Impression materials

Dr. Sheetal Kotni
I PGT
IMPRESSION
MATERIALS
Dr.Sheetal Kotni
I PGT
Dept. of Conservative Dentistry &
Endodontics

An impression is a negative reproduction of the tissue.
A cast is defined as the positive replica of upper or lower jaw, which serves the
purpose of construction of various restorations. Positive replication of the form of
prepared tooth constitutes an individual die.

Ideal characteristics of an impression material
● Should be to sufficiently fluid to adapt to oral tissues.
● Should be viscous enough to contain in a tray.
● Should be able to set into a rubbery or rigid solid in the moth in a reasonable
time(<7min).
● Should be resistant to distortion or tearing when removed from the mouth.
● Should be dimensionally stable long enough to allow one or more casts to be
poured.
● Should be biocompatible.
● Should be cost effective.
● There should be no release of gas or byproduct during the setting of
impression or cast and die material.
Environmental conditions, type of tissue dictate choice of materials,quality of the
impression, and quality of the cast.

GUIDELINES FOR A GOOD IMPRESSION
1. A homogenous, uniform blend of the impression material evident in the
impression
2. The material is uniformly spread over the entire tray, without too much material
overflowing
3. No tray surface shown through the impression material
4. No tooth contact with the tray
5. Details of the prepared tooth surface and margins visible with no tears or
roughness of the margins
6. Part of the unprepared tooth surface adjacent to the prepared margins visible
7. No voids or pulls on margin detail

Based on setting
mechanism
Examples
Reversible ● Impression compound
● Dental waxes
● Agar hydrocolloids
Irreversible ● Alginate
● Zinc oxide eugenol
● Elastomers
Thermoset ● Polyether
● Silicones
Thermoplastic Impression compound
CLASSIFICATION (A/c to Materials used in Dentistry, S. Mahalakshmi )

Based on flexibility Examples
Inelastic ● Plaster of Paris
● Impression compound
● Zinc oxide eugenol
Elastic ● Elastomers
● Alginates
● Agar hydrocolloids
Based on amount of pressure Examples
Mucostatic ● Zinc oxide eugenol impression
paste
● Impression plaster
Mucocompressive ● Impression compound

Based on type of tray Examples
Perforated metal tray Alginate hydrocolloid
Water-cooled metal tray Agar hydrocolloid
Custom tray ● Zinc oxide eugenol
● Impression plaster
● Elastomeric impression
material

INELASTIC IM
● Lack the property of flexibility- rigid once set.
● Undergo permanent distortion when subjected to tensile stresses.
1. Impression plaster
2. Impression waxes
3. Impression compound
4. Zinc oxide eugenol impression paste

IMPRESSION PLASTER
● Type I gypsum product-b-calcium sulfate hemihydrate.
● Sets to a rigid mass by a chemical reaction- irreversible one.
● Current use of impression plaster has declined because of the brittle nature of
the material.
● End product-dihydrate.
● Stored in closed metal container- To prevent deterioration and
contamination by moisture.
● The viscosity of impression plaster is thin and hence it is claimed as a
mucostatic impression-No pressure over tissues.
● Flow of material-wash impression-window prep over custom tray.
● Rather than normal seating of tray-gentle puddling recommended.

USES OF I.PLASTER
1. Used to record completely edentulous arches and regions (window technique).
2. Used in dental soldering procedures for assembling and recording relationships
of crowns and pontics.
3. It can also be used as a bite registration material, though it demands a scaffold
of wax for support during bite registration

PROS & CONS of I. Plaster
1. The hydrophilic nature and thin
consistency allows it to flow and record fine
details with least pressure.
2. It has minimal dimensional change
compared to hydrocolloids.
3. The cost is minimal and manipulation of
the material does not require costly
equipment
1. Unpleasant taste and its water absorbing
nature-increased dry sensation in the
patient’s mouth.
2. Increased fluidity - gag reflex
3. Due to its brittleness, it cannot be used in
areas with undercuts.
4. May irritate the underlying soft tissues due
to the heat evolved during the setting
process
5. Sometimes separation from cast may
become difficult if separating medium is not
applied properly.

IMPRESSION WAXES
● Thermoplastic organic compounds containing saturated hydrocarbons, such
as paraffin, ceresin, and bee wax.
● Flow readily at mouth temperature-mouth temperature waxes.
● Classified as
I. Border molding wax
II. Corrective impression wax
III. Occlusal (bite) registration wax.

BORDER MOLDING WAX CORRECTIVE
IMPRESSION WAX
BITE REGISTRATION
WAX
● Simultaneous molding of
all the borders of a
complete denture special
tray.
● Consistency of the wax -
easy- temperature
change of water bath.
● W.T - no concern -
material continues to flow
in the mouth.
● no odor,no irritation at
right temperature,
● e.g., Adaptol
● Used as wax veneer over
an original impression to
contact and register the
details of the soft tissues.
● Records the mucous
membrane and
underlying tissues in a
functional state.
● Used to reline partial
dentures.
● Flow rate-measured by
penetration tests should
be 100% at 37°C
● E.g.,Iowa and korecta
waxes
● Used to transfer the
maxillomandibular
relations recorded
intraorally to the
articulator.
● Being widely replaced by
addition silicone
elastomers due to their
high elastic recovery and
excellent dimensional
stability compared to
waxes.
● Flow measured by
penetration tests at 37°C
ranges from 2.5% to
22%, e.g., Alu wax.

