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4. Benefits of Finishing and Polishing Restorative
Materials
Principles of Cutting, Grinding, Finishing, and
Polishing
Abrasion and Erosion
Abrasive Instrument Design
Types of Abrasives
Finishing and Polishing Procedures
Dentifrices
Conclusion

5. KEY TERMS

7. Abrasive :A hard substance used (or grinding,
finishing, or polishing a less-hard surface.
Buffing: Process of producing a lustrous
surface through the abrading action of fine
abrasives bound to a nonabrasive binder
medium.

8. Bulk reduction: Process of removing excess material by
cutting or grinding a material with rotary instruments to
provide a desired anatomic form.
Contouring: Process of producing a desired anatomical
form by cutting or grinding away excess material.
Cutting: Process of removing material from the substrate
by use of a bladed bur or an abrasive embedded in a
binding matrix on a bur or disk.

9. Finished and polished restoration: A prosthesis
or direct restoration whose outer surface has
been progressively refined to a desired state of
surface finish.
Finishing: Process of removing surface defects
or scratches created during the contouring
process through the use of cutting or grinding
instruments or both.

10. Glaze ceramic: A specially formulated
ceramic powder that, when mixed with a
liquid,
applied to a ceramic surface, and heated to an
appropriate temperature for a sufficient time,
forms a smooth glassy layer on a dental
ceramic surface.
Grinding: Process of removing material from a
substrate by abrasion with relatively coarse
particles.

11. Natural glaze :A vitrified layer that forms on the surface
of a dental ceramic containing a glass phase when the
ceramic is heated to a glazing temperature for a specified
time.
Over glaze: Thin surface coating of glass formed by
fusing a thin layer of glass powder the matures at a lower
temperature than that associated with the ceramic
substrate.
Polish: Luster or gloss produced on a finished surface.
Polishing: Process of providing luster or gloss on
a material surface.

13. Benefits of Finishing
and Polishing
Restorative Materials

14. Finished and polished restorations provide
three benefits of dental care :
Oral health,
Function, and
Aesthetics.
A well-contoured and polished restoration
oral health by resisting the accumulation of
food debris and pathogenic bacteria.

15. This is accomplished through a reduction in
total surface area and reduced roughness of
the restoration surface.
Smoother surfaces have less retention areas
and are easier to maintain in a hygienic state
when preventive oral home care is practiced
because dental floss and the toothbrush
bristles can gain more access to all surfaces
and marginal areas.

16. Tarnish and corrosion activity of some dental materials
can be significantly reduced.
Oral function is enhanced with a well-polished
restoration.
Rough material surfaces lead to the development of
high-contact stresses that cause the loss of functional aid
stabilizing contacts between teeth.

17. Roughness on ceramics also act as stress
concentration points.
Finishing and polishing surfaces can improve the
strength of the restoration, especially in areas under
tension.
 Finally, aesthetic demands may require the dentist to
handle highly visible surfaces of restorations differently
than those that are not accessible.

19. PRINCIPLES OF CUTTING, GRINDING,
FINISIHING, AND POLISHING

20. Even though there are distinct differences in
function of cutting, grinding and polishing, at
times they overlap, depending on the hardness,
shape the abrasive particle used and the speed of
the handpiece.

21. Grinding, finishing, and polishing systems vary
considerably. They consist of abrasive-coated
paper or plastic disks, abrasive impregnated
tipped mandrels, diamond-bonded burs, and
abrasive pastes.

22. The goals of finishing and polishing
procedures are to obtain the desired anatomy,
proper occlusion, and the reduction of
roughness, gouges, and scratches that were
produced by the contouring and finishing
instruments.

23. The instruments available for finishing and
polishing restorations include fluted carbide
burs, diamond burs, stones, coated abrasive
disks and strips, polishing pastes, and soft and
hard polymeric cups, points, and wheels
impregnated with specific types and sizes of
abrasive particles.

24. Subtle differences distinguish the cutting, grinding,
and polishing processes.
A cutting operation usually refers to the use of a
bladed instrument or the use of any instrument in a
bladelike fashion. Substrates may be divided into
large separate segments, or they may sustain deep
notches and grooves by the cutting operation.

25. High-speed tungsten carbide burs have numerous
regularly arranged blades that remove small shavings of
the substrate as the bur rotates.
The unidirectional cutting pattern reflects the action of
the regularly arranged blades

26. The pattern produced by a diamond bur

27. A separating wheel is an example of an instrument that
can be used in a bladelike fashion.
A separating wheel does not contain individual blades,
but its thin design allows it to be used in a rotating
fashion to slice through cast metal sprues and die stone
materials.

