4. Polyether
Composition
Setting Reaction
Properties of clinical interest
Advantages & Disadvantages
General properties of elastomeric impression materials
Working and setting time
Dimensional Stability
Reproduction of oral structure details
Disinfection
Tear strength
Biocompatibility
Shelf life
Effects of mishandling
Recent Advances
References
5. INTRODUCTION
The function of an impression material is to accurately
record the dimensions of oral tissues & their inter
relationship.
In the making of an impression , a material is placed
against the oral tissues to set.
The impression gives negative reproduction these
tissues.
Various materials are available for the same which are
either chemically or thermally induced ;rigid or elastic.
6. History
• Historically impression
making was accomplished
with inelastic materials for
both soft & hard tissues.
• Hydrocolloid was initially
introduced to make
impressions of hard tissues
in place of inelastic
materials.
7. HISTORY
After world war II , advances in
polymer technology brought to
the dental profession a group
of synthetic rubbery materials
called ELASTOMERS.
Polysulfides at the beginning
of the fifties (1950), were the
first elastomeric impression
material used in the world of
dentistry.
8. ELASTOMERS
Elastomers refer to a group of rubbery polymers,
which are either chemically or physically cross
linked.
They can be easily stretched & rapidly recover their
original dimensions when applied stress is released.
Most of them are two component system supplied in
paste foam in which setting occurs through
Chain lengthening polymerization
Chemical cross linking
9. Chemically , there are four kinds of elastomers used
as an impression materials :-
1) Polysulphides
2) Condensation -polymerizing silicone
3) Addition -polymerizing silicone
4) Polyether
10. According to viscosity they are classified as
Light body
Medium body / Regular body
Heavy body
Putty
11. Regardless of type all elastomeric impression materials
are supplied as two components system. i.e. Base and
Catalyst
Light and regular body materials supplied in cartridges
to be used with auto mixing tips and dispensers.
Putty consistency is supplied in jars.
13. POLYSULFIDE RUBBER IMPRESSION
MATERIAL
The first rubber impression material was Polysulfides.
The main component of polysulfide materials is a
multifunctional mercaptan (-SH) or polysulfide
polymer.
It was flexible but did not have the major dimensional
changes as in alginate & agar during storage.
Furthermore, the material was much stronger & more
resistant to tearing than alginate & agar.
They are classified as light , regular, or heavy bodied,
depending upon their viscosity & flow under load.
14. COMPOSITION
Base
Multifunctional mercaptan (-SH) called POLYSULFIDE
POLYMER as a major ingredient
INERT FILLER – lithopone , titanium dioxide , zinc sulfate ,
copper carbonate or silica.
PLASTICIZER – dibutyl phthalate
ACCELERATOR - Sulfur
Catalyst or accelerator
Lead dioxide with or without manganese dioxide
FILLER and PLASTICIZER as in base paste.
OLEIC and STEARIC acid as retarder.
15. Setting reaction
Mercaptan + lead oxide Polysulfides + H2O
Hot and humid conditions will accelerate the setting
reaction.
16. Properties of clinical interests are
Working time of the material is between 4 – 6
minutes.
Final setting time is usually in the range of 12 – 16
minutes from the start of mixing.
The permanent deformation values are between 2% to
3%, obtained when the material is held under 12%
compression for 30seconds.
This indicates that the Polysulfides are not perfectly
elastic & compression during removal should be
minimum.
17. Polysulfides shrink 0.3-0.4 % during first 24 hours
, & thus models & dies should be prepared
promptly.
It is hydrophobic - mouth should be dried thoroughly
before making an impression
They provide excellent reproduction of details.
They are highly compatible with model plaster &
high strength stones.
Impressions can be metallized by electroplating.
They have excellent shelf life.
18. ADVANTAGES
High tear strength
Comes in a number of different viscosity's
Long working time
Long shelf life
DISADVANTAGES
Lead oxide in base paste may have toxic effects
Unpleasant rubbery smell
Can only be used in a special tray
Stretching leads to distortion
19. SILICONE RUBBER IMPRESSION
MATERIAL
The disadvantages of the Polysulphides material are
their objectionable odor, the staining of clothes by the
lead oxide, the amount of effort required to mix the
base with the accelerator , the rather long setting
times, the moderately high shrinkage on setting , & the
fairly high permanent deformation
This material developed to over come some of the
disadvantages of poly sulfide.
20. Based on the type of polymerization reaction
1) Condensation silicones
2) Addition silicones
These names identify the type of polymerization
reaction
24. The working time is shorter (45 secs) for silicones
compared with the polysulphides , & the setting times
likewise are shorter ,in the range of 6 to 8 minutes.
The silicone impression materials are very
hydrophobic , hence dry areas of mouth are required
for the impression.
