Impression materials /certified fixed orthodontic courses by Indian dental academy

Impression Materials

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INDIAN DENTAL ACADEMY
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Plaster
Non-elastic

Compound
Waxes

Impression
Materials

ZnO - Eugenol
Agar (reversible)

Aqueous
Hydrocolloids

Alginate (irreversible)

Elastic

Polysulfide
Non-aqueous
Elastomers

Condensation

Silicones
Polyether

Addition

O’Brien Dental Materials & their Selection 1997

Aqueous
Hydrocolloids
Elastic

Agar (reversible)
Alginate (irreversible)
Polysulfide

Non-aqueous
Elastomers

Condensation

Silicones
Polyether

Addition


Impression Materials
• Non-elastic
• Elastic
– Aqueous hydrocolloids
• Agar
• Alginate

– Non-aqueous elastomers
• Polysulfide
• Silicones
– Condensation
– Addition

• Polyether


Indications
• Diagnostic casts
– preliminary
– opposing

• Indirect
reconstruction
– fixed
– removable

• Bite registration
Giordano Gen Dent 2000

Elastomeric Impression Materials
• Viscoelastic
– physical properties vary
• rate of loading

• Rapidly remove
– decreases permanent
deformation
• chains recoil from a recoverable distance

– increases tear strength
Phillip’s Science of Dental Materials 1996

Aqueous Hydrocolloids
• Colloidal suspensions
– chains align to form fibrils
– traps water in interstices

• Two forms
– sol
• viscous liquid

– gel
• elastic solid

• Placed intra-orally as sol
– converts to gel
• thermal or chemical process

Aqueous Hydrocolloids
• Semi-permeable membranes
– poor dimensional stability

• Evaporation
• Syneresis
– fibril cross linking continues
• contracts with time
• exudes water

• Imbibition
– water absorption
• swells


Reversible Hydrocolloid
(Agar)
• Indications
– crown and bridge
• high accuracy

• Example
– Slate Hydrocolloid (Van R)


Composition
• Agar

• Potassium sulfate

– complex
polysaccharide

– improves gypsum
surface

• seaweed

• Water (85%)

– gelling agent

• Borax
– strength
cool to 43 C

agar hydrocolloid (hot)
(sol)

agar hydrocolloid (cold)

heat to 100 C

(gel)


Manipulation
• Gel in tubes
– syringe and tray material


Manipulation
• 3 chamber conditioning unit
– (1) liquefy at 100°C for
10 minutes
• converts gel to sol

– (2) store at 65°C
– place in tray
– (3) temper at 46°C for 3 minutes
– seat tray
– cool with water at 13°C for 3 minutes
• converts sol to gel

Advantages
• Dimensionally accurate
• Hydrophilic
– displace moisture, blood, fluids

• Inexpensive
– after initial equipment

• No custom tray or adhesives
• Pleasant
• No mixing required

Disadvantages
• Initial expense
– special equipment

• Material prepared in advanced
• Tears easily
• Dimensionally unstable
– immediate pour
– single cast

• Difficult to disinfect

Irreversible Hydrocolloid
(Alginate)
• Most widely used
impression material
• Indications
– study models
– removable fixed partial dentures
• framework

• Examples
– Jeltrate (Dentsply/Caulk)
– Coe Alginate (GC America)

Composition
• Sodium phosphate

• Sodium alginate

– retarder

– salt of alginic acid

• Filler
• Potassium fluoride

• mucous extraction of
seaweed (algae)

• Calcium sulfate

– improves gypsum
surface

– reactor

2 Na3PO4 + 3 CaSO4
Na alginate + CaSO4
(powder)

Ca3(PO4)2 + 3 Na2SO4
H2 O

Ca alginate + Na2SO4


(gel)


Manipulation
• Weigh powder
• Powder added to water
– rubber bowl
– vacuum mixer

• Mixed for 45 sec to 1 min
• Place tray
• Remove 2 to 3 minutes
– after gelation (loss of tackiness)
Caswell JADA 1986

Advantages
• Inexpensive
• Easy to use
• Hydrophilic
– displace moisture, blood, fluids

• Stock trays


Disadvantages
• Tears easily
• Dimensionally unstable
– immediate pour
– single cast

• Lower detail reproduction
– unacceptable for fixed pros

• High permanent deformation
• Difficult to disinfect

Non-Aqueous Elastomers
• Synthetic rubbers
– mimic natural rubber
• scarce during World War II

