2. Elastomeric impression materials
• These are basically synthetic rubber based materials which were
initially called as Rubber Impression materials but currently they are
known as Non aqueous Elastomeric Impression materials
• A material that is used when an extremely accurate impression is
essential. The term elastomeric means having elastic or rubberlike
qualities.
•
3. Classification of Elastomeric impression materials:
• Till now the Elastomeric impression materials are devided into
3types based on the material used
• 1-polysulfied
• 2-polyether
• 3-silicone
- Addition
-condensation
•
4. Polysulfide Impression Material
These materials are also known as thiokol rubbers as they
are derived from thiols
Base: polysulfide. and an inert filler, such as titaniumdioxide
-activator paste :(containing lead dioxide, which gives the
distinctive brown colour, sulphur and dibutyl or
dioctylphthalate).
Catalysts: Copper hydroxides, zinc peroxide, organic
hydroperoxide
fig (1)
5. • Indications
• –complete denture
• –removable & fixed partial denture
• Advantages
• Good wettability
• Good surface detail
• Easy to remove
• High tear strength
• Disadvantages
• a long working and setting time (8 to 10 minutes)
• High permanent deformation
• Unpleasant taste and odour
• Must pour within 1 hour
• Take care when disinfecting
6. Manipulation and Technique Considerations for
Polysulfide Material
-Dispense pastes at the top
of the mixing pad.
-Mix pastes with the tip of
a spatula to incorporate the
material first.
• Transfer the material to
the fresh surface of the mixing pad
. and Thinnen polysulfide film
fig (2)
7. • Impression should be removed quickly after setting-do
not rock the tray
• The setting process or the polysulphide impression
material is highly susceptible to changes in
environmental conditions, such as temperature and
humidity variation
fig (3)
8. POLYETHER IMPRESION MATERIAL
Composition:
• The polyethers come as two-paste system
• Base paste : imine terminated polymer(polyether)
• Accelerator paste:Alkyl aromatic sulfonate
Indications
• –crown and bridge
• –bite registration
Advantages
• 1- Hydrophilic
• 2-Good surface detail
• 3-Good dimensional accuracy
• 4-Good resistance to deformation
• 5-Highly acceptable to patient
• 6-good dimensional stability
fig (4)
9. Disadvantages:
• 1-stiffness requires blocking undercuts Difficult to remove and
thus multiple casts can’t be poured
• 2-High permanent deformation
• 3-Swells in disinfectants or moist environments
• 4-low tear strength
• 5-Take care when disinfecting
• 6-slightly more expensive
10. Silicones
• There are two important groups of silicone impression materials.
One group is known as the condensation-cured silicones and the other
as the addition-cured silicones. Both are based on the polydimethyl
siloxane polymer but have different end groups, giving rise to
different curing mechanisms.
Syringe tray special tray stock tray
fig (5)
11. CONDENSATION SILICONES
• Also known as conventional silicones. These materials are based on a
polydimethyl siloxane polymer with hydroxyl terminal groups.
Composition:
• Base paste : Containing silicone fluid and a filler.
• Activator paste: tetra-ethyl silicate (the crosslinking agent).
• It is important that the amount of activator paste used is carefully
controlled. Insufficient TES gives rise to an incomplete cure, leaving a
material with poor mechanical characteristics, such as high permanent
set. Conversely an excess of TES also gives an incomplete cure, leaving
many unreacted ethyl end groups
12. • Advantages:
• .1- Good surface detail (dry surfaces)
• 2-Good dimensional accuracy
• 3-low permanent deformation
• 4-Wide range of viscosities
• 5-Easy to disinfect
• 6-Highly acceptable to patient Pleasant odor & no staining
.Disadvantages:
• 1-Hydrophobic
• 2-Shrinks on storage
• 3-Must pour within 1 hour
• 4-low tear strength
•
13. Addition-Cured Silicones
• These materials are similar to the condensation-cured silicones, in
that they are also based on a polydimethyl Siloxane polymer;
however, in this case the terminal groups are vinyl’s group
The addition-cured silicones present as a :
• Base paste :polyvinyl siloxane, silanol and a filler
• Catalyst paste: polyvinyl siloxane, platinum catalyst and a filler.
fig (6)
15. • Indications
• –crown and bridge and implant
• –denture
• –bite registration
CONSISTENCIES
Putty The addition-cured silicones - wash
fig (7)
16. • The elastomeric impression materials are available in a range of
viscosities, depending on the amount of filler that is incorporated
• Polysulphides : heavy, medium and light bodied impression ,paste
forms are available, there is no putty version.