‘Blow holes‘ are likely to occur in the impression as the
material fails to drive away the residual moisture.
Tear strength is lower than polysulfides.
permanent deformation due to shrinkage caused by
the evaporation of ethyl alcohol is also high (1-3%). So
cast should be poured immediately.
25. Advantages
custom tray not required
Clean & pleasant
Good working time
Disadvantages
High polymerization shrinkage
Volatile by-product
Low tear strength
Hydrophobic
27. ADDITION SILICONE
The addition silicones are frequently called polyvinyl
siloxane or vinyl polysiloxane impression material
In contrast to the condensation silicones, the addition
reaction polymer is terminated with vinyl groups & is
cross linked with hydride groups activated by a
platinum catalyst
29. Setting reaction
Vinyl siloxane + Silane siloxane Silicone rubber
No volatile byproducts are formed in this reaction , &
minimal dimensional changes occur during
polymerization.
If proper balance is not maintained (due to incorrect
proportion or impurities) , hydrogen gas is produced
which results in pin point voids in stone models.
30. • Pleasant odor and color
• Excellent reproduction of surface details
• Mixing time of 45 secs ,setting time of 5-9 mins.
• The production of little or no byproduct in the cross-
linking reaction of the addition curing material results in
a very stable impression
• Stone pouring delayed by 1-2 hours
• Good shelf life of 1-2 yrs
• Good tear strength (3000gm / cm2)
31. Silicone elastomers are inherently hydrophobic material -
a characteristic which can cause imperfections in
impressions if the area to be recorded are not thoroughly
dried.
Surface active agents have been incorporated into the
materials in order to make the material more hydrophillic.
This surfactant migrates to surface of impression material
and has its hydrophilic segment oriented towards the
surface – making the surface more wettable by water.
32. ADVANTAGES
Ease of use
Fast setting
Good shelf life
Dimensionally stable
Excellent surface detail
DISADVANTAGES
Hydrophobic
No flow if sulcus is moist
Low tear strength
High cost
34. POLYETHER
Polyether elastomeric impression material was
introduced in Germany in the late 1960s
It has good mechanical and dimensional stability
But the working time is short and it is very stiff and
expensive.
35. Base Paste
Poly ether polymer
Colloidal silica (filler)
Glycol ether or phthalate (plasticizer)
Accelerator paste
Aromatic sulfonate ester (cross-linking agent)
Colloidal silica (filler)
Phthalate or glycol ether (plasticizer)
Available as 3 viscosities: light, medium & heavy bodied.
36. Setting reaction
It is a polyether based polymer that is cured by a
reaction between aziridine rings, which are at the end
of the branched polyether molecules
The main chain is probably a copolymer of
ethylene oxide & tetrahyrdofurane
Polyether + Sulfonic ester Crosslinked rubber
37. Mixing time is 30 secs, setting time of 8 mins
Dimensional stability is very good.
Pleasant odor and taste
They have adequate tear resistance & elastic properties
approaching those of the silicones
Polyethers are hydrophilic & hence can be used in
where effective moisture control is difficult
38. Advantages
Least hydrophobic
Good stability
Accuracy
Ease of use
Disadvantages
May cause allergic reaction due to the sulphonic acid
ester.
Poor tear strength.
Rapid setting time (ie short working time).
Stiff set material (sometimes hard to remove from
mouth).
39. Properties of elastomeric
impression materials
Working and setting times
Dimensional stability
Reproduction of oral structure details
Disinfection
Tear strength
Biocompatibility
Shelf life
Effect of mishandling
40. Working and setting times
Mean working time (min) Mean setting time (min)
Impression
Material
23.C 37.C 23.C 37.C
Polysulfide 6.0 4.3 16.0 12.5
Condensation
Silicone
3.3 2.5 11.0 8.9
Addition
Silicone
3.1 1.8 8.9 5.9
Polyether 3.3 2.3 9.0 8.3
WT : Addition silicone < Polyether < Condensation Silicone < Polysulfide
ST : Addition silicone < Polyether < Condensation Silicone < Polysulfide
41. DIMENSIONAL STABILITY
There are 6 major sources of dimensional changes.
1. Polymerization shrinkage
2. Loss of a condensation reaction by-product (water or
alcohol).
3. Thermal contraction from oral to room tempreture.
4. Absorption of water or disinfectant over a period of time.
5. Incomplete recovery of deformation because of
viscoelastic behaviour.
The change in linear contraction is of greater magnitude
for polysulfide and condensation silicone materials than
for poly ether and addition silicone.
Linear Contraction : Addition Silicone < Polyether < Polysulfide < Condensation Silicon
42. REPRODUCTION OF ORAL
STRUCTURE DETAIL
The surface reproduction test reveals that elastomers
can record details to the finest degree.
But these details may not always reproduce on stone
die or cast which may be because of the
hydrophobicity of some of these materials.
