Elastic impression materials /certified fixed orthodontic courses by Indian dental academy

INDIAN DENTAL ACADEMY
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Contents
•Introduction
•Definition
•Classification
•Requirements
•Elastic impression materials
•Impression making with elastomers
•Methods of making impressions
•Comparative properties
•Hydrocolloids
•Review of Literature
•References
•Conclusion

Definition
•GPT-8 - Impression - A negative likeness or a
copy in reverse of the surface of an object;
an imprint of the teeth and adjacent
structures for use in dentistry.
•GPT-8 – Impression material – Any substance
or Combination of substances used for
making impression or negative reproduction


classification
RIGID

ELASTIC

Set by chemical
reaction

-plaster
ZnOE

-alginate
-non aqueous
elastomers

Set by
temperature
change

compound

Agar hydrocolloid


REQUIREMENTS
They should be fluid enough to adapt to the oral
tissues
They should be viscous enough to be contained in
the tray
while in the mouth they should transform into rigid
state within reasonable time (approximately 7min)
The set impression should not distort when
removed.

Impression should be dimensionally stable till
the cast is poured.
Material should be biocompatible
Material should be economical
Should be compatible with die and cast materials
Should record the teeth and tissue accurately

ELASTIC IMPRESSION
MATERIALS
• Definition:


Chemically there are four types of
elastomers
• Polysulfide
• Condensation polymerizing silicone
• Addition polymerizing silicone
• Polyether


Each type is further divided into
four viscosity classes
• Light body
• Medium / regular body
• Heavy body
• Putty

• The current ADA specification recognizes
three types of rubber like impression
materials.
• The classification type is based upon
selected elastic and dimensional change of
the set material, accordingly


ADA classification
Max
permanent
deformation

Max flow in
compression

Max
dimensional
change in 24
hrs

Type-1

2.5

0.5

- 0.5

Type-2

2.5

0.5

- 1.0

Type-3

5.5

2

- 0.5


GENERAL PROPERTIES
• Excellent reproduction of surface details. The low
viscosity is able to record find details
• They are hydrophobic. So oral tissues in the area
of impression should be dry.
• Co-efficient of thermal expansion of elastomers is
high. So thermal contraction of set material
occurs when transferred to room temperature


•

Tear strength is excellent. So
impressions can be removed from thin
areas.

•

The elastomeric materials can be
copper/silver plated

•
•

Shelf life of elastomers is good
Dimensional stability

Representative linear contraction of four elastomeric impression materials

• For visco-elastic material slow elastic recovery may
control for sometime after withdrawal of the
impression, producing dimensional change. In this
case the dimensional change results in more
accurate impression.
• But many impression materials contain volatile
substances either as primary components or as by
products of setting reaction. Loss of such volatile
materials results in shrinkage of impression
material resulting in decrease in accuracy. So for
majority of materials, accuracy can be maintained
by powering the cast soon after the removal of
impression.

Dimensional changes occur due to:
Curing shrinkage
Loss of byproducts
Polyether being hydrophilic absorbs
water and loses soluble plasticizers
causing change in dimension
Thermal contraction when transferred
from mouth to room temperature


Incomplete elastic recovery after
deformation during removal
Amount of filler
Uniform thickness of material gives more
accurate impression
Time of pouring of impression. Impression
should be powered after elastic recovery
and before dimensional change


POLYSULFIDES
Also called as mercaptan or Thiokol
MODE OF SUPPLY
• It is supplied in tubes as base and
accelerate in paste form
• Available in three viscosities
• Light bodied
• Medium bodied
• Heavy bodied

COMPOSITION
•BASE PASTE

FUNCTION

Polysulfide polymer – 80-85% This is further polymerized
and cross linked to form
rubber
Filler (Titanium dioxide zinc
sulfate) – 16-18%

To provide required strength

Plasticizer (Dibutyl Phthalate) To provide appropriate
viscosity
Small quantity of sulphur –
To accelerate the reaction
0.5%

Accelerator paste
Lead dioxide – 60-68%

To react with thiol group
causing setting and give
brown colour

Filler and plasticizer

To provide strength and to
give adequate viscosity

Oleic / stearic acid

Act as retarder to control
rate of setting reaction

CHEMISTRY AND SETTING
REACTION
• The main component of
polysulfide is a
multifunctional
mercaptan (-SH) or
polysulfide polymer.
These linear polymer
contains pendent –SH
groups
•
•


