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1. ABRASION AND POLISHING
Introduction:
The finishing and polishing of restorative dental materials are
important steps in the fabrication of clinically successful restorations.
The techniques employed for these procedures are meant not only for
the removal of excess material but also to smoothen the rough surfaces.
The finishing of dental restoration prior to their placement in the
oral cavity has therefore three benefits viz.
A) To promote oral hygiene - by resisting the accumulation of food
debris and pathogenic bacteria.
B) Enhance oral function - a well polished surface aids in gliding
movement of the feed over occlusal surfaces and between
embrasure spaces (smooth restoration contacts minimise wear
rates on opposing and adjacent teeth. e.g. materials like ceramics
which contain phases harder than the teeth enamel and dentine).
C) To improve aesthetics.
The materials employed for finishing and polishing of dental
restorations are generally termed as Abrasives. Thus an understanding
of the characteristics/features with their properties of these materials and

2. the process of abrasion would aid in 'improved clinical usage of these
materials and techniques.
Individual Considerations:
I) Abrasion:
Craig has defined abrasion as:
"A process of wear whereby a hard rough surface (like a sand
paper disk) or hard irregular shaped practicles (like those in an abrasive
slurry) plough grooves in a softer material and cause materials from
these grooves to be removed from the surface".
It has been stated by Skinner's that abrasive could be a “two
body” or a "three body process."
To understand this more specifically the terms viz. Wear,
Abrasive Wear and Erosive Wear need more specific understanding
I) Wear - is a material removal process th3t 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 finished is termed as a SUBSTRATE.
II) Abrasive Wear

3. This could be of two types
a) Two body wear - occurs when abrasive particles are firmly
bonded to the surface of the abrasive instrument and no other
abrasive particles are used. E.g. a diamond bur abrading a teeth.
b) Three body wear - When the abrasive particles are free to
translate and rotate between two surfaces . E.g. dental
prophylaxis pastes (between tooth and rubber cup).
III) Erosive Wear
This is caused by articles impacting a substrate surface, carried
by either a stream of air or stream of liquid. Erosive wear should be
differentiated from chemical erosion more commonly known as acid
etching which involves acids and alkalis instead particles to remove the
substrate material.
Chemical erosion is employed to prepare teeth surfaces for
bonding purposes and not for finishing of materials.
Desirable Characteristics Of An Abrasive-
1. It should be irregular in shape so that it presents a sharp edge.

4. [-Jagged particles are more effective. Round sand particles and cubicle
particles of sand paper are poor abrasives].
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 / body strength.
Abrasive point should always fracture rather than dull out so that
always a sharp point or edge is available. The cuts also helps in
shredding debris accumulated from the work e.g. grinding wheel
against a metal.
4. Abrasive should possess attrition resistance so that it does not wear.
Design Of Abrasive Instruments
The abrasives employed could be one of the following three types, viz.:
A) Abrasive Grits
B) Bonded Abrasives
C) Coated Abrasive Disks And Strips
A) Abrasive Grits
Abrasive grits are derived from (abrasive) materials that have
been crushed an passed through series of mesh screens to obtain

5. different particle size ranges. The grits are classified as - COARSE,
MEDIUM COARSE, MEDIUM FINE and SUPER FINE according to
the particle size ranges.
B) Bonded Abrasives
These consists of abrasive particles incorporated through a binder
to for grinding tools.
The abrasive particles bonded by four general methods viz.:
i) Sintering
ii) Vitreous Bonding [Glass/ Ceramic]
iii) Resinoid Bonding [Usually perenolic resin]
iv) Rubber Bonding [usually silicon rubber]
i). Sintering: Sintered abrasives are the strongest variety since the
abrasive particles are fused together.
ii). Vitreous Bonded: are mixed with a glassy / ceramic matrix
material, cold pressed to the instrument shape and fired to fuse
the binder.
iii). Resin Bonded: are cold/hot pressed and then heated to cure the
resin.

