material surface.

3. BENEFITS OF FINISHING AND POLISHING
RESTORATIVE MATERIALS
ORAL HEALTH
• By resisting the
accumulation of food
debris and pathogenic
bacteria.
• Easier to maintain in a
hygienic state when
preventive home care is
practiced.
ORAL FUNCTION
• Oral function is enhanced-
food glides more freely
over occlusal and
embrasure surfaces
during mastication.
• Lower contact stresses, so
can improve the strength
of the restoration,
especially in areas that
are under tension.
• Minimize wear rates on
opposing and adjacent
teeth ( Ceramics).
AESTHETICS
• Highly mirror-like
restoration surfaces
preferred for the invisible
areas(posteriors) but is
discouraged for anterior
visible teeth to gain a
more natural appearance.
• Tarnish and corrosion
activity of some dental
materials can be
significantly reduced

4. ABRASIVE INSTRUMENTS

5. ARMENTARIUM FOR
FINISHING POLISHING
Fluted carbide burs.
Diamond burs.
Stones.
Coated abrasive discs & strips.
Polishing pastes.
Soft & hard polymeric cups, points &
wheels.
Polishing brushes.
Muslin (Woven Cotton Fabric) Wheels.

6. FLUTED CARBIDE BURS

7. DIAMOND BURS

8. STONES

9. COATED-ABRASIVE DISCS & STRIPS
Paper-backed abrasive
disc/strip.
Myler backed abrasive
disc/strip (moisture resistant)

10. TYPICAL BONDED ABRASIVE INSTRUMENTS
From left to right
Vitreous-bonded
abrasive wheel &
points (1-3)
Rubber-bonded
abrasive bullets

11. POLISHING PASTES

12. POLYMERIC CUPS/POINTS/WHEELS

13. POLISHING BRUSHES

14. TYPES OF ABRASIVES

15. NATURAL ABRASIVES MANUFACTURED ABRASIVES
Ailzansas Stone
Chalk (paste)
Corundum (white stone)
Diamond
Natural (super abrasive)
Synthetic
Emery (Coated disks)
Garnet (Coated disks & arbor bands).
Pumice (rubber-bonded , flour)
Quartz ( Coated discs)
Sand
Tripoli
Zirconium Silicate (coated disks & strips)
Cuttle (coated abrasive)
Kieselguhr
Silicon Carbide (coated disks & as vitreous-
bonded & rubber-bonded instruments).
Aluminium Oxide (bonded/coated abrasives &
air-propelled grit abrasives)
Synthetic Diamond,
Rouge
Tin Oxide

16. NATURAL ABRASIVES USES
Ailzansas Stone
Chalk (paste)
Corundum (white stone)
Diamond
Natural (super abrasive)
Synthetic
Emery (Coated abrasive disks)
Garnet (Coated disks & arbor
bands.
Pumice (rubber-bonded , flour)
For fine grinding of tooth enamel and metal alloys.
To polish tooth enamel, gold foil, amalgam & plastic materials.
Grinding metal alloys.
Mostly used on ceramic and resin-based composite materials.
Manufacture of diamond saws, wheels, burs, blocks & polishing pastes.
May be used for finishing metal alloys or acrylic resin materials.
Used in grinding metal alloys and acrylic resin materials.
polishing tooth enamel, gold foil, dental amalgam, and acrylic resins.

17. NATURAL ABRASIVES USES
Quartz ( Coated discs)
Sand
Tripoli
Zirconium Silicate (coated
abrasive disks & strips)
Cuttle (coated abrasive)
Kieselguhr
used primarily to finish metal alloys, and they may also be used to grind
dental enamel.
Applied under air pressure to remove refractory investment materials
from base metal alloy castings. They are also coated onto paper disks
for grinding of metal alloys and acrylic resin materials.
Polishing metal alloys & some acrylic resin materials.
Used as a component of dental prophylaxis pastes
Polishing of metal margins and dental amalgam restorations.
Coarser form is called Dialomaceous earth, used as a filler in many
dental materials, such as the hydrocolloid impression materials.

