Elastic impression materials/ dentistry online

ELASTIC
IMPRESSION
MATERIALS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

Contents
• Introduction
• History
• Definition and classifications
• Ideal requirements
• Impression materials and techniques
- Elastomeric materials
- Hydrocolloids
• Latest advances
• Conclusions
• Referenceswww.indiandentalacademy.com

“I often say that when you can measure what
you are speaking about, and can express it in
numbers, you know something about it; but
when you cannot measure it in numbers, your
knowledge is of a meager and unsatisfactory
kind; it may be the beginning of knowledge,
but you scarcely in your thoughts advanced
to the stage of science, whatever the matter
may be.”
LORD KELVIN

History:
• 18th
and 19th
century bees wax.
• 1782 William Rae – used wax with POP.
• 1925-28 Development of Hydrocolloids.
• 1930 – A W Ward and E B Kelly introduced ZOE
• 1936-40 Alginate by S.William Wilding.
• 1950 introduction of elastomers.
• 1960 Introduction of polyether in Germany.
• 1988 Latest addition and light cured elastomers.
• 1990-2000 New auto devices and delivery systems.
• Research continues….

DEFINITIONwww.indiandentalacademy.com

“An impression is essentially a negative or reverse
replica of any entity. In dentistry, this replica is of the
teeth and its supporting and surrounding structures.”

1. By generic chemical name: Silicone material or ZOE or
commercial brand names.
2. By the manner in which they harden or set
Chemical / irreversible Temp / reversible
• Plaster of Paris
• ZOE
• Alginate
• Elastomers
Thermoplastic
• Impression
compound
• Wax
•Agar

3. According to the ability of the set material to be
withdraw over undercuts :Elastic
impression materials
Non-elastic or Rigid
impression materials
 Agar
 Alginate
 Impression compound
 ZOE
Hydrocolloid Rubbers
 Polysulfide.
 Poly
silicones.
 Polyether.

4. According to the use of the materials in dentistry
A) Materials used for obtaining impression of dentulous
mouth

Alginate

Agar

Non-aqueous Elastomers
B) Materials used for obtaining Impression of edentulous
mouth:
• Impression Compound
• Impression Plaster
• Zinc Oxide eugenol
• Wax

MucocompressiveMucostatic
5. According to the viscosity or tissue displacement:
- Impression plaster - Impression
- Agar Compound
- Alginate - Putty elastomers

Ideal Requirements of DentalIdeal Requirements of Dental
Impression MaterialsImpression Materials

1. Fluid enough to adapt to the oral tissues
2. Viscous enough to be contained in the tray
3. In mouth should transform (set) into a rubbery or
rigid solid in a reasonable amount of time: setting
time less than 7min
4. Set impression should not distort or tear when
removed from mouth
5. Impressions made be dimensionally stable until the
cast can be poured
6. Impression made should maintain dimensional
stability after removal of cast to enable making of a
second or third cast from same impression
7. Biocompatible
8. Material, associated processing equipment, and
processing time should be cost effective

Elastomers
or
Rubber base Impression materials

• 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 are converted into
solid rubber at room temperature

Types:
I. According to chemistry
1) Polysulfides
2) Polysilicones – condensation & addition
3) Polyether
II. 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

General Properties:
 Excellent reproduction of surface details
 Generally hydrophobic (except poly ether)
 Good elastic properties (repeated pouring is possible)
 Dimensional inaccuracies are lower but exist due to
various reasons
 Excellent tear strength.
 Extended shelf-life
 Generally higher cost
 Requires tray adhesive or mechanical interlocking

CHARACTERSTICS
• Rheological properties- play major role
• Viscous pastes- setting reaction-
viscoelastic properties
• Viscoelasticity describes dependence of
an impression materials response to the
speed of removal
• Maxwell-Voigt viscoelastic model

