IMPRESSION MATERIAL

1. IMPRESSION MATERIAL AND
TECHNIQUE
PRESENTED BY =
DR. MANISH
SUNDESHA
1ST PG STUDESNT
GUIDED BY =
DR. NITIN MIRDHA
DR. BOBBIN Gill
DR. VAISHAK

2. CONTENT
• DEFINITION
• PROPERTIES OF AN IMPRESSION MATERIAL
• CLASSIFICATION OF IMPRESSION MATERIALS
• RIGID IMPRESSION MATERIALS
• ELASTIC IMPRESSION MATERIAL
• ELASTOMERIC IMPRESSION MATERIALS
• IMPRESSION TECHNIQUES

3. DEFINITION
• Impression = A negative likeness or a copy in reverse of the
surface of on abject; an imprint of the teeth and adjacent
structure for use in dentistry (GPT 8 ).
• Impression material = Any substance or combination of
substances used for making impression or negative
reproduction (GPT 8).

4. PROPERTIES OF AN IMPRESSION MATERIAL
1. Should be nontoxic and nonirritant to dentist and patient.
2. Acceptable to the patient.
a. Have a pleasant taste, odor, consistency and color.
b. Should set quickly once placed in the mouth.
3. Should be accurate.
a. Accurate surface detail.
b. Elastic properties with freedom from permanent deformation
after strain.
c. Dimensionally stable.
4. Have adequate shelf life for storage and distribution.

5. 5. Be economical.
6. Handling properties.
a. Sufficient working time.
b. Set quickly in mouth (saves chairside time).
c. Be easy to use with the minimum equipment.
d. Satisfactory consistency and texture.
7. Have adequate strength so that it will not break or tear
while removing from the mouth.
8. Should be compatible with the die and cast materials.

6. CLASSIFICATION OF IMPRESSION
MATERIALS
1. According to mode of setting and elasticity.
2. According to tissue displacement during impression procedure.
3. According to their uses in dentistry.

7. ACCORDING TO MODE OF SETTING AND
ELASTICITY
Mode of setting Rigid Elastic
Set by chemical reaction
(irreversible or thermoset)
Impression plaster, Zinc
oxide eugenol
Alginate hydrocolloid
Nonaqueous elastomers -
e.g. polysulfide, silicone
Set by temperature change
(reversible/ thermoplastic)
Compound, Waxes Agar hydrocolloid

8. ACCORDING TO TISSUE DISPLACEMENT
1. Mucostatic
•e.g.- plaster, zinc oxide
eugenol, low viscosity
alginates, low viscosity
elastomeric materials, etc.
2. Mucocompressive
(Mucodisplacive)
•e.g. - compound, high
viscosity alginates, high
viscosity elastomers, etc.

9. ACCORDING TO THEIR USES IN DENTISTRY
•Impression materials used for complete denture
prosthesis :-
Impression plaster, impression compound and impression paste set to a
hard rigid mass, and hence cannot be removed from undercuts without
the impression being fractured or distorted. Therefore these materials
are best suited for edentulous mouth.
•Impression materials used for dentulous mouths :-
On the other hand alginates and rubber base impressions are
sufficiently elastic to be withdrawn from undercut areas. Such elastic

10. RIGID IMPRESSION MATERIALS
• As mentioned earlier the rigid impression materials are
1. Impression plaster
2. Impression compound
3. Zinc oxide eugenol impression paste
4. Impression waxes

11. IMPRESSION COMPOUND
• Synonyms Modeling compound or modeling plastic.
• CLASSIFICATION
Type I - Impression compound
Type II - Tray compound
• SUPPLIED AS
sheets, sticks, cakes and cones in a variety of colors.

12. APPLICATIONS :-
Type I
1. For making a preliminary impression in an edentulous mouth
2. For impressions of full crown preparations where gingival tissues
must be displaced.
3. Peripheral tracing or border molding.
Type II
4. To check undercuts in inlay preparation.
5. To make a special tray.
Single tooth impression
In conservative dentistry, an impression is made of a single tooth in which a cavity
is prepared. The compound is softened and carried in a copper band. The filled
band is pressed over the tooth and the compound flows into the prepared cavity.
Complete denture impressions
In complete denture fabrication, it is common to make two sets of impressions—the
preliminary and the final impression. The preliminary impression is made in a stock
tray. A study cast made from this is used to construct a custom tray or special tray.
The custom tray is used to make the final impression.

