prosthodontics, dentistry

1. Finishing And Polishing
Materials

2. AIM
 To get a prosthesis or restoration i.e.
aesthetically pleasing.
 The prosthesis has a self cleansing
property of its own by resisting the
accumulation of food debris.

3. FINISHING AMD POLISHING
Finishing & Polishing
involves following
steps:
1. Cutting
2. Grinding
3. Finishing
4. Polishing

4. PRINCIPAL OF CUTTING
 Cutting is the process of
removing material from
the substrate by the use
of an abrasive
embedded in a binding
matrix.
 Cutting refers to gross or
bulk reduction and is the
first step towards getting
the desired shape of the
prosthesis.

5. PRINCIPAL OF GRINDING
 Grinding is the process
of removing material
from a substrate by
abrasion with a relatively
coarse material.
 Grinding refers to the
contouring of the
prosthesis to its final
desired shape.

6. PRINCIPAL OF FINISHING
 Finishing is the process of removing
surface defects or scratches created
during the contouring process through
the use of cutting or grinding instrument.
 Finishing is carried out with relatively
less coarse material. A 16 or 18 flute
carbide bur is preferred for smoother
finish.

7. PRINCIPAL OF POLISHING
 The purpose of polishing is to provide an
enamel like luster to the restoration.
 While polishing each step is followed by
the use of progressively finer polishing
media until no further improvement in
surface finish is observed.

8. PRINCIPAL OF BUR DESIGNING
 BUR : Bur is the term
applied to all rotary
cutting instruments
that have bladed
cutting heads.
 Two designs that have
considerable effect on
bur performance are;
1. Spiral angle
2. Crosscut

9. SPIRAL ANGLE
 Spiral angle is the
angle formed by bur
blade and the long
axis of the bur.
 Burs with spiral
design works like a
reel type lawn
mower used for
cutting the grass.

10. SPIRAL ANGLE
 As the instrument rotates each blade is
brought into contact with the tooth
Surface at one end first rather than all
points simultaneously.
 In this fashion each blade starts cutting
before the preceding blade has finished
and thus the cutting action is more
smooth and uniform.

11. SPIRAL ANGLE
 Spiral angle also makes the motion of
the bur not exactly at right angles to the
substrate thus producing a slicing action
and causing chipping off of the substrate.
 This promotes chip clearance thus
avoiding a three body abrasive action.

12. CROSSCUT
 Crosscut bur designs have notches in
the blade edges to increase cutting
effectiveness at slow and medium
speeds.
 Notches in two successive blades are
not in line with each other so as the first
blade passes it leaves a dig in the
substrate surface that is cleared by he
following blade.

13. BUR DESIGN
 The cutting edges of a bur are called as
blades.
 The depression area between two
successive blades is called as flutes.
1. The lesser the no. of flutes the more is
bulk reduction but there is less finish.
2. The more the no. of flutes the better is
the finish.

14. BLADE DESIGN
 Each blade has two faces:
1. Rake Face :This is the face that is in
direction of rotation and makes contact with
tooth structure before removal.
2. Clearance Face: The face of the blade that
follows the edge of the blade as the bur
rotates is known as clearance face. This face
removes the chipped off material.

15. BLADE ANGLES
 Blade design
consists of three
basic angles:
1. Rake Angle
2. Clearance angle
3. Edge angle

16. Points To Ponder
 Negative rake angle helps remove hard
material.
 Edge angle is related to the resistance of
the blade to fracture.
 Clearance angle provides a stop to the
digging of the of bur in substrate and
clears chips from the substrate. It also
reduces friction.

17. ABRASION
 Abrasion is the wearing off of the
surface particles of a substrate when it
is brought in contact with a material
having a higher hardness index.
 Abrasion can be:
1. Two body abrasion
2. Three body abrasion

18. ABRASION
 Two body abrasion occurs when
abrasive particles are firmly attached to
the surface of the abrasive instrument
and no other abrasive particle is used.
 Three body abrasion occurs when
abrading particles are free to translate
between two surfaces.