MAXWELL-VOIGT MODEL

Uses:
1. Impression material for all applications including
- Fixed partial dentures
- Dentures and edentulous impressions
2. Border moulding of special trays (poly ether)
3. Bite registration
4. As duplicating material for refractory casts
• All elastomers - two paste systems (base & catalyst)
• Putty consistency – supplied in jars
Supplied as:

POLY SULFIDES:
Ist
elastomer to be introduced
mercaptan/Thiokol

Composition:
Base Paste:
Liquid Polysulfide Polymer - 80 to 85 %
Inert fillers
(Titanium dioxide, zinc sulfate - 16 to 18 %
copper carbonate or silica)
Reactor Paste
Lead dioxide - 60 to 68 %
Dibutyl phthalate - 30 to 35 %
Sulfur - 3 %
Other substances like Magnesium
stearate (retarder) & deodorants - 2 %

Tray adhesive:
Butyl rubber or styrene/acrylonitrile dissolved in a volatile
solvent such as chloroform or a ketone.

Chemistry and Setting Reactions
The lead dioxide reacts with the poly sulfide polymer
 Chain lengthening by oxidation of the terminal -SH groups
 Cross-linking by oxidation of the pendant -SH groups
Exothermic reaction - 3 to 40
C rise in temp.
It is accelerated by heat and moisture
PbO2 + S
HS - R- SH HS - R-S-S-R-SH + H2O
Mercaptan + Lead dioxide Poly sulfide + Water
T-butyl hydro peroxide – alternative to PbO2www.indiandentalacademy.com

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 elastomers
7. It is hydrophobic - so the mouth should be dried thoroughly before making an
impression
8. The shelf life is good (2 years)
Properties:

Silicone Rubber
Impression Material:
Developed to over come some of the
disadvantages of poly sulfide

Based on the type of polymerization reaction
1) Condensation silicones
2) Addition silicones
Types

• Also known as conventional silicone.
• Available in light, medium and putty consistency
CONDENSATION SILICONE:
Base Accelerators
Polydimethyl siloxane
(hydroxy-terminated)
Orthoethyl silicate – cross
linking agent
Colloidal silica or microsized
metal oxide (filler) 35-75%
Stannous octoate - catalyst
Color pigments
COMPOSITION:

CH3 OC2H5
Sn
OH-Si-OH + C2H5O-Si- OC2H5 Silicone + CH3CH2OH
octoate
CH3 OC2H5
Dimethyl + orthoethyl Silicone + ethyl
siloxane silicate rubber alcohol
 Ethyl alcohol - byproduct - evaporate - shrinkage &
dimensional instability
 Tray adhesive – Polydimethyl siloxane & Ethyl silicate
SETTING REACTION:

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..
• Biologically inert.
• Compatible with all gypsum products.

Addition silicones:
Also called as polyvinyl siloxanes
Better properties than condensation silicones.

Base:
Poly (methyl hydrogen siloxane)
Other siloxane prepolymers
Fillers
Accelerator:
Divinyl poly siloxane
Other siloxane pre polymers
Platinum salt: Catalyst (chloroplatinic acid)
Palladium (Hydrogen absorber)
Retarders
Fillers
Composition:

CH3 CH3 CH3 CH3
Pt salt
Si-H + CH2=CH-Si Si-CH2-CH2-Si
activator
CH3 CH3 CH3 CH3
Vinyl + Silane Silicone
siloxane siloxane rubber
SETTING REACTION:
• No by product, but imbalance  hydrogen gas  air bubbles in
the stone models
• To avoid this palladium is added.

CLINICAL SIGNIFICANCE:
Sulfur compounds retard the setting of silicones
One source of sulfur contamination is from latex gloves
Vinyl gloves should be used
•Clair D. Reitz and Nereyda P. Clark 1988 on the setting of vinyl
polysiloxanes and condensation silicone putties when mixed
with gloved hands.
•Winston W. L. Chee, T. E. Donovan and R. L. Kahn in 1991on
indirect inhibition of polymerization of polyvinyl siloxane
impression material

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
• Extremely hydrophobic, some manufacturers add a surfactant
(detergent) to make it more hydrophilic
• Good shelf life of 1-2 yrs
• Good tear strength (3000gm / cm2
)

Poly ether Rubber
Impression material
• Introduced in Germany in late 1960’s
• Good mechanical properties and dimensional stability, but
short working time, very stiff material and expensive

Composition:
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.