13. REQUIREMENTS OF IMPRESSION COMPOUND
An ideal impression material should
1. Harden at or little above mouth temperature.
2. Be plastic at a temperature not injurious or harmful to oral tissues.
3. Not contain irritating or toxic ingredients.
4. Harden uniformly when cooled without distortion.
5. Have a consistency when softened which will allow it to reproduce fine d
6. Be cohesive but not adhesive.
7. Not undergo permanent deformation or fracture while withdrawing the
from the mouth.
8. Be dimensionally stable after removal from the mouth and during storag
9. Exhibit a smooth glossy surface after flaming.
10. Withstand trimming with sharp knife without flaking or chipping after
11. Should not boil and lose volatile components on flaming.

14. COMPOSITION :- Ingredient Parts
Resin 30
Copal resin 30
Carnauba wax 10
Stearic acid 5
Talc 25
Coloring agent
(e.g.rouge)
PROPERTIES OF IMPRESSION COMPOUND :-
FUSION TEMPERATURE :- The temperature at which the material looses its hardness or
brittleness on
heating or forms a rigid mass upon cooling is referred to as fusion temperature. FUSION
TEMPERATURE= 43.5 °C.
THERMAL PROPERTIES :-
Thermal conductivity :- Impression compound has very low thermal conductivity, i.e. they are
poor conductors of heat.

15. MANIPULATION
• STICKS :-
• Manipulation of stick compound for border molding of a custom tray.

16. CAKES :-
(A) This water bath maintains a
steady softening temperature(65-
75 °C) and is ideal for softening
impression compound.
(B)A slightly oversized
stock metal tray.
(C)Placing the material in the
is known as loading the tray.

17. ADVANTAGES AND DISADVANTAGES
ADVANTAGES
• The material can be reused a number of
times (for the same patient only) in case
of errors.
• Inaccurate portions can be remade
without having to remake the entire
impression.
• Accuracy can be improved by flaming the
surface.
• The material has sufficient body to
support itself especially in the peripheral
portions. It does not collapse completely
if unsupported by the tray.
DISADVANTAGES
• Records less detail because of its high
viscosity.
• Compresses soft tissues during
impression.
• Distortion due to its poor dimensional
stability.
• Difficult to remove if there are severe
undercuts.
• There is always the possibility of
overextension especially in the
peripheries.

18. ZINC OXIDE EUGENOL IMPRESSION PASTE
Zinc oxide and eugenol based products are widely used in dentistry.
1. Cementing and insulating medium.
2. Temporary filling material.
3. Root canal filling material.
4.Surgical pack in periodontal surgical procedures.
5. Bite registration paste.
6. Temporary relining material for dentures.
7. Impressions for edentulous patients.

19. CLASSIFICATION :-
ADA specification No. 16.
(1) Type I or Hard
(2) Type II or soft
AVAILABLE AS :-
In paste form in two tubes
Base paste (white in color)
Accelerator or reactor or catalyst paste (red in color)
Base Paste Accelerator paste
Ingredient Wt. % Ingredient Wt. %
Zinc oxide 83 % Oil of cloves or
eugenol
12 %
Vegetable or mineral
oil
17 % Gum or polymerized
rosin
50 %
Filler (Silica type) 20 %
Lanolin 3 %
COMPOSTION :-

20. SETTING TIME
Working time
There should be sufficient time for mixing, loading onto the tray
and seating the impression into the mouth.
Setting time
Once the material is in place, it should set fast.
Initial setting time Final setting time
Type I 3-6 minutes 10 minutes
Type II 3-6 minutes 15 minutes

21. PROPERTIES
• Consistency and flow :- A paste of thick consistency can compress the tissues. A thin free flowing
material copies the tissues without distorting them. the spread is
Type I pastes — 30 to 50 mm
Type II pastes — 20 to 45 mm
Clinically, these materials have a very good flow.
• Detail reproduction
It registers surface details quite accurately due to the good flow.
• Rigidity and strength
The impression should resist distortion and fracture when removed from the mouth after setting.
The compressive strength of hardened ZOE is approximately 7 MPa two hours after mixing.
• Dimensional stability
The dimensional stability is quite satisfactory.
• Biological considerations
Some patients experience a burning sensation in the mouth due to eugenol. It can also cause
tissue irritation.