6. iv). Rubber Bonded: made in a manner which is similar to resin
bonded.
As far as bonded abrasives are concerned the type of bonding
employed affects greatly the grinding behaviour of the tool on the
substrate. Bonded abrasives that tend to disintegrate rapidly on the
substrate are weak and result in increased abrasive costs. Bonded
abrasives that disintegrate very slowly tend to clog with the grinding
debris and result in loss of abrasive efficiency. Thus an ideal binder
would be one which would hold the abrasive to the instrument
sufficiently long as to cut, grind or polish the substrate and yet release
the abrasive particle before its efficiency is lost or before heat build-up
causes thermal damage to the substrate.
The type of binder is also intimately related to the life of the tool
in use. In most cases the binder is impregnated throughout which an
abrasive so that as an abrasive particle is wrenched during use another
abrasive particle takes its place as the binder wears e.g. for diamond
rotary instrument electroplated with a nickel base matrix is used as a
binder.
The heat generated during abrasive activity is dependent on the
efficiency of the abrasives. Cooling however maybe required for e.g. in

7. abrading polymeric materials, excessive heat should be avoided as it can
cause stress relief and warpage (E.C.Combe).
It is important that a bonded abrasive must always be TRUED
and DRESSED before use.
Truing - procedure where bonded abrasive is first run against a harder
abrasive block until it rotates in the handpieces without eccentricity or
run out when placed on the substrate. Therefore TRUING is done for
proper shaping of the bonded abrasive.
Dressing - Like Truing is done for proper shape of the abrasive and also
for two other purposes.
1) Dressing reduces width to correct working size and shape
2) Users to remove clogged debris (ABRASIVE BLIN I KING]
from the abrasive instrument to restore working efficiency.
C) Coated Abrasive Disks And Strips
These abrasives are supplied as disks and finishing strips. They
are fabricated by securing abrasive particles to a flexible backing
material [heavy weight paper or Mylar].

8. The disks are available in different diameters with thin and very
thin backings. Moisture - resistant backings are advantageous as the
abrasive stiffness is reduced by water degradation.
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. During this cutting process the shaving thus formed is
powdered usually clogs the abrasive which thus makes periodic cleaning
of the abrasive necessary.
Abrasive Action On Metals
On abrading metallic restorations, the metallic grain structure
usually gets disoriented. The more abrasion the greater is the associated
disorientation. Strain hardening of the abraded metal usually
accompanies the grain disorientation. (Strain hardening is a process
wherein - the metal becomes stronger, harder and less ductile - when
greater stresses are induced at the grain boundaries to provide slipping
of the lattice network].
In the abrading of metals the crystalline structure of the surface is
disturbed, sometimes to a depth. of 10m, However this surface affect

9. varies with different metals. e.g. inductile metals [such as gold] less of
the surface metal may be removed by the abrasive than in a brittle metal.
Abrasive Action On Resins
The surface disturbance produced by abrasion on resins however
leads to the creation of surface stresses that may cause distortion if the
abrasion is too rigorous. The heat - generated during this abrasion
partially relieves the stresses.
If this heat generated is excessive it may even relieve stresses
created during processing which leads to warpage of the resin along
with melting of the surface of the resin. The heat generated is directly
proportional to the efficiency of the abrasives.
Factors Affecting Rate
Rate of abrasion of given material by a given abrasive is
determined primarily by three factors.
1) Size of the abrasive particle - larger the size - greater
the abrasion.
2) Pressure of the work against the abrasive

10. When work is pressed against the abrasive scratches are deeper
and abrasion is more rapid - so greater chances of abrasive to fracture.
3) Speed at which the abrasive particle travels across the
work.
Greater the speed greater would be the rate of abrasion.
Speed employed is two types. viz.
- Rotational speed
- Linear speed - speed with which particles pass over the work.
- Linear speed required is 5000 ft/min.
- Linear speed is related to rotational speed as follows:
V =  dn where
V = Linear speed
d = diameter of abrasive
n = revolutions per minute.
Factors Influencing The Efficiency Of Abrasives
These factors are as follows:
i). The hardness of the abrasive particle of diamond is hardest,
punice, garnet etc., are relatively mild].
ii). The shape of the abrasive particle

