The document provides information on various impression materials used in dentistry. It discusses the ideal properties required for an impression material and classifies materials as either elastic or inelastic, and aqueous or non-aqueous. Specific materials discussed in detail include impression plaster, impression compound, zinc oxide eugenol paste, alginate, agar, polysulfide, silicones, and polyether. The composition, properties, advantages, disadvantages and manipulation of each material is explained.

1. IMPRESSION
MATERIALS
LECTURE BY:
Dr. BRAJENDRASINGHTOMAR
MDS
ASSOCIATEPROFESSOR
PROSTHODONTICS& IMPLANTOLOGY

2. Content ……
1. Introduction
2. Ideal requirement of an impression material
3. Classification of impression material
4. Inelastic impression materials
-Impression plaster
-Impression compound
-Zinc oxide eugenol paste
5. Elastic impression material
a. Elastic aqueous impression material
-Agar
-Alginate
- modified alginates
- laminate technique
- duplicating material

3. b. Elastic non aqueous impression material
-polysulfide
-Silicones
-condensation silicone
-addition silicone
-Polyether
- making an impression
- multiple mix technique
-putty wash technique
- monophase technique
6. references

4. Introduction
Construction of a model or cast is an important
step in numerous dental procedures. Various
types of casts and models can be made from
gypsum products using an impression mold or
negative likeness of dental structure. The dentist
designs and constructs both removable and
fixed prostheses on a gypsum cast. Thus the
cast must be an accurate representation of oral
structures, which requires an accurate
impression.

5. • IMPRESSION:
A negative likeness or copy in reverse of the
surface of an object; an imprint of the teeth and
adjacent structures for use in dentistry.
• IMPRESSION MATERIALS:
Any substance or combination of substances
used for making an impression or negative
reproduction.

6. To produce accurate replica of intra and extra
oral tissues, the impression material should be
1. Sufficiently fluid to adapt to the oral tissues.
2. Viscous enough to be contained in a tray.
3. Able to transform (set) into rubbery or rigid
solid in the mouth in a reasonable time.
4. Resistant to distortion or tearing when
removed from the mouth.
5. Dimensionally stable long enough to allow
one or more cast to be poured,
6. Biocompatible, and
7. Cost effective
Phillip’s Science of Dental Materials

7. Classification of impression material
Impression material can be classified
according to their.
1. Composition
2. Mechanism of setting
3. Mechanical properties and
4. Application
Phillip’s Science of Dental Materials

8. According to setting mechanism
Irreversible
• Implies that chemical
reaction have occurred
and that the material
cannot revert to a
previous state
• For example: alginate,
Zinc oxide eugenol,
impression plaster and
elastomeric impression
materials
Reversible
• Such as agar and
impression compound,
soften upon heating and
solidify slightly above
body temperature with
no chemical change
taking place.
Phillip’s Science of Dental Materials

9. According to mechanical properties
Setting Mechanism Inelastic Elastic
Chemical reaction
irreversible
Impression plaster
Zinc oxide eugenol
Alginate, polysulfide,
polyether
Cond. Silicon
Add. silicon
Thermally induced
physical reaction
reversible
Impression
compound
Agar
Phillip’s Science of Dental Materials

10. According to their application
• Elastic impression material can be stretched
or compressed and they can rebound when
removed from the mouth, the are capable of
accurately reproducing both hard and soft
structures of the mouth.
• Inelastic impression material such as ZOE
paste and plaster are ideal for making
impression of edentulous jaw structures or
soft tissues because, in the proper
consistency they do not compress the tissue
during seating of the impression trays.
Phillip’s Science of Dental Materials

11. Impression
Materials
Non-elastic
Elastic
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
Plaster
Compound
ZnO - Eugenol
Waxes
O’Brien, Dental Materials & their Selection

12. Non-elastic
Plaster
Compound
ZnO - Eugenol
Waxes

13. Impression plaster
• Impression plater is CaSO4 beta
hemihydrate used at a water/powder ratio of
approximately 0.5 to 0.6.
• Its fluidity makes it suitable for making
impressions of soft tissues under
uncompressed state.

14. Composition
• CaSO4 . 0.5H2O β-hemihydrate: main
reactive agents
• Potassium sulfate – to reduce expansion but
accelerates setting
• Borax – a retarder to prolonge setting time
• Alizarin: 0.04% color pigment ( to distinguish
impression plaster and model)
• Diatomaceous earth, quartz, lime - to make
the plaster more brittle
• Flavoring agent: to offset the bad taste of
plaster.

15. Properties
w/p ratio: 0.5-0.6
Setting time: 3-5 minutes
Setting expansion: maximum 0.15%
Wet strength : is 6Mpa
Advantages
1. Reproduces good surface details
2. Setting time is under the control of
operator
3. Setting expansion is less
4. Stable on storage over long time

16. Disadvantages
1. Set impression is brittle and may
fracture
2. Bad taste and rough feel
3. Water absorbing – dry sensation
4. Exothermic heat is disliked by
many patients
5. Require separating medium before
pouring cast

17. Impression compound
• Impression compound is also called as modeling
plastic
• It is classified as nonelastic, mucocompressive
and reversible ( thermoplastic impression
material, which set by physical change.

18. Classification
According to ADA specification no 3, impression
compound is classified as
Type I – Low fusing material
a) Impression compound
• It is supplied in the form of sheets about 4-5
mm thick
b) Green stick compound
• Supplied in stick form and available in
different colors.
Type II- High fusing material e.g. tray compound
• Used for constructing impression tray into
which another impression material is carried
to make a corrective wash impression.

19. COMPOSITION
COMPONENT WT% FUNCTIONS
Natural or synthetic resin
Copal resin 20%
Rosin- 20%
40 • Provide thermoplasticity
• Gives the qualities of flow and
cohesion
Waxes ( Bee’s wax,
carnauaba wax, paraffin
wax)
7 • Provides thermoplasticity
• Characterizes the softening
temperature and produces smooth
surface.
Stearic acid, shellac, and
Gutta- Percha
3 Acts as a plasticizers which improves
plasticity and workability
Diatomaceous earth,
French chalk or talk
50 Acts as filler
• Increases strength
• Reduces flow at mouth temperature
• Reduces COTE
Coloring agent Traces Gives characteristic color.

