2. Elastomers refers to a group of rubber polymers
which are either chemically or physically
crosslinked , easily stretched and rapidly recover
to their original dimension when the applied
stress is released.
Chemically there are four kinds of elastomers
Polysulfide
Condensation silicon
Polyether
Addition silicon
4. COMPOSTION
BASE PASTE
Polysulfied polymer
Filler ---- Lithophone or titanium dioxide
Plasticizer--- Dibutyl phthalate
Accelerator – sulfur 5%
CATALYST PASTE
Lead dioxide --- initiator
Plasticizer -----same as those added in base paste
Retarder --- Oleic or stearic acid
5. Chemistry
The basic ingredient of the polymer paste is a
polyfunctional mercaptan or polysulfide polymer.
This linear polymer contains approximately 1
mol% of branches to provide enough pendant
mercaptan groups as chain cross-linking sites. This
polymer is usually cross-linked with an oxidizing
agent such as lead dioxide. It is the lead dioxide
that gives polysulfide its characteristic brown
color. During the condensation reaction of the
lead dioxide with the SH groups of the polysulfide
polymer, two phenomena occur: (1) chain-
lengthening polymerization from the reaction
with the terminal -SH groups, and (2) cross-
linking from the reaction with the pendant -SH
group
6. Because the pendant groups compose only a small
percentage of the available-SH groups, initially, the
polymerization reactions result in chain lengthening,
which causes the viscosity to increase. The subsequent
cross-linking reactions tie the chains together, forming
a three-dimensional network that confers ,elastic
properties to the material .
7. MANIPULATION
With the proper lengths of the two pastes squeezed onto a
mixing pad or glass slab, the catalyst paste is first collected
on a stainless steel spatula and then distributed over the
base, and the mixture is spread out over the mixing pad.
The mass is then scraped up with the spatula blade and
again smoothed out. The process is continued until the
mixed paste is of uniform color, with no streaks of the base
or catalyst appearing in the mixture. If the mixture is not
homogeneous, curing will not be uniform, and a distorted
impression will result.
8. Medium-body and heavy-body polysulfide impression
pastes are extremely viscous and sticky. Consequently,
they are difficult to mix. However, if sufficient force is
applied and spatulation is performed rapidly, the
material will seem thinner and easier to handle, This
phenomenon is known as pseudoplasticity.
9. Working and Setting Times
. Working and setting times for the various kinds of
elastomeric materials, as measured by an
oscillating rheometer, An increase in temperature
accelerates the curing rate of all these elastomeric
impression materials and thus decreases both
setting and working times. Cooling is a practical
method of increasing the working time of most
polysulfide impression materials. This can be
accomplished by storing the materials at a low
room temperature or by mixing on a chilled, dry
glass slab. Then, when the impression material is
carried to the mouth, setting time is decreased by
the higher oral temperature. oleic acid is also an
effective retarder for the lead dioxide-cured
polysulfide materials. Conversely, adding a drop of
water accelerates the curing rate.
10. The curing rate of some, but not all, of the
polysulfide impression materials is sensitive to
alterations in the base: accelerator ratio. However,
mechanical properties can be adversely affected
when marked changes in the base: accelerator
ratio occur. Altering the base:accelerator ratio to
change the working or setting time is not
economical, because a portion of the paste is not
used. Moreover, because the accelerator paste
contains a retarder as well as a reactor, increasing
the base: accelerator ratio may not produce a
predictable change in the polymerization rate.
11. RHEOLOGY.
Polysulfide ranks as one of the least stiff of the
elastomeric impression materials. This flexibility
allows the set material to release from undercut
areas and be removed from the mouth with a
minimum of stress. Despite the lack of stiffness,
the unset material has a high level of viscosity. This
thick consistency of the uncured material helps
displace any unwanted fluid present while seating
the impression. Also, the excess material extruded
from the tray does not flow easily because of the
high viscosity, reducing the potential discomfort to
the patient during seating of a tray.
12. Tear Energy. Polysulfides have the highest resistance to tearing.
DIMENSIONAL STABILITY.
The stone cast should be poured up immediately
because the impression is the most accurate
immediately after removing it from the mouth.
The following are sources of dimensional change:
1. During setting most polymers contract slightly
during cross-linking, because tied together, the
chains occupy less volume, and there is a reduction
in bond length.