IMPRESSION COMPOUND
● ADA Spec. No.- 3.
● Alternative names- Dental compound, model compound, model plastic,
impression composition.
● Dispensing- Sheets and sticks, cakes, cylinders.
● Classification-
I- Low fusing- Impression compound-Oral impressions
II- High fusing- Tray compound-Forming trays in oral cavity
● Thermally reversible, rigid when cold, and plastic when heated to a few
degrees above mouth temperature- Thermoplastic material.
● Colors-different softening and working temperatures.

COMPONENT % Function
Natural/Synthetic resin 40 Thermoplasticity Imparts flow and cohesion
Compound wax 7 Organic
matrix,Thermopla
sticity
Principal ingredient,
Shellac, Stearic acid, GP 3 Plasticizer
Talc, diatomaceous earth 50 Filler ● Provide working consistency ( to increase the
viscosity at temperatures above that of the
mouth)
● Increases the rigidity of the compound at
room temperature.
● Strengthen or reinforce the principal ingredients
Pigments Colour
COMPOSITION OF IMPRESSION COMPOUND

● Flow:
TYPE FLOW FUSION
TEMPERATURE
37 degrees C 45 degrees C
I < 6% > 85% 43.5 degrees C
II < 2% 70-85% > 50 degrees C

PROPERTIES
● Thermodynamic material.
● Poor thermal conductivity
● Undergoes linear contraction, as
the compound cools from mouth
temperature to room
temperature. Highly viscous.
● Mucocompressive material.
● Direct flame softening may volatize
compound.
● Prolonged immersion- Leaching of
constituents.
● Wet kneading- Increases the flow of
hardened compound.
● Water temperature should not be too
high/low- 60-65 degrees C.
● Water bath to be lined with napkin.
● Cold water can be sprayed on the tray
while it is in the mouth until the
compound is thoroughly hardened prior
to removal of the impression tray.
PRECAUTIONS

Green stick//Pinnacle stick compound

USES
1. Edentulous arch impressions
2. In partially dentulous patients having deep palates, impression compound is
added to the palate area to customize the stock tray- provides additional support
for alginate or polyvinyl siloxane materials.
3.In preliminary impressions of partial dentures to support edentulous areas or
saddle areas, so as to facilitate better study models.
4. In fixed prosthodontics- check undercuts in tooth preparations. It is also used in
copper band impressions. Copper band is used as a carrier for the impression
compound to capture the details of the prepared tooth( tube impression).
Not followed these days because of its demerits- injures the gingival tissues,
accurate details of finish line are not captured, and temperature of the compound

5. To stabilize the rubber dam during restorative procedures.
6. The high biocompatibility and rigid nature of the material- using it as a surgical
dressing following surgeries of the palate to close the sealing of the nasal cavity
from the oral cavity.

ADVANTAGES OF I.C
1. Edentulous arches- high viscosity
- records the full depth of the sulcus
2. The copper ring impression
technique- where moisture control is
a problem
3. Reusable for the same patient.
4. It is economical.
5. It is easy to use.
6. It is non irritant and nontoxic.
7. It has a good shelf life
1. Poor dimensional stability
2. Doubts about its reversibility -
Probable inability to survive chemical
treatments used for decontamination
and disinfection of impressions.
3. Very high viscosity limits the degree
of fine details.
4. Fairly rigid after setting and has poor
elastic properties.
DISADVANTAGES OF I.C

ZINC OXIDE EUGENOL PASTE
● ADA SPECIFICATION NO. 16.
● Dispensed as: Two paste system( base and reactor), P L system.
● Commercial name- DPI Impression paste, SS White Impression paste.

SETTING REACTION.
●Ionic in nature
●First reaction - hydrolysis of zinc oxide to its hydroxide .
●When the two pastes are mixed, the phenol –OH of the eugenol acts as a weak
acid and undergoes an acid-base reaction with zinc hydroxide to form a salt, zinc
eugenolate.
●Accelerators-zinc acetate and calcium chloride
●Retarders- water droplets, cooling the spatula and/or the glass slab, and adding
inert oils and waxes
As water is used for initiation and obtained
as a byproduct, the reaction can also be
described as an autocatalytic reaction.