20. PROPERTIES
• Biological properties : non toxic and non
irritant
• Rheological properties:
It is highly viscous . The very high viscosity is
significant in two ways:
1. Limits the degree of fine detail , which can
be recorded
2. Characterizes compound as a muco-
compressive material.

21. Flow: the flow of impression compound can be beneficial or a
source of error.
1. The impression compound should soften at a point just
above the mouth temperature and should exhibits high flow
to conform to the tissue and register surface detail.
2. The impression compound should hardened at mouth
temperature and exhibit a minimum flow so that it can be
withdrawn without any distortion.
• Factor affecting flow:
1. Temperature, time and amount of load
2. Wet kneading
FLOW
Material At 37º C At 45º C
TYPE 1 Impression
compound
Less than 6 % More than 85%
TYPE 2
Tray compound
Less than 2 % 70-85%

22. Thermal properties:
• Fusion temperature: fusion temperature is probably the
temperature at which the crystalline fatty acids solidify. Above this
temperature the fatty acid are liquid and probably plasticize or
lubricate the softened material to form a smooth plastic mass
while the impression is being obtained.
• Glass transition temperature: this is the temperature at
which the material looses its hardness or brittleness on heating or
forms a rigid mass upon cooling.
• Thermal conductivity :Thermal conductivity of the impression
compound is low. Due to lack of conductivity setting is not uniform.
So the impression must be given adequate time to softens or
hardens uniformly.

23. • COTE: impression compound has a high COTE ( 200-
500 ppm) and undergoes considerable shrinkage on
removal from the mouth.
• The average linear contraction of compound on cooling
from mouth temperature to room temperature varies
between 0 .3 - 0.4%
Mechanical properties:
• Dimensional stability: dimensional changes or distortion
can occur on standing the impression due to the
relaxation of stresses. Stresses are incorporated due to
the following reasons:
• High value of COTE
• Poor thermal conductivity
• Relatively large temperature drop from mouth to room
temp.

24. Manipulation
1. Softening : can be softened by thermostatically
controlled water bath or open flame. But they are
normally softened by using water bath at 55-60º
C.
2. Kneading: the compound is removed from the
water bath and kneaded with the fingers in order
to obtain uniform plasticity throughout the mass
3. Loading: the compound is kneaded to suitable
shape and placed in an impression tray (non
perforated trays)
4. Tempering: the outer surface of the compound
can be waved over the flame or spray cold water
on metal tray just before it is inserted in the
mouth.

25. 5. Making impression : the compound along with tray is
then inserted into the mouth. The impression is
retained until it cools to mouth temperature.
6. Removal: after it has completely hardened the
impression is removed from the mouth and washed,
dried and trimmed.

26. Precaution:
1. when direct flame is used, the compound should not be allowed to
boil or ignite so that important constituents are volatilized.
1. Prolonged immersion or over heating in water bath is not indicated.
The compound may become brittle or grainy because some of the
low molecular weight ingredients may be leached out.
2. The temperature of water bath should not be more than 60º C.
otherwise the material become sticky and unmanageable due to
leaching of some of the components ( stearic acid ).
3. The water bath should be lined with napkin or gauze otherwise the
material will adhere to the water bath.
4. Material should be given adequate time to soften or harden
uniformly
5. Premature removal of impression from the mouth should be avoided
as it may result in distortion of impression.

27. Advantages
1. Can be used for compressive soft tissues
2. Can be used for any technique requiring a close
peripheral seal.
3. Can be used in combination with other material
4. Can be added and readopted.
5. Relatively cheap
Disadvantages
1. Does not reproduce fine surface detail
2. Can only give an accurate impression with long and
difficult technique.
3. As it can be softened and reused it tends to become
unhygenic .
4. The therml properties are not ideal large COTE and
low thermal conductivity.

28. Zinc Oxide Eugenol impression paste
• Classified as rigid or inelastic and mucostatic
impression material that sets by chemical
reaction.
• ADA specification no. 16
• uses:
1. Impression material for edentulous mouths
2. As a surgical dressing
3. Bite registration paste
4. Temporary filling material
5. Root canal filling material
6. Cementing medium &
7. Temporary relining material for dentures.
• Usually supplied as two pastes in collapsible tubes.

29. Composition
Ingredient Wt
%
functions
Zinc oxide ( French
processed or USP)
87 • Reactive ingredient which takes part in
setting reaction.
• It should be firmly divided and should
contains less amount of water
Fixed vegetable oil or
mineral oil ( olive or
linseed oil)
13 • Paste former
• Plasticizer- provide smoother and more
fluid mix
• Retarder –retards the rate of reaction
and increases the setting time.
• Aids in masking the action of eugenol
as an irritant
Base paste

30. Ingredient Wt% functions
Oil of cloves or eugenol 12 • Reactive ingredient which takes part in setting reaction.
• Oil of cloves contain 70-85 % of eugenol, in some times used
because it produces less of a burning sensation when it
contact the patients soft tissues.
Gum or polymerized rosin 50 • Facilitates the speed of reaction and produces a smoother
homogenous mix
• Gives body and coherence to the mixed material
• Imparts thermoplastic property to the set impression so that it
can be softened in hot water for removal from the cast
Filler ( silica type) kaolin, talc,
etc
20 • Used to form paste with eugenol
• Increases strength of the mixed paste
lanolin 3 • Plasticizer
Resinous balsam
(Canada or Peru balsam
10 • To increases flow and improve mixing qualities
Accelerator solution (CaCl2 or
MgCl2 )
5 • Accelerates the setting reaction
Color pigments traces • To distinguish from other paste
• Enables through mixing to be achieved as indicated by a
homogenous color, free of steaks in the mixed material
Reactor paste

31. Setting reaction
• On mixing the two paste a reaction between zinc
and eugenol begins. The basis of the reaction is the
phenolic-OH group of eugenol acts as a weak acid
and undergoes and acid base reaction with ZnO to
form a salt “zinc eugenolate”