22. MANIPULATION
(A) Equal lengths of base and reactor pastes are
dispensed.
(B) Mixing is done with a stainless steel
spatula using circular motions until a
streak free mix is obtained

23. • Mixing time 1minute.
Mechanical mixing A rotary mixing device can also be used

24. ADVANTAGES AND DISADVANTAGES
ADVANTAGES
1. It has enough working time to complete
border molding.
2. It can be checked in the mouth repeatedly
without deforming.
3. It registers accurate surface details.
4. It is dimensionally stable.
5. Does not require separating media since it
does not stick to the cast material.
6. Minor defects can be corrected locally
without discarding a good impression.
DISADVANTAGES
1. It requires a special tray for impression
making.
2. It is sticky in nature and adheres to
tissues.
3. Eugenol can cause burning sensation
and tissue irritation.
4. It cannot be used for making
impression of teeth and undercut areas as
it is inelastic in nature.

25. REVERSIBLE HYDROCOLLOIDS—AGAR
• Classification BASED ON VISCOSITY
Type 1 — Heavy bodied (for use as tray material)
Type 2 — Medium bodied (for use as tray or syringe material)
Type 3 — Light bodied (for syringe use only)
Type 3A — Light bodied for agar-alginate combination technique
• USES
1. Widely used at present for cast duplication (e.g. during the fabrication of cast
metal removable partial dentures, etc.).
2. For full mouth impressions without deep undercuts.

26. 3. It was used extensively for FPD impressions prior to
elastomers.
4. As a tissue conditioner.
SUPPLIED AS
Gel in collapsible tubes (for impressions).
As cartridges or gel sticks (syringe material).
In bulk containers (for duplication).
COMPOSITION
Ingredient Wt. %
Agar 13–17%
Borates 0.2-0.5%
Potassium sulphate 1–2%
Wax, hard 0.5-1%
Thixotropic materials 0.3–0.5%
Alkylbenzoates 0.1%
Coloring and flavoring
agents
Traces
Water Balance (around 84%)

27. MANIPULATION
Hydrocolloid conditioner
Water cooled rim lock trays
Impression
syringes
Connecting
water hose
Agar
tray
material
in tubes
Agar
syringe
materia
l

28. Hydrocolloid conditioner
46 °C for about two minutes with the material loaded in the tray. This reduces the temperatu
so that it is tolerated by the sensitive oral tissues. It also makes the material viscous.
Impression Trays
Rim lock trays with water circulating devices are used. The rim lock is a beading on the insid
of the tray border which helps to retain the material (as agar does not adhere to the tray). It
an inlet and outlet for connecting the water tubes.
Making the Impression
The tray containing the tempered material is removed from the bath. The outer surface of th
agar sol is scraped off, then the water hoses are connected, and the tray is positioned in the
mouth by the dentist. Water is circulated at 18–21 °C through the tray until gelation occurs .
the tray into position, three stops of compound are prepared on non-involved teeth. A post
dam is constructed with compound to prevent distal flow of the impression material. In a
deep palate case, compound is placed on the palatal aspect of the tray in order to provide a
uniform thickness of the hydrocolloid. The mandibular tray is prepared by placing compound
on the distal aspect to limit the impression material. Black tray compound is used as it is not
affected in the tempering bath.
Working and Setting Time
working time ranges between 7 - 15 minutes
setting time - 5 minutes.

29. PROPERTIES OF AGAR HYDROCOLLOIDS
• Gelation, liquefaction and hysteresis Most materials melt as well as
resolidify at the same temperature. However, in agar, this does not
coincide. Gelation (solidification) occurs at 37 °C approximately,
whereas liquefaction (melting) occurs at a higher temperature, i.e.
60–70 °C higher than the gelation temperature. This temperature lag
between liquefaction and gelation is known as hysteresis.
• Syneresis and imbibition (dimensional stability) Since hydrocolloids
use water as the dispersion medium, they are prone for dimensional
change due to either loss or gain of water. If left in a dry atmosphere,
water is lost by syneresis and evaporation, and if it is immersed in
water, it absorbs water by a process known as imbibition.

30. Flow
The material is sufficiently fluid to record the fine details if
correctly manipulated.
Accuracy and dimensional change
Agar impressions are highly accurate at the time of removal
from the mouth, but shrink when stored in air or 100% relative
humidity and expand when stored in water. The least
dimensional change occurs when the impressions are stored in
100% humidity (for not more than one hour).