2. After setting, the by-product (water) of the
condensation reaction is lost, which causes
shrinkage.
13. 3. Although polysulfide impression materials are water
repellent, the materials can absorb fluids if exposed to
water, a disinfectant, or a high-humidity environment
over time.
4. After setting, there is incomplete recovery of
deformation because of the viscoelastic properties.
14. HANDLING TECHNIQUE.
A polysulfide impression of a number of teeth can
be obtained at one time with the use of syringe and
tray materials. To provide a less viscous material
for use with the syringe, most manufacturers have
provided impression materials with at least two
consistencies: one for use with the tray and a
thinner one for use with the syringe. The syringe
type may also have longer working and setting
times. In addition, the syringe material contains
less filler particles, so it has greater polymerization
shrinkage and more thermal contraction. For these
reasons, it is not advisable to use the syringe
material alone.
15. The method of using both the syringe and the tray
materials is often referred to as the multiple mix
technique because two separate mixtures are
required with two separate mixing pads and
spatulas. With the elastomeric impression
materials, the mix thickens as it begins to set.
Although the consistency may be acceptable for
the tray material, it may be too thick to be
extruded from the syringe. Thus, it is advisable to
mix the tray material first and fill the tray with a
uniform thickness of material and set it aside,
while a second person begins mixing and filling
the syringe. The material is injected from the filled
syringe within and around the prepared teeth. The
filled tray is then carried to place and seated over
the syringe material.
16. The two materials should cure together. Timing the
procedure is critical because if the tray or the syringe
material becomes too set, they may not cohere. If
either material has progressed past its working time
when the two are brought together, the bond between
them will not be strong. Polysulfide has a long
working time, which can be beneficial for the student
who is just learning to make an impression,
17. DISINFECTION of polysulfides is my 10 mins
immersion in 10% solution of hypochlorite .
SHELF LIFE.. To maximize the shelf life, always
keep the tubes tightly closed when they are not in
use. Storage in a cool environment is also
advisable. ADA Specification No. 19 requires that
after storage of the base and accelerator for 7 days
at 60 ± 2° C (140 ± 3.6° F), the material must still
meet the test for permanent deformation. If the
shelf life is exceeded, the components of the pastes
may separate. Poor elastic behavior exhibited as
high "set" values (lowrecovery) is another
indication that the material has exceeded its shelf
life
18. ADVANTAGES
Long working time
Proven accuracy
High tear resistance
Less hydrophobic
Inexpensive to use Long
shelf life
DISADVANTAGES
Requires a custom tray
Must be poured in stone
immediately
Potential for significant
distortion
Odor offends patients
Messy and stains cloths
Advantages and Disadvantages of
Polysulfide Materials
20. CHEMISTRY
The polymer consists of an -w-hydroxy-terminated
polydimethyl siloxane The condensation
polymerization of this material involves a reaction
with trifunctional and tetrafunctional alkyl
silicates, commonly tetraethyl orthosilicate, in the
presence of stannous octoate These reactions can
take place at ambient temperatures; thus, the
materials are often called roomtemperature
vulcanization (RTV) silicones. The average RTV
polymer chain consists of about 1000 units. The
formation of the elastomer occurs through a cross-
linking between terminal groups of the silicone
polymers and the alkyl silicate to form a three-
dimensional network
21. .Ethyl alcohol is a by-product of the condensation
setting reaction. Its subsequent evaporation
probably accounts for much of the contraction
that takes place in a set silicone rubber.
Improvements in the chemistry of the cross-
linking reactions have resulted in addition
reaction silicones that are discussed in a
subsequent section. The advantages of the newer
silicones resulted in a significant drop in the use of
the condensation silicones. However, the
information in this section on these original
silicone impression materials is useful since it sets
the stage for the discussion of the addition
22. COMPOSTION
It is supplied as base paste and a low viscosity liquid or
catalyst paste . Because the catalyst paste is liquid
colloidal silica or micro sized metal oxide is added as
filler to form a paste
23. Manipulation.
Condensation silicones are supplied as a base paste
and a liquid catalyst or reactor. A length of the
base is dispensed from the tube onto a graduated
mixing pad. Then, one drop of the liquid catalyst is
added for each unit length of base. These materials
are somewhat difficult to mix because of the
disparity in the viscosity of the two components.
However, the color difference of the two
components provides a visual clue as to how
completely the two are blended; for example, a
homogeneous mix has a uniform color.