29. A grinding operation removes small particles
of a substrate through the action of bonded or
coated abrasive instruments.
Grinding instruments contain randomly
arranged abrasive particles.
Each particle may contain several sharp points
that run along the substrate surface and
remove particles of material.

30. For example a diamond-coated rotary
instrument may contain many sharp diamond
particles that pass over a tooth during each
revolution of the instrument.

31. Because particles are randomly arranged,
innumerable unidirectional scratches are
produced within the material surface.

32. It shows a tooth surface ground by a diamond
bur. Cutting and grinding are both considered
to be predominantly unidirectional in their
course of action. This means that a cut or
surface exhibits cuts and scratches oriented in
one predominant direction.

33. Different types of burs have unique effects on
surfaces. The 16-flute carbide produces a
smoother finish than the 8-flute carbide bur,
but the latter removes material more rapidly.
Similarly, the coarsest diamond bur removes
material quickly but leaves a rougher surface.

36. Polishing procedures, the most refined of the
finishing processes, remove surface particles.
Each type of polishing abrasive acts on an
extremely thin region of the substrate surface.
Polishing progresses from the finest abrasive
that can remove scratches from the previous
grinding procedure and is completed when the
level of surface smoothness is achieved.

37. Each step is followed by the use of progressively
finer polishing media until no further improvement in
surface finish is observed. The final stage produces
scratches so fine that they are not visible unless
greatly magnified.

38. Examples of polishing instruments are rubber
abrasive points, fine-particle disks and strips,
and fine-particle polishing pastes. Polishing
pastes are applied with soft felt points, muslin
(woven cotton fabric) wheels, prophylaxis
rubber cups, or buffing wheels.

39. A nonabrasive material should be used as an
applicator while using polishing pastes. Felt,
leather, rubber, and synthetic foam are
popular applicator materials for buffing.
A common feature of some of these materials
is their porous texture that allows fine
abrasive particles to be retained during the
buffing procedure.

40. Polishing is considered to be ,multidirectional
in its course of action. This means that the final
surface scratches are oriented in many
directions.
Some examples of ground and polished
surfaces are shown

43. Bulk Reduction ProcessBulk Reduction Process

44. Bulk reduction can be achieved through the use
of instruments such as diamond, carbide, and
steel burs, abrasive-coated disks, or separating
disks. Whereas diamond burs and abrasive-
coated disks provide this action by grinding, steel
and carbide burs remove materials through a
cutting action of the hard blades.

45. Abrasive-coated disks are popular instruments
for bulk reduction of resin-based composite
restorations. For bulk reduction, the clinician
should choose 8 to 12-fluted carbide burs or
abrasives with a particle size of 100μm or larger
with sufficient hardness (9 to 10 Mohs hardness).

48. Even though contouring can be achieved during
bulk reduction, in some cases it requires finer
cutting instruments or abrasives to provide better
control of contouring and surface details. At the
end of this process, the desired anatomy and
margins should be established.

49. The smoothness of the surface at this stage
depends on the instrument used and may require
extra steps to establish a smoother surface
Usually, 12 to 16 fluted carbide burs, or
abrasives ranging in size from 30 to 100μm,
provide the fine contouring action.

52. In general, finishing and polishing processes
require a stepwise approach, introducing finer
scratches to the surface of the substrate in order to
methodically remove the deeper scratches. This
process may require several steps to reach the
desired surface smoothness.

53. Surface imperfections can be an integral part of
the internal structure , or they can be created by
the instruments that are used for gross removal
because of the size of the abrasives or the flute
geometry. Finishing provides a relatively
blemish-free, smooth surface.

54. The finishing action is usually accomplished
using 18- to 30-flute carbide burs, fine and
superfine diamond burs or abrasive between 8
and 20μm in size.

57. The purpose of polishing is to provide an enamel-
like luster to the restoration. Smaller particles
provide smoother and shinier surfaces. The speed
of achieving a luster, however, depends on the
hardness and size of the abrasive particles and the
method of abrasion (e.g., two-body abrasion or
three-body abrasion).

58. Ideally, abrasive particles ranging up to 20 μm provide
luster at a low magnification. At the end of this process,
there should be no visible scratches. However there will
always be scratches that are detectable at higher
magnification.

59. The surface must be cleaned between steps,
because an abrasive particle left on the surface
from the previous step can cause deep scratches.
The quality of the surface finish and polish can
be characterized by the measurement of the
surface roughness using a profilometer, an
optical microscope, or a scanning electron
microscope (SEM).

60. In clinical practice, the surface luster is usually
judged without magnification. Even though, most
of the time surface smoothness is correlated with
the luster, as in cases such as resin-based
composite restorations, the smoothest surface
does not necessarily provide the most lustrous
surface.