32. Manipulation
• Mixing of the two paste is accomplished on an oil
impervious paper or glass mixing slab.
• The proper proportional of the two paste is
generally obtained by squeezing two strips of paste
of the same length, one from each tube, onto the
glass slab.
• A flexible stainless steel spatula is typically used
for the mixing procedure.
• The two strips of contrasting colors are combined
with the first stroke of the spatula, and the mixing is
continued for approximately 1 min, or as directed
by the manufacturer until a uniform color is
achieved

33. Properties
• Non toxic material but those containing eugenol can
be irritant
• Leaving a persistent taste, unpleasant
• Setting time : the material are classified as hard
paste ( type I) or soft paste (type II). The final should
occur within 10 minutes for a type I paste and 15
minutes for a type II paste.
• Factors affecting setting time:
1. Temperature
2. Humidity
3. Altering ZnO paste to eugenol
4. Mixing time
5. Chemical modifiers like CaCl2, MgCl2, and water (
accelerator) , add retarder ( boroglycerin, inert oils and
waxes.

34. • Consistency:
According to ADA specification no 16 it should be
30-55mm for type I & 20-45 mm for type II.
• Dimensional stability:
Satisfactory, a negligible shrinkage of less than 0.1%
may occur during setting
There is no dimensional changes after setting.
• Rigidity and strength;
The compressive strength of a hardened ZnOE is
about 7Mpa

35. Advantages
1. They are accurate, register details well and
are dimensional stable.
2. They adhere well to dried surfaces of
compound, resin and shellac bases.
3. Easy to manipulate
4. In expensive
Disadvantages
1. Require special tray for making impression
2. May cause burning sensation or irritation to
the oral tissues
3. Instruments are difficult to clean

36. Aqueous
Hydrocolloids
Agar (reversible)
Alginate (irreversible)
Elastic

37. Hydrocolloids
Hydrocolloids are the colloids that contains
water as the dispersion medium
Colloid: A solid, liquid, or gaseous substance
made up of large molecule that remain in
suspension in a surrounding continuous
medium of different matter.

38. • Sol : a colloidal system in which the
dispersed phase is a solid and dispersion
medium is liguid.
• Gel : a heterogeneous biphasic system in
which a liquid is dispersed in a solid
dispersion medium is known as gel.
• Gelation : gelation is a process of
conversion of viscous liquid sol into a
semisolid jelly like substance ( sol gel)

39. Agar
• Agar hydrocolloid impression material are
compounded from reversible agar gels. When
heated, they liquefy or go into sol state and on
cooling they return to the gel state.
• ADA specification no. 11
• Supply : these material are supplied in two form
1. Tray material
2. Syringe material
The only difference between two types is difference
in color and greater fluidity in the syringe material.

41. Composition :
Ingredient % Functions
Agar 13-17 To provide the dispersed phase of sol and the continuous fibril
structure
Borax 0.2 – 0.5 To improve the viscosity of the sol and strength of the gel
Potassium sulfate 1-2 Gypsum hardener – to counteract the inhibiting effect of borax
and agar on the setting of gypsum model material.
Alkyl benzoate 0.1 Preservative- to prevent the growth of mould in the impression
material during storage
Diatomaceous earth ( clay,
silica, wax )
0.3-0.5 Filler to control viscosity, rigidity and strength
Water 85.5 To provide the continuous phase in the sol and second
continuous phase of the gel, the amount controls the flow
properties of the sol and the physical properties of the gel.
Thymol Trace Bactericide
Glycerin Trace Plasticizer
Coloring and flavoring
agents
Trace To improve the appearance and taste

42. Manipulation :
• Reversible hydrocolloid are normally
conditioned prior to use, using a specially
designed hydrocolloid conditioner.
• This consist of three temperature controlled
compartments containing water.
1. Liquefying component
2. Storage component
3. Conditioning ‘or’ tempering component.
• Liquefaction of gel: the filled syringe and tubes
are placed in one of the water baths of a hydrocolloid
conditioner at 100 ºC for 10 -15 minutes

43. • Storage of the sol: after the agar gel is
converted into sol, the tubes and syringes are
then placed in storage bath, which is
maintained at 63 ºC to 66 ºC. It can be stored
at this chamber for several hours.
• Conditioning or tempering : the material that is
used to fill the tray must be cooled or
tempered. When the impression is to be taken,
the storage agar sol is squeezed in a
perforated water cooled tray, a gauge pad
placed over the top of the tray and the tray is
placed in conditioning bath at 43 ºC to 45 ºC
for 3-10 minutes. The purpose is to:
1. Increase the viscosity of the sol so that it will
not flow out of the tray
2. Reduce the temperature enough so that the
material will not be uncomfortable to the
patient.

44. • Impression making: the syringe material is taken
directly from the storage compartment and applied to the
prepared teeth. Before placing the tray material in the
mouth, the water soaked outer layer of tray material is
blotted with a dry gauge sponge.
• Then the tray is immediately brought into position and
seated with passive pressure.

45. Gelation: gelation is accomplished by circulating cool water
approximately 18 – 23 ºC through the tray for 3-5 min.
The coolest area of the sol are converted to gel rapidly. So material in
contact with tray sets more rapidly than in contact with oral tissues
due to its lack of conductivity.
During the gelation process. The tray must be held in the mouth until
gelation has proceeded to a point at which the gel strength is
sufficient to resist the deformation or fracture.
Removal : after the gelation, the impression is removed rapidly from
the mouth with a single, sudden jerk in a direction parallel to the long
axis of the tooth.

46. Properties
• They are non toxic , non irritant to the oral tissue.
Viscosity of the gel:
After liquefaction the material is sufficiently liquid to
record all the finer details. Agar is available is two
viscosities tray and syringe.
• Gelation time : it is approximately 5 minutes.
• Gelation temperature: according to ADA
specification no. 11 gelation temperature should not
be less than 32 degree C. and should not be more
that 45 degree.
• Gel strength: According to ADA specification no. 11
the gel strength should not be less than 0.245 Mpa

47. • Tear strength : it is about 715 g/cm. it is very low.
So use minimum thickness of 3-5 mm.
• Flexibility: its about 4-15 %
• Permanent deformation: 1.5 %
• Elastic recovery is 98.5 %
• Dimensional stability: unstable
• Impression trays: water cooled perforated
impression trays are used
• Compatibility with gypsum: agar is compatible with
die stone.
• Electroplating : cannot be electroplated
• Disinfection: by iodophore bleach or 2 %
gluteraldehyde

48. Advantages
1. Reproduces finer
details
2. Used for model
duplication
3. Sufficiently flexible
4. High elastic recovery
5. Can be reused
Disadvantages
1. Dimensional instability
2. Impression cannot be
electroplated
3. Low tear strength
4. Elaborated and
expensive equipment is
required for manipulation.