An oxidizing agent like lead dioxide is used to
initiate polymerization.
Polymerization occurs by
a.Chain lengthening by oxidation of terminal -SH
group
b.Cross linking by oxidation of pendent –SH group


Reaction yields water as by
product

HS

SH

+

HS

SH

SH
SH

HS

SH
SH
PbO2

HS

HS

SH

S–S

S

S


SH
SH + PbO + H2O


PROPERTIES
Unpleasant odour and colour
It has a long setting time of 8.12minutes
Mixing time is 45 seconds
Excellent reproduction of surface detail
Dimensional stability.
The curing shrinkage is high (0.45%)
Has the highest permanent deformation
(3.5%)
This improves with time. So pouring of
model should be delayed by half an hour

Tear strength is 4000 gms/cm2
It has good flexibility. A 2mm
spacing in the tray is sufficient to
make the impression.
It is hydrophobic. So impression
area should be dry
Shelf life is good i.e. 2 years

SILICONE RUBBER IMPRESSION
MATERIALS
• Types:
•
Two types of silicone impression
materials are available based on the type of
polymerization reaction occurring during
setting
• Condensation silicone
• Addition silicone

• MODE OF SUPPLY
•
Available as base and catalyst in paste form.
The condensation silicone catalyst can also be
supplied as a liquid. The putty is supplied in jars.
Condensation silicone is available in three
•
viscosities.
• Light bodied
• Medium bodied
• Putty
•
Addition silicone is available in four viscosities


CONDENSATION SILICONES
Composition of Base paste
Hydroxyl terminated
polydimethyl siloxane

Undergoes cross linking to
form rubber

Colloidal silica

Filler


Reactor paste
Tetraethyl orthosilicate

Cross linking agent

Stannous octate

Catalyst


REACTION
It is a condensation reaction
Polymerization occurs as a result of cross
linkage between orthoethyl silicate and
terminal hydroxyl group of dimethyl
siloxane to form a three dimensional
network
Stannous octate acts as a catalyst
Ethyl alcohol is by product. Its evaporation
probably accounts for much of the
condensation taking place in set silicone
impression

• PROPERTIES
Pleasant colour and odour
Setting time is 6-8 minutes, mixing time is 45
seconds
Excellent reproduction of surface details
Dimensional stability is low due to high curing
shrinkage (0.4-0.6%) and shrinkage due to
evaporation of ethyl alcohol. To avoid this cast
should be poured immediately.
Tear strength is 3000gm/cm2
It is hydrophobic. So impression field should be
dry
Can be electroplated with silver or copper

ADDITION SILICONES
•
•
•
•
•
•
•

Superior to condensation silicones
Also called polyvinyl silioxane impression materials.
COMPOSITION
•fillers
Base:
Polymethyl hydrogen siloxane
Other siloxane prepolymers
Fillers

•
•
•
•

Divinylpolydimethyl siloxane
Other siloxane prepolymers
Fillers
Platinum salt-catalyst

• Accelerator

• CHEMISTRY AND SETTING REACTION
• It is an addition reaction
• In this case polymer is terminated
with vinyl groups and it is cross linked
with silane (hydride group). The
reaction is activated by platinum salt


• No reaction byproduct develops as long as
correct proportions of vinyl siloxane and silane
siloxane are maintained
• -sulfur compounds retard the setting of addition
silicone.


PROPERTIES
Pleasant colour and odour
Good reproduction of surface details
Setting time is 4-7 minutes and mixing time is 45
seconds
It has the best dimensional stability among all
elastomers. It has low curing shrinkage (0.17%) and
low permanent deformation (0.05-0.3%)
Good tear strength (3000gm/cm2)
It is hydrophobic so impression field should be dry
Can be electroplated with copper/silver
Shelf life ranges from 1-2 years

POLYETHER
• Mode of Supply:
• Available as base and accelerate paste
in tubes
• Available in three viscosities
•Light bodied
•Medium bodied
• Heavy bodied

COMPOSITION
• Base:
• Polyether polymer
• Colloidal silica
glycol ether (or) phthalate
• Accelerator Paste:
• Alkyl aromatic suffonate
• Colloidal silica
• Phthalate

Cross linked to form rubber
Acts as filler
Plasticizer
Initiates cross linking
Filler
Plasticizer


REACTION
.


