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2. Introduction
Soft and rubber-like & are known as elastomers or synthetic rubbers.
As per ADA Sp. No. 19 - non-aqueous elastomeric dental impression
materials.
Liquid polymers which can be converted into solid rubber at room
temperature
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3. Introduced in late 1950’s – popular
drawbacks of hydrocolloids
- poor dimensional stability
- inadequate tear resistance
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4. Requirements
1. Capable of plastic to rigid body transformation
2. Acceptable for a patient
non-toxic, non-irritant, tasteless,
reasonable setting time up to 5-7 min
3. Good handling properties – easy to prepare/mix plastic before set, but viscous
enough not to flow out of a tray (thixotropic), adequate working and setting times
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5. After being set:
4. Accuracy and detail reproduction (25-50μm),
5. Dimensionally stable
6. Resistant to mechanical stress - elastic and rigid
7. Compatible with model materials
8. Resistant to disinfectant solutions
9. Cost effective
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6. Important terms
Elastic/plastic deformations
Strength
Pseudoplastic/thixotropic
Hydrophilic/hydrophobic
Working time
Setting time
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12. Pseudoplasticity/thixotropy of fluids
Property of certain gels or other materials to become liquefied
(less viscous) when shaken ,stirred ,patted ,or vibrated-
thixotropic.
Character of material to become more fluid when applied force
is increased ,shear thinning effect: Pseudoplastic.
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15. Working time & Setting time
Working time – a period from the start of mixing to the final time at which
the impression can be seated in the mouth without its distortion
Setting time – a period from the start of mixing till the impression becomes
elastic enough to resist deformation during its withdrawal from the mouth
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16. Polymerization shrinkage of elastomers is usually compensated for using a
combination of:
1. Highly filled-viscous material „Putty“ for preliminary impression (low polymer
content - of low shrinkage)
2. Low filled-low viscosity „wash“ or„light“ impression material (high
polymer content - higher elasticity but higher shrinkage)
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17. Setting occurs through a combination of chain lengthening
polymerization and chemical cross linking
- condensation reaction
- addition reaction
The chains of these materials uncoil on stretching and upon removal of
the stress they bounce back or snap back to their relaxed entangled state
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18. Types:
According to chemistry
1) Polysulfides
2) Polysilicones – condensation & addition
3) Polyether
According to Viscosity
1) Light body or syringe consistency
2) Medium or regular body
3) Heavy body or tray consistency
4) Very heavy body or putty consistency
ADA Classification
Based on selected elastic properties & dimensional changes
1) Type I
2) Type II
3) Type III
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19. Polysulfide impression materials
Composition
Base
polysulfide polymers
fillers
plasticizers
Catalyst
lead dioxide (or copper)
fillers
By-product
water
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21. Properties:
1. Unpleasant odor and colour - stains linen & messy to work with
2. Extremely viscous and sticky - mixing is difficult
3. Mixing time is 45 seconds
4. Long setting time of 12.5 (at 370
C) - Patient discomfort
5. Excellent reproduction of surface detail
6. Dimensional stability:
- Curing shrinkage is high 0.45%.
- It has the highest permanent deformation (3 to 5%)
among the elostomers
7. It is hydrophobic - so the mouth should be dried thoroughly before making an impression
8. It can be electroplated
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22. Advantages
The best tear strength
Long working time and set time
Good reproduction of surface detail
Good flow before setting
Good bond with tray adhesive
Stable in disinfectant solutions
Relatively inexpensive
Disadvantages
Unpleasant odor and taste
Poor recovery from deformation
Poor dimensional stability
Should be poured within one hour.
Can not be repoured.
Should be used with custom trays
Staining of clothes due to the Lead oxide
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24. HO – Si – O – Si - O -
H
CH3
CH3 CH3
CH3 n
HO – Si – O – Si - O -
H
CH3
CH3 CH3
CH3 n
C2H5
O
OC2H
5
Si
C2H5
O
OC2H
5
HO – Si – O – Si - O -
CH3
CH3 CH3
CH3 n
HO – Si – O – Si - O -
CH3
CH3 CH3
CH3 n
OC2H
5
Si
OC2H
5
+ 2C2H5OH
Setting reaction
metal organic ester
ethanol
Dimethyl + orthoethyl Silicone + ethyl
siloxane silicate rubber alcohol
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25. Properties:
Pleasant odor and color.