31. ADVANTAGES AND DISADVANTAGES OF
AGAR HYDROCOLLOID
ADVANTAGES
1. Accurate dies can be prepared, if the material is
properly handled.
2. Good elastic properties help reproduce most
undercut areas.
3. It has good recovery from distortion.
4. Hydrophilic, moist mouth not a problem. It also
gives a good model surface.
5. It is palatable and well tolerated by the patient.
6. It is economical when compared to synthetic elastic
materials.
7. It can be reused when used as a duplicating
material (reuse is not recommended when used as
impression material).
DISADVANTAG
ES
1.Does not flow well when compared to newly
available materials.
2. During insertion or gelation the patient may
experience thermal discomfort.
3. Tears relatively easily. Greater gingival retraction is
required for providing adequate thickness of the
material.
4. Only one model can be poured.
5. Has to be poured immediately. Cannot be stored
for too long.
6. Requires special and expensive equipment.
7. Although it can be reused, it is impossible to
sterilize this material. Also with repeated use there
may be contamination of the materials and a
deterioration in its properties.

32. IRREVERSIBLE HYDROCOLLOID—ALGINATE
• TYPES
Type I — Fast setting.
Type II — Normal setting
SUPPLIED AS
Commonly in bulk packing
In preweighed packets for individual impression
A plastic scoop is supplied for dispensing the bulk powder and a
plastic cylinder is supplied for measuring the water.
Dust free alginates
Chromatic alginates Alginates which change color on setting

33. APPLICATIONS
1. It is used for impression making
–– When there are undercuts.
–– In mouths with excessive flow of saliva.
–– For partial dentures with clasps.
2. For making preliminary impressions for complete dentures.
3. For impressions to make study models and working casts.
4. For duplicating models.
COMPOSITION :-
Ingredients % wt. Function
Sodium or potassium or
triethanolamine
alginate
15% Dissolves in water and reacts with
calcium ions
Calcium sulfate (reactor) 16% Reacts with potassium alginate and forms
insoluble calcium alginate
Zinc oxide 04% Acts as a filler
Potassium titanium fluoride 03% Gypsum hardener
Diatomaceous earth 60% Acts as a filler
Sodium phosphate (retarder) 02% Reacts preferentially with calcium sulfate
Coloring and flavoring agent Trac e.g. wintergreen, peppermint, anice,

34. PROPERTIES OF ALGINATE HYDROCOLLOID
• Taste and Odor :- Alginate has a pleasant taste and smell. Over the years,
manufacturers have added a variety of colors, odors and tastes to make it as
pleasant as possible to the patient. Flavors include strawberry, orange, mint
etc.
• Flexibility :- Lower W/P ratio (thick mixes) results in lower flexibility.
• Elasticity and Elastic Recovery Alginate hydrocolloids are highly elastic (but
less when compared to agar) and about 98.2% elastic recovery occurs. Thus,
permanent deformation is more for alginate (about 1.8%). Permanent
deformation is less if the set impression is removed from the mouth quickly.
• Dimensional Stability :- Set alginates have poor dimensional
stability due to evaporation, syneresis and imbibition.
Therefore, the cast should be poured immediately. If storage is
unavoidable, keeping in a humid atmosphere of 100% relative

35. MANIPULATION
• The proper W/P ratio as specified by the manufacturer should be
used (usually one measure water with two level scoops of powder.
The water measure and scoop are supplied by the manufacturer).
The water is taken first. The powder is sprinkled in to the water in
the rubber mixing bowl . The mixing is started with a stirring
motion to wet the powder with water. Once the powder has been
moistened, rapid spatulation by swiping or stropping against the
side of the bowl is done. A vigorous figure-eight motion can also
be used.