CHEMISTRY & SETTING REACTION
H O O H
CH3– C - CH2– C – O – R – O – C - CH2– C - CH +  Crosslinked
rubber
N N
CH2-CH2 CH2-CH2
Polyether + Sulfonic ester  Crosslinked rubber
Exothermic reaction  4-50
C

Properties:
1. Pleasant odor and taste
2. Mixing time is 30 secs, setting time of 8 mins
3. Dimensional stability is very good.
Curing shrinkage is low (0.24%)
The permanent deformation is also low (1-2%).
4. Very stiff (flexibility of 3%), needs extra space,
around 4 mm is given.
5. Hydrophilic (moisture control not critical)
6. Shelf life extends upto 2 years

Property Polysulfide Condesn
. Addn
. Polyether
Working time (min) 4-7 2.5-4 2-4 3
Setting time (min) 7-10 6-8 4-6.5 6
Tear strength (N/m) 2500-7000 2300-2600 1500-4300 1800-4800
By product H2O Ethanol - -
Custom tray YES NO NO NO
Unpleasant odour YES NO NO NO
Multiple casts NO NO YES YES
% contraction (24hr) 0.40 – 0.45 0.38 – 0.60 0.14 – 0.17 0.19 – 0.24
Stiffness (1= > stiff) 3 2 2 1
Distortion (1= > Dist) 1 2 4 3www.indiandentalacademy.com

RECOMMENDED DISINFECTANTS
MATERIAL DISINFECTANTS
Polysulfide Glutaraldehyde, Cl compounds,
Iodophors & Phenolics
Silicones ------ do --------
Polyether Cl compounds or Iodophors
Alginate ------ do --------
ZOE Glutaraldehyde or Iodophors
Impression compound Cl compounds or Iodophors

AUTOMATIC DISPENSING & MIXING DEVICES
ADVANTAGES:
- More uniform mix
- Less air bubbles
- Reduced working time

Different methods of making impressions
1. Single mix or mono-phase technique:
- Regular viscosity elastomer is used (addition silicone/polyether)
- Paste is mixed, part of it is loaded on to the tray & the
remaining onto the syringe
- Syringe material is injected onto the prepared area & tray
material is seated over it.

Multiple
mix
technique
DISADV:
Higher viscosity
material may displace
more fluid wash
material

RELINE OR 2-STAGE PUTTY
WASH TECHNIQUE
• Preliminary impression is made with a putty consistency
using a thin plastic sheet or spacer over it (acts as a spacer)
• Light body is injected around the prepared tooth
• The plastic sheet is removed & putty impression is seated
back

ELASTOMERIC IMPRESSION
MATERIALS: PROPERTIES
WORKING AND SETTING TIMES
• Working time- begins at the start of mixing and ends
just before the elastic properties have developed
• Setting time- time elapsing from the beginning of mixing
until the curing has advanced sufficiently so that the
impression can be removed from the mouth with a
minimum of distortion
• Increase in temperature- accelerates curing time
• Increase in viscosity- decrease in working and setting
time

Dimensional stability
1. Polymerization shrinkage
2. Loss of byproduct
3. Thermal contraction from oral to room
temperature
4. Imbibition
5. Incomplete recovery of deformation
because of viscoelastic behavior

Reproduction of oral detail
The rubber impression materials are capable of
reproducing detail more accurately than can
be transferred to the stone die or cast
ELASTICITY
Elastic properties of elastomeric impression
materials improve with an increase in curing
time in the mouth
Permanent deformation following strain in
compression increases in following order-
addition silicone, condensation silicone,
polyether and polysulfide

Tear strength
• Measures the resistance to fracture of
elastomeric material subjected to a
tensile force acting perpendicular to a
surface flaw
Biocompatibility
Polysulfide- lowest cell death count
Polyether- highest cell toxicity

RECENT ADVANCES
IN
ELASTOMERS

Visible light cured impression material:
• Polyether urethane dimethacrylate.
• Introduced in early 1988 by GENESIS and L D
CAULK.
• Two viscosities: Light and heavy.