49. Alginate impression material
• This material is based on alginic acid, which is
prepared from brown seaweed ( algae)
• ADA specification no. 18
• Types
1. Fast set
2. Normal set
• Supply : supplied as powder and available in
two forms
a) Bulk containers &
b) Small sealed packets and sachets.

51. Composition
Ingredient % functions
Soluble alginate, ( Na,
K, ,or tri ethenol
amine alginate
15 Main reactive ingredient forms sol with water. Reacts with Ca ions
to form gel of calcium alginate.
Calcium sulfate
dihydrate
16 Reactor –releases Ca. ions to react with soluble algianate to form
insoluble calcium alginate gel
Tri sodium phosphate 2 Retarder – to react preferentially with Ca ions and provides
sufficient working time before gelation
Diatomaceous earth 60 Filler-to increase strength and stiffness of the gel structure.
Zinc Oxide 4 Filler – has some influence on physical properties and setting
time of the gel
Potassium titanium
fluoride
3 Gypsum hardener to counteract the inhibiting effect of alginate on
setting of die material and improve the surface of the model
Flavoring agents (
winter
green/peppermint
trace To provide pleasant taste to make it more acceptable to thee
patient
Color pigments traces To provide characteristic color

52. Gelation
• On mixing the powder with water a sol is formed and
the alginate , the calcium salt , and phosphate begin to
dissolve.
• Calcium sulfate rapidly reacts with soluble alginate to
produce an insoluble calcium alginate gel in an
aqueous solution.
• The production of calcium alginate is so rapid that it
does not allow sufficient working time. Thus , a
retarder, tri sodium phosphate is added to the solution
to prolong the working time.

53. • Trisodium phosphate react with calcium sulfate in
preference to the soluble alginate to give a precipitate of
calcium phosphate, this reaction delays the supply of
calcium ions required for the gelation reaction and thereby
increasing the working time.
• When all the sodium phosphate has reacted with the
calcium ions begin to react with the soluble alginate to
produce calcium alginate as a gel. As the reaction
proceeds, the degree of cross-linking increases and gel
develops elastic properties.

54. Manipulation :
Proportioning :
the container of the powder should be shaken before use to get
uniform distribution of constituents. The powder dispensing
scoop is slightly over filled, tapped gently with spatula to fill the
voids in the voids in the dispensing scoop and to ensure a
reproducible volume of the powder is used in each mix. The
blade of the spatula is then used to scrape off the excess from
the top of the cup.
• For maxillary impression :
2 scoop of powder + 1 measure of water by volume
15 g of powder + 40 ml of water by weight.
• For mandibular impression :
1 scoop of powder + ½ measure of water by volume
7.5 g of powder + 20 ml of water

55. • Mixing : the measure powder is shifted
into premeasured water that has been
placed in a clean rubber bowl. The
powder is incorporated into water by
careful spatulation.
• Once the powder has been wetted, the
material is mixed with a vigorous figure
8 motion with the mix being swiped or
stropped between the blade of the
spatula and sides of the mixing bowl
with intermittent rotation of the bowl.
• Mixing time is about 45 seconds.
• Loading: the mixed alginate is
transferred to a perforated tray by using
mixing spatula and is generally added to
the posterior portion of the tray and
pushed towards anterior portion.

56. • Impression making: the loaded tray is carried to the
patient’s mouth to record the impression, the posterior portion
of the tray is usually seated first then the anterior part. The
tray is held gently until the alginate sets.
• Removal : after the seal between the impression and
peripheral tissue is broken the tray and impression should be
removed with a single sudden jerk to minimize permanent
deformation.
• Washing: it should be washed under running tap water and
excess water should be shaken off.
• Disinfection: the impression can be disinfected by 10
minutes immersion or spray with sodium hypochlorite or
glutaraldehyde or iodopher.

57. Properties
• Biological properties: nontoxic and non irritant to the
oral tissues.
• Gelation time:
Type I : fast set 1-2 minutes
Type II : normal set 2-4.5 minutes
Controlling of gelation time
1. By altering W/P ratio or mixing time
2. By adding retarder to the material
3. By altering the temperature
• Permanent deformation: According to ADA
specification no 18 permanent deformation should be
less than 3%
• Elastic Recovery is 97%

58. • Gel strength: 0.343 Mpa
Factors affecting strength.
1. Decrease in w/p ratio within limits increases strength
2. Both under and over spatulation decreases strength
• Tear strength: tear strength varies from 300-700
gm/cm2. it is very low. So use minimum thickness of 3-
5 mm
• Flexibility : 5-20%
• Dimensional stability: dimensionally unstable due to
syneresis and imbibition. So cast should be poured
immediately after taking the impression.
• Impression trays: perforated trays are used for
mechanical interlocking of the material.
• Shelf life: alginate impression material have a shorter
shelf life. They deteriorate rapidly at higher
temperature. Not to stock material more than 1 year

59. Advantages
• Reproduces excellent surface detail.
• High elastic recovery
• Record undercuts
• Comfortable to the patient
• It is hygeinic since fresh material used each time
• It is inexpensive
Disadvantages
• Dimensionally unstable
• Low tear strength
• Cannot be electroplated
• No proper storage medium
• Cannot be added if faulty

60. Modified alginates:
• Dust free or Dust-less alginates:
• Conventional alginates contain diatomaceous earth in the form of fine particles
as filler. However, during storage of the material, these filler particle were
found to settle due to high density leading to inhomogeneous distribution of the
filler. In order to achieve uniform distribution, the container is tumbled before
mixing.
• On opening the container, about 5 to 10% of the filler particles in the form of
dust are evolved. Dust may also be evolved from the material during its initial
mixing with water. It was reported that the size of these particles is similar to
that of asbestos fibers and their prolonged inhalation was reported to cause
silicosis, pulmonary hypersensitivity, and carcinogenesis or fibrogenesis .
• In an attempt to avoid or minimize the dust during manipulation, alginate
powder is coated with de-dusting agent to agglomerate the powder to a more
dense form. In general, glycerin, glycol, polyethylene glycol and/or
polypropylene glycol are used as dedusting agents.

