Impressionmaterials/certified fixed orthodontic courses by Indian dental academy

Impression MaterialsImpression Materials
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

Impression
Materials
Non-elastic
Elastic
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
Plaster
Compound
ZnO - Eugenol
Waxes
O’Brien Dental Materials & their Selection 1997

Elastic
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)

Impression Materials
• Non-elastic
• Elastic
– Aqueous hydrocolloids
• Agar
• Alginate
– Non-aqueous elastomers
• Polysulfide
• Silicones
– Condensation
– Addition
• Polyether www.indiandentalacademy.com

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
– complex
polysaccharide
• seaweed
– gelling agent
• Borax
– strength
• Potassium sulfate
– improves gypsum
surface
• Water (85%)
agar hydrocolloid (hot) agar hydrocolloid (cold)
(sol) (gel)
cool to 43 C
heat to 100 C

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 alginate
– salt of alginic acid
• mucous extraction of
seaweed (algae)
• Calcium sulfate
– reactor
• Sodium phosphate
– retarder
• Filler
• Potassium fluoride
– improves gypsum
surface
2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3 Na2SO4
Na alginate + CaSO4 Ca alginate + Na2SO4
(powder) (gel)
H2O

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

--SH HS---------------------SH HS--
S
H
O
=
Pb
=
O
O
=
Pb
=
OO = Pb = O
H
S
-S-S---------------S-S-
S
S
+ 3PbO + H2O
mercaptan + lead dioxide polysulfide rubber + lead oxide + water
Polysulfide Reaction

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

HO – Si – O – Si - O - H
CH3
CH3 CH3
CH3 n
HO – Si – O – Si - O - H
CH3
CH3 CH3
CH3 n
C2H5O OC2H5
Si
C2H5O OC2H5
HO – Si – O – Si - O -
CH3
CH3 CH3
CH3 n
HO – Si – O – Si - O -
CH3
CH3 CH3
CH3 n
OC2H5
Si
OC2H5
+ 2C2H5OH
Condensation
Silicone
Reaction
metal organic ester
ethanol

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 materialwww.indiandentalacademy.com

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 materialswww.indiandentalacademy.com

Composition
• Improvement over condensation silicones
– no by-product
• First paste
– vinyl poly(dimethylsiloxane)
prepolymer
• Second paste
– siloxane prepolymer
• Catalyst
– chloroplatinic acid
Phillip’s 1996

O
H - Si – CH3
O
CH3 - Si - H
O
---O – Si – CH = CH2
CH3
CH3 CH = CH2 – Si – O ---
CH3
CH3
O
- Si – CH3
O
CH3 - Si -
O
---O – Si – CH2 - CH2
CH3
CH3
CH2 - CH2 – Si – O ---
CH3
CH3
Chloroplatinic Acid Catalyst
Addition
Silicone
Reaction

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)

• Base
– difunctional epimine-terminated prepolymer
– fillers
– plasticizers
• Catalyst
– aromatic sulfonic acid ester
– fillers
• Cationic polymerization
– ring opening and chain extension
Composition

SO3
-
+ R+
CH3 – CH – CH2 – CO2 – CH – (CH2)n – O – CH – (CH2)n – CO2 –CH2 – CH –CH3
N
H2C CH2
R R
m
N
H2C CH2
N
H2C CH2
R – N – CH2 – CH2 – +
N
H2C CH2
N
H2C CH2
R – +
+
Polyether Reaction
catalyst
base
ring opening

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
Silicone
Addition
Silicone
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
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.www.indiandentalacademy.com

• 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.

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