11. Particles with sharp edges are more effective.
iii). Particle size of abrasive
Longer particle size will cut deeper grooves.
vv) Mechanical Properties of the abrasive
If the material breaks - it should form a new cutting edge.
Therefore bareness can be an advantage.
v) Rate of movement of abrasive particles
Slower abrasion - deeper scratches.
vi) Pressure of applied to the abrasive
Too much pressure can fracture the abrasive instrument and
increase heat of friction that has evolved.
vii) Properties of material that is being abraded
A brittle material can be abraded rapidly whereas a malleable and
ductile material [e.g. pure gold] will flow instead of being removed by
the abrasive.
Types of abrasives
According to Craig: The abrasives used can be classified /
grouped as and

12. A) Finishing Abrasives
B) Polishing Abrasives
C) Cleaning Abrasives
A) Finishing Abrasives: These are hard, coarse abrasives used
initially to develop desired contours and removal of 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 that are typically roughened by finishing
abrasives.
C) Cleaning Abrasives : These are soft abrasives with small particle
size and are intended to remove softer materials that adhere to
enamel or a restoration.
These dental abrasives could be employed In the form of three
basic designs as mentioned previously.
Secondly Skinner’s has grouped the abrasives employed in
dentistry as follows:
A) Natural Abrasives B) Manufactured Abrasives
1) Arkansas stone - are generally preferred because of
their more predictable physical
properties

13. 2) Chalk - Silicon carbide
3) Corundum - Aluminium oxide
4) Diamond - Silicon carbide
5) Emery - Aluminium oxide
6) Garnet - Synthetic Diamond
7) Pumice - Rouge
8) Quar - Tin oxide
9) Sand
10) Tripoli
11) Zirconium silicate
12) Cuttle
13) Kieselguhr
Natural Abrasives:
1) Arkansas stone
Semitransclucent, light gray, siliceous sedimentary rock, mended
in Arkansas
- contains micro crystalline quartz.
- small pieces of attached to metal shanks and trued to
various shapes for fine grinding of tooth enamel and metal
always.
2) Chalk
- mineral form of calcite

14. - contains calcium carbonate
- used as a mild abrasive paste to polish teeth enamel, gold
fill, amalgam and plastic materials.
3) Corundum
- is largely replaced by a - Aluminium oxide due to its superior
physical properties.
- However corundum is primarily used for grinding metal
always and is available as a bonded abrasive.
4) Diamond
- transparent, colourless mineral composed of
carbon called super abrasive - because of ability to abrade any
other known substance.
- Hardest substance known.
- used on ceramic and resin based composite
materials.
- supplied as - bonded abrasive rotary instrument.
- flexible metal backed abrasive strips.
- Diamond polishing pastes.

15. 5) Emery - supplied predominantly as wanted abrasive disks. used for
finishing metal alloys or plastic materials.
6) Garnet - the term garnet includes several minerals which possess
similar physical properties like Silicates of Al, Co, Fe, Mg and Mn.
- garnet is dark red, extremely hard and when fractured 'during
abrasive activity forms sharp chisel shaped plates - therefore
making Garnet an effective abrasive.
- garnet is available on coated disks and Arbor box.
- used in grinding metal alloys and plastic materials
7) Pumice - produced from volcanic activity
- flour of pumice is an extremely fine grinded volcanic rock
derivative from Italy
- used in polishing teeth enamel, gold foil, dental amalgam and
acrylic resins.
8) Quartz - the particles are pulverised to form sharp angular particles
which are useful in making coated disks.
- used to finish metal alloys and may be used to grind dental enamel.
9) Sand - mixture of small mineral particles predominantly silica
- particles have rounded to angular shape

16. - used (1) to remove refractory in vestment material from
base metal castings.
(2) coated on paper disks for grinding of metal
alloys and plastic materials
10) Tripoli - derived from a light weight, siliceous sedimentary rock
- could be weight, gray, pink, red or yellow
- gray and red most frequently used.
- used for polishing metal alloys and some plastic materials.
11) Zirconium Silicate - Off white mineral, ground to various Sizes
used to make coated disks and strips.
- also as a component of dental prophylaxis pastes.
12) Cuttle - made from the pulvedsed internal shell of a Mediterranean
marine mollusc, this abrasive is obtained as a white calcareous
powder.
- the related synonyms for this abrasive are cuttlefish and cuttle
bone
- it is obtained as a coated abrasive and useful for delicate
operations like polishing of metal margins and dental
amalgam-restus.