43. DISINFECTION
Material Method Recommended
Disinfectant
Comments
Polysulfide Immersion Glutaraldehyde,
Chlorine compounds,
Iodophors & Phenolics
Disinfectants
requiring >30 mins
exposure times are not
recommended
Condensation
Silicone
Immersion Same as Polysufide Disinfectants
requiring >30 mins
exposure times are not
recommended
Addition
Silicone
Immersion Same as Polysufide Disinfectants
requiring >30 mins
exposure times are not
recommended
Polyether Immersion with
caution – use
disinfectant for short
exposure time <10
mins
Chlorine compounds
or Iodophors
Short term exposures
are essential to avoid
distortion
44. Tear Strength
The amount of force needed to tear a specified test
specimen divided by the thickness of specimen is
called the Tear Strength.
The tear strength from lowest to highest is as follows:
Silicones ( adidition and condensation ) <
polyether < polysulfide
Polysulfides have susceptibility to distortion rather
then tear.
45. Biocompatibility
Despite the fact that the probability of allergic or toxic
reactions from impression materials or their
components is small; the most likely elastomer
induced biocompatibility problem occurs when a
segment of impression material is lodged in patient’s
gingival sulcus.
Comparing the cell cytotoxicity for different
impression materials reveals that
Polysulfide – lowest cell death count.
Polyether – highest cell cytotoxicity scores.
46. SHELF LIFE
The materials do not deteriorate when stored in dry ,
cool environment.
However , if one observers clear liquid being expressed
along with material , it is an indication of plasticizer
segregation and indicative of manufacturing error or
excessive tempreture extremes during storage.
47. EFFECT OF MISHANDLING
1. Rough or uneven surface on impression
Incomplete polymerization premature removal, improper
ratio or mixing, presence of oil or other organic material
Too rapid polymerization- high humidity or temperature
Excessively high accelerator/base ratio with condensation
silicones
2. Bubbles
Too rapid polymerization, preventing flow
Air incorporated during mixing
3. Irregularly shaped voids
Moisture or debris on the surface of tooth
48. 4. Rough or chalky stone cast
Inadequate cleaning of impression
Excess water left on the surface of impression
Excess wetting agent
Premature removal of cast
Failure to delay pour of addition silicone at least 20min
5. Distortion
Lack of adhesion of rubber to the tray
Development of elastic properties in the material before the tray
is seated
Excessive bulk of material
Continued pressure against impression material that has
developed elastic properties
Movement of tray during polymerization
Premature removal from mouth
Improper removal from mouth
Delayed pouring of the polysulfide or condensation silicone
impression
50. VISIBLE LIGHT – CURED POLYETHER
URETHANE DIMETHACRYLATE
• Introduced in early 1988.
• Two viscosities: Light and heavy.
• COMPOSITION
- Polyether urethane dimethacrylate
- Photo initiators
- Photo accelerators
- Silicon dioxide (Filler)
51. Chemistry: Similar to light cured composites
• Long working time and short setting time.
• Blue light is used for curing with transparent impression
trays.
• Tear strength – 6000 to 7500 gm/cm2(Highest among
elastomers)
• Other properties are similar to addition silicone.
• Both light body and heavy body are cured with visible light
having larger diameter probe.
• Curing time approx 3 min.
52. Advantages:
Controlled working time
Excellent properties
Disadvantages:
Special transparent trays
Difficult to cure in remote area
53. BITE REGISTRATION SILICONES
A specialized addition type of silicone.
Show greater stiffness and greater
hardness then regulare impression
silicone.
Have faster setting time – ranging
from as low as 20 seconds to 1 minute.
Does not slump or drip.
Most supplied as cartridges to be used
with a caulking gun.
Commercial names
Exabite - GC
Jet Bite – Coltene Whaledent
54. FIT CHECKING SILICONES
It is a specialized addition type
silicone.
Used for detecting errors in internal
surface of crowns and fixed partial
dentures.
Available as 2 paste system.
The areas of premature contact are
revealed as bare areas , which are
marked and removed.
Commercial name
Fit Checker - GC
55. SILGINAT( Kettenbach LP)
It is a medium viscosity addition-curing elastomeric
polyvinyl silioxane impression material with alginate-like
consistency.
It combines the benefits of Addition silicone and alginates.
It is stable, has a low tear resistance and is easy to disinfect.
Working Time - 76 - 90 seconds
Complete Set Time - 2 min 30 secs
Viscosity - Medium Body
Set Times Available - Regular Set
56. STATUSBLUE(dmg america)
It is a combination of alginate and addition silicone.
It allows for clean and safe impression taking and
delayed pouring.
Re-pouring of impressions also possible.
Working Time - 1:15
Complete Set Time - 1:45
Viscosity - Type Medium Bodied