61. For industrial applications, reflectometers are
used to measure the luster. However, it is
difficult to use them successfully for dental
applications because of the irregular contour and
small size of dental restorations.

62. Heat generation during cutting, contouring
finishing, and polishing processes of direct
restorations is a major concern. To avoid adverse
effects to the pulp, the clinician must cool the
surface with a lubricant, such as an air-water
spray, and avoid continuous contact of high-speed
rotary instruments with the substrate.

63. Intermittent contact during operation is necessary,
not only to cool the surface but also to remove debris
that was formed between the substrate and the
instrument. The effectiveness and the speed of the
contouring, finishing and polishing procedures will
be greatly improved by removal of debris.

66. Dispersions of solid particles are generated
and released into the breathing space of
laboratories and dental clinics whenever
finishing operations are performed. These
airborne particles may contain tooth structure,
dental materials and microorganisms.

67. Such aerosols have been identified as potential
sources of infectious and chronic diseases of the
eyes and lungs and present a hazard to dental
personnel and their patients. Silicosis, also called
grinder’s disease, is a major aerosol hazard in
dentistry because a number of silica-based
materials are used in the processing and finishing
of dental restorations.

68. Silicosis is a fibrotic pulmonary disease that severely
debilitates the lungs and doubles the risk for lung cancer.
The risk of silicosis is substantial because 95% of
generated aerosol particles are smaller than 5μm in
diameter and can readily reach the pulmonary alveoli
during normal respiration.

69. Additionally, 75% of airborne particles are
potentially contaminated with infectious
microorganisms. Furthermore, aerosols can
remain airborne 24 hrs before settling and are
therefore capable of cross-contaminating other
areas of the treatment facility.

70. Aerosol sources, in both the dental operatory and
laboratory environments, must be controlled
whenever finishing procedures are performed. A
concise and informative source of information on
aerosol hazards has been written by Cooley (1984).

71. Aerosols produced during finishing procedures
maybe controlled in three ways:
First, they may be controlled at the source
through the use of adequate infection control
procedures, water spray, and high-volume suction.

72. Second, personal protection, such as safety glasses and
disposable facemasks, can protect the eyes and
respiratory tract from aerosols. Masks should be chosen
to provide the best filtration along with ease of
breathing for the wearer.
Third, the entire facility should have an adequate
ventilation system that efficiently removes any residual
particulates from the air.

76. Wear is a material-removal process that can occur
whenever surfaces slide against each other. The process
of finishing a restoration involves abrasive wear through
the use of hard particles. In dentistry, the outermost
particles or surface material of an abrading instrument is
referred to as the abrasive.

77. The material being finished is called the substrate. In the case of a
diamond bur abrading a tooth surface, such as that illustrated
the diamond particles bonded to the bur represent The abrasive,
and the tooth is the substrate. Also notice that the bur in the high
speed handpiece rotates in a clockwise direction as observed from
the head of the handpiece.

79. Abrasion is further divided into the processes of
two-body and three-body wear.
Two-body abrasion occurs when abrasive
particles are firmly bonded to the surface of the
abrasive instrument and no other abrasive
particles are used. A diamond bur abrading a
tooth represents an example of two-body wear.

80. Three-body abrasion occurs when abrasive
particles are free to translate and rotate between
two surfaces. An example of three-body abrasion
involves the use of nonbonded abrasives, such as
exist in dental prophylaxis pastes. These
nonbonded abrasives are placed in rubber cup,
which is rotated against a tooth or material
surface.

81. Diamond particles may debond from a diamond
bur And cause three-body wear. Likewise,
some abrasive particles in the abrasive paste
trapped in the surface of a rubber cup and cause
two-body wear. Lubricants are often used to
minimize the risk for these unintentional shifts
from two-body to three-body wear and vice
versa.

82. Thus the efficiency of cutting and grinding will
be improved with lubricants. Water glycerin, or
silicone can be used as lubricants. lntraorally, a
water-soluble lubricant is preferred. Excessive
amounts of lubricants may reduce the cutting
efficiency by reducing the contact between the
substrate and the abrasive.

85. Erosive wear is caused by hard particles
impacting a substrate surface, carried by
either a stream of liquid or a stream of air,
such as occurs when sandblasting a surface.
Following figure illustrates schematically
two-body abrasion, three-body abrasion, and
hard-particle erosion.

87. Most dental laboratories have air-driven grit-
blasting units that employ hard-particle
erosion to remove surface material.
A distinction must be made between this type
of erosion and chemical erosion, which
involves chemicals such as acids and alkalis
instead of hard particles to remove substrate
material.

88. Chemical erosion, more commonly called acid
etching, is not used as a method of finishing
dental materials. It is used primarily to prepare
surfaces to enhance bonding or coating.