Mixing time of 45sec & setting time of 8-9mins.
Excellent reproduction of surface details and highly elastic.
Lesser dimensional stability
- high curing shrinkage (0.4 - 0.6%)
- permanent deformation due to shrinkage caused by the evaporation of ethyl
alcohol is also high (1-3%).
Hydrophobic - needs a dry field.
Electroplatable (silver / copper) and has adequate shelf life).
Biologically inert. www.indiandentalacademy.com
26. Advantages
Good recovery from deformation
Good tear strength
Good accuracy
Adjustable working times
No unpleasant odor or taste
Stable in disinfectant solution
Relatively inexpensive
Disadvantages
Hydrophobic: poor moisture
compatibility
Poor dimensional stability
Immediate pour required
Poor bond to tray adhesive
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27. A-silicone impression materials
Base:
Poly (methyl hydrogen siloxane)
Other siloxane prepolymers
Fillers
Accelerator:
Divinyl poly siloxane
Other siloxane pre polymers
Platinum salt: Catalyst (chloroplatinic acid)
Palladium or Hydrogen absorber
Retarders
Fillers
Composition:
No by product www.indiandentalacademy.com
28. O
H - Si – CH3
O
CH3 - Si - H
O
---O – Si – CH = CH2
CH3
CH3 CH = CH2 – Si – O ---
CH3
CH3
O
- Si – CH3
O
CH3 - Si -
O
---O – Si – CH2 - CH2
CH3
CH3
CH2 - CH2 – Si – O ---
CH3
CH3
Chloroplatinic Acid Catalyst
Setting reaction
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29. Properties:
Pleasant odor and color
Excellent reproduction of surface details
Mixing time of 45 secs ,setting time of 5-9 mins.
Best dimensional stability
- low curing shrinkage (0.17 %)
- lowest permanent deformation (0.05 – 0.3 %)
Stone pouring delayed by 1-2 hours
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30. Can be electroplated with silver and copper
Good tear strength (300gm / cm2)
Extremely hydrophobic, some manufacturers add a surfactant
(detergent) to make it more hydrophilic Surfactants added
reduce contact angle
improved
castability
gypsum
wettability??
still need dry field clinically
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31. Advantages
Most accurate material available
Good tear strength
Excellent recovery from deformation
Long term dimensional stability
Hydrophilic
No unpleasant taste or odor
Stable in disinfectant solutions
Available in automixing devices
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32. Disadvantages
Some are hydrophobic
Relatively expensive
Materials are sensitive to contaminants
Latex gloves/Rubber dams (Sulfur
inhibition)
Acrylic temp. residues
Heat
To manipulate the PUTTY
material,
DO NOT wear latex gloves.
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35. Properties:
Pleasant odor and taste
Mixing time is 30 secs, setting time of 8.3 mins
Dimensional stability is very good.
Curing shrinkage is low (0.24%)
The permanent deformation is also low (1-2%).
Very stiff (flexibility of 3%)
Hydrophillic (moisture control not critical)
Electroplatable with silver & copper
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36. Advantages
Long term dimensional stability
Good accuracy
Hydrophilic
Good reproduction of surface details
Good tear strength
Rigid
Good bond with tray adhesive
Ease to use
Disadvantages
Can be too stiff and can cause cast
breakage
Difficult to mix - spatule
May cause allergic reaction
Expensive
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38. Comparison of Properties
Working time:
longest to shortest
agar > polysulfide > silicones > alginate = polyether
Effects of temperature
Increase - both working and setting time decreased by accelerating the curing rate
Decrease - working time increased by refrigerating the materials or mixing on a
chilled dry glass slab
Agar Alginate Polysulfide
Condensation
Silicone
Addition
Silicone
Polyether
Working Time
(min)
7 – 15 2.5 5 – 7 3 2 –4.5 2.5
Setting Time
(min)
5 3.5 8 – 12 6 – 8 3 – 7 4.5
Setting time
•shortest to longest
•alginate < polyether < agar < silicones <
polysulfide
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39. Stiffness:
most to least
polyether > addition silicone > condensation silicone > polysulfide = hydrocolloids
Agar Alginate Polysulfide
Condensation
Silicone
Addition
Silicone
Polyether
Flexibility (%) 11 12 8.5 – 20.0 3.5 – 7.8 1.3 – 5.6 1.9 – 3.3
•Problem when dealing with long, thin preparations of periodontally involved
teeth
• Result in fracture of dies
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40. Tear strength
greatest to least
polysulfide > addition silicone > polyether > condensation silicone >> hydrocolloids
Agar Alginate Polysulfide
Condensation
Silicone
Addition
Silicone
Polyether
Tear
Strength
(g/cm)
700 380 – 700 2240 – 7410 2280 – 4370 1640 – 5260 1700 - 4800
Important property - in inter proximal and sub gingival areas.