17. 13) Kieselguhr - this abrasive is obtained from the siliceous remains of
minute aquatic plants known as diatoms.
- it is an excellent mild abrasive
- the coarser variety of this is known as DIATOMACEOUS
EARTH which is used as filler in many dental materials.
- appropriate precautions must be taken while handling this
abrasive as the risk for respiratory silicosis due to long term
exposure of this material is significant.
Manufactured Abrasives
Silicon Carbide:
- This is the first of the synthetic abrasive to be developed
- Two types were manufactured viz. i) green form ii) blue black
form
- Both having similar physical properties
- However the green variety is preferred because substrates are
more visible against the green colour.
- The cutting efficiency of the silicon - carbide abrasives is higher
as the particles are sharp and break to form new sharp particles

18. - supplied as an abrasive in coated disks and vitreous and rubber
bonded instruments the silicon carbide is used in cutting metal
alloys, ceramics and plastic materials.
Aluminium Oxide - This is second synthetic abrasive to be
manufactured.
- This form of alumina is much harder than its natural counterpart
[CORUNDUM] because of its purity.
- The forms usually prepared are
i) White stones - made of sintered aluminium oxide - are used
for contouring of enamel and finishing metal and ceramic
materials.
ii) Variations of the aluminium oxide include those which
chronic compound additions - these, obtained in pink and
ruby colours are obtained as vitreous bonded non-
contaminating mounted stones - used for preparation of
metal ceramic alloys to receive porcelain.
[important to note that remnants of these abrasives should not
interfere with porcelain bonding to the metal studies Therefore show
that carbides are better for this purpose]

19. Synthetic Diamond
- The synthetic/manufactured form of diamond is produced at five
times the level of the natural diamond abrasive
- This synthetic diamond is used for manufacture of diamond saws,
wheels and burs and also diamond locks employed for truing of
bonded abrasives.
- Synthetic diamond abrasives are used primarily on teeth
structure, ceramic materials and resin based components
Rouge
- principle component is iron oxide blended with various binders -
used to polish noble metal alloys
- may be impregnated on paper/fabric - CROCUS CLOTH
Tin Oxide
- is composed of very fine abrasive particles.
- may be employed In an abrasive paste form along with water,
alcohol or glycerine.
- used as a polishing agent for teeth and metallic restorations.

20. Polishing
“Polishing is the production of a smooth mirror like surface
without use of any external form”.
A number of reasons are elucidated for the importance of
polishing dental restoration and teeth these are
i) The smooth polished restorative and teeth [enamel] surfaces are
less receptive to bacterial colonisation and dental plaque
formation.
ii) The polished layer on metallic restoration aids in prevention of
tarnish and corrosion.
iii) Finally, from a clinical view point unpolished restoration with
rough surfaces are uncomfortable for the patient.
The polishing procedure is one which is eventually initiated once
the abrasive mechanism eliminates or obliterates most of the finer
scratches leaving a smooth finish. This smooth layer or smooth finish
on the surface of the restoration is referred to by skinner’s as a polish.
However, it is difficult to draw or markout an exact line of
differentiation between an abrasive and a polishing agent. For E.g.
given agent having a large particle size and that which produces

21. deep/large scratches on the restoration surface could be termed as an
abrasive. On the other hand a similar agent with a fine particle size
which produces a smooth finish could be termed. as a polishing agent.
The polishing materials also differ in the amount of material they
remove from t he surface.
They remove molecule by molecule and thus provide a smooth
surface. In the process fine scratches and irregularities are filled in by
powdered, particulate being removed from the surface.
The polished layer is therefore thought of as one made up of
minute crystals, thus known as the Micro Crystalline Layer or Beilby
Layer (named after a scientist who first noted such a surface layer after
polishing) which is easily kept clean and has high corrosion resistance.
Surface structure not more than 0.005 mm is removed during
polishing. It is therefore observed that the process of Finishing,
Cutting/Abrading and Polishing have not been differentiated well in
dentistry.
The term finish - would actually relate to the final surface
achieved/applied to a material or the character of the surface of the
material.