91. The inherent strength of cutting blades or
abrasive particles of a dental instrument must
be great enough to remove particles of
substrate material without becoming dull or
fracturing too rapidly. The durability of an
abrasive is related to the hardness of its
particles or surface material.

92. Hardness is a surface measurement of the
resistance of one material to be plastically
deformed by indenting or scratching another
material. The first ranking of hardness was
published in 1820 by Friedrich Mohs, a
German mineralogist. He ranked 10 minerals
to one another by their relative scratch
resistance.

93. The least scratch-resistant mineral, talc, received a
score of one and the most scratch-resistant
mineral, diamond, received a score of ten. Mohs’
scale was later expanded in the 1930s to
accommodate several new abrasive materials that
received scores in the 9 to 10 range.

95. Abrasive instrument design
Abrasive grits
Abrasive grits are derived from materials that
have been crushed and passed through a series of
mesh screens to obtain different particle size
ranges. Following Table lists grit and particle
sizes for commonly used dental abrasives. Dental
abrasive grits are classified as coarse, medium
coarse, medium, fine, and superfine according to
particle size ranges.

97. Experience generally indicates which grades
of an abrasive give the best results in
finishing a given material. Keep in mind that
the rate of material removal is not the only
important factor.

98. The surface finish obtained with each abrasive
is just as important. If too hard an abrasive is
used, or if the grain size is too coarse for use
on a given material, deep scratches result in
the substrate that cannot be removed easily in
subsequent finishing operations.

99. Additionally, if an abrasive does not have the
proper particle shape or does not break down in
a manner that creates or exposes new sharp-
edged particles, it will tend to gouge the
substrate.

100. Bonded Abrasives
Bonded abrasives consist of abrasive particles that
are incorporated through a binder to form grinding
tools such as points, wheels, separating disks,
coated thin disks, and a wide variety of other
abrasive shapes.

101. Particles are bonded by four general methods:
Sintering,
Vitreous bonding (glass or ceramic),
Resinoid bonding (usually phenolic resin), and
Rubber bonding (latex-based or silicone-based rubber).

102. Because most of the rubber wheels, cups, and
points contain latex, a known allergen, all residues
must be removed from polished surfaces.

103. Abrasive disks are used for gross reduction,
contouring, finishing, and polishing of restoration
surfaces. Most types of disks are coated with
aluminum oxide abrasive. Abrasive strips with
either a plastic or metal backing are also
available to smooth and polish the proximal
surfaces of all direct and indirect bonded
restorations.

104. Metal strips are usually limited to situations in
which very tight proximal contacts are involved.
They are particularly useful for ceramic
restorations, but are also used for composites and
amalgams. However, care must be taken to avoid
lacerating the gingival tissues.

105. The metal-backed strips are more costly, but they
can be autoclaved and used several times if they
are not damaged. Plastic-backed strips are used
primarily for composites, compomers, hybrid
ionomers, and resin cements.

106. Sintered abrasives are the strongest type
because the abrasive particles are fused
together. Vitreous-bonded abrasives are
mixed with a glassy or ceramic matrix
material, cold-pressed to the instrument
shape, and fired to fuse the binder. Resin-
bonded abrasives are cold-pressed or hot-
pressed and then heated to cure the resin.

107. Several examples of bonded abrasives are
illustrated in Figure.

108. A bonded abrasive instrument should always
be trued and dressed before its use. Truing is a
procedure through which the abrasive
instrument is run against a harder abrasive
block until the abrasive instrument rotates in
the handpiece without eccentricity or runout
when placed on the substrate.

109. The dressing procedure, like truing, is used to
shape the instrument, but it accomplishes two
different purposes as well. First, the dressing
procedure reduces the instrument to its correct
working size and shape. Second, it is used to
remove clogged debris from the abrasive
instrument to restore grinding efficiency
during the finishing operation.

110. The clogging of the abrasive instrument with
debris is called abrasive blinding. Abrasive
blinding occurs when the debris generated
from grinding or polishing occludes the small
spaces between the abrasive particles on the
tool and reduces the depth that particles can
penetrate into the substrate. As a result,
abrasive efficiency is lost and greater heat is
generated.

111. A blinded abrasive appears to have a coating
of the substrate material on its surface.
Frequent dressing of the abrasive instrument
during the finishing operation on a truing
instrument, such as that illustrated in Figure
below maintains efficiency of abrasive in
removing the substrate material.

113. Binders for diamond abrasives are manufactured
specially to resist abrasive particle loss rather
than to degrade at a certain point and relase
particles. One reason For this is that diamond is
the hardest material known - so hard that
diamond abrasive particles do not lose their
cutting efficiency against substrates.