USES OF ZnOE paste
1. For making secondary/definitive
impression of completely edentulous
arches.
2. As a denture relining material
3. Used for interocclusal bite
registration
4. As a surgical pack paste for
periodontal wound healing
1. Nontoxic
2. Adherence to tissues
3. Good surface detail in thin sections
4. Good dimensional stability
5. Stable on storage and has good
shelf life
6. Biocompatibility of ZOE impression
paste is same as ZOE cement.
PROPERTIES

ADVANTAGES
1. Dimensionally stable
2. Good surface details -Mucostatic.
3. Can be reinforced with wax or
compound for bite registration.
4. Can be added and recorded if
found guilty.
DISADVANTAGES
1. Cannot be used in undercut areas
2. Eugenol allergy and burning
sensation are experienced by some
patients.
3. Requires a special tray- time
consuming.
4. Non elastic.
5. Sticky.
Disinfection- 2% glutaraldehyde

MODIFICATIONS OF ZnOE Paste
Modification Bite registration paste Surgical paste Non-eugenol paste
Objectives To record inter-occlusal
relationship as it offers almost
no resistance to closing of
mandible and is stable
To develop a softer and
slower setting reaction
paste which can be used
as a surgical paste
To overcome
drawbacks of eugenol
allergy
Compositio
nal
variations
More plasticizer ● More eugenol
● Less accelerator
● More filler
● More plasticizer
● Antibiotics
● Eugenol replaced
by O-EBA
Application
s
Records the occlusal
relationship between natural
and artificial teeth
Gingivectomy or
periodontal surgeries
Patients irritable to
eugenol

ELASTIC IM
The inability of rigid impression materials to record the accurate details in undercut
areas lead to the advent of the elastic impression material.
All flexible impression materials are polymeric in nature; they are cross-linked in a
three-dimensional network.
Elastic impression materials can be classified into two types based on their
composition:
1. Hydrocolloids
2. Elastomers

HYDROCOLLOID IM
● Polysaccharides.
● Fourth state of matter, i.e., colloidal state.
● Derived from the extracts of marine algae.
● The sizes of the colloid particles range from 1 to 200 nm.

CHARACTERISTICS OF HYDROCOLLOIDS
● During impression making, the material sets from a flowable state to a solid
state-sol-gel transformation.
● A sol is a colloidal dispersion of very small particles in a continuous liquid
medium and a gel is a suspension that behaves like an elastic solid.
● If a hydrocolloid contains an adequate concentration of the dispersed phase,
the sol, under certain conditions, may change to a gel. In the gel state, the
dispersed phase forms agglomerates in the form of chains or fibrils, also
called micelles.
● The fibrils may branch and intermesh to form a brush-heap structure with
capillary attraction or adhesion.

Disinfection of hydrocolloid impressions
● Due to imbibition of water, the impression should not be left immersed in a
liquid disinfectant;
● Rather a disinfectant spray should be used.
● Iodophor, sodium hypochlorite, or synthetic phenols.
● Glutaraldehyde is not recommended for hydrocolloids.
● The time of exposure to the disinfectant is 10 minutes.
● Hence after removal of the impression from the mouth, it is washed
thoroughly with water, sprayed with the disinfectant, wrapped in a paper towel
soaked in the disinfectant, and sealed in a plastic bag for the time period of
disinfection.

AGAR(reversible) hydrocolloid
● ADA SPECIFICATION NO. 82; ISO 1564:1995.
● Agar-agar (so called in Malay) is an edible marine red alga (seaweed) from
which agar material is extracted.
● It was first discovered in 1925 by Alphons Poller, an Austrian, who named it
“Nogacoll”.
● It was later introduced into dentistry in 1928 as “Dentacol.”
● The chemical name of this polymer is “agarose.” It is a sulfuric ester of linear
polymer of galactose.
● First successful elastic impression material used in dentistry.
● Dispensing: gel in 2 consistencies- tray material, syringe material.

Agar composition
COMPONENT % FUNCTION
Agar 13-17 Dispersion medium of gel
Borax 0.2-0.5 Increases strength
Potassium sulfate 1-2 Accelerator
Alkyl benzoate 0.1 Preservative
Diatom. earth 0.3-0.5 Filler
Water 85 Dispersion medium of sol
Thymol Trace Bactericide
Glycerin Trace Plasticizer
Colour,flavouring agents Trace Improves appearance, taste

SOL GEL TRANSFORMATION
● Mechanism of gelation- Imbibition.
● Temp. changes the KE of the molecule.
● Drop in temp. Increases the viscosity by forming fibrils and the distance
between particles decreases, so KE decreases, so gelation occurs.
Sol Gel
Cool(37deg.)
Hot(100deg.)
Gelation time(
mins.)
Elastic
recovery(%)
Flexibility(
%)
Gel
strength(
MPa)
Tear strength
(g/cm sq.)
Disinfection Dimensioanl
stability
5 98.5 4-15 >0.245 715 ● Iodophore
immersion-
10min
Unstable
(syneresis
,imbibition)

Agar manipulation
1. Liquefaction chamber- Liquefy and store it as a sol at 100°C for 10mins.
2. Storage chamber- Store the material in sol condition until it is needed at 65
degrees C.
3. Tempering chamber- . The tray material must be cooled or tempered so as not
to traumatize the oral tissues. For immediate preparation step, a tube of
hydrocolloid sol is removed from storage bath, the tray is filled, a gauze pad is
placed over top of the tray material(to prevent imbibition), and the tray is placed in
the tempering section (45°C) of the conditioning unit. The tempering time is brief
(3–10 minutes), just sufficient to ensure that all the material has reached a lower
temperature. Tempering decreases the viscosity of the hydrocolloid material so
that it does not flow out of the tray.
These three compartments are present in the conditioning unit.

