Elastomeric impression materials include polysulfide, condensation silicone, addition silicone, and polyether rubbers. They set via polymerization reactions, with setting times of 8-12 minutes on average. Polysulfide and condensation silicone set via condensation reactions producing water or alcohol as byproducts, while addition silicone and polyether set via addition reactions without byproducts. Polysulfide has the highest detail reproduction but all materials exhibit some polymerization shrinkage. Materials are available in light, medium, heavy or putty consistencies for use with stock or custom trays. Proper manipulation is required for accurate impressions.

1. Elastomeric Impression
Materials

2. Elastomeric =
Rubber-like polymers that show an
elastic behavior at the time of load
application
These polymer molecules have
weak interaction in between
(Van der Wall forces), although
they are tied together in 3D
network.
On stretching (on loading) chains
uncoil
At rest (off loading) chains snap back
ChemicalNature

3.  Higher tear strength
 More stable dimensionally in
storage
(No Synersis, Imbibation or Evaporation)
 Ability to be electroplated
But, Quite Expensive !!!!But, Quite Expensive !!!!
Incomparisonto
hydrocolloids

4. Elastomeric
impression
materials
Polysulfide
(hydrophobic)
Silicones
Polyether
(hydrophilic)
Condensation
Silicone
(hydrophobic)
Addition
silicone
Hydrophobic
type
Hydrophilic
type
Fourdifferent
types

5. Presentation
forms Materials’
Consistency
Light
Medium
Heavy
Putty
Silicone materials only

7. Polysulfide RubberPolysulfide Rubber
Impression MaterialImpression Material

8.  CHEMISTRY
A. Composition:
 Base paste
1. LMW Polysulfide with two terminal and one pendant
SH groups
2. Fillers (Titanium dioxide)
3. Plasticizer (Dibutyl phethalate)
 Catalyst paste
1. Lead dioxide (Brown) or organic peroxides (Gray)
reactor
2. Fillers (Titanium dioxide)
3. Plasticizer (Dibutyl phethalate)
Polysulfide
Rubber

9. Polysulfide
Rubber
B. Setting Reaction:
+Pb+H2o
HS----R----SH HS----R----SH
SH SH+
PbO2
+Pb+H2o
HS----R----SH HS----R----SH
SH SH+
PbO2
HS----R----SH HS----R----SH
SH SH+
PbO2
 Condensation polymerization
(exothermic + shrinkage) with
releasing of H2O as reaction
by-product
 It occurs as a series of simple
oxidation reactions
 Oxidation of terminal SH
groups  polymer chains
 Oxidation of pendent SH
groups  Cross-linking

10.  Material sets via condensation polymerization
reaction
 Water is the reaction by-product
 Evaporation of water + polymerization shrinkage 
Dimensional changes in storage
 Water could cause air bubbles in stone cast
 Polysulfide is hydrophobic, and can be electroplated
 Lead dioxide is toxic and has bad smell, so it
has been replaced in recent products by
peroxide compounds
Polysulfide
Rubber
 OBVIOUS CHARACTERS

12. Condensation SiliconeCondensation Silicone
Impression MaterialImpression Material

13.  CHEMISTRY
A. Composition:
 Base paste
1. LMW silicone polymer with terminal OH groups
2. Fillers (Colloidal silica or titanium dioxide) (white)
 Catalyst paste
1. Alkyl silicate (Cross linking)
2. Tin dilaurate or Stannous octoate (Activator)
Condensation
Silicone

14. HO Si - O - Si OH +
CH3
CH3 CH3
CH3
Si
C2H5OC2H5O
C2H5O C2H5O
C2H5OH+
HMW Silicon Polymer Ethyl Alcohol
Dimethyl Siloxane Alkyl Silicate
Stanous
Octoate
HO Si - O - Si OH +
CH3
CH3 CH3
CH3
Si
C2H5OC2H5O
C2H5O C2H5O
C2H5OH+
HMW Silicon Polymer Ethyl Alcohol
Dimethyl Siloxane Alkyl Silicate
Stanous
Octoate
HO Si - O - Si OH +
CH3
CH3 CH3
CH3
HO Si - O - Si OH +
CH3
CH3 CH3
CH3
Si
C2H5OC2H5O
C2H5O C2H5O
Si
C2H5OC2H5O
C2H5O C2H5O
C2H5OH+
HMW Silicon Polymer Ethyl Alcohol
Dimethyl Siloxane Alkyl Silicate
Stanous
Octoate
B. Setting Reaction:
 Condensation poly-merization (exothermic + shrinkage)
releasing C2H5OH as reaction by-product
 It occurs as a series of cross-linkage of siloxane polymer
to alkyl silicate in presence of the activator, to form a 3D
polymer network
Condensation
Silicone