114. Diamond particles are bonded to metal wheels and
bur blanks with special heat-resistant resins such as
polyimides. The super-coarse through fine grades
are then plated with a refractory metal film such as
nickel. The nickel plating Provides improved
particle retention and acts as a heat sink during
grinding.

115. Titanium nitride coatings are used as an
additional layer on some of the recent diamond
abrasive instruments to further extend their
longevity.
Finishing diamonds used for resin-based
composites contain diamond particles 40μm or
less in diameter, and many are not nickel-plated.

116. Therefore they are highly susceptible to debonding
and should always be used with light force and
copious water spray to ensure retention of the very-
fine diamond particles. Diamond but should always
be used with water spray and at rotational speeds
of less than 50,000 rpm.

117. Disposable diamond burs recently gained popularity
from maintenance and OSHA viewpoints because of
three factors:
(1) Optimal instrument efficiency,
(2) Concerns over the reuse of disinfected abrasive
devices and
(3) Minimal heat build-up.

118. Diamond instruments are preshaped and trued; they
are not treated as other bonded abrasives. Diamond
cleaning stones are used on the super-coarse
through fine grades to remove debris build-up and
to maintain grinding efficiency.

119. An example of a diamond cleaning stone is shown
in Figure following. Cleaning stones should not be
used on finishing diamonds because their bonded
particles are quickly removed. Manufacturers
provide special operating and cleaning instructions
for these instruments.

123. Coated abrasives are fabricated by securing
abrasive particles to a flexible backing material
(heavyweight paper, metal, or Mylar) with a
suitable adhesive material. These abrasives
typically are supplied as disks and finishing
strips. Disks are available in different diameters
and within and very thin backing thicknesses.

124. A further designation is made in regard to
whether or not the disk or strip is moisture-
resistant. It is advantageous to use abrasive
disks or strips with moisture resistant
backings because their stiffness is not reduced
by water degradation.

125. Furthermore, moisture acts as a lubricant to improve cutting
efficiency. Examples of coated abrasives are shown here.

128. Polishing pastes are considered as nonbonded
abrasives and are primarily used for final polishing.
They need to be applied to the substrate with a
nonabrasive device such as synthetic foam, rubber,
felt, or chamois cloth. The abrasive particles are a
persed in a water-soluble medium such as glycerin
for dental application. Aluminum oxide and
diamond are the most popular nonbonded
abrasives.

129. Abrasive motion
The motion of abrasive instruments is classified
as rotary, planar, or reciprocal. In general, burs
are considered rotary, disks are planar, and
reciprocatng handpiece provide a cyclic motion
and are reciprocal in relationship to their
direction of motion. Different sizes of abrasives
can be incorporated with each motion

130. Reciprocating hand pieces especially provide
the benefit of accessing interproximal and
subgingival areas to remove overhangs, to
finish subgingival margins without creating
ditches, and to create embrasures.

133. Many types of abrasive materials are available,
but only those commonly used in dentistry are
discussed in this section. Natural abrasives
include Arkansas stone, chalk, corundum,
diamond, emery, garnet, pumice, quartz, sand,
tripoli, and zirconium silicate.

134. Cuttle and kieselguhr are derived from the
remnants of living organisms.
Manufactured abrasives are synthesized
materials that are generally preferred because of
their more predictable physical properties.
Silicon carbide, aluminum oxide, synthetic
diamond, rouge, and tin oxide are examples of
manufactured abrasives.

136. Arkansas stone is a semitranslucent, light gray,
siliceous sedimentary rock mined in Arkansas.
It contains microcrystalline quartz and is dense,
hard, and uniformly textured. Small pieces of
this mineral are attached to metal shanks and
trued to various shapes for fine grinding of
tooth enamel and metal alloys.

138. One of the mineral forms of calcite is chalk, a
white abrasive composed of calcium carbonate.
Chalk is used as a mild abrasive paste to polish
tooth enamel, gold foil, amalgam, and plastic
materials.

140. This mineral form of aluminum oxide is usually
white. Its physical properties are inferior to those
of manufactured alpha (α) aluminum oxide,
which has largely replaced corundum in dental
applications. Corundum is used primarily for
grinding metal alloys and is available as a
bonded abrasive in several shapes. It is most
commonly used in an instrument known as a
white stone.

142. Diamond is a transparent, colorless mineral
composed of carbon. It is the hardest know
substance. Diamond is called a superabrasive
because of its ability to abrade any other known
substance.

143. Diamond abrasives are supplied in several
forms, including bonded abrasive rotary
instruments, flexible metal-backed abrasive
Strips, and diamond polishing pastes. They
are mostly used on ceramic and resin-based
composite materials.