61. • Surface-active substances and hydrocarbons such as squalene,
decane, or specific isoparaffin have also been tried.
• Attempts have also been made to partially substitute diatomaceous
earth as fillers in the alginate.
• Sepiolite, a natural mineral fiber containing magnesium silicate with a
mean particle size of 1 to 40 in about 20% was added to alginate as
a substitute. Sepiolite, when added traps the alginate particles thus
reducing dust generation.
• Tetrafluoroethylene, on the other hand, traps the alginate particles by
forming cow-web like structure due to the stresses applied during
manipulation.
2. Siliconized alginates: alginates modified by the
incorporation of silica particles have been developed.
These are supplied as two pastes, which are mixed
together. Tray and syringe consistencies are
available. They have superior consistency when
compared to unmodified alginates.

62. 4. Alginates in the form of sol : they are
supplied as two paste system. One contains
the alginate sol while the second contains
calcium reactor. They may be supplied in
both tray and syringe viscosities.
5. Modified by the addition of chemical
indicator: the purpose is to indicate different stages
of the manipulation, chemical reaction taking place
and change in PH of the Mix. The indicator
incorporated gives a color change in different stages.
• For example:
violet during spatulation
pink - ready to load
White – material has set

63. 5. Alginate containing disinfectant :Recently
developed alginates contain disinfectant in the
material itself that destroy the microorganisms.
• e.g. COE hydrophilic gel ( GC America)- it’s a dust
less alginate that contains 1 % Chlorhexidine diacetate,
Jeltrate plus antimicrobial alginate ( Dentsply/caulk)
conatins 1.7% didecyl-dimethyl ammonium chloride.

64. Laminate technique ( Alginate- Agar
technique ) :
• In this technique the agar material is injected onto the
prepared teeth and alginate in an impression tray
positioned over it. Alginate gels by a chemical reaction
whereas Agar gels by means of contact with cooler
alginate rather than circulating water. The impression
may be removed in about 4 minutes.
Advantages :
1. Cost of equipment is
lower because only
syringe needed to
heat.
2. Elimination of water
cooled tray
3. Records all the finer
details.
disadvantages :
1. Poor dimensional
stability
2. The bond between
Alginate and Agar is
not always strong.
3. Highly viscous alginate
may displace the Agar
during seating.

65. Duplicating material:
• Both types of hydrocolloid are used in the dental
laboratory to duplicate dental casts or models for the
construction of prosthetic appliances and orthodontic
models.
• Agar hydrocolloid is more popular because it can be
used many times.

66. Elastic
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Addition
Condensation

67. Elatomeric impression materials
• Elastomeric comprise a group of synthetic polymer
based impression materials that are chemically
cross linked when set and that can be stretched
and yet rapidly recover to their original dimensions.
• They are supplied in two component, a base paste
and a catalyst paste ( or liquid) that are mixed
before making impressions.
• They are often formulated in several consistencies,
including extra low, low medium, heavy and putty,
in increasing order of filler content.

68. Polysulfide
• Alternative names:
- Mercaptan impression material-by chemistry
- Thiokol- first manufacturing company.
- Vulcanized impression materials- by
processing technology
• Supplied as two paste in collapsible tubes ( base
and catalyst)

69. Composition
Ingrediant % functions
Moderately low molecular
wt. polysulfide polymer with
terminal –SH groups.
74-80 This is further polymerized and cross-
linked to form rubber.
Moderately low molecular
wt. polysulfide polymer with
pendant –SH groups.
2 Undergoes cross- linking, which
reduces permanent deformation during
removal from the oral cavity.
Reinforcing fillers, eg TiO2,
chalk, lithopone( BaSO4
+ ZnSO4)
16-18 Paste former. Improves strength. Gives
body and control viscosity. Modifies
physical properties
Plasticizers ( Dibutyl
phthalate)
0.5 To confer appropriate viscosity of the
paste.
Base

70. Composition
Ingrediant % functions
Lead dioxide (PbO2) 78% Oxidizing agent. Undergoes
polymerization and cross- linking by
oxidation of –SH group. Gives
characteristic dark brown color to the
paste and has a bad smell.
sulfer 3 To facilitate the reaction or as a
promoter, involve in the setting reaction
Dibutyl phthalate 17 To form a paste with PbO2 and sulfer
Inert oils ( stearic acid) 2 Retarder to control the rate of reaction
Deodorants Trace To offset the unpleasant smell of PbO2
Catalyst

71. Setting reaction
• On mixing the two pastes, the terminal and
pendant –SH groups are oxidized by PbO2 to
produce polysulfide rubber with elimination of
water as a byproduct.
• Chain lengthening- terminal –SH group
• Cross linking – pendant –SH group.

72. Properties
• Non toxic and non irritating to the oral tissues,
• bad smell and odor
• Working time
3-6 minutes
• Setting time
7-10 minutes
Factors affecting setting time:
1. Temperature: in temperature working &
setting time.
2. By altering the base/reactor ratio – but it is not
recommended.
3. Adding a drop of water accelerates the curing rate
4. Addition of retarder such as oleic acid working &
setting time

73. • Permanent deformation
permanent deformation is measured as the % of
deformation that occurs when the test sample is
held under 12 % strain for 30 seconds
Permanent deformation of polysulfide
impression material is 3%
Elastic recovery ER is 97%
• Flexibility
It is the amount of strain produced when the
sample is stressed between 100 -1000 g/cm.
it is approximately 5-10%

74. • Tear strength
Tear strength ofa polysulfide is 4000g/cm.
• Dimensional stability
These material are dimensionally unstable
Because:
1. Polymerization shrinkage occurs during cross linking
2. Evaporation of volatile by product (H20) that causes
shrinkage.
3. After removal from the mouth, incomplete recovery due to
viscoelastic properties.
4. Thermal contraction
• Hardness: hardness of polysulfide material is 30. when
measured with shore A durometer

75. • Disinfection: immerse the impression for
about 10 minutes in 10 % sodium hypochlorite
solution.
• Compatibility with gypsum:
These material are compatible with die stones.
Multiple dies can be poured but the successive
dies are less accurate.
• Shelf life: these materials have got adequate
shelf –life
• Reproduction of details: these materials are
capable of reproducing small lines of 0.025
mm width.