PROPERTIES
Pleasant odour and taste
Setting time is short 3.5minutes, mixing
time is 30 seconds
Good dimensional stability
Curing shrinkage is 0.24%
Polyether absorb water and can change in
dimension. So should not be stored in
contract with water or in humid climates

It is extremely stiff
Tear strength is 3000gm/cm2
Hydrophilic, has good compatibility
with stone
Can be electroplated
Good shelf life i.e., more than 2
years.

IMPRESSION MAKING WITH
ELASTOMERS
•
1.
2.
3.
4.
5.

It involves five steps
Preparing a tray
Preparing the material
Making impression
Removing the impression
Preparing stone casts and dies

•

Preparing a tray:
•
•
•
•
•

Impressions are usually made with custom
trays. Perforated stock trays are used for
making impression in putty.
To prepare a custom tray, an alginate
impression is made and stone cast is
constructed
Teeth are covered with modeling wax (1 or 2
sheets approximately 3-4mm) to act as spacer
and stops are provided
Custom tray is prepared with tray material
Slightly roughened surface of tray inside
improves retention.

•

Preparing the material:
•
•
•
•
•

Materials are provided in two paste tubes
Same length of materials should be dispensed
on to mixing pad
Catalyst paste is first collected on to spatula
and then distributed over the base
Mixing should be thorough, uniform in colour
with no streaks of base of catalyst
If one of the components is in liquid form
such as catalyst for condensation silicone, a
length of base is dispensed from tube onto
the mixing pad and a drop of catalyst is added
for each unit length of base.

•Putty consistence are dispensed by
volume using equal number of scoops and
kneaded.
•Automatic mixing and dispensing devices
are available used for light, medium and
heavy body consistencies.
•It consists of a double barrel gun with
mixing tip. The tip consists of spiral
inside. The mixing tips vary in diameter
length and size of the tip opening for
specific consistency.

• It has the advantages over hand mixing
• Less air bubbles
• Reduced working time
• More uniform mix

• A recent development in the automatic
mixing and dispensing device is a dynamic
mechanical mixer. Materials are supplied in
plastic bags housed in a cartridge. Device
uses a motor to drive parallel plunger that
force the materials into a mixing tip and the
spiral inside the mixing tip rotates as the
materials are extruded through the tip.
With this uniform mix of even higher
viscosity material can be achieved

•

Making of impression
•

•
•
•
•
•

Initially tray is coated with adhesive
that forms bond between tray and
impression material. Slightly roughened
surface of tray increases adhesion.

METHODS OF MAKING IMPRESSION
Three techniques
Single mix technique
Multiple mix technique
Reline technique

• Single Mix technique:
• Viscosity used is regular body
• Method:
•
The paste is mixed and part of it is loaded
into tray and part into syringe. The syringe
material is then injected on to the prepared area.
Then tray is seated over it.

• Multiple mix technique:
•
Viscosity used is heavy body and light body
• Method:
•
The two viscosities are mixed simultaneously
on separate pads. Heavy body is loaded onto
the tray and light body in to syringe. The syringe
material is injected into area of preparation. Tray
with heavy body is seated over it.

• Reline technique:
•
Viscosity used is putty and light
body
• Two approaches are present
• Two stage procedure
• Single stage procedure


• For two stage procedure, thick putty material is placed in
stock tray and a preliminary impression is made. This
forms an intra oral custom tray. Space for light body or
was is provided wither by cutting away some of the putty
or by using thin polyethelene sheet as a spacer between
putty and prepared teeth.
• A mix of thin wash material is placed into putty and putty
was combination tray is seated finally to make
impression.

• For single stage procedure, was material is
syringed into place and then unset putty is
seated over light body but the disadvantage
is that putty may displace light body.
• Removal of the impression:
• The material is checked for set by probing
with the blunt instrument. Then impression
is dislodged from the mouth with a steady
pressure

•

Preparation of stone casts and dies:
•
•
•

All non aqueous elastomeric impression
material are compatible with all types of
gypsum products.
The hydrophobic nature of VPS material
make them compatible with epoxy resins
used for more accurate casts and dies.
Surfactant can be applied to improve the
ability of hydrophobic impression material
surfaces to be wet by stone.


• Disinfection:
• Condensation silicones, addition silicones
and polysulfides can be disinfected with all
EPA registered disinfectants without major
changes provided disinfection time is short.
The impressions should be immersed for the
specified time and after it should be
removed, rinsed and cast is poured.
• A satisfactory solution for most elastomers
is 2% Glutaraldehide

•
1.
2.
3.
4.
5.