145. The advantages of synthetic diamonds over
natural diamonds include their controllable,
consistent size and shape, as well as their lower
cost compared with natural diamonds. The shape
of the diamonds determines the binder needed
for its use. The binders can be either resin or
metal. Resin-bonded diamonds have sharp
edges.

146. During use, the sharp edges break down and
expose new sharp edges and corners. On the
other hand, metal-bonded diamonds are
regular and more consistent in size. They
function as cutting points or edges primarily
through the benefit of their hardness rather
than their shape.

147. Larger synthetic diamond particles appear greenish
because of the chemical reaction with nickel during
the manufacturing process. Manufactured diamond
is used almost exclusively as an abrasive and is
produced at five times the quantity of natural
diamond abrasive. This abrasive is used in the
manufacture of diamond saws, wheels, and burs.

148. Blocks with embedded diamond particles are used
to true other types of bonded abrasives. Diamond
polishing pastes are also produced from particles
smaller than 5µm in diameter. Synthetic diamond
abrasives are used primarily on tooth structure,
ceramic materials, and resin-based composite
materials.

150. This abrasive is a grayish-black corundum
that is prepared in a fine-grain form. 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.

152. The term garnet includes a number of different
minerals that possess similar physical
properties and crystalline forms. These
minerals are the silicates of aluminum, cobalt,
iron, magnesium, and manganese, The garnet
abrasive used in dentistry is usually dark red.

153. Garnet is extremely hard and, when fractured
during the grinding operation, forms sharp,
chisel-shaped plates, making it a highly effective
abrasive. Garnet is available on coated disks and
arbor bands. It is used in grinding metal alloys
and acrylic resin materials.

155. Volcanic activity produces this light-gray, highly
siliceous material. It is used mainly in grit form
but can be found in some rubber-bonded
abrasives. Both pumice forms are used on acrylic
resin materials. Flour of pumice is an extremely
fine-grained volcanic rock derivative from Italy
that is used in polishing tooth enamel, gold foil,
dental amalgam, and acrylic resins.

157. The most commonly used form of quartz is
very hard, colorless, and transparent. It is the
most abundant and widespread of minerals.
Quartz crystalline particles are pulverized to
form sharp, angular particles that are useful in
making coated abrasive disks. Quartz abrasives
are used primarily to finish metal alloys, and
they may also be used to grind dental enamel.

159. Sand is a mixture of mineral particles
predominantly composed of silica. The particles
represent a mixture of colors, making sand
abrasives distinct in appearance. Sand particles
have a rounded to angular shape. They are applied
under air pressure to remove refractory investment
materials from base metal alloy castings. They are
also coated onto paper disks for grinding of metal
alloys and acrylic resin materials.

161. This abrasive is derived from a lightweight,
friable siliceous sedimentary rock. Tripoli can be
white, gray, pink, red, or yellow. The gray and red
types are most frequently used in dentistry. The
rock is ground into very fine particles and formed
with soft binders into bars of polishing compound.
Tripoli is used for polishing metal alloys and
some acrylic resin materials.

163. Zircon or zirconium silicate is supplied as an
offwhite mineral. 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 pastes.

165. Commonly referred to as cuttlefish, cut bone, or
Cuttle, this abrasive is a white calcareous powder
made from the pulverized internal shell of a
Mediterranean marine mollusk of the genus
Sepia. Cuttle is available as a coated abrasive and
is useful for delicate abrasion operations such as
polishing of metal margins and dental amalgam
restorations.

167. This material is composed of the siliceous
remains of minute aquatic plants known as
diatoms. The coarser form of kieselguhr is
called diatomaceous earth and is used as a filler
in many dental materials, such as the
hydrocolloid impression materials.

169. This extremely hard abrasive was the first of the
synthetic abrasives to be produced. Green and
blue-black types of silicon carbide are produced ;
both types have equivalent physical properties.
The green form is often preferred because
substrates are visible against the green color.
Silicon carbide is extremely hard and brittle.
Particles are sharp, and they break to form new
sharp particles.

170. This results in highly efficient cutting of wide
variety of materials, including metal alloys,
ceramics, and acrylic resin materials. Silicon
carbide is available as an abrasive in coated
disks and as vitreous-bonded and rubber-bonded
instruments.

172. Fused aluminum oxide was the second synthetic
abrasive to be developed. Synthetic aluminum
oxide (alumina) is made as a white powder and can
be much harder corundum (natural alumina)
because of its purity. Alumina can be processed
with different properties by slight alteration of the
reactants in the manufacturing process. Several
grain sizes of alumina are available, and it has
largely replaced emery for several abrasive uses.

