USEFUL FOR FIRST BDS

1. ABRASIVES AND POLISHING AGENTS
By Dr Puttaraj tk
Prof and H.O.D.Dept of Prosthodontics

3. ABRASION AND POLISHING AGENTS
I. 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 removal of excess material but also
to smoothen rough surface.
 Th e finishing of dental restorations prior to their
placement in the oral cavity has therefore three
benefits viz

5.  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
embrassure 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 esthetics.
 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 the process of abrasion would aid
in improved clinical usage of these materials and techniques.


6. II. INDIVIDUAL CONSIDERATIONS
 1. Abrasion
 Craig has defined abrasion as :
 “A process of wear whereby a hard rough surface (like a
sand paper disk) or hard irregular shaped particles (like
those in a 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 wear 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 understanding

7. Wear
 – 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
 finished is termed as a SUBSTRATE.

8. II) Abrasive wear
 : This could be of two types :
 i. 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 eg, a
diamond bur abrading a teeth.
 ii. Three body wear – when the abrasive particles are free
to translate and rotate between two surfaces Eg, dental
prophylaxis pastes (between tooth and rubber cup)

10. . 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.
 Chemical erosion is employed to prepare teeth
surfaces for bonding purposes and not for finishing of
materials.

11. DESIGN OF ABRASIVE INSTRUMENTS
 The abrasives employed could be one of the three
types, viz:
 A. Abrasive Grits.
 B. Bonded Abrasives.
 C. Coated Abrasive Disks and Strips.

12.  A. Abrasive Grits
 Abrasive grits are derived from (abrasive) materials
that have been crushed and passed through series of
mesh screens to obtain different particle size ranges.
 The grits are classified as –
1.COARSE,
3.MEDIUM FINE and
3.SUPER FINE according to
particle size ranges.

14. B. Bonded Abrasives
 These consists of abrasive particles incorporated
through a binder to form grinding tools.
 The abrasive particles are bonded by 4 general
methods :
 1. Sintering.
 2. Vitreous bonding (Glass/Ceramic).
 3. Resin bonding (usually phenolic resin.
 4. Rubber bonding (usually silicone rubber).

15.  1. Sintering – Sintered abrasives are the
strongest variety since the abrasive particles
are fused together.
 2. Vitreous Bonded – Are mixed with a
glassy or ceramic matrix material, cold
pressed to the instrument shape and fired to
fuse with the binder.
 3. Resin Bonded – are cold or hot pressed
and then heated to cure the resin.
 4. Rubber Bonded – made in a manner
which is similar to resin bonded.

16. 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).
 The disks are available in different diameters with thin
and very thin backings.
 Moisture – resistant backings are advantageous as the
abrasive stiffness is not reduced by water degradation

21. ABRASIVE 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 and usually clogs the abrasive which thus
makes periodic cleaning of the abrasive necessary.

22. Abrasive Action On Metals
 On abrading metallic restorations, the metallic grain
structure usually gets disoriented.
 The more the abrasion the greater is the associated
disorientation.
 Strain hardening of the abraded metal usually
accompanies the grain disorientation. (

23. Abrasive Action on Resins
 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.

24. TYPES OF ABRASIVES
 I. According to Craig : The abrasives used can be classified
grouped as and :
 A. Finishing Abrasives.
 B. Polishing Abrasives.
 C. Cleaning Abrasives.
 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 that are typically roughened by
finishing abrasives.
 Cleansing Abrasives :These are soft abrasives with small
particle size and are intended to remove softer materials that
adhere to enamel or a restoration.

25. Skinner’s
 Secondly Skinner’s has grouped the abrasives
employed in dentistry as follows:
 A. Natural Abrasives.
 B. Manufactured Abrasives.

26. Skinner’s classification
A. Natural Abrasive
 1. Arkansas Stone
 2. Chalk
 3. Corundum
 4. Diamond
 5. Emery
 6. Garnet
 7. Pumice
 8. Quartz
 9. Sand
 10.Tripoli 11.Zirconium silicate
 12.Cuttle
 13.Kleselguhr
 Are generally preferred because of their more predictable physical properties.
B. Manufactured Abrasives
 1. Silicon carbide
 2. Aluminium oxide
 3. Synthetic diamond
 4. Rouge
 5. Tin oxide

48. Non abrasive polishing
COMPOSITE GLAZING—BY unfilled
resin nano particles
CERAMIC GLAZING---subjecting high
temperatures
ELECTROLYTIC GLAZING—by
electrochemical process

50. Recent advancements

51. Uses

55. Superfinishing by the Magnetic Abrasive
Finishing Process
 . Magnetic Abrasive Finishing (MAF) is a non-
conventional superfinishing process in which
magnetic abrasive particles interact with a magnetic
field in the finishing zone to remove materials to
achieve very high surface finishing and deburring
simultaneously.

56. SUMMARY & 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.