18. MANUFACTURED ABRASIVES USES
Silicon Carbide (coated disks & as vitreous-bonded
& rubber-bonded instruments).
Aluminium Oxide (bonded/coated abrasives & air-
propelled grit abrasives)
Synthetic Diamond,
Rouge
Tin Oxide
for fine grinding of tooth enamel and metal alloys.
white stones, popular for adjusting dental enamel &
for finishing metal alloys, Resin-based composites &
ceramic materials.
to polish high noble metal alloys.
Polishing teeth and metallic restorations in the mouth

19. CUTTING, GRINDING, FINISHING & POLISHING

20. FACTORS AFFECTING THE RATE OF MATERIAL
REMOVAL
The speed of the hand-piece.
The Pressure applied.
The concentration , size , type & shape of the abrasive particle used.
The relative roughness of the abraded/cut surfaces.

21. THE GOALS OF FINISHING & POLISHING
To obtain the desired anatomy/proper occlusion.
The reduction of roughness, gouges, and scratches that were produced by
the contouring and finishing instruments.
The polished surface should be smooth enough
to be well tolerated by oral soft tissues and
to resist bacterial adhesion and excessive plaque accumulation.

22. PRINCIPLES OF CUTTING, GRINDING & FINISHING
Particles of a substrate are removed by the action of a harder abrasive that comes into
frictional contact with it.
With rotary instrumentation, the blades of a carbide bur or the tips of abrasive
particles transfer the force to the substrate.
This contact must generate sufficient tensile and shear stresses to break atomic bonds
and release a particle from the substrate.
These tensile and shear stresses are induced within both the substrate and the rotary
instrument.
The instrument will fail to function if the stress that develops in any part of the cutting or
grinding surface exceeds its strength compared with the strength of the substrate. Blade
edges will become dull, and abrasive particles will fracture or tear away from their
binder.

23. BULK REDUCTION/CONTOURING
GRINDING CUTTING
Instruments used
Diamond burs
Abrasive-coated disks
8-12 fluted carbide burs used for
cutting.
12-16 fluted carbide burs used for
Contouring.
Instruments used
Steel burs
Tungsten Carbide burs
Abrasives with a particle size of 100
um or larger with sufficient hardness (9-
10 mohs hardness).
Abrasives ranging in size from 30-
100um, used for fine contouring.

24. • Tooth cut by a High-speed Tungstun Carbide bur, the regular pattern of
removal of tooth structure corresponding to the regular arrangement of
blades on the bur.
• Unidirectional cutting pattern (small shavings).
Carbide bur
• Tooth ground by diamond bur, the multiplex scratches formed by the random
arrangement of abrasive particles on the diamond bur.
• Unidirectional grinding.
Diamond bur
• Photomicrograph of the bonded diamond particles on a coarse diamond bur
(x150 )
Bonded
diamond
particles
THE CUTTING/GRINDING OPERATION

25. Tungsten carbide finishing burs
16-fluted (left), smoother finish, Slow material removal.
8-fluted (right) , less smooth finish, Rapid material removal.
Fine diamond bur
Slow material removal.
Smooth surface finish.
Medium-grit diamond bur
Coarse-grit diamond bur
Rapid material removal.
Rougher surface finish.

26. A course diamond bur
A 12-flute Carbide bur
A 16-flute Carbide bur
An abrasive impregnated finishing disk
An abrasive impregnated polishing disk.
SEM images of the
surface of a resin-based
composite after the
grinding, finishing, and
polishing processes using
live instruments

27. POLISHING
The purpose of polishing is to provide an enamel-like luster to the restoration.
The speed of achieving a luster, depends on the hardness and size of the abrasive
particles & the method of abrasion (e.g., two-body abrasion or three-body abrasion).
Smaller particles provide smoother and shinier surfaces. Ideally, 20um abrasive
particles provide luster at a low magnification with no visible scratches.
The surface must be cleaned between steps, because an abrasive particle left on the
surface from the previous step can cause deep scratches.
The quality of the surface finish and polish can be characterized by the
measurement of the surface roughness using a profilometer, an optical microscope, or a
scanning electron microscope (SEM).
In clinical practice, the surface luster is usually judged without magnification.