24. The putty material is supplied as a very thick paste
and a liquid accelerator. Because the putty is so
viscous, it is packaged in a jar rather than a tube
and dispensed by volume using a scoop. The
manufacturer's directions indicate the number of
drops of accelerator needed for each scoop. Again,
producing a wellmixed material is not easy when
putty and an oily liquid are mixed, so some
manufacturers have formulated a two-paste putty
system. With either system, the best mixing
technique is to knead the material with the fingers.
Wearing gloves adds another complication,.
because some latex gloves contain a sulfur
component that inhibits the setting Of the putty.
25. Working and setting time
Temperature has a significant influence on the rate of
curing for condensation silicone impression materials.
Chilling the material or mixing on a cool slab slows the
reaction rate. Altering the base: catalyst ratio is
another effective and practical method of changing
the curing rate of these impression materials. When
the base: catalyst ratio is modified, it is wise to test the
setting time for the new ratio before it is used for a
patient.
26. ELASTICITY.
Condensation silicone impression materials are more
ideally elastic than polysulfides. They exhibit minimal
permanent deformation and recover rapidly when
strained. Like polysulfides, these materials are not very
stiff, which means it is not difficult to remove them
from undercuts without distortion.
27. RHEOLOGY.
The viscoelastic characteristics of' these materials
suggest that they can respond elastically (snap
back like springs) or as viscous liquids that easily
sustain permanent deformation (never return to
the exact same spot, like dashpots). The material is
more likely to respond as an elastic if it is strained
rapidly; hence, impressions must be removed
quickly so that the deformation is elastic and
recoverable. Prolonging the strain by removing the
impression slowly increases the chance for the
permanent deformation to occur because the poly-
mer chains respond in a viscous manner.
28. TEAR ENERGY.
The tear resistance is low for condensation silicone
impression materials. Although they do not tear as
easily as alginates or agar hydrocolloids, they must be
handled carefully to avoid ruining a margin of a crown
preparation when it is torn.
29. DIMENSIONAL STABILITY.
The excessive polymerization shrinkage of the
condensation silicones requires a modification of
the impression-making technique to produce
accurate impressions. Rather than the custom
tray-multiple mix technique recommended for
polysulfides, a putty-wash technique is used for
condensation silicones. This technique is able to
compensate for the poor dimensional stability of
these materials. The amount of linear contraction
is two to four times greater than for the other
impression materials In addition to the large
setting shrinkage, the dimensional instability is
also caused by the loss of the volatile reaction
product, ethyl alcohol.
30. Polysulfides undergo condensation polymerization,
but the reaction product, water, is a relatively small
molecule; thus, this loss has a much smaller effect
on the material than the loss of the larger alcohol
molecule resulting from the silicone condensation
reaction. Because the polymerization reaction
continues even after the material is "clinically set,"
the polymerization shrinkage continues. Once the
impression is removed from the mouth, the
evaporation of the reaction by-product occurs
continuously. Thus, the most accurate model is
obtained by pouring up the impression with a
gypsum stone slurry immediately.
31. BIOCOMPATIBILITY
Silicon is one of the most biologically inert materials
SHELF LIFE.
The alkyl silicates are slightly unstable, particularly if
they are mixed with a tin compound to form a single
catalyst liquid. Thus, a limited shelf life may result
because of oxidation of the tin component ,within the
catalyst. Shelflife failure may also occur as a result of
degradation of the base or cross-linkage of the base
during storage.
32. HANDLING TECHNIQUE.
A putty-wash technique is frequently used for making
condensation silicone impressions. First, the thick putty
material is placed in a stock tray, and a preliminary
impression is made. This results in what is essentially an
intraoral custom-made tray formed by the putty. Space for
the light-bodied "wash" material is provided either by
cutting away some of the "tray" putty or by using a thin
polyethylene sheet as a spacer between the putty and the
prepared teeth. After the spacer is removed, a mix of the
thin-consistency wash material is placed into the putty
impression, and then the putty wash is seated in the mouth
to make the final impression. This method is referred to as
the two-stage putty-wash technique or the reline techniq~e.
For reliable reproduction of sharp angles in cavity
preparations, it is often necessary to use a syringe and
inject the wash material within and onto the preparations.