36. Mixing Time
For fast set alginate—45 seconds.
For normal set alginate—60 seconds.
Working Time
Fast set alginate—1.15 minutes.
Normal set alginate—2 minutes.
Setting Time
Type I (fast set)—1.15–2.0 minutes
Type II (normal)—3–4.15 minutes

37. ADVANTAGES AND DISADVANTAGES OF
ALGINATE
ADVANTAGES
1. It is easy to mix and manipulate.
2. Minimum requirement of equipment.
3. Flexibility of the set impression.
4. Accuracy if properly handled.
5. Low cost.
6. Comfortable to the patient.
7. It is hygienic, as fresh material must be used
for each impression.
8. It gives a good surface detail even in
presence of saliva.
DISADVANTAGE
S
1. Cannot be electroplated so metal dies are
not possible.
2. It cannot be corrected.
3. Distortion may occur without it being
obvious if the material is not held steady while
it is setting.
4. Poor dimensional stability—it cannot be
stored for long time.
5. Poor tear strength.
6. Because of these drawbacks and the
availability of better materials, it is not
recommended where a higher degree of

38. ELASTOMERIC IMPRESSION MATERIALS
• The first elastomeric or rubber-based ‘impression material’ to be introduced was polysulfide
which was introduced in 1950.
• According to their chemistry
1. Polysulfide
2. Condensation polymerizing silicones
3. Addition polymerizing silicones
4. Polyether
• Classification based on viscosity
• Type 0—Putty consistency (very heavy)
• Type 1—Heavy-bodied consistency (tray consistency)
• Type 2—Medium-bodied consistency (regular bodied)
• Type 3—Light-bodied (syringe consistency)

39. According to wettability or contact angle
Impression materials are also classified as
1. Hydrophilic, if their contact angle is from 80 to 105°.
2. Hydrophobic, if their contact angle is from 40 to 70°.
USES OF ELASTOMERIC IMPRESSION MATERIALS
1. In fixed partial dentures for impressions of prepared teeth.
2. Impressions of dentulous mouths for removable partial dentures.
3. Impressions of edentulous mouths for complete dentures.
4. Polyether is used for border molding of edentulous custom trays.
5. For bite registration.
6. Silicone duplicating material is used for making refractory casts
during cast partialdenture construction.

40. SUPPLIED AS:-
Regardless of type all elastomeric impression materials are
supplied as two component (base and catalyst) systems.
• Collapsible tubes
• Cartridges—light and regular body material are also
supplied in cartridges to be used with static mixing tips and
dispensers
• Putty consistency is supplied in jars

41. POLYSULFIDES
• SUPPLIED AS :- They are supplied as a two-paste system in collapsible
tubes.
Available in three viscosities
 Light bodied
 Medium bodied
 Heavy bodied

42. Composition :-
Base paste
Ingredient Wt. percent
Liquid polysulfide polymer 80-85 %
Inert fillers (Titanium dioxide, zinc
sulfate,copper carbonate or silica)
16-18%
Reactor paste
Ingredient Wt. percent
Lead dioxide 60–68%
Dibutyl phthalate 30-35%
Sulfur 3%
Other substances like magnesium,
stearate (retarder) and deodorants
2%

43. PROPERTIES :-
1.Unpleasant odor and color.
2. These materials are extremely viscous and sticky. Mixing is difficult. However, they exhibit
pseudoplasticity, i.e. if sufficient speed and force is used for spatulation, the material will
seem easier to handle. The mixing time is 45 seconds.
3. It has a long setting time of 12.5 minutes (at 37 °C). In colder climates setting can take as
longer. This adds to the patient’s discomfort. Heat and moisture accelerate the setting
time (sets faster in the mouth).
4. Excellent reproduction of surface detail.
5. Dimensional stability The curing shrinkage is high (0.45%) and continues even after
setting. It has the highest permanent deformation (3–5%) among the elastomers. Elastic
recovery improves with time and so pouring of the model should be delayed by half an
hour.
6. It has high tear strength (4000 g/cm).
7. It has good flexibility (7%) and low hardness. A 2 mm spacing in the tray is sufficient for
making an impression.
8. It is hydrophobic so the mouth should be dried thoroughly before making an impression.
Care should also be taken while pouring the stone to avoid air pockets.

44. CONDENSATION SILICONE
• SUPPLIED AS :-
Paste Supplied as two pastes in unequal sized collapsible tubes. The base paste
comes in a larger tube while the catalyst paste is supplied in a much smaller
tube.
Putty The putty is supplied in a single large plastic jar . The catalyst may be in
paste form or sometimes it may be supplied as a liquid.
Available in three viscosities
Light bodied
Medium bodied
Putty

45. COMPOSITION :-
Ingredient Wt. percent
Polydimethyl siloxane (hydroxy—
terminated)
80–85%
Colloidal silica or microsized metal
oxide filler
35-75%
Color pigments 16-18%
Ingredient Action
Orthoethyl silicate crosslinking agent
Stannous octoate catalyst
Base
Reactor paste/accelerator