• Polyethers
• These materials are available only in a single viscosity and can be
used in a special tray using a single viscosity mix.
• CCS & ACS
• A wide range of viscosities are available, varying from a putty, to a
heavy, a medium and a light bodied material Thus, these materials can
also be used in a wide range of impression techniques.
17. Mechanical Properties
1-Stiffness
• The stiffness of the impression material once it has set can be a major
consideration in the case with which it is removed from undercuts.
PS < CCS < ACS < PE
2-Permanent Set
• Ideally, when the impression is removed from an undercut, the deformation
that results should be totally and immediately recoverable. it is important that
the elastomeric materials are removed from the mouth by a sharp tug.
PS > PE > CCS > ACS
3-Tear Strength
• The tear strength of the impression material is also important when an
impression is taken of the dentate patient.
PS > PE > CCS > ACS
• too high a tear strength may give rise to difficulties in removing the
impression from the mouth in Cases where the impression material has flowed
into the interdental spaces.
18. • 4-Reproduction of Surface Detail
All of the elastomeric impression materials are able to reproduce the details
of the surface very accurately when a low-viscosity material is employed.
• the lower the viscosity, the better the reproduction
• 5-Dimensional Stability and Accuracy
Is affected by the amount of filler present, in that the higher the filler
loading, the smaller the shrinkage
• The amount of light bodied material used should always be kept to a
minimum.
PE =ACS < PS < CCS
19. MIXING SYSTEMS
hand mixing,
static Automixing,
dynamic mechanical mixing
• Hand mixing
• hand mixing is with the two putty systems, offered both with
condensation and addition silicones. Scoops are supplied by the
manufacturer for dispensing, and the putties are most often
kneaded with fingers until free from streaks.
20. Static Automixing
fig (8)
The base and catalyst are in separate cylinders of the
plastic cartridge.
The cartridge is placed in a mixing gun containing two
plungers that are advanced by a ratchet mechanism to
extrude equal quantities of base and catalyst
21. • dynamic mechanical mixing
• The catalyst and base are
supplied in large plastic bags
housed in a cartridge, which is
inserted into
the top of the mixing machine.
A new, plastic mixing tip is placed
on the front
of the machine, and when
the button is depressed
parallel plungers push against
the collapsible plastic bags,
thereby opening the bags and
forcing material into the dynamic mixing tip
fig (9)
22. Impression Technique
Twin-Mix Technique
Two-Stage With Spacer Technique
Two-Stage Without Spacer Technique
Twin-Mix Technique
fig (10)
23. • 1-The potential problems with this technique are
related to the removal of the addition-cured silicones
• 2- Another problem that may arise is that the putty
may displace the wash in areas where surface accuracy is
desirable.
Two-Stage With Spacer Technique
•
fig (11)
24. • more of the wash material is required in this
technique than in the twin-mix approach, and this means
that there is more setting shrinkage, as the wash has a
much lower filler content. This is especially the case
with the condensation-cured silicones, which also show
more shrinkage on storage.
• Two-Stage Without Spacer Technique
The two-stage without spacer technique is inappropriate for
addition-cured silicones because the primary impression
would be extremely difficult to remove from undercuts,
once it has set, due to the high stiffness of the putty
25. • DISINFECTING IMPRESSIONS
For addition silicone (hydrophobic) soak sodium hypochlorite
(1:10concentration) for 3 minutes
Polyether materials cannot be immersed in disinfectants due to
potential for absorption and distortion only spray