173. Aluminum oxide is widely used in dentistry to
make bonded abrasives, coated abrasives, and air-
propelled grit abrasives. Sintered aluminum oxide
is used to make white stones, which are popular
for adjusting dental enamel and for finishing metal
alloys, resin-based composites and ceramic
materials.

174. Pink and ruby variations of aluminum oxide
abrasives are made by adding chromium
compounds to the original melt. These
variations are sold in a vitreous-bonded form
as non contaminating mounted stones for the
preparation of metal-ceramic alloys to receive
porcelain.

175. Remnants of these abrasives and other debris
should be removed from the surface of metals
used for metal-ceramic bonding so as not to
prevent optimal bonding of porcelain to the metal
alloy. A review by Yamamoto (1985) suggests
that carbide burs are the most effective
instruments for finishing this type of alloy
because they do not contaminate the metal
surface with entrapped abrasive particles.

177. Iron oxide is the fine, red abrasive
component of rouge. Like tripoli, rouge is
blended with various soft binders into a
cake form. It is used to polish high the
metal alloys.

179. Tin oxide is an extremely fine abrasive used
extensively as a polishing agent for polishing
teeth and metallic restorations in the mouth. It
is mixed with water, alcohol, or glycerin to
form a mildly abrasive paste.

182. The most commonly used abrasive pastes
contain either aluminum oxide (alumina) or
diamond particles. Alumina pastes should be
used with a rotary instrument and increasing
amounts of water as polishing proceeds from
coarser to finer abrasives. Diamond abrasive
pastes are used in a dry condition.

183. The instruments that apply the paste to the
material surface are equally important, These
include ribbed prophy cups (the ribbed type or
the more flexible, nonribbed type), brushes,
and felt wheels.

184. Abrasive pastes have several disadvantages.
First they are relatively thick and cannot gain
access into embrasures. Second, the pastes
tend to splatter off of the instruments. Third,
heat is generated when insufficient coolant is
used or when an intermittent polishing
technique is not used.

186. The ideal surface for ceramic restorations is a
polished and glazed surface. The production
of a glaze layer through a natural glaze or
overglaze process will not necessarily yield a
smooth surface if the initial ceramic surface
has significant roughness.

187. The smoothest surfaces can he achieved extraorally
before a prosthesis is cemented. In the mouth
however, minor roughness can be successfully
polished without compromising the surface quality.
In addition, polishing can improve the strength
within the surface region of a ceramic prosthesis
because it removes pores and microcracks.

188. Adequate cooling is important in vivo when
finishing and polishing ceramic restorations.
Using an air-water spray and maintaining
intermittent contact between the restoration and
the rotary instrument are critical during the
operation.

189. Continuous contact between the restoration
and the rotary instrument should be avoided.
Heatless stones (silicone carbide) provide
heat reduction and can be used as an
alternative. Several kits are available for
finishing and polishing ceramic restorations.

190. Manufacturer’s instructions should be followed when
using different systems. Depending on the preference
of the dentist, a general technique is as follows:
(1) Contour with flexible diamond disks, diamond
burs, heatless or polymer stones or green stones
(silicone carbide).
(2) Finish with white or abrasive-impregnated rubber
disks, cups, and points. This process may require two
or three steps, depending on the system used.

191. (3) Polished with fine abrasive impregnated
rubber disks, cups, and points, or, if necessary,
use a diamond paste applied with a brush or felt
wheel.
(4) Apply an overglaze layer, or natural glaze the
ceramic if necessary. For intraoral polishing, use
intermittent application of rotating instruments
with a copious amount of water as a coolant.

193. Acrylic resins are relatively soft materials. To
avoid overheating, apply a large amount of pumice
slurry to the surface. Intermittent contact with the
substrate also helps to avoid overheating. The
following technique steps are recommended:

194. (1) Contour with tungsten carbide bur and
sandpaper.
(2) Use a rubber point to remove the scratches.
(3) Apply pumice with a rag wheel, felt wheel,
bristle brush, or prophy cup, depending on the size
of the area that needs to be polished.
(4) Apply tripoli or a mixture of chalk and alcohol
with a rag wheel.

197. As an alternative to the use of rotary instrument
cutting, air-abrasive systems can deliver a fine,
precisely controlled high-pressure stream of 25-
to 30µm aluminum oxide particles to remove
enamel, dentin, and restorative materials.
Because air abrasion generates minimal heat or
vibration, the potential for tooth chipping or
microfracturing is minimized.

198. These systems have been used for the following
applications: cavity preparation, removal of
defective composite fillings, endodontic access
through porcelain crowns, minimal preparation to
repair crown margins, tunnel preparations,
superficial removal of stains, cleaning of tooth
surfaces before adhesive bonding and roughening
of internal surfaces of indirect porcelains or
composite restorations before adhesive bonding.

