ABRASIVES--AND--POLISHING-AGENTS pdf.pdf

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1. ABRASIVE & POLISHING
AGENTS
Dr.K.SHEELA,MDS
Department of Prosthodontics

2. DEFINITIONS
Abrasion
Craig, has defined abrasion as :
“A process of wear where by a hard rough surface
( like a sand paper disk ) or hard irregular shaped
particles ( like those in a slurry ) plough grooves in
a softer material and cause materials from these
grooves to be removed from the surface”.
Skinnerhas stated abrasion to be either a two body
process or a three body process.

3. Finishing:
The term finishing denotes to cut or remove the
excess . It is usually performed with coarser
abrasives when compared to polishing .
Polishing:
The use of progressively finer abrasives to remove
scratches and give a high shine or luster to the
material .
To understand this more specifically , the terms
such as abrasive wear and erosive wear need more
specific understanding.

4. Wear:
It is a material removal process that can occur
whenever surfaces slide against each other . In
dentistry , the outermost particle or the surface
material of an abrading instrument is referred to
as ABRASIVE . The material being abraded is
called as Substrate .

5. Abrasive wear : Two types –
Two Body Wear:
Occurs when abrasive particles are firmly bonded to
the surface of the abrasive instrument and no other
abrasive particles are used eg. A diamond bur
abrading a tooth.
Three body wear:
occurs when the abrasive particles are free to
translate and rotate between two surfaces eg. action of
prophylaxis paste as they are applied to tooth enamel
by a rubber cup.

6. Erosive wear:
Thisiscausedbyhardparticlesimpactinga
substratesurface,carriedeitherbyastreamofair
orastreamofliquid.Erosivewearshouldbe
differentiatedfromchemicalerosionmore
commonlyknowasacidetchingwhichinvolves
acidsandalkalisinsteadofhardparticlesto
removethesubstratematerial.

7. Factors affecting the rate of abrasion :
1. Concentration of the abrasive particles
2. Size of the particles : expressed in millimeters
classified as –fine, medium and coarse.
3. Speed :
The faster the speed , faster will be the rate of abrasion.
4. Pressure of the abrasive particles against the surface
being abraded :
Heavy pressure will lead to formation of deeper
scratches and faster removal of the substrate .

8. Factors influencing the efficiency of the abrasives :
1. Hardness of the abrasive particle.
2. Rate of movement of the abrasive particles.
3. Properties of the material being removed.
A brittle material can be abraded rapidly whereas a
malleable and ductile material eg. Gold will flow
instead of being removed by the abrasive.

9. Design of Abrasive Instrument
Finishing and
polishing
devices
Abrasive and
polishing
devices
Loose
abrasives
Bonded
abrasives
Coated
abrasives
Cutting
instruments

10. Loose abrasives or grits :
They are derived from abrasive materials that
have been crushed and passed through series of
mesh screens to obtain different particle sizes-
Coarse, medium coarse, medium fine and super
fine.
Loose abrasive polishing pastes contain a fine
particle size distribution of either aluminium
oxide or diamond particles dispersed in a water
soluble vehicle , such as glycerine.

11. Bonded abrasives
These consists of abrasive particles incorporated
through a binder used for grinding tools.
The matrix is usually an elastomeric material such
as rubber or silicone compound, but can also be
rigid and non elastic in nature.
Eg. Bullet or Pointed white stone used at low
speed .

12. The abrasives are bonded by four methods:
1. Sintering.
2. Vitreous bonding.
3. Resinous bonding.
4. Rubber bonding.

13. Coated Abrasives
They are usually in the
form of a mylar, paper or
some other polymeric
backing, wherein the
abrasive particles are
distributed on the surface
of the backing or some
other symmetric matrix
design.
The abrasive particles are
retained on the surface of
the disc or matrix by an
adhesive polymeric

14. Air Abrasive Technology
As an alternative to the use of rotary cutting,air
abrasive systems can deliver a fine,precisely
controlled high-pressure stream of 25to30um
aluminium oxide particles to remove enamel,
dentin,and restorative materials.
Because air abrasion generates minimal heat or
vibration, the potential for tooth chipping or
micro fracturing is minimized.

15. A controlled delivery of air , water and
sodium bicarbonate slurry to remove
plaque and stains from tooth surfaces is
also employed for Dental Hygiene
procedures.

16. Skinners has grouped abrasives as
Natural abrasives:
Arkansas stone Sand
Chalk corundum Tripoli
Diamond Cuttle
Emery Quartz
Garnet Kieselguhr
Pumice
Zirconium silicate
Manufactured abrasives: Silicon carbide
Aluminum oxide
Synthetic diamond
Rouge
Tin oxide

17. 1. Arkansas Stone :
Semi-translucent , light grey , siliceous
sedimentary rock mended in Arkansas
Contains mico-crystalline quartz .
Small pieces are attached to metal shanks and trued
to various shapes for fine grinding of tooth enamel.
2. Chalk :
mineral form of calcite
contains calcium carbonate
used as a mild abrasive paste to polish teeth enamel ,
gold fillings ,…

18. Corundum :
Largely replaced by alpha aluminium oxide due to its
various superior physical properties .
Available as bonded abrasive and is used primarily to
grind metals .
Diamond :
Transparent colorless mineral composed of carbon
called SUPER-ABRASIVEbecause of its ability to
abrade any known substance .
Hardest substance known .
Used on ceramic and resin based composite materials.
Supplied as –bonded abrasive , diamond abrasive
pastes , abrasive strips .

