The wearing away of a substance or
structure through a mechanical process,
such as grinding, rubbing or scraping.
TYPES OF ABRASION
ABRASION MAY BE:
A two body process
e.g. action of a diamond bur on
A three body process
e.g. Pumice applied with a
SUPPLIED AS :
In dentistry the abrasive is applied to the work by a
variety of tools.
► paper / plastic coated:
The abrasive particles may be glued
on to a paper or plastic disc that can be attached to
a handpiece .sand paper belongs to this category.
► Stainless steel coated strips:
The abrasive (e.g.diamond ) may
be attached to stainless steel or plastic strips. This
category is similar to the above.
In case of diamond rotary instruments the
diamond chips are attached to steel wheels,discs and
cylinders by electro-plating with nickel based matrix.
In grinding wheels and dental stones, the abrasive
particles are mixed with a bonding agent that holds the
particles together. before hardening, the matrix material
with the abrasive is moulded to form tools of desired
Powder form :
An abrasive may also be mixed with water or
glycerine and to form a paste or slurry. It is applied with
felt cone, rubber cup or brush and used for smoothening
irregularities, e.g. pumise powder.
CAKE FORM :
They are also available in the form of cakes.
RUBBER IMPREGNATED :
Abrasives can be incorporated into rubber or
shellac discs or cups for “soft grade” abrasion.
PASTE FORM :
The abrasive is made into a paste and
supplied in a tube, e.g.Ivoclar polishing paste,
tooth paste, etc.
Abrasion is affected by properties of the
abrasive as well as the material being abraded.
The important properties are hardness, strength,
ductility and thermal conductivity.
MECHANISM OF ABRASIVE
The action of an abrasive is
essentially a cutting action.
Each tiny particle presents a sharp
edge that cuts through the surface
similar to a chisel.
A shaving is formed which crushes
to a fine powder.
This powder clogs the abrasive tool
and frequent cleaning is required.
STRESS, STRAIN AND HEAT PRODUCTION
In denture resins,too rigorous abrasion introduces
The generation of heat during abrasion partially
relieves such stresses, but if it is too great, it may
relieve processing stresses and a warpage may
The resin surface may even melt.
Similarly ,high speed cutting of tooth structure
generates excessive heat which can lead to
Therefore, it is very important to control the heat
by air/water spray and intermittent cutting.
RATE OF ABRASION
The rate of abrasion of a given material by a given abrasive is
determined primarily by three factors.
SIZE OF THE PARTICLES :
Larger particles cause deeper scratches in the
material and wear away the surface at a faster rate.
The scratches caused by the coarse abrasive
must then be removed by finer ones.
Heavy pressure applied by the abrasive will
cause deeper scratches and more rapid removal of material.
Heavy pressure is not advisable as it can
fracture or dislodge the abrasive from the grinding wheel.
The higher the speed, the greater the
frequency per unit of time the particles
contacts the surface.
Increasing the speed increases the
rate of abrasion.
Finishing abrasive :
finishing abrasives are hard, coarse abrasives
which are used initialy to develop contour and remove
gross irregularities. E.g. coarse stones.
Polishing abrasives :
polishing abrasives have finer particle size and
are less hard than abrasives used for finishing. They
are used for smoothening surfaces that have been
roughened by finishing abrasives. e.g. polishing cakes,
Cleansing abrasives :
cleansing abrasives are soft materials with small
particle sizes and are intended to remove soft deposits
that adhere to enamel or a restorative material.
TYPES OF ABRASIVES :
1)Emery consists of a natural oxide
of aluminium called corundum.
2)There are various impurities
present in it such as iron oxide, which
may also act as an abrasive.
3)The greater the content of
alumina, the finer the grade of emery.
4)Pure alumina is also used as a
ALUMINIUM OXIDE :
aluminium is manufactured
2) it can be produced in fine grain
sizes and has partially replaced emery for
mineral comprises of silicates of
aluminium, cobalt, magnesium, iron, and
2) garnet is coated on paper or cloth
3) it is used on discs which are
operated on handpieces.
It is a highly siliceous material of volcanic origin
and is used either as an abrasive or polishing agent.
1) consists of siliceous remains of minute aquatic
plants known as diatoms.
2) it is excellent as a mild abrasive and polishing
This mild abrasive and polishing agent.
1) Rouge is a fine red powder composed of iron
2) It may be impregnated on paper or cloth
known as “crocus cloth”
3) It is an excellent polishing agent for gold and
noble metal alloys.