Influenced by
Consistency - increased viscosity increases tear strength
Manner of removal - rapid rate of force during removal increases tear strength
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41. Agar Alginate Polysulfide
Condensation
Silicone
Addition
Silicone
Polyether
Flow (%) -- -- 0.4 – 1.9 < 0.10 < 0.05 < 0.05
Light body materials flow readily into minute details
Tray or heavy body material provide more rigidity to the impression
Early versions of light body tended to flow off the prepared tooth with time - newer PVS
and polyether are thixotropic
•Flow
•Lowest to highest
•polyether < addition silicone < condensation silicone <polysulfide
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42. Dimensional stability
best to worst
addition silicone > polyether > polysulfide > condensation silicone > hydrocolloid
Agar Alginate Polysulfide
Condensation
Silicone
Addition
Silicone
Polyether
Shrinkage, 24 hours
(%)
Extreme Extreme 0.4 – 0.5 0.2 – 1.0 0.01 – 0.2 0.2 – 0.3
stability
1 hour
100%
RH
Immediate
pour
1 hour Immediate pour 1 week
1 week kept
dry
Five major sources of dimensional changes
Polymerization shrinkage
Loss of by product (water or alcohol) during condensation reaction
Thermal contraction from oral temperature to room temperature
Imbibition - exposed to water, disinfectant or high humidity environment
over a period of time
Incomplete recovery of deformationwww.indiandentalacademy.com
43. Elastic recovery:
best to worst
addition silicone > condensation silicone >polyether > agar >alginate >polysulfide
Agar Alginate Polysulfide
Condensation
Silicone
Addition
Silicone
Polyether
Elastic Recovery
(%)
98.8 97.3 94.5 – 96.9 98.2 – 99.6 99 – 99.9 98.3 – 99.0
A material with 1% permanent deformation has 99% elastic recovery
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44. Castability
best to worst
hydrocolloids > hydrophilic addition silicone > polyether > polysulfide > hydrophobic
addition silicone = condensation silicone
Agar Alginate Polysulfide
Condensation
Silicone
Addition
Silicone
Polyether
Wettability and
castability
Excellent Excellent Fair Fair Fair to good Good
Wettability
•best to worst
•hydrocolloids > polyether > hydrophilic addition silicone > polysulfide > hydrophobic
addition silicone = condensation silicone
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45. Cost
lowest to highest
alginate < agar = polysulfide <condensation silicone < addition silicone <
polyether
Agar Alginate Polysulfide
Condensation
Silicone
Addition
Silicone
Polyether
Cost Low Very low Low Moderate
High to
very high
Very high
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47. Summary
Study models
Alginate most widely used
inexpensive
displaces moisture
lower detail reproduction
dimensionally unstable
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48. Summary
Prosthesis
Addition silicones most popular
accurate
dimensionally stable
user friendly
expensive
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49. Manipulation
Uniform bulk of materials
Adhesion of impression tray to the material
Pouring of impression materials
Viscosity control
Adequate mixing
DCNA 2004www.indiandentalacademy.com
50. TRAYS
All impression materials shrink upon setting
Reversible hydrocolloid - a thermoplastic
Elastomers - polymerization shrinkage
Accurate impression - uniform amount of bulk in the impression is
imperative - uniform shrinkage throughout the body of the impression
DCNA 2004www.indiandentalacademy.com
51. Reversible or Irreversible hydrocolloid -maximum accuracy with a cross
sectional thickness of 4-6 mm - Stock trays
Elastomeric impressions - most accurate when used with a cross sectional
thickness of 2 mm
- Custom tray
DCNA 2004www.indiandentalacademy.com
54. Stock plastic trays
One or two single units
Do not have sufficient rigidity
Not expensive
Contra indicated - fixed bridge work - flexibility adversely affects inter
preparation, cross arch and anteroposterior dimensions
Fundamentals of fixed prosthodontic 3rd ed :Shilingburgwww.indiandentalacademy.com
55. Stock metal trays
Coated steel or stainless steel - combine the convenience of stock
plastic trays with the rigidity of custom trays.