• Large polymers
– some chain lengthening
– primarily cross-linking

• Viscosity classes
– low, medium, high, putty
– monophasic

Polysulfide
• First dental elastomers
• Indications
– complete denture
– removable fixed partial denture
• tissue


• Examples
– Permlastic (Kerr)
– Omni-Flex (GC America)


Composition
• Base
– polysulfide polymers
– fillers
– plasticizers

• Catalyst
– lead dioxide (or copper)
– fillers

• By-product
– water


Polysulfide Reaction
--SH

HS---------------------SH
=
Pb

S
H

O

S + 3PbO + H O
2
S

=

=

Pb

-S-S---------------S-S-

O

=

O

HS--

O = Pb = O

O

H
S
mercaptan + lead dioxide

polysulfide rubber + lead oxide + water


Manipulation
• Adhesive to tray
• Uniform layer
– custom tray

• Equal lengths of pastes
• Mix thoroughly
– within one minute

• Setting time 8 – 12 minutes
• Pour within 1 hour

Advantages
• Lower cost
– compared to silicones and polyethers

•
•
•
•

Long working time
High tear strength
High flexibility
Good detail reproduction

Disadvantages
• Poor dimensional stability
– water by-product
– pour within one hour
– single pour

• Custom trays
• Messy
– paste-paste mix
– bad odor
– may stain clothing

• Long setting time

Condensation Silicone
• Indications
– complete dentures

• Examples
– Speedex (Coltene/Whaledent)
– Primasil (TISS Dental)


Composition
• Base
– poly(dimethylsiloxane)
– tetraethylorthosilicate
– filler

• Catalyst
– metal organic ester

• By-product
– ethyl alcohol

Phillip’s 1996

CH3

Condensation
Silicone
Reaction

CH3

HO – Si – O – Si - O - H
CH3

CH3

C2H5O

OC2H5

n
Si

CH3

CH3

HO – Si – O – Si - O - H
CH3

CH3

C2H5O

OC2H5

n
metal organic ester

CH3

CH3

HO – Si – O – Si - O CH3

CH3

OC2H5
n

+ 2C2H5OH

Si
CH3

CH3

HO – Si – O – Si - O CH3

ethanol

CH3

OC2H5
n

Manipulation
• Mix thoroughly
– paste - paste
– paste - liquid

• Putty-wash technique
– reduces effect of polymerization shrinkage
– stock tray
• putty placed
• thin plastic sheet spacer
• preliminary impression
– intraoral custom tray

• inject wash material

Advantages
• Better elastic properties
• Clean, pleasant
• Stock tray
– putty-wash

• Good working and setting time


Disadvantages
• Poor dimensional stability
– high shrinkage
• polymerization
• evaporation of ethanol

– pour immediately
• within 30 minutes

• Hydrophobic
– poor wettability

Addition Silicones
• AKA: Vinyl polysiloxane
• Indications
– denture
– bite registration

• Examples
–
–
–
–
–

Extrude (Kerr)
Express (3M/ESPE)
Aquasil (Dentsply Caulk)
Genie (Sultan Chemists)
Virtual (Ivoclar Vivadent)
Click here for DIS evaluations

of VPS impression materials

Composition
• Improvement over condensation silicones
– no by-product

• First paste
– vinyl poly(dimethylsiloxane)
prepolymer

• Second paste
– siloxane prepolymer

• Catalyst
– chloroplatinic acid

Phillip’s 1996

CH3
---O – Si – CH = CH2

Addition
Silicone
Reaction
CH3

O
H - Si – CH3

CH3

O

CH3
CH = CH2 – Si – O ---

CH3 - Si - H

CH3

O

O

Chloroplatinic Acid Catalyst

---O – Si – CH2 - CH2 - Si – CH3
CH3

O

CH3

CH3 - Si - CH2 - CH2 – Si – O --O

CH3


Manipulation
• Double mix
– custom tray
• heavy-body

– light-body to prep

• Putty-wash
– stock tray

Craig Adv Dent Res 1988

Advantages
• Highly accurate
• High dimensional stability
– pour up to one week

•
•
•
•

Stock or custom trays
Multiple casts
Easy to mix
Pleasant odor

Disadvantages
• Expensive
• Sulfur inhibits set
– latex gloves
– ferric and Al sulfate
retraction solution