Composition:
- Polyether urethane dimethacrylate
- Photo initiators
- Photo accelerators
- Silicon dioxide (Filler)
Chemistry: Similar to light cured composites

Properties:
• 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.

Manipulation:
• Both light body and heavy body are cured with
visible light having larger diameter probe.
• Curing time approx 3 min.
Adv: - Controlled working time
- Excellent properties
Disadv: - Special transparent trays
- Difficult to cure in remote area

D.H. Pratten and M. Novetsky. Study on
detailed reproduction of soft tissues: A
comparison of impression materials.
1. Low viscosity polysulfide and ZOE
produced fewer and smaller
impression voids than low or medium
viscosity hydrophobic addition
silicones
2. Polyether and hydrophilic addition
silicone produced casts with more soft
tissue detail than low-viscosity
polysulfide or ZOE

COMMON FAILURES
• Rough or uneven surface on
impression
1. Incomplete polymerization- premature
removal, improper ratio or mixing, +ce
of oil or other organic material
2. Too rapid polymerization- high
humidity or temperature
3. Excessively high accelerator/base
ratio with condensation silicones

• Bubbles
1. Too rapid polymerization,
preventing flow
2. Air incorporated during mixing
• Irregularly shaped voids
1. Moisture or debris on the surface
of tooth
• Rough or chalky stone cast
1. Inadequate cleaning of
impression
2. Excess water left on the surface
of impression
3. Excess wetting agent
4. Premature removal of cast
5. Failure to pour delay of addition
silicone at least 20min

• Distortion
1. Lack of adhesion of rubber to the tray
2. Development of elastic properties in the
material before the tray is seated
3. Excessive bulk of material
4. Continued pressure against impression
material that has developed elastic
properties
5. Movement of tray during polymerization
6. Premature removal from mouth
7. Improper removal from mouth
8. Delayed pouring of the polysulfide or
condensation silicone impression

Materials used for maxillofacial prosthetic
reconstruction
• IDEAL QUALITY
1. Compatibility, biologic and mechanical
2. Flexibility, replicating restored tissue
3. Light weight, replicating bulk tissue
4. Translucency, depth in coloration
5. Ease of processing
6. Nonconductive, minimal heat and cold transfer
7. Durability, resistance to handling, environment
8. Ease of duplication
9. Availability, inexpensive
10. Hygienic, cleanable with disinfectants

RTV-Silicone Elastomers
• Room temperature-vulcanizing silicone
elastomers
• Internal coloring difficult-silica fillers for
tensile strength- to mask yellowing
• During mixing air entrapment persists
• Tear resistance inadequate- once
started at an edge void or nick-
propagates

HTV-Silicone Elastomers
• Heat-vulcanizing silicone elastomers
• Designed for higher tear resistance
• Requires intense milling
• Cured at elevated temperatures in heat
transferring metal molds
• Improved biocompatibility with human
excised donor tissues, biologically and
mechanically

Hydrocolloids:
• Kola - ‘glue’ and ‘oid’- like, a ‘glue-like’ character.
• Colloids are classified as the fourth state of matter , they
lie between suspension and solutions.
• Characterized by their unique dispersion of particles held
together by primary or secondary forces.
• The size of the particles larger than solutions & range from
1 to 200nm

• The colloidal materials that are dissolved in water are termed
hydrocolloids
• If the change of sol to gel is thermal and reversible –
reversible hydrocolloid (agar)
• If the change of sol to gel is chemical and irreversible -
irreversible hydrocolloid (alginate)
• An important characteristic of gels is the processes of syneresis
and imbibition.
• These both alter the original dimensions of the gel