Perforated or rim lock trays – basically used for mechanical retention in
addition to tray adhesives
Fundamentals of fixed prosthodontic 3rd ed :Shilingburgwww.indiandentalacademy.com
56. Custom trays
Custom tray improves the accuracy of an elastomeric impression by limiting
the volume of the material
Reducing two sources of error
Stresses during removal
Polymerization shrinkage
Fundamentals of fixed prosthodontic 3rd ed :Shilingburgwww.indiandentalacademy.com
57. Fabrication
Custom trays - constructed on the diagnostic cast using a layer of base
plate wax as the spacer
Polymethylmethacrylate
Photo-cure bisacryl materials (Triad)
PVS putty materials
Thermoplastic trays
Fundamentals of fixed prosthodontic 3rd ed :Shilingburg
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58. PMM trays should be fabricated at least
24 hours in advance - stability
Tray should extend 3-5 mm from gingival margin
Wax spacer covered with tin foil to permit easy removal of the spacer from the
tray
Fundamentals of fixed prosthodontic 3rd ed :Shilingburgwww.indiandentalacademy.com
59. DUAL ARCH TRAYS
Trays are available in both anterior and posterior designs and consist of an
outer rim that is spanned by a mesh fabric
Any elastic impression material - more rigid- bodied materials are preferred
Fundamentals of fixed prosthodontic 3rd ed :Shilingburgwww.indiandentalacademy.com
60. If bucco - lingual width of the alveolar ridge is wider than the width of
the tray - outer rims will be wedged apart when the patient closes into the
impression material – resulting in distorted impression - tray can be
modified by cutting the mesh
Fundamentals of fixed prosthodontic 3rd ed :Shilingburgwww.indiandentalacademy.com
62. Liquid rubber (e.g. butyl rubber) dissolved in a volatile solvent
such as chloroform or ketone
Silicones :polydimethyl siloxane & ethyl silicate
Form an adhesive bond to the tray
Roughening the surface of custom trays increases the adhesive bond
strength
Painted in a thin layer on the internal surface of the tray and the
tray borders atleast 7-15 minutes before making the impression
W.Patrick :An overview of impression materials vol4www.indiandentalacademy.com
63. Mixing:
Paste form -> equal lengths of base and reactor paste
taken over the mixing pad - reactor paste is first spread
over the base paste, mixing continued until a smooth,
homogenous, streak free mix is obtained.
When reactor supplied in liquid form -> number of drops
per unit length are recommended by manufacturer.
Two putty system -> kneaded between the fingers
O’Brien dental materials and their selection 3rd
ed
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65. Used for light and medium viscosity materials
prepackaged cartridges
disposable mixing tip
The cartridge inserted in a gun like device, and base and catalyst are extruded into
the spiral mixing tip, where mixing occurs as they progress to the end of the tube.
Philip’s science of dental materials 11th
edwww.indiandentalacademy.com
66. Advantages
Greater uniformity in proportioning and in mixing.
Less air incorporated into the mix.
Mixing time reduced.
Less chance of mix getting contaminated
Less wastage of material.
Philip’s science of dental materials 11th
edwww.indiandentalacademy.com
68. The device uses a motor to drive parallel plungers that force the materials
into a mixing tip, and the spiral inside the mixing tip rotates as the
material are extruded through the tip
Higher viscosity material can be mixed
Internet sourceswww.indiandentalacademy.com
69. Effects of mishandling elastomers
Rough or uneven surface on impression
Bubbles
Irregularly shaped voids
Rough or chalky stone cast
Distortion
Philip’s science of dental materials 11th
edwww.indiandentalacademy.com
71. Visible light cured impression material:
• Polyether urethane dimethacrylate.