• Pumice teeth before
impressing
• Short working time
• Lower tear strength
• Possible hydrogen gas release
– bubbles on die
– palladium added to absorb

Manikos Aust Dent J 1998

Addition Silicones
• Surfactants added
– reduce contact angle
– improved
• castability
– gypsum

• wettability??
– still need dry field clinically


Pratten J Dent Res 1987
Mandikos Aust Dent J 1998

Polyether
• Indications
– bite registration

• Examples
–
–
–
–
–

Impregum F (3M/ESPE)
Permadyne (3M/ESPE)
Pentamix (3M/ESPE)
P2 (Heraeus Kulzer)
Polygel (Dentsply Caulk)


Composition
• Base
– difunctional epimine-terminated prepolymer
– fillers
– plasticizers

• Catalyst
– aromatic sulfonic acid ester
– fillers

• Cationic polymerization
– ring opening and chain extension

Polyether Reaction
R

R

base

CH3 – CH – CH2 – CO2 – CH – (CH2)n – O – CH – (CH2)n – CO2 –CH2 – CH –CH3
m
N

N
H2C

CH2

H2C

+ R+

CH2

catalyst
SO3-

R– N+
H2C

N

+
CH2

H2C

R – N – CH2 – CH2 – N +
CH2

ring opening

H2C

CH2


Manipulation
– stock or custom tray
• very stiff

• Paste-paste mix
• Auto-mixing
– hand-held
• low viscosity

– mechanical dispenser
• high viscosity

Advantages
•
•
•
•
•

Highly accurate
Good dimensional stability
Stock or dual-arch trays
Good surface detail
Pour within one week
– kept dry

• Multiple casts
• Good wettability

Disadvantages
• Expensive
• Short working time
• Rigid
– difficult to remove from undercuts

• Bitter taste
• Low tear strength
• Absorbs water
– changes dimension

Handling Properties
Agar

Alginate Polysulfide

Condensation
Silicone

Addition
Silicone

Polyether

Preparation

Boil,
temper,
store

Powder,
water

2 pastes

2 pastes or
paste/liquid

2 pastes

2 pastes

Ease of Use

Technique
sensitive

Good

Fair

Fair

Excellent

Good

Patient
Reaction

Thermal
Shock

Pleasant,
clean

Unpleasant,
stains

Pleasant,
clean

Pleasant

Unpleasant
clean

Ease of
removal

Very
easy

Very
easy

Easy

Moderate

Moderate

Moderate
to difficult

Disinfection

Poor

Poor

Fair

Fair

Excellent

Fair


Handling Properties
Condensation Addition
Silicone
Silicone

Agar

Alginate

Polysulfide

Polyether

Working
Time (min)

7 – 15

2.5

5–7

3

2 –4.5

2.5

Setting Time
(min)

5

3.5

8 – 12

6–8

3–7

4.5

Stability

1 hour
100% RH

Immediate
pour

1 hour

Immediate
pour

1 week

1 week
kept dry

Wettability
and
castability

Excellent

Excellent

Fair

Fair

Fair to
good

Good

Cost

Low

Very low

Low

Moderate

High to
very high

Very high


Properties
Agar

Alginate Polysulfide

Condensation
Silicone

Addition
Silicone

Polyether

Elastic
Recovery (%)

98.8

97.3

94.5 – 96.9

98.2 – 99.6

99 – 99.9

98.3 – 99.0

Flexibility (%)

11

12

8.5 – 20.0

3.5 – 7.8

1.3 – 5.6

1.9 – 3.3

Flow (%)

--

--

0.4 – 1.9

< 0.10

< 0.05

< 0.05

Shrinkage, 24
hours (%)

Extreme

Extreme

0.4 – 0.5

0.2 – 1.0

0.01 – 0.2

0.2 – 0.3

Tear Strength
(g/cm)

700

380 –
700

2240 – 7410

2280 – 4370

1640 –
5260

1700 4800


Comparison of Properties
• Working time
– longest to shortest
• agar > polysulfide > silicones > alginate = polyether

• Setting time
– shortest to longest
• alginate < polyether < agar < silicones < polysulfide


• Stiffness
– most to least
• polyether > addition silicone > condensation silicone >
polysulfide = hydrocolloids

• Tear strength
– greatest to least
• polysulfide > addition silicone > polyether >
condensation silicone >> hydrocolloids