Reversible Hydrocolloid – AGAR
 Introduced by “Alphous poller of Vienna” in 1925
 Adopted commercially as “Dentacol” in 1928
 It was the first successful elastic impression material
 Agar is an organic hydrophilic colloid extracted from certain
“Seaweed”
 It is a sulphuric ester of a linear polymer of galactose
 Though highly accurate, it has been largely replaced by
alginates and elastomers due to its cumbersome manipulation

ComponentComponent FunctionFunction CompositionComposition
(%)(%)
AgarAgar Brush Heap structureBrush Heap structure 13 – 1713 – 17
BorateBorate StrengthStrength 0.2 – 0.50.2 – 0.5
Pot. SulfatePot. Sulfate Gypsum hardenerGypsum hardener 1.0 – 2.01.0 – 2.0
Wax, ZO, Silica, DM,Wax, ZO, Silica, DM,
etc.etc.
FillerFiller 0.5 – 1.00.5 – 1.0
Thixotropic materialsThixotropic materials ThickenerThickener 0.3 – 0.50.3 – 0.5
WaterWater Reaction mediumReaction medium Balance 84%Balance 84%
AlkylbenzoatesAlkylbenzoates PerservativePerservative 0.10.1
Composition:

The Material is supplied as:
 Gel in collapsible tubes (for impressions)
 A number of cylinders in a glass jar (syringe material)
 In bulk containers (for duplication)
Manipulation:
Agar hydrocolloid requires special equipments
- Hydro colloid conditioner
- Water cooled rim lock trays

Conditioner Consists of:Conditioner Consists of:
a. Boiling or liquefaction section: 10 mins in boiling water (1000
C).
b. Storage section: 65-680
C is ideal it can be stored till needed
c. Tempering section: 460
C for about 2mins

WATER COOLED RIM LOCK TRAYS

FINAL IMPRESSION WITH AGAR

Advantages:
1. Hydrophilic Impression material
2. Good elastic properties, Good recovery from distortion
3. Can be re-used as a duplicating material
4. Long working time and low material cost
5. No mixing technique
6. High accuracy and fine detail recording
Disadvantages:
1. Only one model can be used
2. Extensive and expensive equipment required
3. Impossible to sterilize for reuse
4. Low dimensional stability & tear resistance

Uses of Agar:
1. Widely used at present for cast duplication
2. For full mouth impression without deep undercuts
3. As tissue conditioner
4. Was used for crown & bridge before the advent of elastomers

Laminate technique or agar-alginate
combination technique
• Injecting syringe agar material onto the prepared tooth
• Placing an impression tray with alginate over the
injected syringe agar
Wet field technique
• Area to be recorded is flooded with warm water
• Syringe agar material – quickly & liberally over prepared tooth
• Immediately, tray agar placed over the syringe agar

Irreversible HydrocolloidIrreversible Hydrocolloid
oror
AlginateAlginate

• ‘Algin’ - a peculiar mucous extract yielded by Algae (brown
seaweed).
• In England, 40 yrs later, “S. William Wilding” received the
patent for alginate as impression material.
• Alginate was developed as a substitute for agar when it
became scarce due to II world war.
• Currently, alginate is more popular than agar because,
 It is easy to manipulate
 It is comfortable for the Patient
 It is relatively inexpensive and does not require
elaborate equipmentwww.indiandentalacademy.com

Component Function Wt%
Potassium alginate Soluble alginate 15
Calcium sulfate Reactor 16
Zinc oxide Filler particles 4
Potassium Titanium fluoride Accelerator 3
Diatomaceous earth Filler Particles 60
Sodium phosphate Retarder 2
COMPOSITION OF ALGINATE