15.  Material sets via condensation polymerization
reaction
 Ethyl alcohol is the reaction by-product
 Evaporation of alcohol + polymerization shrinkage 
Dimensional changes in storage > that of polysulfide
 Alcohol could cause air bubbles in stone cast
 Cond. silicone is hydrophobic, and can be
electroplated either with silver or copper
Condensation
Silicone
 OBVIOUS CHARACTERS

17. Addition SiliconesAddition Silicones
Impression MaterialsImpression Materials

18. AdditionSilicones  CHEMISTRY
A. Composition:
 Base paste
1. Poly methyl hydrogen siloxane (Hydried or silane
terminated silicone)
2. Other Siloxane pre-polymers
3. Fillers
 Catalyst paste
1. Divinyl poly(dimethyl siloxane)
2. Platinum salt activator (Chloroplatinic acid)
3. Siloxane pre-polymers
4. Fillers

19. B. Setting Reaction:
 Addition polymerization (exothermic + shrinkage) with no
release of by-product
 It occurs as a series of cross-linkage between vinyl-
terminated silicon and silane-terminated (hydried) silicon
molecules, in presence of the catalyst (platinum salt) to
form a 3D polymer network
 A side reaction (Releasing hydrogen gas  Air bubbles in
gypsum cast) may occur if :
1. No balance between vinyl siloxane and the hydried silicone
2. Moisture react with hydrides of the base polymer
 Adding noble metal (platinum or palladium) to the
composition will act as hydrogen absorber
AdditionSilicones

20.  Adding surfactants (surface tension reducing
agents) to the composition of add. silicone help
turns the material to be hydrophilic (water lover)
 Advantages:
1. Better wetting of soft tissue  registration of better details
2. ↓ Air bubbles in gypsum cast
 Disadvantages:
1. Difficult to be electroplated
2. Setting reaction could be retarded in presence of sulfur (in
latex gloves) or sulfate compounds (in gingival retraction
cords)
 HYDROPHILIC SILICONEAdditionSilicones

21.  Material sets via Addition polymerization reaction
(No by-product)  More dimensionally stable than
condensation-polymerized materials
 Hydrogen gas may release from a side reaction in
presence of moisture or imbalance of the reactants.
But, adding noble metal to the composition prevents
the release of hydrogen gas  no air bubbles in the
gypsum cast
 Add.silicone is hydrophobic and can be
electroplated, however adding of surfactants turns
the material hydrophilic
AdditionSilicones
 OBVIOUS CHARACTERS

23. Polyether RubberPolyether Rubber
Impression MaterialImpression Material

24.  CHEMISTRY
A. Composition:
 Base paste
1. LMW polyether with terminal imine groups
2. Filler (colloidal silica)
2. Plasticizer (dibutyl phethalate or glycoether)
 Catalyst paste
1. Aromatic sulfonate reactor (Sulfonic acid ester)
2. Fillers
3. Plasticizer
PolyetherRubber

25.  CHEMISTRY
B. Reaction: (Cont.d)
 Material sets via ring opening addition poly-
merization reaction (No by-product) of imine-
terminated polyether with the aromatic sulfonate
 LIGHT-CURED POLYETHER
 It is based on polyether-urethane dimethacrylate,
photo-initiator, accelerator, and silicone filler (has
refractive index similar to resin that helps in
maximizing the depth of curing)
 This material is no longer be used
PolyetherRubber