4. Impression recording- The syringe material is taken directly from the storage
compartment. It is first applied to the base of the preparation and then the rest of
the prepared tooth is covered.
The tempered tray material is then immediately brought into the position in the
mouth and seated with light pressure and held in place passively to avoid
displacement and distortion.
5. Gelation- . Gelation is accelerated by circulating cool water, approximately
18°C–21°C through the tray for 3–5 minutes. It is important that tray be held in the
mouth until the gelation has proceeded to a point at which the gel strength is su
cient to resist deformation.
6. Removal- Single sudden jerk parallel to the long axis of the tooth.
7. Washing and cast pouring- Shake to remove excess water, pour cast
immediately.

USES
1. It is used primarily for making
impression for fixed and partial
dentures.
2. It is widely used in laboratory
duplicating materials.
3. It is also used in triple tray
technique for bite registration.

ADVANTAGES
1. It has an elastic recovery of 98.8%
2. It is cheap, accurate when poured
immediately, and reusable.
DISADVANTAGES
1. Complicated to use and requires
costly equipment
2. Dimensionally unstable.
3. Electroplating is not possible
4. Temperature alterations may
cause discomfort to the patient
5. Diffcult to disinfect properly

ALGINATE
● ADA SPECIFICATION NO. 18; ISO 1563:19.
● Based on a natural substance, alginic acid (anhydro-b-d-mannuronic acid)
derived from a brown marine alga.

Alginates with higher guluronic acid levels normally show a stronger interaction
with calcium, and hence, yield greater gel strength. For impression-making
purposes, the alginate is richer in mannuronic acid.

● Organic glycol-makes alginate dust free(silica).
● ZnO
● Diatom. Earth
● TYPES
1. Traditional alginates- Single-component system: It is supplied as powder to
which water has to be added to initiate the reaction
2. Modified alginates Two-component system/modified alginates: One
component is alginate in the form of sol and the other component contains the
calcium reactor. It is supplied both in syringe viscosity and tray viscosity forms

PROPERTIES
GELATION
TIME(min)
Elatic
recovery
(%)
Flexibilit
y(%)
Gel
strength(
MPa)
Tear
strength(
g/cm
sq.)
Disinfect
ion
Dimensi
onal
stability
Type I 1-2 97 5-20 >0.343 300-700 Iodophor
e
immersio
n
Unstable(
syneresis
and
imbibition
)
Type II 2-45

SETTING REACTION
When the alginate powder is mixed with water, the sodium and potassium salts of
alginic acid readily dissolve to give an alkaline solution.
The delay is achieved by the addition of phosphates which consume the Ca2+
ions released from the alginate powder as it dissolves in water. Once all the
phosphate ions are used up, the still releasing Ca2+ ions then take part in the
reaction to form calcium alginate and setting starts suddenly.

CONTROL OF ST
● Retarders like trisodium phosphate.
● Cooling of bowl and spatula( to prevent
premature gelation)

MANIPULATION
1. Proportioning
2. Powder-water mixing- Fig. 8, final mix shouldnt drip from spatula.
3. Loading- From post. To ant.
4. Recording
5. Removal-Single sudden jerk.
6. Washing and disinfection
7. Casting immediately else a gap of 1 hr in humid environment is permissible
after covering with wet cloth.
A perforated stainless steel or plastic tray can be used since the alginate flows
through these perforations and helps in retention, and prevents separation of
the impression material from the tray during removal from the mouth.

GYPSUM COMPATIBILITY
The water content , borax, sodium salt in impression inhibits the setting of gypsum
at the surface. These discrepancies can be resolved by adding gypsum hardener
(sulfate in the formulation of agar) and gypsum accelerator (potassium titanium
fluoride in alginate).

ADVANTAGES
1. Easy to manipulate.
2. Since it is hydrophilic, it does not
require dry field for impression
making.
DISADVANTAGES
1. does not reproduce the finer details of
the oral tissues that are required for proper
fabrication of the restoration.
2. A slight variation in W/P ratio has a
significant effect on the tear strength and
the elasticity of the impression material
USES
1. To obtain study casts and models for orthodontic purposes.
2. To obtain preliminary study casts for fabrication of prosthesis.
3. As a preliminary impression to construct a custom tray for a more accurate secondary impression.
4. To take impressions for fabrication of temporaries for indirect restorations.

LAMINATE TECHNIQUE- The tempered low viscosity agar is syringed over the
teeth and alginate is used as tray material. The chemically set alginate cools the
agar. It negates the use of cumbersome water-cooled trays, but is still able to use
the agar to record the fine details of the prepared teeth with less consumption of
the material. It is a cost-effective and less time-consuming method. Drawbacks of
the technique are (a) bond between agar and alginate is not very strong and (b)
there is displacement of agar by alginate during seating of the tray due to its
higher viscosity.