SETTING REACTION:
Alginic acid is a linear polymer of Anhydro- B-D mannuronic
acid of high molecular weight
Two main reactions occurs during setting:
i) 2 Na3 PO4 + 3 Ca SO4 Ca3 (PO4)2 + 3 Na2 SO4
(Sodium phosphate) (Calcium sulphate)
(Retarder) (Reactor)
ii) Sodium Alginate + Ca SO4 + H2O Ca Alginate + Na2 SO4
(Powder) (Reactor) (Gel)

Types: Type I - Fast Setting
Type II - Normal Setting
Latest advances - Modified Alginates:
1. In the form of a sol, containing the water. A reactor of plaster
of Paris is supplied separately.
2. 2 paste system, one containing the alginate sol, the second the
calcium reactor. These materials are said to contain silicone
and have superior tear resistance.www.indiandentalacademy.com

3. Chromatic alginates: contain acid/base indicator that change
colour at different critical points, indicating mixing time,
loading into mouths & setting.
4. Dustless Alginate:
To avoid dust inhalation - coating the material with a glycol.
5. Siliconised Alginates:
Alginates modified by the incorporation of silicone polymers
which improve the physical properties.www.indiandentalacademy.com

Manipulation: - 15 gm. Powder : 40 ml of water
- figure-of-eight motion, swipe & strop
Control of gelation time:
1. By manufacturers : by adding retarders
2. By Dentist - Cold water : Longer is the geln
. time
- Warm water : Shorter is the geln
. time
Types Mixing time Working time Setting time
I- Fast set 45 sec 1.25 mins 1-2 mins
II- Normal
set
60 sec 2 mins 2 - 4.5 mins

Advantages:
1. Easy to mix and manipulate.
2. Minimum requirement of equipment.
3. Accuracy (if properly handled)
4. Low cost
5. Comfortable to the patient
6. Hygienic (as fresh material is used for each impression)
Disadvantages:
1. Distortion occurs easily
2. Poor dimensional stability (poured within 15 min.)
3. Poor tear strength

Uses:
1. Complete denture prosthesis & orthodontics
2. Mouth protectors
3. Study models and working casts
4. Duplicating models

COMPARISON BETWEEN HYDROCOLLOIDS
Properties Agar Alginate
Flexibility 20 % 14 %
Elasticity &
elastic recovery
98.8 % 97.3 %
Reprodn
. of
details
25 um < agar
Tear strength 715 gm/cm2
350-700 gm/cm2
Comp. strength 8000 gm/cm2
500-8000 gm/cm2
Diml
. Stability Better Poor
Reuse Possible Not possible
Manipulation Conditioner & rim
lock trays
Normal trays

CONCLUSION

References:
• Kenneth J. Anusavice: Philips’ Science of Dental Materials Eleventh
Edition
• William J. O’Brien: Dental Materials Properties and Selection
• E. C. Combe: Notes on Dental Materials Fifth Edition
• John F. McCabe: Applied Dental Materials Seventh Edition
• V. K. Subbarao: Notes on Dental Materials Fourth Edition
• Clair D. Reitz, DDS and Nereyda P. Clark, DMD The setting of vinyl
polysiloxane and condensation silicone putties when mixed with gloved
hands. JADA Vol. 116:371-5, 1988
• Winston W.L. Chee, T.E. Donovan, R.L. Kahn. Indirect inhibition of
polymerization of a polyvinyl siloxane impression material: a case
report, Quint. Int. Vol. 22:133-5, 1991
• D. H. Pratten, M. Novetsky. Detail reproduction of soft tissues: A
comparison of impression materials. JPD Vol. 65:188-191, 1991
• John F. Lontz: State-of-the-Art Materials Used for Maxillofacial
Prosthetic Reconstruction DCNA- Vol. 34, No. 2, April 1990
• Terry E. Donovan, Winston W. L. Chee:A review of contemporary
impression materials and techniques DCNA- Vol. 48, No. 2, April 2004

Thank you
For more details please visit

Elastic impression materials/ dentistry online

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