76. Advantages
1. Long working tme
2. High tear resistance
3. High flexibility
4. Inexpensive
5. Long shelf life
6. Impression can be
electroplated
Disadvantages
1. Disagreeable taste
2. Longer setting time
3. Dimensionally unstable
4. Needs a special tray
5. Can stain the cloths
6. Second pour is less
accurate.

77. Condensation silicone
• Also called as room teperature
vulcanizing silicones
• They are supplied as
1) Two paste system ( base paste + reactor paste)
2) Base paste + reactor liquid

78. Composition
Ingrediant functions
Moderately low molecular
wt. Polysilicone polymer
with terminal –OH groups.
Or hydroxyl terminal poly
( dimethyl-siloxane)
It undergoes polymerization and cross
linking to form rubber.
Reinforcing fillers ( 33-35%)
Copper carbonate, colloidal
silica
1. As a paste former
2. Increase strength of set rubber
3. Gives body and controls viscosity
and modifies physical properties.
Base

79. Ingrediant functions
Tri or tertra functional alkyl
silicate or tetra ethyle ortho
silicate.
Acts as a cross-linking agent
.
Tin or stannous octoate
[Sn(C7H5COO)2]
Acts as a catalyst
• To form a paste
• To control the viscosity
Reinforcing filler or
thickening agents ( colloidal
silica)
To indicate uniform mix.
Color pigments To distinguish from the base paste..
Reactor paste

80. Setting reaction
On mixing the two components a reaction begins
immediately in which the terminal hydroxyl groups of
polysilicone prepolymer chain react with cross-linking
agents (tetraethylorthosilicate). Under the influence of a
catalyst ( tin octate)
Ethyle alcohol is a byproduct of the condensation
reaction.

81. Properties
• May be considered as non toxic. Tin octate or
stannous octate may be toxic
• Available in various viscosities like light,
regular, heavy and putty like elastomers.
• They are very hydrophobic and are repelled
by water or saliva hence a dry field of
operation is necessary.
• Working time
2-3 minutes
• Setting time
6-10minutes

82. Factors affecting setting time:
1. Reaction is sensitive to temperature. Cooling the
material or mixing on a cooler glass slab will
increase working and setting time
2. By altering base /reactor ration
• Elasticity: condensation silicones are more ideally
elastic than polysulfides.
• Permanent deformation is 0.7%
• Elastic recovery is 99.3 %
• Flexibility : is 2-7% not very stiff which means it is
not very difficult to remove them from undercuts
without distortion.

83. • Tear strength : tear strength is lower than
polysulfides. 3500 g/cm but they do not tear as
easily as hydrocolloids.
• Dimensional stability : dimensional stability is not
good due to:
1. Large polymerization shrinkage ( 0.6-1%)
2. Loss of volatile reaction byprduct ( ethyl alcohol), which
produces a measurable wt. loss (0.9%)
3. Thermal contraction
• Reproduction of details:
These materials are capable of reproducing lines of 0.025 mm
width

84. • Compatibility with gypsum :
These material are compatible with die stone
• Electroplating:
die can be electoplated with silver or copper. But
because of their dimensional stability after setting,
stone dies are more frequently made than metal
• Hardness: hardness of condensation silicone is 43
measured by shore A durometer.
• Impression trays : stock trays are normally
preferred
• Disinfection: immersing in most of available
antimicrobial solutions for less than one hour.

85. • Color contrast: base paste is colorless. Dyes are
added to the colorless reactor paste to indicate the
completion of mixing.
• Shelf life: limited shelf life because of oxidation of the
tin compound with in the catalyst.

86. Advantages :
1. Adequate working and mixing time.
2. Clean and pleasant odor and no staining .
3. Adequate tear strength
4. Better elastic properties on removal.
5. Available in complete range of viscosities
thus allowing flexibility in choosing and
impression techniques.
6. Less distortion on removal

87. Disadvantages :
1. Poor dimensional stability
2. Adequate accuracy only when poured
immediately.
3. Need for a dry dield of operation since it is
hydrophobic
4. Poor shelf life.

88. Addition silicones
• This material is often called a polyvinyl siloxane
(PVS) or vinyl siloxane (VPS) impressin material.
• In contrast to condensation silicon, the addition
silicone is based on addition polymerization
between divnylpolysiloxane and polymethyl
hydrosiloxane.
• Supplied as two paste system and are available all
four viscosities. Also available as single
consistency called single phase or mono phase and
can be used both as tray and syringe consistency
due to its pseudoplastic nature.

89. Composition
Ingrediant functions
Moderately low molecular
wt. polysilicone prepolymer
with silane terminal group or
poly ( methyl hydrogen
silicone)
• Takes part in the polymerization
reaction
Reinforcing fillers Control viscosity and modifies the
physical properties.
Base

90. Composition
Ingrediant functions
Moderately low molecular
wt. polysilicone prepolymer
with vinyl terminal group or
poly(dimethyl vinyl siloxane)
Reinforcing fillers (powdered
silica)
• Main reactive ingredient
• Takes part in the polymerization
reaction
• Paste former
• Increases strength
• Gives body and control viscosity
• Modifies physical properties
Chloroplatinic acid (H2PtCl6)
Low molecular weight liquid
polymer of the same type as
the base polymer.
Finely divided Pt or Pb
Color pigments
Acts as a catalyst
• Retarder
• Provide working and setting time
To absorb H2 gas evolved or as a
scavenger for H2 gas.
To distinguish it from base paste and
for indicating completion of mixing.
Reactor

91. Setting reaction
• On mixing the two paste, platinum
catalyzed addition reaction occurs
causing coss-linking between the
two types of siloxane prepolymer .

