It occurs when a hard, rough surface slides along a softer surface and cuts a series of grooves. The wearing away of a substance or structure through a mechanical process, such as grinding, rubbing or scraping . Polishing is production of smooth mirror like surface without use of any external form.

1. ABRASION AND POLISHING
Dr. Ibadat Jamil
Assistant professor
Dep. Of Prothodontics

2. ABRASION: It occurs when a hard, rough surface slides along a
softer surface and cuts a series of grooves.
The wearing away of a substance or structure through a
mechanical process, such as grinding, rubbing or scraping
(GPT-8).
TYPES OF ABRASION
Abrasion may be:
• Two body wear – occurs when abrasive particles are firmly
bonded to the surface of the abrasive instrument and no
other and abrasive particles are used e.g, a diamond bur
abrading a teeth.
• Three body wear – when the abrasive particles are free to
translate and rotate between two surfaces Eg, dental
prophylaxis pastes (between tooth and hand rubber cup).

3. • Erosive wear – This is caused by hard particles
impacting a substrate surface, carried by either a
stream of air or a stream of liquid.
• Erosive wear should be differentiated from chemical
erosion more commonly known as acid etching
which involves acid and alkalis instead of the hand
particles to remove the substrate material.

4. SUPPLIED AS:
• Paper/plastic coated –e.g Sand paper
• steel or plastic strips
• Electroplating bonding
• Bonded stones In grinding wheels and dental stones
• Powder form
• Rubber impregnated
• Paste form

5. DESIRABLE CHARACTERISTICS OF AN
ABRASIVE
1. It should be irregular in shape so that it presents a
sharp edge.
2. It should be harder than the work it abrades. If it
cannot indent the surface to be abraded then it
cannot cut it and therefore wears out.
3. Abrasive should posses a high impact strength.
4. Abrasive should posses attrition resistance so that it
does not wear.

6. ABRASIVE ACTION
• The mode of action of the abrasives is similar
to that of the dental burs that is it is merely a
cutting action.
• Each fine abrasive particle thus presents as a
sharp edge which cuts through the surface
similar to a pointed chisel.

7. FACTORS AFFECTING RATE OF ABRASION:
1. Size of the abrasive particle – larger the size – greater
the abrasion
2. Pressure- of the work against the abrasive when work
is pressed against the abrasive scratches are deeper
and abrasion is more rapid.
3. Speed- Greater the speed, greater would be the rate of
abrasion.

8. FACTORS INFLUENCING EFFICIENCY
OF THE ABRASIVES
1. The hardness of the abrasive particle - diamond is hardest,
pumice and garnet etc are relatively mild.
2. The Shape of the abrasive particle - particles with sharp
edge are more effective.
3. Particle size of the abrasive - Longer particle size will cut
deeper grooves.
4. Mechanical properties of the abrasive (If the material
breaks, it should form a new cutting edge. Therefore
brittleness can be an advantage).
5. Rate of movement of the abrasive particles - slower
abrasion – deeper scratches.
6. Pressure applied to the abrasive - too much pressure can
fracture the abrasive instrument and increase heat of friction
that has evolved.

9. TYPES OF ABRASIVES
According to Craig : The abrasives used can be classified
grouped as:
A. Finishing Abrasives - These are hard, coarse abrasives
used initially to develop desired contours and remove off
gross irregularities.
B. Polishing Abrasives - These have a smaller particle size
and are less hard than abrasives used for finishing. They
are used for smoothening surfaces .
C. Cleansing Abrasives - These are soft abrasives with
small particle size and are intended to remove softer
materials that adhere to enamel or a restoration.

10. Skinner’s has grouped the abrasives as follows:
Natural Abrasives:
1. Chalk
2. Diamond
3. Emery
4. Garnet
5. Pumice
6. Sand
7. Tripoli
8. Zirconium silicate
9. Kleselguhr
Manufactured Abrasives:
1. Silicon carbide
2. Aluminium oxide
3. Synthetic diamond
4. Rouge
5. Tin oxide

11. Natural Abrasives :
Chalk
• Contains calcium carbonate.
• Used as mild abrasive paste to polish teeth enamel
, gold foil, amalgam and plastic materials.
Diamond
• It is a transparent colourless mineral composed of
carbon called superabrasive because of its ability to
abrade any other known substance.
• It is the hardest substance known.
• Used on ceramic and resin based composite
materials.