26.  Material sets via Addition polymerization reaction
(No by-product)  More dimensionally stable than
condensation polymerized materials
 Set material is so stiff (as a result of high rate of
crosslinking), so tray adhesive must be used to
retain the material within the tray at the time of
removing an impression
 Polyether is hydrophilic and can absorb water in
wet condition (swelling), accordingly
 Can not be electroplated
 should be stored in dry environment to preserve its
dimensional accuracy
 OBVIOUS CHARACTERSPolyetherRubber

27. Comparative PropertiesComparative Properties
of Elastomeric Impressionof Elastomeric Impression
MaterialsMaterials

28.  Biological properties:
1. Lead dioxide (polysulfide) is toxic, but following
the manufacturer’s instruction will decrease this
risk
2. Alcohol by-product (cond. Silicone) is irritant to
oral soft tissues
3. Aromatic sulfonate (polyether) is irritant, but
proper mixing will decrease this irritability
Comparative
Properties

29.  Interfacial properties:
1. Hydrophilicity…
 Polysulfide, cond. Silicone, & add. Silicone are
hydrophobic
 Hydrophilic silicone and polyether are Hydrophilic
2. Compatibility with model and die materials...
 Hydrophilic materials can not be electroplated
 Polysulfide could be electroplated with silver, while
silicones could be electroplated either with silver or
copper
 hydrophobic materials may cause air bubbles in stone
casts
Comparative
Properties

30.  Interfacial properties: (cont.d)
3. Separating media…
 There is no need (elastic materials) for separating
medium before pouring the cast
4. Detail reproduction…
 Although, hydrophilic materials show better
registration of details than hydrophobic ones,
Polysulfide is the best detail reproducer due to its
higher flow rate
Comparative
Properties

31.  Mechanical properties:
1. Flexibility...
Polysulfide > Cond. Silicone > add. Silicone > polyether
2. Flow...
Polysulfide > Cond.silicone > Polyether > Add. Silicone
3. Permanent deformation…
Polysulfide > Cond.silicone > Polyether > Add. Silicone
4. Tear strength…
Polyether > polysulfide > silicones
5. Recovery…
Rubber materials are viscoelastic, so impressions should
be poured 30 min after removal from the patient mouth
in order to get the whole elastic and delayed recovery of
imp.mat.
Comparative
Properties

32.  Chemical properties:
1. Dimensional changes…
Cond. silicone > polysulfide > Polyether > add silicone
 All materials are associated with setting (polymerization)
shrinkage
 All condensation polymerized materials are less stable in
storage as a result of evaporation of the reaction by-
product
2. Odor…
Lead dioxide-containing polysulfide has bad smell
Comparative
Properties

33.  Practicability:
1. Mixing time... (45 sec.- 1 min.)
2. Working time... (average 5 min.)
3. Setting time... (average 8-12 min)
4. Coast... higher than hydrocolloids
5. Shelf life…storage in refrigerator elongate the
shelf life
6. Disinfection… could be done either by spray or
short immersion technique using NaOCl, Iodofore or
Glutaraldehyde. Care should be expressed with
hydrophilic materials (not immersed for long time)
Comparative
Properties

34. Materials’ ManipulationMaterials’ Manipulation
Manipulation

35.  Mixing:
1. Using paper pad (Glass slab) and Spatula
Light, medium and heavy consistencies
2. Hand Kneading
Heavy or putty consistency
3. Automixer and Dispenser
Cartridge form only (Light, medium, heavy)
4. Automatic mixing
All consistencies, special electric mixer + special material form
Manipulation

36. Manipulation

37.  Trays:
1. Stock tray...
 Used with heavy and putty consistency
 Retention come through; tray perforations, rim locks, or tray
adhesive
2. Special tray…
 Used with light and medium consistency
 Retention comes from; tray perforations and tray adhesive
3. Wash impression...
 Some times heavy or putty impressions act as special tray for
light consistency material
Manipulation

38.  Uses:
1. Impression making...
 Copper ring impression
 Monophase impression
 Double mix single phase impression
 Double mix double phase impression (over-wash impression)
 Closed mouth-double arch impression
2. Occlusal bite registration…
A specially supplied rubber material is used for this purpose
(commonly cartridge form)
Manipulation

39. Your CommentsYour Comments
are appreciatedare appreciated