46. PROPERTIES
1. Pleasant color and odor & nontoxic .
2. Setting time is 6–9 minutes. Mixing time is 45 seconds.
3. Excellent reproduction of surface details.
4. Dimensional stability is comparatively less because of the high curing
shrinkage .
5. Tear strength (3000) g/cm is lower than the polysulfides.
6. It is stiffer and harder than polysulfide. The hardness increases with time.
The spacing in the tray is increased to 3 mm to compensate for the stiffness.
7. It is hydrophobic. The field should be well-dried before making an
impression. Care should also be taken while pouring the cast to avoid air
entrapment.

47. ADDITION SILICONES (POLYVINYL
SILOXANE)
• These materials were introduced subsequent to the introduction of the condensation
silicones . These new materials had better properties when compared to the
condensationsilicones.
• It is also known as polyvinyl siloxane. Currently, the addition silicones are very
popular and is perhaps the most widely used elastomeric impression material
worldwide.
SUPPLIED AS
• Tubes The base and catalyst pastes come in equal sized tubes.
• Cartridge form with static mixing tips For use with a dispensing gun.
• Putty jars Two equal sized plastic jars—containing the base and catalyst.
• A larger electric driven autodispenser and mixing device is also available.

48. Available in four viscosities
Light bodied
Medium bodied
Heavy bodied
Putty
COMPOSITION :-
Base paste Reacter
Poly (methyl hydrogen siloxane) Divinyl polysiloxane
Other siloxane prepolymers Other siloxane prepolymers
Fillers (amorphous silica or
fluorocarbons)
Platinum salt - catalyst (chloroplatinic
acid)
Palladium - hydrogen absorber Fillers
Retarders
Coloring agents

49. PROPERTIES
1. Pleasant odor and color.
2. Excellent reproduction of surface details. Polyvinyl siloxanes are currently considered
to reproduce the greatest detail of all the impression materials.
3. Setting time ranges from 5 to 9 minutes. Mixing time is 45 seconds. Working time
may be extended by chilling the tubes. Gains of up to 90 seconds have been reported
when the materials are chilled to 2 °C.
4. It has the best dimensional stability among the elastomers. It has a low curing
shrinkage (0.17%) and the lowest permanent deformation (0.05–0.3%).
5. Early materials had the problem of hydrogen gas formation. If hydrogen gas is
liberated pouring of stone is delayed by 1–2 hours to prevent formation of air bubbles in
the stone cast. Current materials do not have this problem because of the addition of
palladium.
6. It has good tear strength (3000 g/cm).
7. It is extremely hydrophobic, so similar care should be taken while making the
impression and pouring the wet stone. Some manufacturers add a surfactant (detergent)
to make it more hydrophilic.
8. It has low flexibility and is harder than polysulfides. Extra spacing (3 mm) should be

50. POLYETHER RUBBER IMPRESSION MATERIAL
• Polyether was introduced in Germany in the late 1960s. It has good
mechanical properties and dimensional stability. Its disadvantage was that
the working time was short and the material was very stiff.
AVAILABLE AS:-
• Available as base and accelerator in collapsible tubes, cartridges.
• Currently, it is available in three viscosities.
Light bodied
Medium bodied
Heavy bodied

51. COMPOSITION:-
BASE
Reactor/accelerator paste
Ingredient Wt. Percent/Function
Polyether polymer 80-85%
Colloidal silica Filler
Glycolether or phthalate Plasticizer
IngredientF Function
Aromatic sulfonate ester Crosslinking agent
Colloidal silica Filler
Phthalate or glycolether Plasticizer

52. PROPERTIES:-
1. Pleasant odor and taste.
2. The sulfonic ester can cause skin reactions.
3. Setting time is around 6–8 minutes. Mixing should be done quickly that is
30 seconds. Heat decreases the setting time.
4. Dimensional stability is very good. Curing shrinkage is low (0.24%). The
permanent deformation is also low (0.8–1.6%). However, polyethers absorb
water and can change dimension. Therefore, prolonged storage in water or in
humid climates is not recommended.
5. It is extremely stiff (flexibility 3%). It is harder than polysulfides and
increases with time. Removing it from undercuts can be difficult, so additional
spacing (4 mm) is recommended.
6. Tear strength is good (3000 g/cm).