92. Properties
• Biocompatible & causes less tissue reaction than
condensation silicones.
• Do not possess an unpleasant taste or odor and are
acceptable by the patient.
• They are available in complete range of viscosities i.e. light,
regular, heavy and putty body. It helps the operator to
choose the material with suitable flow properties for
example double mix double impression
( putty + light )
• Pseudoplasticity: addition silicone exhibits pseudoplastic
properties , i.e. viscosity gradually decreases as the shear
stress increases.
• Working time
2-3 minute
• Setting time
6-8 minutes

93. • Factors affecting setting time:
1. Increase in either temperature or humidity will
decreases working and setting time
2. Material can be refrigerated before mixing of the
material on a cool glass slab to increase the working
time and setting time.
3. Both working and setting times can be prolonged by
the addition of retarders.
• Elasticity : they are most ideally elastic
• Permanent deformation : is vey less that is 0.07%
• Elastic recovery: is 99.93%
• Tear strength: tear strength is adequate 3500 g/cm
• Flexibility: 2-3 %

94. • Dimesional stability
Dimensional stable because:
1. Clinically set material is so close to being completely
cured.
2. No volatile byproducts
3. Primary dimensional change comes from thermal
shrinkage.
4. Impression does not have to poured immediately.
Most manufacturers claimed that pouring could be
delayed up to 7 days.
• Surface reproduction:
These material are capable of reproducing lines
of 0.025 mm

95. • Hardness: hardness is about 55 when
measured with shore A durometer.
• Compatibility with gypsum:
-hydrophobic
-so it is difficult to wet the surface of
the impression by gypsum slurry.
- use of surfactant
• Electroplating : can be electroplated with
silver and copper to form electroplated dies.
• Disinfection: disinfected by 10-15 minutes
immersion in 2% Glutaraldehyde or 10%
hypochlorite solution.

96. • Impression trays: either stock or
special tray can be used
• Tray adhesive : tray adhesive contains
poly ( dimethyl siloxane ) or other
silicone that react with the impression
material.
• Color contrast: different viscosity of
same material are supplied in different
colors.
• Shelf life: it is about 2 years

97. Advantages:
1. Pleasant to handle
2. Excellent elasticity
3. Shorter setting time
4. Adequate tear strength
5. High dimensional stability
6. Impression can be stored for about 7 days
7. Impression can be electroplated
8. Available in complete range of viscosities
9. Produce a highly accurate impression
10. Multiple accurate dies can be poured

98. Disadvantages:
1. More exoensive especially with automatic
mixing device.
2. Shorter working time
3. May release hydrogen gas on setting and
produce pinpoint voids in the die.
4. High surface tension causes difficulty in
pouring
5. Moisture incompatibility (hydrophobic)
6. Low flexibility value difficult to remove from
undercuts.

99. Polyether impression material
• They are dispensed as three –paste
system ( base + reactor + body
modifier )
• and are available in single consistency
( heavy or regular body)

100. Composition
Ingrediant functions
Moderately low molecular
wt. polyether prepolymer
with ‘imine’ terminal group
Becomes cross-linked to form rubber
Inert fillers ( colloidal silica) Gives body, control viscosity and
physical properties
plasticizers Aids in mixing
Base paste
Ingrediant functions
Ester derivative of aromatic
sulphonic acid ( benzene
sulphonic acid)
Cross linking agent
Inert fillers ( colloidal silica) Gives body, control viscosity and
physical properties
Plasticizers ( glycol ether
phthalate)
To form paste
Reactor

101. Ingrediant functions
Optyl phthalate and 5%
methyl cellulose
To reduce the stiffness
To reduce the viscosity of unset
material
Provides more working time
Body modifier

102. Setting reaction
• When two paste are mixed together a cationic
ring opening addition polymerization occurs.
• Distinct activation, initiation and propagation
stages may be identified in the reaction.
• The reaction is of addition type with no
byproduct being formed.

103. Properties
• The presence of aromatic sulphonic acid
catalyst in the reactor paste causes irritation.
• Hypersensitivity or contact dermatitis.
• Original polyether are supplied as one
viscosity.
• Mixing time
30 – 45 seconds
• Working time
2-4 minutes
• Setting time
6-8 minutes

104. • Elasticity : polyether are slightly elastic they
have slightly higher permanent deformation
than addition silicons.
• Permanent deformation is about 1.1%
• ER is 98.9 %
• Flexibility: polyether are less flexible flexibility
is 2%
• Tear strength: tear strength is lowest 2700
g/cm
• Hardness : hardness is about 84 it is high so
more force is needed to remove the
impression

105. • Dimensional stability : They are dimensional
stable because
1. No volatile byproduct
2. Less polymerization shrinkage
3. High stiffness of the matrial
4. Polyethers exhibits the least amount of
distortion from the loads imposed on the set
material
• Surface reproduction: capable of producing ‘v’
shaped groove of 0.025mm width.
• Compatibility with gypsum: pouring the cast is
easier, polyether are somewhat hydrophilic.

106. • Impression trays: Either stock or special tray
can be used.
• Disinfection: by immersing in 2%
glutaraldehyde solution for less than 10
minutes.
• Shelf –life: is adequate when stored under
normal environmental condition.

107. Advantages
1. Faster working and setting time
2. Less hydrophobic-better wetting
3. Less distortion on removal
4. Good dimensional stability and excellent elastic
recovery
5. Multiple dies can be poured with great accuracy
6. Pseudoplasticity
7. Long shelf life.

108. Disadvantages
• More expensive
• High stiffness value after setting
• Low tear strength
• Impression are difficult to electroplate
• Not available in complete range of viscosities
• Poor dimensional stability under high humid
conditions.
• Catalyst can be sensitizer.