22. If this explanation for the term finish is accepted then others viz.
cutting/abrading, grinding and polishing could be considered as a series
of steps encompassed within the process finishing.
However minor differences do exist in the cutting, grinding and
polishing procedures.
i) A cutting operation - as cited by Skinners "refer to the use of
bladed instrument or any instrument in a blade like fashion". The
substrate of the cutting operation may be divided into large
separate pieces or may sustain deep notches and grooves by the
cutting operation.
ii) A grinding operation removes small particles of a substrate
through the action of bonded or coated abrasive Instruments. The
grinding Instruments may contain randomly arranged abrasive
particles e.g. a diamond coated rotary instrument.
It is important to note here the cutting a nd grinding are both
Unidirectional in their course of action.
iii) The Polishing Operation is one of the most refined finishing
process. It produces scratches so fine that they are visible only
when greatly magnified. The ideally polished surface is one

23. which would be automatically smooth with no surface
imperfections.
Polishing is considered to be Multi Directional in its course of
action.
Examples of polishing : Instruments are
1) Rubber abrasive Points
- Fine particle disks and steps
- Fine particle polishing pastes - applied with soft felt
points, muslin wheels, prophy cups or buffing wheels.
iv) Electrolytic Polishing:
- is a reverse of electroplating
- alloy to be polished is made the anode of the electrolytic cell.
- as current passes ionic material from anode is dissolved leaving a
bright surface.
- excellent method for Co-Cr alloys, used in denture bases

24. Polishing Procedure (for resins)
The steps involved are
i) Smoothen the work with a coarse abrasive to produce large
scratches.
ii) Remove large scratches with a finer abrasive but difference in
fineness should not be too great as it causes streaking in the final
surface. Keep changing direction of the abrasion so that new
scratches appears at right angles to the coarser scratches, to
ensure uniform abrasion.
iii) Continue using fine abrasive until scratches are no longer visible
to the eye then accomplish
- Primary polishing with punice flour with a canvas buff wheel
[mainly for resins].
- Then the work is cleaned to remove all abrasive particles and
then punice and water paste of a muddy consistency is applied
and buffing done till a bright and well polished surface is
obtained. Glycerine is preferred instead of H20 because water
could evaporate, glycerine maintains consistency.

25. - Clean the work with soap water and change to a lannel (rotate at
high speed) buff wheel. Polishing cake with grease is held
against buff wheel to impregnate with the agent.
- Apply light pressure to avoid excessive heat generation.
Care should be taken to avoid use of abrasive tool or slurry in a
dry condition.
- Which would reduce efficiency of abrasive ard also increased
heat.
Speed employed for Polishing -
- is more than that for abrasion.
- linear speed of range 7500 - 1 0000 ft/min.
Composites :
- The smoothest surface on a freshly inserted composite can be
obtained by allowing polymerisation to occur against an inserted
Mylar matrix.
- Use of green / carbide stones / 12 - blade carbide burs is also
accepted for removal of excess near enamel margins of macro
filled resins.
This is followed by use of

26. - Aluminium oxide disks - for accessible areas finishing
- White source stones of suitable shapes - inaccessible areas.
- Fine and micro fine diamonds - finishing of micro filled resins.
Hazards Encountered In Finishing And Polishing Procedures
Aerosol Hazard:
Aerosols, the dispersion of solid and liquid particles in air are
generated whenever finishing and polishing operations are performed.
The dental aerosols contain teeth structure, dental materials,
micro organisms.
These aerosols are potential sources of infections and chronic
diseases of eyes and lungs.
Silicosis/grinder's disease is a major aerosol hazard in dentistry
because of a number of silica based materials are used in processing and
finishing dental restorations.
These aerosols can remain airborne for more that 24 hours before
settling and are therefore c2oable of cross contaminating other zones of
the treatment facility.
Aerosols produced during the finishing procedures can be
controlled following three ways controlled at the source through