53. MANIPULATION OF ELASTOMERIC
IMPRESSION MATERIALS
• The 5 main mixing techniques are
1. Hand or manual spatulation
2. Manual kneading
3. Rotary table assisted mixing
4. Static or extrusion mixing
5. Dynamic mechanical mixing
• HAND MIXING - Pastes in tubes :-Hand or manual spatulation and is primarily used
elastomers supplied in tubes.

54. KNEADING – PUTTY
Kneading is primarily employed for very heavy or putty consistency elastomers. In case of addition
silicones, equal scoops of base and accelerator are dispensed. With condensation silicones, the required
number of scoops of base and recommended amount of liquid or paste accelerator is taken. In either
case mixing is done by kneading between the fingers. Mixing is continued until a streak free mix is
obtained.
ROTARY TABLE -ASSISTED MIXING
The technique is similar to that described for zinc oxide impression pastes. The pastes are dispensed on
to a rotating table . The spatula is used to scoop and flatten the pastes alternately and continuously as
the table rotates until a uniform mix is obtained.
STATIC OR EXTRUSION Mixing
Static mixing also known as ‘extrusion mixing’, has grown in popularity over the years, primarily
because of its high accuracy and convenience. Extrusion mixing is a method by which two or more
material components are extruded simultaneously from their separate primary containers through a

55. Static mixing tip showing internal helical mixers.
Advantages of static mixing:-
1. Shorter mixing time.
2. More uniform proportioning and mixing.
3. Less voids.
4. Mix can be delivered directly to the tray or impression site.

56. Dynamic Mechanical Mixing:-
Another device is an electrically operated dynamic mechanical mixer . The base and catalyst
are supplied in large plastic bags which are loaded in to the machine. On pressing a button,
the material is mixed and extruded through the tip, directly into the impression tray.
Two representative dynamic mechanical mixing devices.

57. IMPRESSION TECHNIQUES:-
• Classification of elastomeric impression techniques
• Based on the viscosity used
1. Single viscosity technique
2. Dual viscosity techniques
a. Dual viscosity technique using light body-heavy bodied
b. Putty-wash technique
• Based on the number of stages used
1. One stage technique
2. Two stage technique(wash impression.)

58. 1. One -stage single viscosity (MONOPHASE) Techni que
Tray used Resin custom tray with 2–4 mm spacing.
Viscosity Medium only.
Method The paste is mixed and part of it is loaded on to the tray and part into a syringe.
The syringe material is then injected on to the prepared area of impression. The tray with
material is seated over it. The material is allowed to set.
This technique utilizes the principle of shear thinning. The same material when ejected
under pressure through the syringe tip it exhibits pseudoplasticity and behaves like a
material with lower viscosity. Shear thinning allows as single material to be used as both
syringe and tray material.
2. One -stage dual viscosity (dual -PHASE) Techni que
Tray used Resin custom tray with 2–4 mm spacing.
Viscosity used (a) Heavy bodied and (b) light bodied.
Method The two viscosities are mixed simultaneously on separate pads. The heavy body is
loaded into the tray while the light bodied is loaded into the syringe. The syringe material
is injected over the preparation. The tray containing the heavy body if then seated over it.
Both materials set together to produce a single impression.

59. Two-stage putty Reline (Two-stage Putty -wash Techni que)
Tray used Perforated stock tray.
Viscosity used (a) Putty and (b) Light body.
Equal quantities of base and catalyst is dispensed. Mixing by kneading until uniform color is achieved. A plastic sheet spacer is placed to provide space for
the final impression material.
Making the preliminary impression. The completed preliminary impression.
The final impression material dispensed in to
the preliminary impression.

60. Simultaneously some material is loaded in to the syringe. The syringe material is injected around
the prepared tooth/teeth.
The loaded tray is seated in the mouth.
The completed impression.

61. One -stage putty RELINE (one -stage PUTTY-WASH
techni que)
Tray used Perforated stock tray.
Viscosity used (a) Putty and (b) Light body.
Method Unlike the previous technique, the putty and light
body are dispensed and mixed simultaneously. The putty is
loaded into a perforated stock tray whereas the light body is
injected on to the prepared tooth. The tray is then taken to
the mouth and pressed into position. The heavier putty forces
the lighter material into the details. Both material set
simultaneously to produce an accurate impression.