ALGINATE FAILURE CAUSES REMEDIES
Grainy material ● Prolonged mixing
● Too less W/P ratio
● Proper mixing.
● Proper W/P ratio
Tearing ● Inadequate bulk
● Moisture contamination
● Premature removal from mouth
● Prolonged mixing
● Tray should be held in mouth
till complete gelation
● 45 sec. mixing
External bubbles ● Under gelation
● Air incorporated during mixing
● Mixing should be surped bw
blade of spatula and walls of
the bowl
Rough/chalky
stone cast
● Inadequate cleaning of impression
● Excess water left in impression
● Premature removal of model
● Prolonged model duration in impression
● Impression to be cleaned under
running tap water
● Excess water to be shaken off
● Cast to be seperated after
30mins
Distortion ● Impression not poured immediately
● Tray removed early or late
● Immediate Impression pour
● Single jerk after gelation

MODIFICATIONS
Modification Dust free alginate Siliconised
alginate
Alginate in the
form of sol
Alginate
containing
indicators
Alginate with
disinfectant
Objectives To prevent
carcinogenesis or
fibrogenesis to
prolonged dust
inhalation
Improving tear
strength
To minimise
technique
sensitivity
To indicate different
stages of
manipulation
Disinfectant within
the material
Compositional
variation
Dedusting agent-
glycol
Silicone polymer
incorporation
2 paste-alginate sol
with water,calcium
reactor,tray/syringe
viscosity
Colour indicators Ammonium salts

● Fusion temperature-the degree of temperature at which a substance melts;
the point of fusion.
● Eugenol free ZOE paste.
● 2 paste alginate

Materials used in dentistry, S. Mahalakshmi

CLASSIFICATION
ELASTOMERIC IMPRESSION
MATERIAL
POLYSULFIDES SILICON
POLYSILOXANES
CONDENSATION
SILICON
ADDITION SILICON
(VINYL
POLYSILOXANE)
POLYETHER
LIGHT CURE
POLYERHER
URETHANE
DIMETHACRY
LATE.
64

ELASTOMERICIMPRESSION
65
MATERIAL (ADA no 19)
These materials are classified as synthetic rubbers, developed to
mimic natural rubber when it became difficult to obtain during
WORLD WAR II.
They are liquid polymers and can be
converted to rubber at room temperature when mixed with
catalyst.
They undergo polymerization or cross linking to produce a firm
elastic solid.

ELASTOMERS
● A group of synthetic polymer-based impression materials that are chemically
cross-linked when set and that can be stretched and yet rapidly recover to
their original dimensions, like vulcanized natural rubber when the applied
stress is released.
● Chemically, 3 elastomers based on polymers-Polysulfide, Silicone, Polyether.
● Supplied in 2 components-Base paste, catalyst paste which are mixed before
making impressions.
● Formulated in several consistencies-
❖ Extra low
❖ Low
❖ Medium
❖ Heavy
❖ Putty
Filler content ● Extra low,low-Available for
condensation, addition silicones
● Light body, heavy body-Polysulfides
● Hydrocolloids-Elastic,not elastomeric

POLYSULFIDES
67
• First synthetic elastomeric impression material introduced in
1950
• 2 paste system
• Available in low, medium and high consistencies
• Made up of a base and accelerator/reactor
• Brands- COE-FLEX, PERMALASTIC, NEOPLEX etc.

COMPOSITION
68
Anusavice. Philips science of dental materials 11th Edition: Elsevier
Composition Function
Polysulfide polymer(-SH,mercaptan gp) Principal ingredient
Titanium oxide and Zinc Fillers
Sulphate ,copper carbonate or silica Strengthener
Dibutyl phthalate Plasticizer (confers viscosity to base)
The Base
The Accelerator
Lead dioxide, hydrated copper oxide or organic
peroxide
Reactor
Sulfur Promoter accelerates the reaction
Oleic acid or Stearic acid Retarder controls setting reaction

PROPERTIES
70
• Working time: 5-7 min (longest among elastomers)
• Setting time: 8-12 min
• Pouring the cast: impression must be poured within 30 min to 1
hr
ST(min) Elastic
recovery(%)
Flexibility(%) Tear
strength(g/
cm sq.)
Detail
reproduction
Dimensional
stability
Disinfection
10-20 97 5-10 4000 Yes No NaOCl,Iodophore,
Glutaraldehyde,phenol
comp.

