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Elastomers
or
Rubber base Impression
materials
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INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
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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 Introduced in late 1950’s – popular
drawbacks of hydrocolloids
- poor dimensional stability
- inadequate tear resistance
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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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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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Important terms
 Elastic/plastic deformations
 Strength
 Pseudoplastic/thixotropic
 Hydrophilic/hydrophobic
 Working time
 Setting time
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Elastic/plastic deformations
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Recovery from deformation
combination of a spring and a dashpot – a model of
viscoelasticity
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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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Hydrophilic/hydrophobic
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Strength
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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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 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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 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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 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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Polysulfide impression materials
Composition
 Base
 polysulfide polymers
 fillers
 plasticizers
 Catalyst
 lead dioxide (or copper)
 fillers
 By-product
 water
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--SH HS---------------------SH HS--
S
H
O
=
Pb
=
O
O
=
Pb
=
OO = Pb = O
H
S
-S-S---------------S-S-
S
S
+ 3PbO + H2O
mercaptan + lead dioxide polysulfide rubber + lead oxide + water
Polysulfide Reaction
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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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 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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Condensation Silicone
 Base
 poly(dimethylsiloxane)
 tetraethylorthosilicate
 filler
 Catalyst
 metal organic ester
 By-product
 ethyl alcohol
Composition
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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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 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
 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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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
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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 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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 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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 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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 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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polyether
 Base
 difunctional epimine-terminated prepolymer
 fillers
 plasticizers
 Catalyst
 aromatic sulfonic acid ester
 fillers
 Cationic polymerization
 ring opening and chain extension
Composition
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 Polyether + Sulfonic ester  Crosslinked rubber
Setting reaction
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 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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 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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Impression Material Usage*
 Crown & Bridge
 vinylpolysiloxane 81%
 alginate 38%
 polyether 28%
 Inlays and Onlays
 vinylpolysiloxane 71%
 polyether 22%
 alginate 20%
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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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 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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 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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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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 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
 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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 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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 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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 Regularly-Used Impression Materials
Alginate 88%
Polyvinyl Siloxane 85%
Polyether 27%
Other 6%
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Summary
 Study models
 Alginate most widely used
 inexpensive
 displaces moisture
 lower detail reproduction
 dimensionally unstable
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Summary
 Prosthesis
 Addition silicones most popular
 accurate
 dimensionally stable
 user friendly
 expensive
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Manipulation
 Uniform bulk of materials
 Adhesion of impression tray to the material
 Pouring of impression materials
 Viscosity control
 Adequate mixing
DCNA 2004www.indiandentalacademy.com
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
 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
Stock trays
Stock plastic trays Stock metal trays Clear trays
•Non-perforatedNon-perforated
•PerforatedPerforated
•Rim lock traysRim lock trays
•Non-perforatedNon-perforated
•PerforatedPerforated
•Dual arch traysDual arch trays
Fundamentals of fixed prosthodontic 3rd ed :Shilingburgwww.indiandentalacademy.com
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 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
 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
 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
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
www.indiandentalacademy.com
 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
 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
 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
Tray adhesive
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 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
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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Automatic Mixing devices
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 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
 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
Dynamic mechanical mixer
Internet sources
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 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
 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
 RECENT ADVANCES IN ELASTOMERS
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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
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
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
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
www.indiandentalacademy.com
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.
www.indiandentalacademy.com
 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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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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 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.
www.indiandentalacademy.com
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
www.indiandentalacademy.com
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.
www.indiandentalacademy.com
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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Elastomeric impression materials / dental implant courses

  • 1. Elastomers or Rubber base Impression materials www.indiandentalacademy.com INDIAN DENTAL ACADEMY Leader in continuing Dental Education
  • 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 www.indiandentalacademy.com
  • 3.  Introduced in late 1950’s – popular drawbacks of hydrocolloids - poor dimensional stability - inadequate tear resistance www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 6. Important terms  Elastic/plastic deformations  Strength  Pseudoplastic/thixotropic  Hydrophilic/hydrophobic  Working time  Setting time www.indiandentalacademy.com
  • 10. Recovery from deformation combination of a spring and a dashpot – a model of viscoelasticity www.indiandentalacademy.com
  • 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. www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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) www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 19. Polysulfide impression materials Composition  Base  polysulfide polymers  fillers  plasticizers  Catalyst  lead dioxide (or copper)  fillers  By-product  water www.indiandentalacademy.com
  • 20. --SH HS---------------------SH HS-- S H O = Pb = O O = Pb = OO = Pb = O H S -S-S---------------S-S- S S + 3PbO + H2O mercaptan + lead dioxide polysulfide rubber + lead oxide + water Polysulfide Reaction www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 23. Condensation Silicone  Base  poly(dimethylsiloxane)  tetraethylorthosilicate  filler  Catalyst  metal organic ester  By-product  ethyl alcohol Composition www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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. www.indiandentalacademy.com
  • 33. polyether  Base  difunctional epimine-terminated prepolymer  fillers  plasticizers  Catalyst  aromatic sulfonic acid ester  fillers  Cationic polymerization  ring opening and chain extension Composition www.indiandentalacademy.com
  • 34.  Polyether + Sulfonic ester  Crosslinked rubber Setting reaction www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 37. Impression Material Usage*  Crown & Bridge  vinylpolysiloxane 81%  alginate 38%  polyether 28%  Inlays and Onlays  vinylpolysiloxane 71%  polyether 22%  alginate 20% www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 46.  Regularly-Used Impression Materials Alginate 88% Polyvinyl Siloxane 85% Polyether 27% Other 6% www.indiandentalacademy.com
  • 47. Summary  Study models  Alginate most widely used  inexpensive  displaces moisture  lower detail reproduction  dimensionally unstable www.indiandentalacademy.com
  • 48. Summary  Prosthesis  Addition silicones most popular  accurate  dimensionally stable  user friendly  expensive www.indiandentalacademy.com
  • 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
  • 52. Stock trays Stock plastic trays Stock metal trays Clear trays •Non-perforatedNon-perforated •PerforatedPerforated •Rim lock traysRim lock trays •Non-perforatedNon-perforated •PerforatedPerforated •Dual arch traysDual arch trays Fundamentals of fixed prosthodontic 3rd ed :Shilingburgwww.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 www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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
  • 67. Dynamic mechanical mixer Internet sources www.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
  • 70.  RECENT ADVANCES IN ELASTOMERS www.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 www.indiandentalacademy.com
  • 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. www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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. www.indiandentalacademy.com
  • 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. www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com
  • 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. www.indiandentalacademy.com
  • 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 www.indiandentalacademy.com