APPLICATIONS:
Impressions for fixed partial dentures
Impressions for removal partial dentures
Impressions for complete dentures
polyether is used for Border moulding
To make impressions for implant
procedure
6. In maxillofacial prosthesis

COMPARATIVE PROPERTIES OF
ELASTOMERS
PROPERTIES

POLYSULFIDES

CS

AS

POLYETHER

FLOW

high

low

very low

very low

VISCOSITY

low

moderate

high

high

CREEP

high

moderate

low

very low

TEAR
STRENGTH

2500-7000 2300-2600 1500-4300 18004800

%CONTR 0.40-0.45 0.38-0.60
ACTION
4-9%

3-6%

3%

DIMENTI 0.4%
AL
CHANGE

0.6%

0.15%

0.23%

CONTACT 820
ANGLE

980

9853

490

excellent

excellent

excellent

STRAIN

TISSUE
DETAIL

14-17%

0.14-0.17 0.19-0.24

excellent


SHELF
LIFE

fair

poor

excellent

fair

ST

8-12min

6-8min

4-7min

3-5min

WT

4-7min

2.5-4min

2-4min

3min

medium

high

veryhigh

STIFFNE low
SS


AGAR (REVERSIBLE
HYDROCOLLOID
•

Sears introduced reversible hydrocolloids in
1937.
• Definition:


• MODE OF SUPPLY:
•
Supplied as gel in collapsible tube
• or as Cylinders in a jar


COMPOSITION:INGREDIENT

WEIGHT(%)

FUNCTION

agar

13-17

To provide
dispersed phase

borate

0.2-0.5

Provides strength

sulfate

1-2

Gypsum hardener

wax

0.5-1

filler

Thixotropic
materials

0.3-0.5

thickener

water

balance

Reaction medium


• PROPERTIES:
• The ADA specification No 11 sets standard properties
required by agar hydro colloidal material.
• Flow:
•
The material should be able to record the fine
details
• Gelatin temperature:•
After boiling for 8 min, the material should be fluid
enough to be extruded from container. After tempering
the solution should be homogenous and should set
between 37 and 45 when cooled.

•
•
•
•

Flexibility:
The ADA specification requirement for
flexibility allows a range of 4% to 15% at a
stress of 14.2 psi.
Elasticity and elastic recovery:Agar hydrocolloids are highly elastic in
nature and elastic recovery occurs to the
extent of 98%

•
•

Accuracy and dimensional stability
Agar impressions are highly accurate at the
time of removal from mouth but shrink when
stored in air and expand when stored in water.
The least dimensional change occurs when
stored in 100% humidity but immediate pouring
of cast is recommended.


•
•

•

Working and setting time:Working time ranges between 7-15 minutes
and setting time is about 5 minutes. They can
be controlled by regulating flow of the water
through cooling tubes.
Tear and Compressive strength
Tear strength is 4 psi
Compressive strength is 800 gm/cm2.

• MANIPULATION:
•
Conditioning until is required for
manipulation of agar.
• The Conditioner consists of
• Boiling section
• Storage section
• Tempering section.

• In boiling section, the material is kept for 10 min for
liquefaction.
•
Then material is stored in storage section at 650 in
sol form until it is required.
•
Material is tempered at 45. for 3 to 10 min so as to
be tolerated by the patient.
•
Just before the tempering process for the bray
material is completed, the syringe material is directly
taken from the storage compartment and applied to be
teeth. The water soaked on the layer of the tray
hydrocolloid is removed from the container and gauge is
removed.

• The tray is immediately brought into position and
seated with tight pressure and held with a very
light force.
•
Gelatin is accelerated by circulating cool
water (18-21) through the tray for 3-5 min. After
the gelatin is over, the tray is removed suddenly
with a snap.


• STORAGE OF AGAR IMPRESSION:
•
Storage should be avoided .
Storage in air results in dehydrations,
and storage in water results in
expansion. If storage is unavoidable it
can be stored in100% relative
humidity for not more than 1 hour.


• Advantages:
1. Accurate dies can be prepared if
handled properly.
2. Good elastic property and
reproduces undercuts properly
3. Well tolerated by patient
4. Used for duplicating models.