19. ABRASION

20. EROSION
 Erosion is caused by
hard particles
impacting a
substrate surface
caused either by
stream of liquid or
stream of air .

21. EROSION

22. ABRASIVE INSTRUMENT DESIGN
 ABRASIVE GRIT: they are derived from
materials that have been crushed and
passed through a series of mesh screens to
obtain different particle size. They are
classified as coarse, medium coarse, fine
and superfine.

23. ABRASIVE GRIT

24. ABRASIVE INSTRUMENT DESIGN
 BONDED ABRASIVE
 Bonded abrasive consist of
abrasive particles that
incorporated through a binder
to form grinding tools such as
points, wheels, separating
disks, coated thin disks.
 Particle are bonded by four
methods
 Sintering
 Vitreous bonding
 Bonding resinoid
 Rubber bonding

25. ABRASIVE INSTRUMENT DESIGN
 ABRASIVE DISKS
 Abrasive disks are used for gross
reduction, containing finishing and
polishing of restorative surfaces.
 ABRASIVE STRIPS
 Abrasive strip’s are used to smoother
and polish the proximal surfaces of a/c
direct and indirect bonded restorations.

26. ABRASIVE INSTRUMENT DESIGN
 SINTERED
ABRASIVE
 Sintered abrasive
are the strongest
type because the
abrasive particle are
fused together.

27. ABRASIVE INSTRUMENT DESIGN
 VITREOUS – BONDED
ABRASIVES
 Vitreous – bonded
abrasives are mixed with
a glossy or ceramic
matrix material, cold
pressed to the
instrument shape and
fixed to fused binder.

28. ABRASIVE INSTRUMENT DESIGN
 RESIN BONDED ABRASIVES
 Resin bonded abrasives are cold
pressed or hot pressed and then heated
to cure the resin. Hot pressing has an
advantage as it yields an abrasive binder
with extremely low porosity.

29. ABRASIVE
 A bonded abrasive
instrument
undergoes two
processes to
achieve its
maximum cutting
efficiency:
1. Truing
2. Dressing
procedure

30. TRUING
 Truing is the
procedure through
which the abrasive
instrument is run
against a harder
abrasive block until
the instrument
rotates without
eccentricity or run
out.

31. DRESSING PROCEDURE
 Dressing procedure is same as truing.
It serves two functions:
1. It reduces the instrument to its correct
working size and shape.
2. It is used to remove clogged debris
from the abrasive instrument.

32. ABRASIVE BLINDING
 Abrasive blinding refers to the clogging
of the abrasive instrument with debris .
 It occurs when the debris generated from
the grinding occludes the small spaces
between the abrasive particles on the
tool and reduces the depth to which the
material can penetrate.

33. NON – BONDED ABRASIVES
 Non bonded abrasive work on the
principal of three body abrasion.
 Polishing pastes are an example of non
– bonded abrasive. They are used
primarily as fine polishing materials.
They need to be applied to the substrate
with a non- abrasive instrument such as
rubber cup.

34. ABRASIVE MOTION
 The motion of
abrasive instrument
are classified as :
1. Rotor
2. Planar
3. Reciprocal

35. TYPES OF ABRASIVE
 ARKANSAS STONE Arkansas stone is
a semi translucent rock. It contains
microcrystalline quartz and is dense,
hard and uniformly textured. This mineral
is attached to metal shanks and trued to
various shapes for fine grinding of tooth
enamel and metal alloys.

36. CHALK
 One of the mineral forms of
calcite a white abrasive
composed of calcium
carbonate. It is used as a
prime polishing abrasive in
polishing paste.

37. NATURAL DIAMOND
 Diamond is transparent,
colorless, and mineral
composed of carbon.
Diamond abrasives are
supplied in several
forms including bonded
abrasive rotary
instruments, flexible
metal – backed abrasive
strips and diamond
polishing paste.