201. Often referred to as air polishing, air-abrasive
polishing is based on the controlled delivery of an
air, water, and sodium bicarbonate slurry to remove
plaque and stains from tooth surfaces. Compared
with rubber cup and prophylaxis paste techniques,
it is more time-effective, and it is possible to access
many tooth surfaces with this technology.

202. However, it is reported that surfaces of softer
restorations, such as glass ionomers, can be
damaged. Therefore it should be used with
caution around cosmetic restorations.

205. Dentifrices, available as toothpastes, gels, and
powders, provide three important functions.
First, their abrasive and detergent actions
provide more efficient removal of debris, plaque,
and stained pellicle compared with use of a
toothbrush alone. Second, they polish teeth to
provide increased light reflectance and superior
aesthetic appearance.

206. The high polish, as an added benefit, enables
heat to resist the accumulation of microorganism
and stains better rougher surfaces. Finally,
dentifrices act as vehicles for the delivery of
therapeutics agents with known benefits; for
example, fluorides, tartar control agents,
desensitizing agents, and remineralizing agents.

207. Fluorides improve resistance to caries and
may, under a proper oral hygiene regimen,
enhance the remineralization of incipient
noncavitated enamel lesions. Tartar control
agents, such as potassium and sodium
pyrophosphates, can reduce the rate at which
new calculus deposits from supragingivally.

208. Desensitizing agents with proven clinical
efficacy are strontium chloride and potassium
nitrate. The therapeutic benefits of other
additive such as peroxides and bicarbonates
are under investigation. The products
advertised as “whitening tooth paste” may
contain a abrasive agent alone or a chemical
agent and a abrasive agent. The former type of
additive acts through a surface stain removal
mechanism whereas latter additives act
through a combined mechanism of abrasion
and bleaching.

209. Composition
The abrasive concentration in paste and gel
dentifrices are 50% to 75% lower than those of
powder dentifrices Therefore powders should be
used more sparingly and with greater caution by
patients (especially where cementum and dentin
are exposed) to avoid excessive dentinal
abrasion and pulpal sensitivity.

213. The ideal dentifrice should provide the greatest
possible cleaning action on tooth surfaces with the
lowest possible abrasion rates.
Dentifrices do not need to be highly abrasive to clean
teeth effectively. This is fortunate because exposed
root surface cementum and dentin are abraded at
rates of 35 and 25 times that of enamel, respectively.

214. Currently the preferred means of evaluating
dentifrice abrasivity is to employ irradiated
dentin specimens and brush them for several
minutes with test and reference dentifrices.

215. An abrasivity ratio is then calculated by
comparing the amounts of radioactive
phosphorus ( 32
P) released by each dentifrice, and
this value is multiplied by 1000. A dentifrice
must obtain an abrasivity score of 200 to 250 or
less to satisfy the abrasivity test requirements
proposed by the American Dental Association
(ADA) and the International Organization for
Standardization (ISO).

216. This means that a test dentifrice must abrade dentin at
20% to 25% of the rate of the reference standard to be
considered safe for normal usage. A problem with this
laboratory test is that it does not account for all
variables that would affect abrasivity under in vivo
conditions.
Some of the factors affecting dentifrice abrasivity are :

218. ADA Acceptance Program

219. The ADA designates a dentifrice a “Accepted”
only if the dentifrice meets specific requirements.
First, the abrasivity of the dentifrice must not
exceed the maximum acceptable abrasivity value
of 250. (also a limit for the ISO standard).

220. Second, the manufacturer must produce
scientific data, usually from clinical trials, that
verify any claims the manufacturer wishes to
make on the product package or in commercial
advertisements, which are also periodically
reviewed by the appropriate ADA Council.

222. Toothbrush bristle stiffness alone has been
shown to have no effect on abrasion of hard
dental tissues. However, when a dentifrice is
used, there is evidence that more flexible
toothbrush bristles bend more readily and
bring more abrasive particles into contact
with tooth structure albeit with relatively
light forces.

223. This interaction should produce more
effective abrasion and cleaning action on
areas that the bristles can reach. Battery-
powered toothbrushing devices provide a
variety of cleaning actions that are claimed to
improve tooth-cleaning actions even further
than those achieved by manual toothbrushes.

237. William J. 0’Brien: Dental materials and their
selection
Robert G. Craig: Restorative dental materials.
John F McCabe: Applied dental materials.
E.C.Coombe: Notes on dental materials.
Kenneth J Anusavice: Science of dental
materials.
E.H. Greener: Material science in dentistry.
Bernard G. N. Smith: The clinical handling of
dental material.