33. An alternative to the two-step procedure is to syringe the
wash into place, then seat the unset putty over the
light-bodied material. One difficulty with combining
the wash and putty steps is that the higher viscosity
material may displace the more fluid wash material. If
this occurs, critical areas of the preparation may be
reproduced in putty rather than in the light-bodied
material, but the putty is too thick to replicate the
required detail
34. ADVANTAGES AND DISADVANTAGES OF
CONDENSATION SILICONES COMPARED
WITH POLYSULFIDE MATERIALS
ADVANTAGES
Adequate working and
setting time
Pleasant odor and no
staining
Adequate tear strength
Better elastic
properties on removal
Less distortion on
removal
DISADVANTAGES
Adequate accuracy if
poured immediately
Poor dimensional
stability
Potential for significant
distortion
Putty-wash method is
technique sensitive
Slightly more expensive
Poor to adequate shelf
35. DISINFECTION OF THE IMPRESSION.
Condensation silicone impressions can be immersed in
most of the commercial antimicrobial solutions for a
short period (less than an hour) and not experience
any adverse effects.
37. Chemistry
The addition silicones are frequently called
polyvinylsiloxane or vinyl polysiloxane impression
materials. In contrast with the condensation silicones,
the addition reaction polymer is terminated with vinyl
groups and is cross linked with hydride groups activated
by a platinum salt catalyst. There are no reaction by-
products as long as the correct proportions of
vinylsilicone and hydride silicone are maintained and
there are no impurities. If the proportions are out of
balance or impurities are present, then side reaction will
produce hydrogen gas which results in pinpoint voids in
the stone cast.
38. Composition
Base paste Catalyst paste
Vinyl silicon Divinyl polydimethyl siloxane
Polymethyl hydrogen siloxane Other siloxane prepolymer
Other siloxane prepolymer Platinium salt activator
Hybrid silicone
Retarder
Sulfur contamination from natural latex gloves inhibits
the setting of the addition silicone impression material.
39. Manipulation
The light-body and medium-body vinyl polysiloxanes are
supplied as two pastes, the putty is supplied as two jars
of high-viscosity base and catalyst material. The
similarity of the paste consistencies and the shear-
thinning behavior of these impression materials made the
vinyl polysiloxanes suitable for and automatic dispensing
and mixing device. The advantage is that is greater
uniformity in proportioning and in mixing, less air is
incorporate into the mix, and the mixing time is reduced.
Also, there are fewer possibilities for contamination of
the material.
The mixed impression material is ejected directly into the
adhesive-coated tray or onto the prepared teeth if the
syringe tip is in place.
40. Working and Setting Time.
In contrast with the condensation silicones, the
curing rate of the addition silicones appears to be
even more sensitive to ambient temperature than
are the polysulfides. Working and setting time can
be extended (up to 100%) by the addition of a
retarders as supplied by the respective
manufacturer and by cooling the mixing slab. The
addition silicone can also be refrigerated before
use. This cooling has little effect on viscosity.
Retarders are impractical with the automatic
mixing devices.
41. Elasticity
Distortion on removal from undercuts is virtually
nonexistent, because these materials exhibit the lowest
strain-incompression values (permanent distortion). The
excellent elastic properties present a problem in that the
heavy-body putty material begins to build up elastic
response while still in the working stage. If the material
is compressed elastically during the seating of the
impression, then distortion can occur when the material
elastically rebounds. For most of these materials, the
stiffness is proportional to the consistency of the
materials; for example, putties are stiff, but light-bodied
materials are quite flexible.
42. Rheology.
As one of the most psuedoplastic impression materials,
the effect of increased strain rate on the unset material is
quite pronounced for vinyl polysiloxane. This large
discrepancy between the flow properties of the material
under strong force, such as during syringing, and light
force, such as during seating the tray, has allowed
manufacturers to market the one-step material. One mix
of this medium viscosity material can be used for
capturing the fine detail and recording the bulk of the
oral structures. When syringed, it flows readily and yet
holds its shape when placed in an impression tray. With
these "single-phase" materials intended for both injection
and tray use, the primary consideration is viscosity.
43. Tear Energy
The resistance to tearing is adequate, similar to that of
the condensation silicones. The materials are highly
viscoelastic, so using a rapid strain rate produces an
elastic response and the vinyl polysiloxane are less
likely to tear.