20. Emery :
Consists primarily of a natural oxide of aluminium
called corundum .There are various impurities present
, such as iron oxide which also act as abrasives .
Usually bound to paper discs and can be used on gold or
porcelain .
.

21. Garnet :
Includesseveralminerals,whichpossessimilar
physicalpropertiesandcrystallineformlikesilicates
ofAl,Co,Mg,Mn.Isdarkred,extremelyhardand
whenfracturedduringabrasiveactivityformssharp
chiselshapedplates-thusmakinggarnetaneffective
abrasive.Usuallycoatedonpaperorclothwitha
binder.Cutsbothmetalandporcelain.
Dentureabrasivediscs.

22. Pumice :
Highly siliceous material of volcanic origin .
Suitable for use as an abrasive or a polishing agent
according to its particle size .Can be used for many
operations from smoothening of denture bases to the
polishing of teeth in the mouth .
Quartz :
The particles are pulverized to form sharp angular
particles , which are useful in making coated discs .
Used to finish metal alloys and may be used to grind
dental enamel .

23. Sand :
Is an abrasive agent along with other forms of quartz
Eg. Sandpaper is coated with a dense crystalline
form of quartz called Flint.
Flint is a naturally occurring mineral that chips to
form sharp cutting edges . It is not as durable or
strong as other abrasives , but it is a useful abrasive in
the finishing cast gold .Also available a powder in
sandblasting equipment .

24. Tripoli :
Mild abrasive and polishing agent.
True Tripoli originates from certainporous rocks,
first found in Northern Africa near Tripoli, for
which it was named.
Used for polishing metal alloys and some plastic
metals.

25. Zirconium silicate :
Occurs in nature as Zircon.
Is ground to various particle sizes and used as a
polishing agent .
It is used as a constituent of dental prophylactic pastes
and in abrasive impregnated polishing strips and discs
.
Cuttle :
A fine,relatively soft polishing agent made from
calcified internal shell of cuttle fish .
It is used on paper discs and for delicate operations
like polishing of metal margins.

26. Kieselguhr :
It is composed of siliceous remains of minute
aquatic plants know as diatoms .
The coarser form is called diatomaceous earth ,
which is used as a filler in many dental materials .
It is an excellent mild abrasive and polishing agent .
Precaution should be taken –respiratory silicosis
due to long term exposure .

27. Manufactured abrasives
Silicon carbide :
First of the synthetic abrasives to be developed .
It is the basic material of corundum
Two types are manufactured –green form and blue
black form .
Cutting efficiency of silicone carbide abrasives is
higher as the particles are sharp and break to form
new sharp particles .
Supplied as an abrasive in coated discs, vitreous and
rubber alloys , ceramic and plastic materials .
Most of the steel burs employed for the tooth cutting
are made of silicon carbide .

28. Aluminium Oxide :
This is the second synthetic abrasive to be manufactured
.
Pure aluminium oxide is manufactured from bauxite , an
impure aluminium oxide.
Extremely fine particles of aluminium can be obtained
by a water floation process. In this form it is know as
levigated alumina and it is used extensively for
polishing metallographic specimens .
The formsusually prepared are :
Coarse grit aluminium oxide is the abrasive in brown ,
pink , or coral stones used for finishing metal and
ceramic copings .
A very fine grit (400) is used for the manufacture white
polishing stones, sometimes called Poly stones

29. Synthetic diamond :
The synthetic or manufactured form of
diamond saws, wheels and burs , diamond blocks-
used for truing of bonded abrasives .
They are used primarily on teeth , ceramic
materials.
Rouge:
It is a fine red powder composed of iron oxide.
Usually employed in cake form
It is impregnated on paper or cloth, known as Crocus
cloth
Excellent polishing agent for gold and noble metal
alloys.

30. Tin oxide :
Also called as Putty powder ,it is used as a polishing
agent for teethand metallic restorations in the mouth
It is mixed with water , alcohol or glycerin and used as a
paste.

31. Polishing
Is the production of a smooth mirror like surface
without use of any external form.
If the size of the abrasive is reduced sufficiently, the
scratches finally become extremely fine and may
disappear entirely.
The surface then acquires a smooth shiny layer
referred by Skinner as a POLISH.

32. The polished layer is thought of one made up of
minute crystals, thus know as the “Micro
crystalline layer or Beilby layer”
which is easily kept clean and has high corrosion
resistance.

33. Finishing and polishing of the denture base resin
1.Remove the stone from the denture in small sections.
Use a bur or a saw judiciously in removing the stone
in sections without damaging the denture .
Edentulous casts may have undercut areas and also
cast is stronger than the plastic denture . Injudicious
prying will result in a broken denture
2.A shell blaster is also helpful in removing stone from
the interior of the denture . A pneumatic chisel also
aids in removing stone from the denture .
3. After separating the denture the cast , it is ready for
finishing and polishing .

37. Summary&Conclusion
A lot of materials are available commercially to
perform finishing and polishing. Discretion on the
part of the dentist is necessary to select the right
material for that technique.
Since each manufacturer advocates his own
method, standardization of technique becomes
very difficult.
Every technique follows the use of abrasive grits in
a sequence of coarse to fine to achieve optimal
results.

38. An optimal application of specific devices for
certain restorative materials and specific clinical
situations should be considered in order to
enhance both longevity and esthetics of the
restored teeth.
Also due to rapid development in technology, these
materials and equipment undergo changes. But
one should follow the basic principles of finishing
irrespective of the system or product chosen.