• Disadvantages:
1) Flow is less Compared to recent elastic
impression materials
2) Gelatin may be painful to the patient.
3) Tears relatively easily.
4) Extensive equipment is required


ALGINATE ( IRREVERSIBLE
HYDROCOLLOIDS):•

It is extracted from certain brown seaweed.
The substance is called anhydro-beta-d
mannuronic acid or alginic acid.
• TYPES:• 1) Type II – Fast setting (1-2 min)
• 2) Type II- Normal setting ( 2.4.5 min)

COMPOSITION
INGREDIENT

WEIGHT(%)

FUNCTION

Potassium alginate 15%

Dissolves in water
and reacts with
calcium ions

Calcium sulfate

Reacts with
Potassium alginate
and forms insoluble
calcium alginate

16%


Zinc Oxide

4%

Acts as filler

Potassium titanium
fluoride

3%

Accelerator

Diatomaceous
earth

60%

Filler

Sodium phosphate

2%

Retarder

Coloring and
Flowering agents

TRACES


REACTION
• :•

The chief ingredient of irreversible
hydrocolloid is one of the soluble alginates.
Reaction occurs by a chemical reaction. Soluble
alginates reacts with Calcium sulfate to produce
insoluble calcium alginate as a gel.

• The production of calcium alginate is delayed by
the addition of a third soluble salt to the solution
with which calcium sulfate will react in preference
to the soluble alginate to form an insoluble calcium
salt.
• Thus, the reaction between the calcium sulfate and
the soluble alginate is prevented as long as any of
the added salt is left. The added salt is called
retarder.

• The reactions that occur are
1. 2Na3 PO4 + 3 CaS04
 Ca3 (Po4) + 3 Na2 So4
When the supply of retarder ( trisodium phosphate) is
exhausted, Calcium ions begins to react with potassium
alginate to produce calcium alginate.
• K2n Alg + n CaSo4-nK2So4 + Can Alg


• CONTROL OF SETTING TIME:
•Setting time can be altered by altering of
water.
•As the temperature increases, the
setting time decreases.
•For 10 rise of temperature 1 min
reduction in setting time occurs.
•Bowl and spatula also can be cooled to
increase setting time.

• MANIPULATION:
For manipulations a clean bowl and metal
spatula.
The First step in the manipulation is to prepare a
proper mixture of water and powder. Water is
powered in to bowl and specified weight of
powder is added and powder is carefully
incorporated into water with spatula.

• A vigorous figure 8 motion is best with the mix
being stopped against the sides of bowl with
intermittent rotations of the spatula to press out
air bubbles. The final mix should be smooth
creamy mixture that does not drip off the spatula
when it is raised. Mechanical devices are also
available for mixing. Their advantages are speed
convenience and eliminating human errors.

•
•
•
•
•
•
•
•

Mixing time for
Fast set alginate – 45 Sec
For Normal set - 60 Sec
Over mixing results in
Reduction in final strength as gel fibrils are destroyed
Reduction in working time.
Under mixing Causes
Lack of homogeneity and reduced strength

• MAKING THE IMPRESSION
• A perforated tray is used
• The thickness of alginate impression between the tissue
and the tray should be at least 3mm.
• Before seating the impression, the material should have
developed sufficient body so that it may not flow out of
the tray and gag the patient. Once the tray is seated in
the mouth, it must be held firmly without any movement.
Alginate impressions should not be removed from mouth
for at least 3 minute after gelation has occurred.

• Removal of the impression:
• Alginate impression develops effective seal which
can be freed by running the finger around
periphery. Impression should be removed
suddenly with a jerk. Torquing or twisting should
be avoided. After removal impression should be
washed with water to remove saliva, covered with
wet gauge to prevent syneresis and cast should
be poured as soon as possible.

• PROPERTIES
•
ADA specification No. 18 for alginate sets following
standards
• Working time:

• Fast setting – 1.2 to 2minutes
• Normal setting – 2-4.5minutes
• Setting time:

• Fast setting – 1.2 minutes
• Normal setting – 2-4.5minutes

• Flexibility
•

It is about 14% at a stress of 1000gm/cm2

• Elasticity and elastic recovery:
•

Elastic recovery is 97.3%


• Strength:
•
•
•

The compressive strength of alginate ranges
from 5000-8000gm/cm2.
The tear strength ranges between 350700gm/cm2.
Both these properties are time dependent. If
removal is delayed, strength increases.