27. - adequate infection control procedures
- water spray
- high volume suction
Personal protection -
- safety glasses
- disposable face masks
Adequate ventilation of the entire unit which c--ii'iciently
removes any residual particulates from the air.
Review of Literature
Rotary instrument finishing of micro filled and small particle composite
resins. JADA Aug 1987.
- This study suggests that rotary instrument for finishing
composites must be selected in accordance with the type of
composites used.
- Tungsten Carbide Burs at high speeds for trimming and finishing
micro filled composites are contraindicated because they disrupt
the composite resin surface therefore for micro filled and small
particle resins diamond burs at slow spends are used.

28. - Carbide burs at high speeds on small particle composites
produces a surface free from the characteristic striations and
grooves produced by diamond burs.
Effect of three finishing systems on four aesthetic restorative materials.
Operative Dentistry - 1998.
Two varieties of composites (Hybrid and Micro flied) and two
types of GIC viz. Traditional/conventional GIC and a Resin modified
GIC were employed for this study.
- Impregnated disks and diamond and carbide burs were used.
- No difference was seen in the surface of any of the restorations.
When the mylar matrix were used.
- However the study concluded with the result that abrasive
impregnated disks and aluminium oxide disks provided smoother
finished surfaces on the GIC and Composite than did the
diamond and carbide finishing burs.
A quantitative study of finishing and polishing techniques for a
composite Journal of Prosthetic Dent. 1988.

29. As we know, finishing and polishing of composite has always
been a problem because the resin matrix and inorganic fillers differ in
hardness and do not abrade uniforms!.
This study evaluated and compared six finishing and polishing
techniques to identify the most effective one for micro filled composite
restorations.
These six techniques were as follows:
TECHNIQUE I - Use of disks of medium, fine and superfine grits in
descending order.
TECHNIQUE II - Use of polishing points
TECHNIQUE III - Use of polishing paste with rubber cap
TECHNIQUE IV- Finishing [40m] and polishing [15 m] diamond burs
were used.
TECHNIQUE V - IV followed by polishing points
TECHNIQUE VI - IV followed by polishing pastes

30. Conclusion Of The Study:
Technique I produced the smoothest polished surface
Technique V was second best
“Finishing glass polyalkenoate cements [gic]” M.J.Woodfords BDJ
(1988).
This article reports on the SEM surface examination of GIC after
furnishing procedures using rotary and hard. instrumentation.
Anhydrous water hardening type and an encapsulated type of gics
were employed.
Finishing procedures employed were
1. White stones and Vaseline in the slow hand piece at 5000 rpm.
2. Soft disks (A12O3 disks)and Vaseline in the, slow hand piece at
500 rpm.
3. Tungsten carbide blank in air turbine Hand piece with a water
spray as coolant.

31. Results :
Ideal surface is produced by the matrix (any finishing inevitably
disrupts this surface).
- Soflex discs produce a relatively smooth surface
- Tungsten Carbide disrupts surface of even mature GIC
- Hand instrument cause marginal breakdown.
Summary and Conclusion
Though a varied range of abrasive and polishing agents have
been described with relation to individual dental materials an ideal
abrasive or a polishing agent which would satisfy all polishing needs of
the dental materials, one would say is yet to be developed.
References:
1. Science of Dental Materials
10th
Edition – Kennith Anusavice.
9th
Edition – Ralph W. Philips.
2. Notes on dental materials – 6th
Edition, E.C. Coombe.
3. Notes on dental materials – V.S. Rao.

32. 4. Dental materials – Properties and Manipulation – 4th
Edition,
1987, Craig O’Brien powers.
5. Restorative dental materials.
10th
Edition. 1996, Craig.
6. Contemporary fixed prosthodontics. 2nd
Edition, 1998, Stephen F.
Rosensteil.
7. The polishing of gold castings. JPD, 1959. 9, 668. Troxell R.R.
8. Feudametal of fixed prosthodontics. 3rd
Edition. 1996, Herbert T.,
S Hillenberg.