109. Making impression with elastomeric
materials:
• The use of elastomeric impression material to
fabricate gypsum model, casts, and dies
involve six major steps:
1. Preparing a tray
2. Managing tissue
3. Preparing the material
4. Making an impression
5. Removing the impression and
6. Preparing stone casts and dies

110. Preparation a tray
• The use of a custom tray is recommended to reduce
the quantity of material required to make impressions;
thus any dimensional change attributed to the material
are minimized.
• A custom tray allow a uniform distribution of impression
material between the tray and the object, which also
improve accuracy.
• The use of custom trays for polyether and addition
silicone impression is not critical, since these material
are stiffer and have less polymerization shrinkage than
the polysulfide material.
• Since the less material in the custom tray reduces the
compressibility of the impression, which can make
removal of the impression tray more difficult.

111. Adhesion to the tray
• Elastomers are non-adhesive to the trays. Adhesion
can be achieved by the application of adhesive to the
tray prior to the insertion of the impression material.
• Composition to tray adhesive:
• Polysulfide: Butyl rubber or styrene-acrylonitrile
dissolved in a suitable volatile solvent such as
chloroform
• Polysilicones: poly( dimethyl siloxane) or similar
reactive silicone, which acts as an adhesive for the
rubber and ethyl silicate to create a physical bond with
the tray.
• For putty elastomers, retension can be achieved by
using perforated trays ( mechanical locking)

112. Tissue management
• The margin of the tooth preparation for fixed prosthesis
often extend to or below the free margin of the gingiva.
• To ensure access for the tooth preparation and for the
making the impression it is necessary to displace
gingival tissue, control gingival hemorrhage and control
sulcular fluids
• Methods of gingival displacement
1. Use of gingival retraction cord
2. An electrosurgical unit
3. Or a soft laser can also be used

113. Manipulation of impression materials
• Currently, elastomeric impression
material are supplied for three modes
of mixing
1. Hand mixing
2. Static mixing
3. Dynamic mechanical mixing

114. Hand mixing
• The user should dispense the same length of materials
onto a mixing pad or glass slab,
• The catalyst paste is first collected on a stainless steel
spatula and then spread over the base paste.
• The mixture is then spread over the mixing pad. The
mass is then scraped up with the spatula blade and
spread uniformly back and forth on the mixing pad.
This process is continue until the mixed paste is
uniform in color.
• The two putty system available for condensation and
addition silicone are dispensed by volume using an
equal number of scoop of each material.
• the best mixing technique is to knead the material with
one’s finger until a uniform color is obtained.

115. Static mixing
1. The device used to accomplish this mixing is a gun
for compressing material in a two cylinder cartridge,
which contains the base and catalyst separately, as
well as a mixing tip.
2. The mixing tip is made of helical mixer element in a
cylindrical housing.
3. The mixer element are a series of alternating right
and left turn 180º helixes positioned so that the
leading edge of one element is perpendicular to the
trailing edge of the next.

116. Dynamic mechanical mixing
• The device uses a motor to drive parallel
plungers, forcing the material into a mixing tip
and out into an impression tray or syringe,
meanwhile the motor driven impeller, which is
inside the mixing tip, mixes the material as
they are extruded through the tip.

117. Making an impression
1. Multiple mix technique: this technique is also
called as “ double mix –single impression technique.
• Heavy body –as tray material
• Light body – as a syringe material
• Special tray is required
• Stages :
1. Light body is mixed first and injected to impression
area
2. Meanwhile the heavy body is mixed on a glass slab or
paper pad, loaded on the tray and placed over the
light body material.
3. The light and heavy body materials sets together to
give a single impression in which light body supported
by heavy body and tray. Light body records all the
fine details; whereas heavy body assures optimum
accuracy and dimensional stability

118. 4. When both materials have set together, the impression is
removed with a single sudden jerk to minimize distortion
and is checked for all details.
2. Putty wash technique: also called as double mix-
double mix technique or reline technique
• Putty – for primary impression
• Light body – for secondary impression.
• This technique is most widely used with condensation
silicone and addition silicones
• Stages:
1. Primary impression: putty material is placed in perforated
stock trays ( adhesive coated ) and the impression is
made before preparing the teeth. Space for wash material
is provided either by cutting away some of the putty
material from the original impression or by using a spacer
between the putty and the teeth.

119. 2. Secondary impression:
After tooth preparation, light body is mixed and injected into the
cavity preparation ( sometimes even into the putty impression
tray).
The tray with primary impression is reinserted which acts as a
custom tray for light body.
And held gently until material sets. Then the impression is
removed with a single sudden jerk.

120. 3. Single mix – single impression technique:
• Single consistency ( regular or heavy ) having
pseudoplastic property ( monophasic material )
• Used with addition silicone and polyethers as they have
pseudoplastic property
• This technique require a special tray
• When subjected to a low shear rates during spatulation
or while an impression is made in a tray they have high
viscosity and possess body in the tray.
• The same material can also be used as a syringe
material because a higher shear rates, as they pass
through the syringe tip viscosity decreases.

121. References……
1. Phillips science of dental material 12th edition
2. Craig & powers restorative dental materials 11th edition
3. S. Peter, V. Reiner, Dust-free alginate impression materials, U.S. Patent:
4695322 (1987).
4. Watanabe, Low dusting powdery alginate impression material for dental use,
U.S. Patent: 4543372 (1985).
5. Watanabe, Low dusting powdery alginate impression material for dental use,
U.S. Patent: 4543372 (1985).
6. Chen SY, Liang WM, Chen FN. Factor affecting the accuracy of elastomeric
impression materials. J Dent 2004;32:603-9.
7. Baker PS, Plummer KD, Parr GR, Harry Parker M. Dermal and mucosal
reactions to an antimicrobial irreversible hydrocolloids impression material: A
clinical report. J. Prosthe Dent. 2006;95:190-3.
8. Nathaniel C Lawson, John O Burgess, Mark S Litaker. Tensile elastic
recovery of elastomeric impression material. J Prosthe Dent 2008;100:29-33
9. Stober T, Johnson GH, Schimitter M. Accuracy of the newly formulated vinyl
siloxane ether elastomeric impression material J Prosthet
Dent.2010;103:228-39
10. Peregrina A et al. The effect of different adhesives on vinyl polysiloxane bond
strength of two tray material.
11. Shalinie king, Determining the complex modulus of alginate irreversible
hydrocolloids dental material. Dent mater. 2008;24:1545-8