•

Time from gelation(min)

Compressive strength

0

0 .33

4

0.77

8

0.81

12

0.71

16

0.74


• The final strength depends on
• W/P ratio: Too much or too little water
reduces strength
• Mixing time: Over and under mixing reduces
strength
• Dimensional stability:

•

Alginate impression loses water by
evaporation and shrink in air. If placed in water it
absorbs and swells. So cast should be poured
immediately

• Advantages:
• Easy manipulation
• Minimum equipment
• Low cost
• Accurate if properly handled


• Applications:
• Making impressions for diagnostic casts for
partial dentures
• Making impressions for orthodontic models
• Making preliminary impressions for complete
dentures
• For duplicating models

• LAMINATE TECHNIQUE/ALGINATE AGAR METHOD
•
In this technique agar in the syringe is injected on
to the area to be recorded, an impression tray containing
chilled alginate is placed over it.
• The alginate gets by chemical reaction, where as agar
gels by means of contact with cool alginate. Since agar
is in contact with teeth maximum detail care be obtained.


• MODIFIED ALGINATES:
•
Traditionally alginate is supplied in two component
system, powder and water. But other forms are also
available.
•In the form of a solution containing
water and a reactor of plaster of Paris
•As a two paste system one containing
solution and other calcium reactor. These
materials contain silicone and are supplied
in tray viscosity and syringe viscosity.

• RECENT ADVANCES
• High tear strength alginates: Silicone
reinforced two paste system one with alginate,
other with calcium reactor. It has higher tear
strength
• Self disinfecting alginates containing
iodophor
• Dust free alginates: Organic glycol is used to
agglomerate the dust particles

REVIEW OF LITERATURE
•

Andree, Alfred and Christoph evaluated the
dimensional accuracy of monophase elastic
impression making with addition silicone and
polyether and found no significant change.


•

Josehph, Tamer and David assessed the accuracy of
three putty wash impression technique using same
impression material i.e. VPS. Techniques used were
1) Putty and wash used simultaneously
2) With 2mm relief using prefabricated coping
3) With polythelene space
•
They concluded that PVS with 2wmm relief was the
most accurate


•

Steven O Hondrum assessed the shelf life of
different elastomers like polyether, polysulfide,
additive silicone and found all the materials
were fairly efficacious. But addition silicone
showed better value during 72 month period
and polysulfide with a little change.


•

John Chai, Yutaka investigated modulus of
elasticity, strain and tear energy of VPS,
polysulfide and polyether and concluded that
high strain tolerance of PVS allows their
removal without distortion from undercuts. The
high tear energy of polysulfides indicates their
superior resistance to tear in thin sections.


•

Alvin G. Wee evaluated the accuracy of solid
implant casts fabricated from different
impression materials (Polyether, AS, CS,
polysulfide) and concluded that polyther
(medium) was recommended for direct implant
impression.


• J.A. Payne tested the bond strength of three
elastomers (Hydrosil, Reprosel, impregum) to an
auto polymerized resin tray and concluded that
roughening of tray increased bond strength


• Gordon, Johnson and David evaluated the
evaluated the effect of tray section (acrylic resin
trays, thermoplastic trays and plastic trays) on the
accuracy of elastomers and concluded that
custom made trays of acrylic resin and
thermoplastic material produced casts with better
accuracy


•

Shirley, John H Park and Daneil E. Tira
compared the accuracy of one step putty wash
with two step putty wash of addition silicone
impression. They found different was not
significant.


•

Kern and Reinhold tested the influence of
disinfectants (MD/520 and impresept) on the
accuracy of reversible hydrocolloid and found
accuracy change was not significant.


•

Willium Heisler and Anthony evaluated for
dimensional accuracy and bond strength of
irreversible hydrocolloid with irreversible
hydrocolloid system and found that accuracy
was suitable for clinical use and bond strength
was similar to tear strength of reversible
hydrocolloid.


•

L.W. Carlyle evaluated compatibility of
irreversible hydrocolloid with three dental
stones (Die keen, Quick stone, Hemihydrate).
Results showed that Die keen was most
compatible.


•

Paul, Gardener and Steven conducted a study
to evaluate the effect of storage time in a
100% humid environment on the accuracy of
gypsum casts poured from reversible
hydrocolloid impression and concluded that
reversible hydrocolloid can be stored in 100%
humidity for 60 minutes before pouring.


REFERENCES
Anusavice. Dental Material, 11th edition
Robert G. Craig. Restorative Dental Material
Smith. The clinical handling of Dental material
International Journal of Prosthodontics, 2002;
15: 168-74.
Journal Prosthet Dent, 2000; 83: 161-165


Journal Prosthet Dent, 2001; 85: 73-81.
11: 219-23
5: 55-8.


Journal Prosthet Dent, 1990; 63: 12-15
J Prosthet Dent, 1993; 70: 449-53


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