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.
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
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
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
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
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
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
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
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