• Introduced early 1988 by GENESIS and L D CAULK.
• Two viscosities: Light and heavy.
W.Patrick :An overview of impression materials vol4www.indiandentalacademy.com
72. Properties:
• Long working time and short setting time.
• Blue light is used for curing with transparent impression trays.
• Tear strength – 6000 to 7500 gm/cm (Highest among elastomers)
• Other properties are similar to addition silicone.
W.Patrick :An overview of impression materials vol4www.indiandentalacademy.com
73. Manipulation:
• Both light body and heavy body are cured with visible light having 8
mm or larger diameter probe.
• Curing time approx 3 min.
Adv: - Controlled working time
- Excellent properties
Disadv: - Special transparent trays
- Difficult to cure in remote area
W.Patrick :An overview of impression materials vol4www.indiandentalacademy.com
74. Duplicating materials
Hydrocolloids are used to duplicate dental casts or models
- construction of prosthetic appliances and
orthodontic products
Reversible (Agar) Hydrocolloid
Same composition as impression material - water content is higher
Classification (ANSI/ADA specification No.20)
Type I – Thermo reversible
Type II – Non reversible
Silicones and polyether - expensive
Craig’s restorative dental materials 12th ed
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75. Review of literature:
Pre and post set hydrophilicity of impression
materials were evaluated (j prosth 2007)
Hydrophilicity of one polyether,4 A silicone & 1 C silicone were
evaluated pre and post setting under simulated conditions.
Polyether showed smallest contact angle
Polyether was most hydrophilic of the materials tested.
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76. Mechanical properties of elastomeric impression
materials (H LU, B NGUYEN - 2004 )
Mechanical properties of three commercial elastomeric impression
materials two addition silicone impression materials and one polyether
material with low and high viscosities were compared.
All the products had similar elastic recovery and quite different other
properties.
Polyether had higher strain-in-compression and less tensile strength
compared to addition silicone materials.
Heavy-body materials had higher tear properties and tensile strength
than light-body
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77. The effect of different adhesives on vinyl
polysiloxane bond strength to two tray
materials.(J of prosth 2005)
evaluate the bond of 3 VPS materials with a methylmethacrylate auto
polymerizing and a light-polymerizing tray material, using the adhesive
recommended by the manufacturer of the impression material, and 2
universal adhesives (paint-on and spray-on).
universal spray-on adhesive consistently demonstrated significantly
lower bond strengths than all other adhesives (P<.05). Equivalent or
significantly (P<.05) higher bond strength values were found for the
universal paint-on adhesive for the 3 impression materials tested.
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78. Compare surface detail reproduction between various
combinations of contemporary addition-reaction
silicone impression materials and Type IV gypsum
products.(J of prosth 2005)
All impression materials tested fully reproduced the 20-Mm line.
Different impression materials showed different compatibility with
different Type IV gypsum products.
Not all of impression material and Type IV gypsum products used
exhibited similar compatibility.
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79. Distortion of disposable plastic stock trays when used
with putty vinyl polysiloxane impression materials.
(J of prosth 2005)
Rigidity and ability to resist deformation of 6 commercially available
disposable plastic stock trays and 1 metal stock tray when used in
conjunction with a high-viscosity vinyl polysiloxane impression
material.
disposable plastic trays tested were not sufficiently rigid to resist
deformation when used with very high-viscosity putty material. Metal
stock trays showed significantly less change in cross-arch dimension
than plastic trays
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80. Impression Accuracy of Sectional Stock
Tray System(Prosthodontic Research & Practice 2004)
Evaluated the accuracy of a sectional stock tray for making
impressions.
Making impressions was easier with sectional stock tray. There were no
significant differences (p>0.10) between the sectional stock tray and a
conventional stock tray.
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81. Conclusion
The ability to record consistently good impressions is both a science and
an art.
Impression techniques, methods and materials are evolving and
changing but underlying principles and fundamentals remain
constant.
An ideal impression must be in the mind of the dentist before it
can be in his hand. It is this knowledge and experience that enables
a dentist to create desirable results
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