28. POLISHING
POLISHING PASTES
A non-abrasive material should be used as an applicator.
Soft Felt Points,
Muslin (Woven Cotton Fabric) Wheels,
Prophylaxis Rubber Cups/points,
Buffing Wheels.
A common feature of some of these materials is their porous texture that allows fine
abrasive particles to be retained during the buffing procedure

29. POLISHING PROCEDURES
STEPS
Polishing progresses from the finest abrasive that can remove scratches from the
previous grinding procedure.
Each step is followed by the use of progressively fine polishing media until no
further improvement in surface finish is observed.
Polishing is considered to be multi-directional in its course of action.

30. THE MECHANICS OF HIGH-SPEED
ROTARY INSTRUMENTATION
Black arrow: Direction of rotation of High-speed
Diamond bur (clockwise when viewed by operator)
Grey arrow: Direction of shaving movement of hand-
piece (opposite to da rotation of bur).
Incisal view
FB : Rotational forces of bur at tooth surface
Fo : Opposing force of the operator

31. TWO-BODY ABRASION occurs when abrasive particles are
tightly bounded to the abrasive instrument.
THREE-BODY ABRASION occurs when the abrasive particles are
free to translate & rotate between two surfaces.
HARD PARTICLE EROSION occurs when the abrasive particles
are propelled against a substrate by air pressure.

32. ABRASIVE INSTRUMENT DESIGN
Abrasive grits Bonded abrasives Coated abrasive disks
& strips
Non-bonded
abrasives
Dental abrasive grits are
classified on basis of
particle size as
coarse,
medium coarse,
medium,
fine, and
superfine
Consist of abrasive
particles that are
incorporated through a
binder to form grinding
tools such as points,
wheels, separating disks,
coated thin disks etc.
Particles are bonded by
four general methods:
(1) sintering,
(2) vitreous bonding
(3) resinoid bonding
(4) rubber bonding
Fabricated by securing
abrasive particles to a
flexible backing material
(heavy weight paper,
metal, or Mylar) with a
suitable adhesive
material.
These abrasives typically
are supplied as disks and
finishing strips
Polishing pastes (used for
final polishing).
Applied to the substrate
with a non-abrasive
device such as synthetic
foam, rubber, felt, or
chamois cloth.
The abrasive particles
are dispersed in a water-
soluble medium such as
glycerin for dental
applications.
E.g. Aluminium oxide and
diamond.

33. CLEANING & DRESSING OF BONDED-
ABRASIVE INSTRUMENTS

34. A rubber-bonded abrasive cylinder.
A diamond-coated abrasive dressing tool used to true, shape &
clean the bonded abrasive instrument both before & during the
finishing procedure.
Abrasive instrument with desired working shape after truing.
Instrument blinded with debris.
Lose cutting efficacy & generate more heat.
SEM of the same instrument , revealing debris clogging the
surface.
SEM , Instrument coated with abrasive dressing.
SEM, After dressing, debris removed & abrasive surface restored.

35. Diamond bur in high-speed rotary hand-piece before cleaning.
Running the diamond bur against moistened diamond cleaning
stone for 2-4 seconds.
Cleaned diamond bur with no debris between abrasive particles.

36. FACTORS AFFECTING DENTIFRICE ABRASIVENESS
EXTRA-ORAL FACTORS INTRA-ORAL FACTORS
Abrasive particle type, size & quantity in
dentifrice.
Amount of dentifrice used.
Toothbrush type
Tooth brushing method and force applied
during brushing
Tooth brushing frequency and duration
Patient's coordination and mental status
Salivary consistency and quantity (normal
variations)
Xerostomia induced by drugs, salivary
gland pathology, and radiation therapy
Presence, quantity, and quality of existing
dental deposits (pellicle, plaque, calculus)
Exposure of dental root surfaces
Presence of restorative materials, dental
prostheses, and orthodontic appliances.