MERITS DEMERITS USES
• Good WT
• High tear stength
• High flow
• Better surface detail
• High flexibility
• Special tray required
• Bad odour
• Stain
• Low viscosity
• Byproduct
• Impression of crowns
• Cavity impressions of
inlays, onlays
• Impression of partially
and complete
edentulous mouths

MANIPULATION
Each paste supplied in a dispensing tube with approx. same sized bore diameters at the
tip
Equal lengths of paste extruded from each tube to provide the correct ratio of polymer
to cross-linking agent
Reaction starts at the beginning of mixing and reaches its maximum rate soon after
spatulation is complete
Polymerisation results in chain lengthening and cross –linking with an increase in
molecular weight
72

Reaction slightly exothermic and yields water as a by-product
Hot and humid conditions accelerate the setting of polysulfide impression material
Color- presence of lead oxide
Setting indicated by change of the color of the paste to dark- brown or gray- brown
73

CONDENSATION SILICONES
74
• Followed since 1955
• Commercial name-Accoe, Silene, Speedex, Cuttersil, Turbosil
• Supplied as two-paste system and a low viscosity liquid catalyst or a
two-putty system
• Putty is used as tray material in conjunction with a low-viscosity
silicone called the Putty-wash technique.
• Stock trays are generally used for impression making

- -hydroxyl-terminated polydimethyl siloxane High molecular weight polymer
Silica or calcium carbonate Fillers
76
Tin octoate Metal organic ester
Orthoalkyl silicate Oil-based diluents
Thickening agents Increase viscosity
The Base
The Liquid Accelerator

7
7
Curing involves a reaction of tri- and tetrafunctional alkyl silicates in the presence of
stannous octoate as a catalyst
Sets by cross-linking between terminal groups of the silicone polymers and the alkyl
silicate to form a 3-D network
By-product: Ethyl alcohol
Subsequent evaporation accounts for much of the contraction that takes place in the
setting impression
Extra-heavy or putty consistency developed to counteract the large polymerisation
shrinkage
REACTION

PROPERTIES
79
• Working time: 3 min
• Setting time: 6-8 min
• Pouring the cast: Impression must be poured within first 30
min
ST(min) Elastic
recovery(%)
Flexibility(%) Tear
strength(g/
cm sq.)
Detail
reproduction
Dimensional
stability
Disinfection
6-10 99.3 2-7 3500 Yes No NaOCl,Iodophore,
Glutaraldehyde,phenol
comp.

• High WT and ST
• Biocompatible
• High elasticity
• No staining
• Can be electroplated
• Distortion
• Putty wash-technique
sensitive
• Hydrophobic
inlays, onlays
• Impression of
complete edentulous
mouths

ADDITION SILICONES
Base contains low molecular weight polymer with silane group and filler.
The accelerator contains a moderately low molecular weight polymer
with vinyl terminal groups and filler
7
8
Viscosity Form
LOW SYRINGE
MEDIUM REGULAR
HIGH TRAY
VERY HIGH PUTTY
• Commonly referred to as Polyvinyl siloxanes(PVS)
• Commercial name- Aquasil, polysil, supersil, hydroflex,reprosil.
Availability

8
0
Polymethylhydrosiloxane
Low molecular weight polymer with silane group
+
filler
Divinyl polymethyl siloxane
+
Other siloxane pre-polymers
Catalyst
Platinum salt Retarder-Controls working and setting times
The Base
The Accelerator
COMPOSITION

8
1
PROPERTIES
• Working time: 2 - 4.5 minutes
• Setting time: 3 - 7 minutes
• Cast can be poured upto 1 week after making the
impression
ST(min) Elastic
recovery(%)
Flexibility(%) Tear
strength(
g/cm sq.)
Detail
reproduction
Dimensional
stability
Disinfection
6-8 99.93 2-3 3500 Yes Yes, due to
pseudoplasticit
y
2%NaOCl for 10-
15min.

• Dimensionally stable
• Easy to handle
• Short setting time
• Excellent elasticity
• Can be electroplated
• Hydrogen released during
reaction
• High surface tension
• Hydrophobic
• Low flexibility
• Shorter WT
inlays, onlays
• Impression of partially and
complete edentulous
mouths
• Impressions for making
implant prosthesis,
maxillofacial prostheis.

POLYETHER
• Commercial name- 3M ESPE
Monophase, Impregum F,
Permadyne, Polyjet NF
• Supplied as base and catalyst system
• Base- low molecular weight
polyether
8
3

8
4
Colloidal silica Filler
Glycol ether or phthalate Plasticizer
Benzene sulphonic acid
Alkyl aromatic sulfonate
Reactive ingredient-cross linking(initiator)
Filler and plasticizer
The Base - Polyether
polymer
The
Accelerator
COMPOSITION

REACTION
Polyether sulfonic
ester
cross-linked
rubber
89

• Working time: 2.5 min
• Setting time: 4.5 min
• Cast can be poured upto 1 week after making the
impression
90
PROPERTIES
ST(min) Elastic
recovery(%)
Flexibility(%) Tear
strength(
g/cm sq.)
Detail
reproduction
Dimensional
stability
Disinfection
6-8 98.9 3 3000 Excellent Low
shrinkage(0.24
%)
Permanent
deformation-1-
2%
1-10% NaOCl,
iodophore