44. Dimensional stability
Vinyl polysiloxane impression materials are the most
dimensionally stable of all the existing materials. No
volatile reaction by-product is released to cause the
material to shrink. (Note that the hydrogen gas is not a
true reaction by-product.) The clinically set material is
close to being completely cured, so there is little
residual polymerization to contribute to the dimensional
change. The primary dimensional change comes from
thermal shrinkage as the material cools from mouth
temperature to room temperature.
The impression does not have to be poured in stone
immediately a cast can be poured between 24 hours and
1 week.
45. Biocompatibility.
Vinylpolysiloxane materials are highly biocompatible.
Handling of the Tray
The popularity of a stock tray rather than a custom tray
may be associated with the increased use of the putty
reline technique. The Primary putty impression actually
serves as a custom tray for the wash or reline material.
In general, the tray adhesives for polysulfide, polyether,
and condensation silicones are quite satisfactory.
Certain putty-type silicones require mechanical
retention in the tray, because the adhesive is ineffective.
46. Handling technique
The addition silicone materials, the putty-wash system can,
and frequently does, produce a grossly inaccurate
impression. This occurs if the, putty impression is held
under pressure. Problems can occur because of the pressure
applied to the setting putty when the simultaneous
technique is used, and they can also occur with the set putty
that is used in the two-stage technique. Removing the
impression from the mouth releases the pressure; the putty
recovers but the recovery is excessive since the elastic
precompression is recovered in addition to elastic
deformation recovery from undercut areas. The distortion
that is produced with the stiff, compressible putty results in
shorter and narrower dies. In addition to excessive
pressure, some of the distortion in putty wash impressions
may be attributable to inadequate spacing for the wash
material.
Handling technique
The addition silicone materials, the putty-wash system can,
and frequently does, produce a grossly inaccurate
impression. This occurs if the, putty impression is held
under pressure. Problems can occur because of the pressure
applied to the setting putty when the simultaneous technique
is used, and they can also occur with the set putty that is
used in the two-stage technique
47. . Removing the impression from the mouth releases the
pressure; the putty recovers but the recovery is excessive
since the elastic precompression is recovered in addition
to elastic deformation recovery from undercut areas. The
distortion that is produced with the stiff, compressible
putty results in shorter and narrower dies. In addition to
excessive pressure, some of the distortion in putty wash
impressions may be attributable to inadequate spacing for
the wash material.
48. The addition silicones are supplied in a wide variety
of viscosities, including the single-phase or
monophase viscosity. Even the "less" dimensionally
stable monophase materials are considerably more
accurate and dimensionally stable than the
polysulfides or the condensation silicones
49. Disinfection
Vinyl impression materials are easily disinfected by
immersing in 10% hypochlorite or 2% glutaraldehyde
solutions. Usually, a 10- to I5-minute immersion is
sufficient.
50. Preparation of Stone Casts and Dies.
The hydrophobic characteristics of these vinyl
polysiloxane impression materials make it difficult to
wet the surface, so it is difficult to pour a bubble-free
stone cast from an addition silicone impression
material. To avoid this surfactant spray, a dilute
solution of soap or commercially available wetting
agents maybe preferred.
The impression is also compatible with epoxy resins
used for more accurate cast and dies. These replica
materials can be poured repeatedly in the same
impression, as can also be done with gypsum products.
51. Advantages and Disadvantages of Addition Silicones
Compared with Polysulfide Materials
ADVANTAGES DISADVANTAGES
Shorter setting time Hydrogen gas evolution in
some materials
Easy to mix-automatic
mixing devices
need careful handling and a
very dry field
Adequate tear strength more expensive, especially
with automatic mixing device
Extremely high accuracy
Undetectable distortion on
removal
Dimensionally stable even
after 1 week
52. Shelf Life
Manufacturers claim that the vinyl polysiloxanes have a 2-
year shelf life, which is considerably longer than that of
the condensation silicone. The silicone material tubes or
containers must remain tightly closed because air hastens
their deterioration. The shelf life can be prolonged by
storing the material in a cool, dry environment.
54. Chemistry.
This type of elastomeric impression material was
introduced in Germany in the late 1960s. It is a
polyether-based polymer that is cured by the reaction
between aziridine rings which are at the end of
branched polyether molecules. The main chain is
probably a copolymer of ethylene oxide and
tetrahydrofuran. Cross-linking, and thus setting, is
brought about by an aromatic sulfonate ester of the
type, where R is an alkyl group. This produces cross
linking by cationic polymerization via the amine end
groups.