12. Emery
• This abrasive is a grayish black corundum that is
prepared in a fine grain form.
• Supplied predominantly as coated abrasive disks.
• Used for finishing metal alloys or plastic materials.

13. Garnet
• The term garnet includes several minerals which
possess similar physical properties like Silicates of
Aluminium, Cobalt, Iron, Magnesium and
Manganese.
• Garnet is dark red, extremely hard.
• Garnet an effective abrasive.
• Garnet is available on coated disks.
• Used in grinding metal alloys and plastic materials.

14. Pumice
• It is a highly siliceous material of volcanic origin and is
used either as an abrasive or polishing agent depending
on particle size.
• Used in polishing teeth.
• Smoothening dentures.
Sand
• Sand is used as sand paper or as powder in sandblasting
equipment.
• Particles have rounded to angular shape.

15. Tripoli
• Mild abrasive and polishing agent
• Tripoli originates from certain porous rocks
• First found in North Africa near Tripoli.
Zirconium silicate
• The mineral zircon is ground to various particle sizes.
• Used as a polishing agent.
• It is used in dental prophylactic pastes.
• Used in abrasive impregnated polishing
strips and discs.

16. Kieselgurh
• This abrasive is obtained from the silaceous remains
of minute aquatic plants known as diatoms.
• It is an excellent mild abrasive and polishing agent
• The coarser variety is known as diatomaceous earth
used as a filler for dental materials such as
hydrocolloid impression materials.

17. Manufactured Abrasives
Carbides
• This is the first of the synthetic abrasive to be
developed.
• Silicon carbide and boron carbide are
manufactured by heating silicon and boron at a
very high temperature to effect their union
with carbon.
• Most of the stone burs used for cutting tooth
structure are made of silicon carbide.

18. • The cutting efficiency of silicon carbide abrasives is
higher as the particles are sharp and break to form
new sharp particles.
• Supplied as air abrasive in coated disks and vitreous
and rubber bonded instruments.
• The silicon carbide is used in cutting metal alloys,
ceramics.

19. Aluminium Oxide
• Pure alumina is manufactured from bauxite, an impure
aluminum oxide.
• It can be produced in fine grain size.
• Pure alumina is also used as a polishing agent. Alumina is
used in sandblasting machines.
Rouge
• Principle component is iron oxide blended with various
binders.
• Used to polish gold and high noble metal alloys.
• May be impregnated on papercloth known as CROCUS
CLOTH.

20. Tin Oxide
• Is composed of very fine abrasive particles.
• Mixed with water, alcohol or glycerine and
used as paste.
• Used as a polishing agent for teeth and
metallic restorations.

21. POLISHING
“Polishing is the production of a smooth mirror like
surface without use of any external form”.
• Polishing is usually achieved by an abrasive process.
However a smooth shiny surface can also be achieved
through nonabrasive means. These include:
1. Application of a glaze layer e.g.,
• Glazing of composites
• Glazing of ceramics
2. Electrolytic polishing
3. Burnishing

22. COMPOSITE GLAZING
• A layer of glaze or gloss is applied over the
restoration and cured. This results in a smooth
glossy surface.
GLAZING CERAMICS
• Ceramics are difficult to polish conventionally.
The finished restoration is subjected to high
temperatures. At this temperature the surface
layer melts and flows to produce a smooth
glass-like surface.

23. • In electrolytic polishing the
material is removed through
an electrochemical process
rather an abrasive process.
• This is the reverse of
electroplating. The alloy to be
polished is made the anode
of an electrolytic cell.
• As the current is passed,
some of the anode is
dissolved leaving a bright
surface. This is an excellent
method for polishing the
fitting surface of a cobalt-
chromium alloy denture.
ELECTROLYTIC POLISHING

24. BURNISHING
• A round steel point is rubbed over the margins
of a gold inlay, the metal is moved so that any
gap between the inlay and the tooth can be
closed. A special blunt bur revolving at high
speed can also be used.