• Set polyether impression material produces the highest cell
cytotoxicity.
• Foreign body of impression material can cause severe gingival
inflammation if it is left in a gingival sulcus.
• Contact dermatitis from polyether especially to the dental assistant
has been reported due to polyether catalyst.
7
2
BIOCOMPATIBILITY
Sydiskis RJ, Gerhardt DE. Cytotoxicity of impression materials: J Prosthet Dent

• Highly accurate impression
• Pleasant odour and taste
• Good dimensional stabilty
• Tear strength is good
• Good shelf life
92
ADVANTAGE
S
• Setting times is short,
mixing should be done
rapidly
• Highly expensive
DISADVANTAGES

MANIPULATION
• Equal lengths of two pastes are dispensed on a paper pad for normal mixes. Initial
mixing is accomplished with circular motion and final mixing to produce a mix,
free from streaks is done with broad stroke of spatula.
Mixing is readily accomplished in 45 seconds.
• When catalyst is supplied in liquid form a specific number of drops per unit length
is indicated in the instructions and mixing is accomplished in the manner similar
to the two paste system.
• The putty system uses scoops supplied by the manufactures for dispensing and
may be mixed with heavy spatula or kneaded with hand until free from streaks.
8
8Anusavice. Philips science of dental materials 11th Edition: Elsevier

MANIPULATION OF IMPRESSION MATERIALS
8
9
3 modes of
manipulation
Hand
mixing
Static
mixing
Dynamic
mechanical
mixing
Combe EC, Burke FJ, Douglas WH. Dental biomaterials, 1st edition. Boston: Kluwer; 1999.

Mixture is then spread over the mixing pad
Mass is then scraped up with the spatula blade and spread uniformly back and
forth on the mixing pad
Catalyst paste first collected on stainless steel spatula and then spread over
base paste
Dispense the same length of materials onto a mixing pad or glass slab
95
HAND MIXING

Knead the material with fingers until a uniform color is obtained
2 putty systems(condensation and addition silicone) dispensed by volume using equal
number of scoops of each material
Process continued until the mixed paste is uniform in color with no streaks of the base
or catalyst appearing in the mixture
96

Device used- gun for compressing materials into a 2- cylinder cartridge, which contains
the base and catalyst separately, as well as mixing tip
Mixing tip is made of helical mixer elements in a cylindrical housing
Mixer elements are series of alternating right and left –turn 180°helixes positioned so that leading
edge of one element is perpendicular to the trailing edge of the next
Length of each material is the same as the inner diameter of the cylindrical housing
98
STATIC MIXING
Transforms 2 fluid or paste-like materials into a homogenous mixture without
mechanical mixing

Materials supplied in collapsible plastic bags housing cartridge
inside it
Motor driven impeller mixes the materials as they are extruded through
the tip
Device used- A motor to drive parallel plungers,forcing the materials into a
mixing tip and out into an impression tray or syringe
100
DYNAMIC MECHANICAL MIXING
Only for polyether and addition silicone manipulation

IMPRESSION TECHNIQUES Double mix double
impression technique.
MERITS
• Rapid curing of
putty
• Elimination of
special tray
• Less thermal
contraction
DEMERITS
• Displacement of
light body
• Expensive

DOUBLE MIX SINGLE IMPRESSION
TECHNIQUE
(MULTiPLE MIX TECHNIQUE)
● Special tray
● Merits- Less material required, minimal
distortion, uniform thickness.
● Demerits- Special tray, monomer of tray is
irritant to few patients
● Simultaneous mixing of two people
required
SINGLE MIX SINGLE IMPRESSION
TECHNIQUE
(MONOPHASE TECHNIQUE)
● Special tray
● Merits-Pseudoplasticity, less material
required, dimensionally accurate
● Demerits-High viscosity
● Same impression material for both syringe
and tray.

OBJECTIVE MODIFICATION DISADVANTAGE
HYDROPHILIC
POLYVINYL
SILOXANE
To reduce hydrophobic property
of silicones
Non- ionic surfactant-dilute soap
solution or commercial wetting agent
sprayed onto impression
Electroplating is difficult
LIGHT ACTIVATED
POLYETHER
To enhance light transmission • 1988
• Genesis-name
• 2 viscosities-light, heavy
• Composition-polyurethane
dimethacrylate resin, diketone
photoinitiator, amine
photoaccelerator, 40-60% silicon
dioxide filler
• Light transmissable transparent tray
• Blue light
• Depth-16mm, 20 sec,
Long curing time

FUNCTIONAL IMPRESSION
● Functional impression material-applied to the fitting surface of the denture for
the purpose of acquiring an impression under functional stress, which enables
the denture to be rebased on the impression surface.
● Tissue conditioners are used for this purpose.
● It is used as an adjunct to the main impression.
● Used when it is difficult to determine the extent of the denture base due to the
presence of movable oral tissues.
● Record the extension of the denture in a dynamic form that will later help in
preparing an impression tray for the final impression.