This material was the first elastomers to be developed
primarily to function as an impression material
55. Composition.
The polyether rubbers are supplied as two
pastes. The base contains the polyether
polymer, colloidal silica as filler, and a
plasticizer such as a glycoether or phthalate.
The accelerator paste contains the alkyl –
aromatic sulfonate in addition to the
aforementioned filler and plasticizer.
56. Manipulation
Originally, polyethers were only supplied in one
viscosity. The pseudo plasticity of the materials
allowed one mix to be used for both syringe and
tray material. Subsequently, manufacturers
supplied an additional paste that could be used to
produce a thinner mix.
The component materials required a
reformulation to adapt the material to use with
the automatic mixing devices. Polyether was
changed so that it could be supplied in several
viscosities.
57. Working and Setting Time
The curing rate of the polyethers is less sensitive to
temperature change than that of the addition
silicones some modification in base: accelerator
ratio can be used to extend working time. Use of a
thinner also extends working time with only a
slight increase in setting time.
58. Elasticity
The polyethers have always been considered the
stiffest of the impression materials, excluding the
high viscosity putties. It is difficult to remove from
undercut areas because of the high modulus of
elasticity. The new formulation of regular or
medium body materials is actually less stiff than
the one step hydrophilic polysiloxane impression
material. Polyethers are slightly less elastic than
the vinylpolysiloxane.
59. Rheology
The psuedoplastic characteristics allowed the
original single-viscosity materials to be used as
both syringe and tray materials. The thinner
component was used mostly to reduce the stiffness
of the set material.
60. Tear Energy
Tear resistance is better than that of the
condensation silicon impression ion material.
However, polyether is more prone, to tearing than
polysulfide.
61. Dimensional stability
The stiffness of the material means that the force
needed to remove the impression is greater for
polyether impressions than for the other type of
materials. Yet, the recovery is nearly complete
because of the excellent elastic property of the
polyether. Thus, polyether impression can be
poured immediately, after several hours, or after
several days and the resulting cast will have the
same accuracy. The polyether will exhibit the least
amount of distortion from the loads imposed on the
set material. One property that has a negative effect
on the material is the absorption of water or fluids
and the simultaneous leaching of the water- soluble
plasticizer. Thus, the stored impressions must be
kept in a dry, cool environment to maintain their
accuracy.
62. Biocompatibility.
Originally, there was some concern about
hypersensitivity to the polyether catalyst system. .
However, recent studies indicate no cytotoxic effects
associated with the imine catalyst. Perhaps the most
likely elastomers induced problem for the patient
arises from pieces of the impression material being
left in the sulcus. The irritation can range from minor
to severe.
63. Handling the tray
Regardless of what type of tray is used, it is
important to use an adequate amount of adhesive
so that the stress during removal does not dislodge
the material from the tray.
64. Handling Technique.
Most clinicians continue to use the monophase or
single viscosity material. With a single-viscosity
material only one mix is made and part of the
material is placed in the tray and another portion is
put in the syringe for injection into the cavity
preparation. The fast setting of this material
requires a clinician to work rapidly.
66. Advantages and Disadvantages of Polyethers Compared
with Polysulfides
Advantages Disadvantages
Fast working and setting
times
Adequate accuracy if
poured immediately
Adequate tear strength Poor dimensional stability
Less hydrophobic-better
wetting
Clean but tastes bad
Less distortion on
removal
Stiffness requires
blocking undercuts
Long shelf life Slightly more expensive
67. Handling of the Stone cast
Pouring the stone cast in a polyether impression is
much easier than in one made from silicone material.
It is not a good idea to shorten the setting time of the
stone by trying to remove the cast early this will result
in a weak stone cast which may fracture during
removal.
68. Shelf life of polyether
Storing in a cool, dry environment prolongs the
shelf life. However, chilled polyether impression
material becomes rigid and cannot be mixed. Thus
it is necessary to allow the material to reach room
temperature before using.
69. REFERENCES
Kenneth J,. Anusavice- PhilipsScience of Dental materials-
10th edition
Robert G Craig- Restorative dental Materials- 11th Edition
William J. o brien- Dental matereials and their selection-
3rd edition
Herbet T Shillingburg- Fundamentals of Fixed
Prosthodontics- 3rd edition
Notes on Dental Materials, E. C Combe- 6th edition