38. SYNTHETIC DIAMOND ABRASIVES
 They have the advantage that we can
control and uniform the size and shape
of the particle. Also they are
comparatively cheaper than the natural
form of diamond.
 It is used in dental burs for cavity cutting,
diamond abrasive for finishing of metal
castings and polishing pastes .

39. EMERY
 Emery is used
predominantly in the
form of coated
abrasive disks and is
available in a variety
of grit sizes. It may
be used for finishing
metal alloys or
acrylic resin
materials.

40. GARNET
 Garnet includes a number of different minerals
that posses similar physical properties and
crystalline forms. These minerals are silicates
of aluminum, cobalt, iron, magnesium and
manganese. Garnet is extremely hard and
when fractured during the grinding operation
forms sharp, chisel shaped plates, making if a
highly effective abrasive. It is used in grinding
metal alloys and acrylic resin materials.

41. PUMICE
 Flour of pumice is an
extremely fine – grained
volcanic rock derivative
that is used in polishing
tooth enamel, gold foil,
dental amalgam and
acrylic resin.

42. QUARTZ
 Quartz crystalline
particles are
pulverized to form
sharp, angular
particles that are
useful in making
coated abrasive
disks. They are
primarily used to
finish metal alloys.

43. SAND
 Sand is a mixture of
small particles
predominantly
composed of silica.
Sand particle have
rounded to angular
shape. They are applied
under air pressure to
remove refractory
investment materials
from base metal alloys
casting.

44. TRIPOLI
 This abrasive is derived from a
siliceous sedimentary rock. The
rock is grained into very fine
particles and formed with soft
binders into burs of polishing
compound. It is used for polishing
metal alloys and acrylic resin
materials.

45. ZIRCONIUM SILICATE
 This material is ground to various
particle sizes and is used to make
coated abrasive disks and strips. It is
frequently used as a component of
dental prophylaxis paste.

46. SILICON CARBIDE
 Silicon carbide is extremely
hard & brittle. Particles are
sharp and they break to form
new sharp materials. This
results in highly efficient cutting
of a wide variety of materials
including metal alloys,
ceramics and acrylic resin
materials.

47. ALUMINUM OXIDE
 Aluminum oxide is widely used in
dentistry to make bonded
abrasives, coated abrasives and air
– propelled grit abrasives. Sintered
AlO2 is used to make white stones
which are popular for finishing metal
alloys, resin – based composites
and ceramic materials.

48. TIN OXIDE
 In oxide is an
extremely fine
abrasive used
extensively as a
polishing agent for
polishing teeth and
metallic restorations
in mouth.

49. ABRASIVE PASTE
 Diamond particles or
AIO2 are most
commonly used
abrasive in dental
polishing paste.
Aluminum paste should
be used with a rotor
instrument and
increasing amounts of
water as polishing
proceeds from coarser
to finer abrasives.

50. AIR ABRASIVE TECHNOLOGY
 Air abrasive technology can deliver a fine
precisely controlled high pressure stream
of aluminum oxide to remove enamel,
dentin and restorative materials.
 It has an advantage that it produces less
heat and vibration thus chances of
chipping or micro fracture are less.

51. BIOLOGICAL HAZARDS
 Dental technicians working in dental
labs. Are at high risk to:
 Silicosis; is a fibrotic pulmonary disease
that severely debilitates the lungs and
increases the risk of lung cancer.
 Beriliosis: allergy from beryllium, it
causes enlargement of alveoli in lungs.
Also it is a known carcinogen.

52. To overcome the problem aerosols can be
controlled by :
 With suction machines attached to
finishing and polishing machines.
 With the use of disinfectants, gloves
masks and head caps.
 Maintaining proper air cross ventilation
and sanitization.
 With the use of face screens and
goggles.

53. BIBLIOGRAPHY
 Philips Science of Dental Material-11th
edition.
 The art and science of operative
dentistry- Clliford M. Sturdevant.

54. THANK YOU