Impression
Materials
Conventional
Elastic Non-
elastic
Digital
Direct
intraoral
Indirect
intraoral
110
CLASSIFICATION

DIGITAL IMPRESSION
111
Digital impressions represent innovative methods that enable dentists to construct
a virtual, computer-generated copy of the hard and soft tissues of the oral cavity,
with the use of lasers and other optical scanning machines. The digital method
captures impression data with great accuracy, in minutes, without the need for
traditional impression resources that some patients find inopportune and messy.
Numerous patients consider digital impressions to be an easier and more
comfortable method, in comparison with classical impression techniques.

• Dr. Duret first introduced the CAD/CAM concept to dentistry in 1973 in Lyon,
France in his thesis entitled Empreinte Optique,which translates to Optical
Impression.
• The concept of CAD/CAM systems was further developed by Dr.Mormann, a Swiss
Dentist, and Mr. Brandestini, who was an electrical engineer.
• The first commercially available digital impression system for use in the field of
dentistry was introduced in 1980 pioneered by PROCERA and CEREC.
• Over the last 10 years, systems like 3M LavaC.O.S., CadentiTero, E4D Dentist,
and 3Shape Trioshave been introduced.
• Today, various CAD/CAM systems are now available for dental applications. Each
employs a specific, distinct technique for making impressions. 112
HISTORY

10
0
TECHNIQUES
In office
CAD/CAM
impression
technique
• CEREC(Sirona)
• E4D Technologies
Chairside digital
impression
technique• iTERO
• CEREC
• LAVAC.O.S.
Systems
Fleming PS, Marinho V, Johal A. Orthodontic measurements on digital study models compared with plaster models:
a systematic review. Orthod Craniofac Res 2011;14:1-16.

HOW DOES IT WORK?
Dentist holds a scanning wand which is connected to a digital camera.
This uses blue wavelength light to record images of the teeth to make a 3D computer model.
A 3D model created by the scanning wand is displayed on a computer screen.
A computer model shows how the final impression will look.
Then the data is sent to the milling machine for fabrication of model.
116

10
6
ADVANTAGES
1. Real-time visualization and evaluation
2. Easy to correct, manipulate, or recapture images
3. Segmental image capture
4. Archival digitally, therefore no need to store physical casts
5. No wastage of impression material and therefore environmental friendly
6. Economical, considering no use of impression trays, adhesives, or gypsum
products
7. Do not need to disinfect before sending information to the laboratory
Cho S-H, Schaefer O, Thompson GA, et al. Comparison of accuracy and reproducibility of casts made by
digital and conventional methods. J Prosthet Dent 2015;113(4):310–5.

8. No damage or wear and tear of the stone casts
9. Swift communication with the laboratory via the Internet
11. File transfer capabilities to merge with other files like DICOM (Digital Imaging
and
Communications in Medicine) images using sophisticated software
120

DISADVANTAGES
121
1. Initial cost of equipment and software maintenance fees
2. Learning curve can be difficult for some individuals
5. Closed systems restrict options for transferring STL (standard tessellation language)
files
6. Cannot capture subgingival margins if obscured with blood, saliva, or tissue
8. Scanning patterns need to be followed as per manufacturer’s recommendations

CONCLUSION
122
ALL WE NEED IS AN ACCURATE IMPRESSION.
One must not depend on a material to provide good impressions. Any material is
as good as we the dentist are using it and any material must be used for sometime
for the operator being familiar with its characteristics. Selecting the impression
material depends on the convenience of the dentist.

REFERENCES
123
1. Anusavice- Philips science of dental materials XI Edition
2. Materials used in Dentistry- S.Mahalakshmi
3. Contemporary Orthodontics VI Edition By William R. Proffit
4. V Vidyashree Nandini, K Vijay Venkatesh1, K Chandrasekharan Nair Alginate
impressions: A practical perspective
5. Ward G. Impression materials and impression taking: an historical survey. Br Dent J
1961;110(4):118–9.
6. Fleming PS, Marinho V, Johal A. Orthodontic measurements on digital study models
compared with plaster models: a systematic review. Orthod Craniofac Res 2011;14:1-16.
7. Macchi A, Carrafiello G, Cacciafesta V, Norcini A. Three-dimensional digital modeling and
setup. Am J Orthod Dentofacial Orthop 2006;129:605-10.

9. Donovan TE, Chee WW. A review of contemporary impression materials and
techniques.
Dent Clin North Am 2004;48(2):vi–vii, 445-470.
10. Powers J, Wataha J. Dental materials foundations and applications. 11th edition.
St. Louis (MO): Elsevier; 2017.
11. Stober T, Johnson GH, Schmitter M. Accuracy of the newly formulated vinyl
siloxanether elastomeric impression material. J Prosthet Dent 2010;103(4):228–39.
12. Baxter R, Lawson N, Cakir D, et al. Evaluation of outgassing, tear strength, and detail
reproduction in alginate substitute materials. Oper Dent 2012;37(5):540–7.
13. Demajo JK, Cassar V, Farrugia C, et al. Effectiveness of disinfectants on antimicrobial
and physical properties of dental impression materials. Int J Prosthodont
2015;29(1):63–7. 124

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