TIN OXIDE :
1) Putty powder used as polishing agent for
teeth and metallic restorations in the mouth.
2) It is mixed with water, alcohol or glycerin
and used as paste.
1) It is calcium carbonate prepared by
2) There are various grads and physical forms
available for different polishing techniques.
3) It is sometimes used in dentifrices.
CHROMIC OXIDE :
1)A relativity hard abrasive capable of polishing
a variety of metals.
2) used as a polishing agent for stainless steel.
Sand as well as other forms of quartz is used as
sand paper or as powder in sandblasting equipment.
1) The silicon carbide is sintered, or pressed
with a blinder, into grinding wheels or discs.
2) Most of the stone burs used for cutting tooth
structure are made of silicon carbide.
1) It is the hardest and most effective abrasive
for tooth enamel.
2) The chips are impregnated in a blinder or
plated on to a metal shank to form the diamond ‘stones’
and disks so popular with the dental profession.
• ZIRCONIUM SILICATE :
1) Occurs in nature as zircon.
2) This mineral is ground to various particle sizes and
used as polishing agent.
• ZINC OXIDE :
1) Zinc oxide in alcohol can be used for polishing
• DESIRABLE CHARACTERISTICS OF AN ABRASIVE :
1) Abrasive should be harder than the work it
2) If it cannot indent the surface to be abraded, it
cannot cut it and the abrasive dulls or wears out.
• It is production of a smooth mirror like surface without
much loss of any external form.
• If the particle size of an abrasive is reduced sufficiently,
the scratches become extremely fine and may disappear
• The surface then acquires a smooth shiny layer known
as a polish.
• The polishing agents remove material form the surface
molecule by molecule.
• The microcrystalline layer is referred to as polish layer or
• A polishing agent is employed only after an abrasive
obliterates or eliminates most of the fine scratches,
leaving a smooth finish.
NON –ABRASIVE POLISHING
Polishing is usually achieved by an abrasive process. However , a
smooth shiny surface can also be achieved through non-abrasive
means. These include :
COMPOSITE GLAZING :
A layer of glaze or gloss is applied over the restoration
and cured. This results in a smooth highly glossy surface.
GLAZING CERAMICS :
Ceramics are difficult to polish conventionally. The
finished restoration is subjected to high temperatures. At this
temperature the surface layer and flows to produce a smooth
ELECTROLYTIC POLISHING :
Electrolytic polishing is not truly an abrasive process.
Although material is removed, it is removed through an
electrochemical process rather an abrasive process.
It is related to polishing in that the surface
is drawn or moved. Instead of using many
tiny particles, only one large point is used.
If 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.
• These are agents used with a toothbrush
to cleanse and polish natural teeth.
• They should have maximum cleansing
efficiency with minimum tooth abrasion.
• Highly abrasive dentrifices should not be
used especially when dentin or cementum
• Assists the toothbrush to mechanically
remove stains, debris and soft deposits
from the teeth.
• To impart a polished surface to the tooth.
• Thus, they help to reduce caries, maintain
healthy gingiva, improve esthetics and
reduce mouth odors.
Oral prophylaxis is a widely used
procedure in the dental office.
Prophylactic paste may be available
commercially or can be made in the dental
They are usually employed in paste
form by mixing with a suitable vehicle.
o Remove extrinsic stains, pellicle, materiaalba and oral debris
o Impart a highly polished and esthetic
Different types of abrasives may be
employed, e.g. zirconium silicate,
magnesium silicate, silica, pumice, etc. In
addition, some may contain fluoride in
order to reduce caries.
The prophyjet is a relatively new dental prophylaxis system of removing
An abrasive blasting process is used to mechanically remove extrinsic
stains as well as light supragingival adherent plaque the calculas.
Consists of sodium carbonate, hydrophobic modified silica and
some flavoring agent. The abrasive is available as powder in a small
CLINICAL CONSIDERATIONS :
The prophyjet is directed at 45 angles to the tooth surface. For
obvious reasons it is less effective in proximal areas. The chances of soft
tissue injury exist especially if the tissue is inflamed and friable.
a) The dentures may be brushed using a
soft bristle brush and gentle abrasive or
b) Hard abrasive and stiff bristles should
be avoided because they may produce
scratches on the denture surface.
Chemical cleaners are an alternative to
brushing especially among very old or
a) Alkaline perborates
b) Alkaline peroxides
c) Alkaline hypochlorites
d) Dilute acids.