25. PROCEDURE
METHODS OF ABRASION
• Abrasion may be carried out
• 1. Manually, e.g., proximal stripping of enamel using abrasive
strips.
• 2. Rotary instruments, e.g., burs, wheels, cups, discs, cones,
etc.
• 3. Blasting: The object is blasted with a steady stream of
abrasive.
Smoothen work with a coarse abrasive or bur which leaves large
scratches. These scratches are removed with finer abrasives
but the difference in fineness should not be too great.

26. • After changing to a finer abrasive, the direction of
abrasion should be changed each time if possible, so
that new scratches appear at right angles to the
coarser scratches, for uniform abrasion.
• When the scratches are no longer visible to the eye,
the preliminary polishing can be accomplished with
pumice flour applied with a canvas buff wheel.

27. • A paste is formed of pumice and water to a sticky
‘muddy’ consistency.
• The buff wheel is turned at high speed. Apply the
paste to the work and carry it to the buff. Hold the
work firmly but without excessive pressure.
• Repeat this over the entire surface till the surface is
bright and well polished.

28. DENTIFRICES
• Popularly known as toothpastes these are agents
used with a toothbrush to cleanse and polish natural
teeth.
• They should have maximum cleansing efficiency with
minimum tooth abrasion.
• FUNCTION
1. Assists the toothbrush to mechanically remove
stains, debris and soft deposits from the teeth.
2. To impart a polished surface to the tooth.
3. Thus, they help to reduce caries, maintain healthy
gingiva, improve esthetics and reduce mouth odors.

29. AVAILABLE AS:
• Pastes, powders, liquid and gels.
COMPOSITION:
• The basic component of a dentifrices is the abrasive.
• Specialized dentifrices contain medicaments for
various problems such as sensitivity and gum
diseases.

30. Composition of a typical dentifrices are:
• Abrasives: Dibasic calcium phosphate , Calcium
pyrophosphate , Insoluble sodium meta-phosphate
Hydrated silica , Alumina , Magnesium oxide, etc.
• Water
• Humectants : Glycerin , Sorbitol , Propylene glycol
• Detergents : Sodium lauryl sulfate
• Foaming agents
• Binders : Carboxy methyl cellulose
• Artificial sweeteners : Sorbitol, Saccharin
• Therapeutic :Sodium fluoride , Stannous fluoride Strontium
chloride , Urea , Pencillin , Dibasic ammonium phosphate.
• Coloring and flavoring : Mint

31. PROPHYLACTIC ABRASIVES
• Oral prophylaxis is a widely used procedure in the dental
office.
• The Prophyjet is a relatively new dental prophylaxis system of
removing intraoral stains.
FUNCTION
1. They remove extrinsic stains and oral debris.
2. Impart a highly polished and esthetic appearance.
3. They are applied onto the teeth with the help of rubber cups
or bristle brushes which are attached to a rotary instrument.

32. • An abrasive blasting process is used to mechanically
remove extrinsic stains as well as light supragingival
adherent plaque and calculus.
• The powder is loaded into the device, which then
directs the abrasive through a small nozzle in a
steady stream of air and water.

33. Composition :
• Contains sodium carbonate, hydrophobic modified
silica and a flavoring agent.
• Supplied as powder in sachets or containers.
Clinical considerations:
• The prophyjet is directed at 45º angles to the tooth
surface.
• It is less effective in proximal areas.
• The chances of soft tissue injury exist especially if the
tissue is inflamed and friable.

34. DENTURE CLEANSERS
Dentures collect deposits in the same manner as
natural teeth during their use.
These can be removed by two ways:
• Professional—repolishing in the laboratory or clinic.
• The dentures may be brushed using a soft bristle
brush abrasive or cream.

35. • The dentures are soaked in these chemical solutions
for a prescribed period of time. For e.g Alkaline
perborates, Alkaline peroxides, Alkaline
hypochlorites , Dilute acids.

36. THANKYOU