• Cost
– lowest to highest
• alginate < agar = polysulfide <condensation silicone
< addition silicone < polyether

• Dimensional stability
– best to worst
• addition silicone > polyether > polysulfide >
condensation silicone > hydrocolloid
Phillip’s 1996

• Wettability
– best to worst
• hydrocolloids > polyether > hydrophilic addition
silicone > polysulfide > hydrophobic addition silicone
= condensation silicone

• Castability
– best to worst
• hydrocolloids > hydrophilic addition silicone >
polyether > polysulfide > hydrophobic addition
silicone = condensation silicone

Summary
• Study models
– Alginate most widely used
•
•
•
•

inexpensive
displaces moisture
lower detail reproduction
dimensionally unstable


Summary
• Prosthodontics
– Addition silicones most popular
•
•
•
•

accurate
dimensionally stable
user friendly
expensive


• A good Impression must aid to fulfill M.M.
Devan’s dictum: “It is the perpetual
preservation of what already exists and not
the meticulous replacement of what is
missing.”


• DEFINITION
• A COMPLETE DENTURE IMPRESSION is
the negative registration of the entire denture
bearing, stabilizing and border seal areas, of
either the maxillas or mandible in a plastic
material that becomes relatively hard or set
while in contact with these tissues.

A PRELIMINARY IMPRESSION is made
for the purpose of diagnostic treatment
planning and the construction of a custom
tray while a FINAL IMPRESSION is used
for making the master cast over which the
denture bases are fabricated.


• According to GPT, 7th Edition, 1999
Impression is defined as a negative likeness
or copy in reverse of the surface of an
object; an imprint of the teeth and adjacent
structures for use in dentistry


• The five objectives of an impression as stated by
Carl.D. Boucher in 1944 are
• 1) PRESERVATION OF THE ALVEOLAR
RIDGES. This is achieved by using impression
techniques which cover maximum supporting areas as
possible and using pressure within physiologic limit
of the tissue.
• (2) RETENTION - The factors of retention are (1)
adhesion (2) cohesion (3) interfacial surface tension
(4) mechanical locking into undercuts (5) peripheral
seal and atmospheric pressure and (6) oral and facial
musculature. Henry A. Collet in 1965 stated that
primary retention depends upon close adaptation to
the tissues and is proportionate to the area covered.

• . (3) STABII.ITY - It is the relationship of the
denture base to the underlying bone.
• Samuel Friedman in 1957, stated that stability
is developed in the impression technique
through more intimate contact of the labial
and buccal flanges with the labial and buccal
slopes and of the lingual flanges with the
lingual slopes of the ridges. Boucher stated
that stability requires maximum use of all
bony foundations where the tissues are firmly
and closely attached to bone.

• . (4) SUPPORT - Support is provided by the
maxillary and the mandibular bones and their
covering of mucosal tissue. It is enhanced by
selective placement of pressures that are in
harmony with the resiliency of the tissues that
make up the basal seat.
• (5) ESTHETICS - Role of esthetics in impression
making refers to the development of the labial and
buccal borders, so that they are not only retentive
but also support the lips and cheeks properly.

• Fisher R.D. in 1951 laid down six
fundamental rules for making full denture
impressions –
• (1) Roentgenographics, visual and digital
examination of the oral cavity
• (2) Surgical removal of such abnormal
formations as would prevent successful
completion of impressions.
• (3) the require extension outlines.
• (4) the location and position for area of
variable tissue displaceability (
• 5) the required retention outline and
• (6) the required adaptation.

• IMPRESSION TECHNIQUES may be
classified depending on, [A] Amount of
pressure used (Based on the theories of
impression).
• Pressure technique based on pressure theory
• Minimal pressure technique - based on
mucostatic theory.
• Selective pressure technique -based on
selective pressure theory.


• [B]
1. Open or
•
2. Closed mouth
• [C]
1. Hand-manipulation or
• 2. Functional movements


• [D] Type of tray
• 1. Stock tray : 1. Caulks Edentulous Rimlock
Trays.
• 2. McGowen Winkler Trays (mandibular)
• 3. STO-K Trays. (Square, round or Tapering
shapes of ridges).
•
•
•
•

2. Custom or special tray
1. Shellac
2. Acrylic
3. Wax.

Thank you
Leader in continuing dental education


Impression materials /certified fixed orthodontic courses by Indian dental academy

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