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Impression Materials
Chapter 8
DAE/DHE 203
Impression Materials:
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Used to make replicas of oral structures
“Negative” replica made by impression
Cast material is placed into impression to yield
a “positive” replica of the oral tissue
Allows for the indirect restoration or dental
appliance to be fabricated without the patient
present
Variety of materials for a variety of applications
Uses of Impression Materials:
Used in the fabrication of:
 Indirect restorations:
 Crowns & bridges
 Dental prosthetics
 Temporary crowns
 Orthodontic & Dental
appliances
 Acrylic trays
 Bite registration
 Study models
Uses of Impression Materials:
Characteristics of
Impression Materials:
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Fluid enough to flow around area of interest
Must “set” in reasonable amount of time
Can remove from mouth without distortion
No harmful effects on tissues
Relatively tasteless & odorless
Dimensionally stable until a cast is created
Give detailed reproduction
Compatible with cast materials
Impression Trays:
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Used to carry the material to pt’s mouth
Must be sturdy enough to support the material
Need to be disposed of or sterilized after use
Metallic trays are autoclavable
Stock trays available: full arch, quadrant
Custom trays made of acrylic for most accuracy
Triple trays takes impression of opposing teeth,
occlusal registration, and prep site
Perforated trays have holes for retention of
material
Categories of Impression Materials:
INELASTIC
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Rigid
Cannot be used with
undercuts
For edentulous or
bite registration
ELASTIC
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Flexible & “rubbery”
Used with undercuts
Generally used today
Two subcategories:
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Hydrocolloids (Aqueous)
Elastomers
Inelastic Impression Materials:
Impression Compound
 ZOE Impression Paste
 Plaster
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Inelastic Impression Materials:
Impression Compound:
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Resins + wax
Thermoplastic, solid material
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Heat to soften material
Cool to set material
Physical change only; NO chemical reaction
Forms: plates and sticks
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Soften in water bath (10° warmer than body)
Applied to tray and inserted in mouth to cool
Used as a custom tray
Inelastic Impression Materials:
ZOE Impression Paste:
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Similar formulation as ZOE cements
Pastes mixed together – chemical reaction
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BASE + CATALYST
Applied in thin layer in custom tray for
edentulous arch; or to occlusal surfaces
Sets in 4 – 5 minutes
Elastic Impression Materials:
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Hydrocolloids:
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Reversible Hydrocolloids
Irreversible Hydrocolloids
Elastomers:
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Polysulfides
Polyethers
Condensation Silicones
Addition Silicones - Polyvinylsiloxanes
Elastic Impression Materials:
HYDROCOLLOIDS –
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“water-based” impression materials
Colloid – liquid suspension of particles
Particles derived from seaweed & kelp
Liquid = water
GEL – the rubber-like form of the material
SOL – the material in liquid solution
Not dimensionally stable – must be “poured”
immediately
Hydrocolloids:
Reversible Hydrocolloid:
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Agar – a gelatinous material + water
Thermoplastic – NO chemical reaction
“Reversible” –
Goes from gel, to sol, and back to gel,
by raising and lowering temperature
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Dispensed in tubes & syringes
Very accurate final impression material
Hydrocolloids:
Handling Reversible Hydrocolloid:
Special water baths with 3 chambers are used
1) Material is immersed in boiling tank (212°F)
for 10-20 minutes; turns from gel to sol
2) Place in storage bath (150°F);
10 minutes to few days; remains sol
3) Load tray; immerse in the tempering bath
(110°F); 5-10 minutes; lowers temp for pt comfort
Hydrocolloids:
Handling Reversible Hydrocolloid:
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Load syringe; extrude onto prep site
Seat tray in mouth
Attach cooling hoses to tray
Hold firmly in pt’s mouth until cooled and
transformed to gel state
8) Remove from pt’s mouth and pour
immediately
Reversible Hydrocolloid:
Advantages:
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Very accurate
Excellent
compatibility with
gypsum
Disadvantages:
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Labor-intensive
Poor tear resistance
Poor stability
Need equipment
space and very
organized staff
Hydrocolloids:
Irreversible Hydrocolloid:
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ALGINATE impression material
Formed by chemical reaction
Powder + water; mixed
NOT reversible; SOL to GEL only
Protect from inhalation
Dispensed in cans or bulk packages
Used when less detail is required
Hydrocolloids:
“What are indications for alginate impressions?”
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Study models
Opposing models of final casts
Casts for mouthguards, whitening trays,
custom trays, orthodontic appliances,
provisional crowns, etc.
To fabricate a direct provisional crown
Hydrocolloids:
Handling Alginate:
 Fluff powder and
measure accurately
 Measure water – temp!
 Mix in a flexible,
rubber bowl
 Stir to wet powder
 Strop mixture against
side of bowl to eliminate
air bubbles
 Mix until creamy &
homogeneous; 60 sec.
Hydrocolloids:
Handling Alginate:
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Load alginate into tray
from posterior
Press material into tray
to eliminate voids
Smooth & indent
alginate with wet finger
Use extra alginate to
wipe onto occlusal
surfaces of teeth
Taking an Alginate Impression:
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Bead the tray as necessary
Stand behind patient for maxillary (11:00)
Center tray above teeth and seat posterior
Press tray down & toward anterior and allow
lip to cover tray; material should fill vestibule
Hold tray in patient’s mouth until set (2 - 3 min)
Loosen cheeks and lips with finger
Remove occlusally with a firm snap
Evaluating an Alginate Impression:
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Full coverage, including retromolar area
Tray centered
Clear & sharp impression
No voids, air bubbles, or tears
Has a “peripheral roll” (vestibular area)
If all is OK, rinse & disinfect impression,
pour-up in stone/plaster, or store in humid bag.
Irreversible Hydrocolloid:
Advantages:
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Easy & economical
Many applications
Patient comfort
Excellent wetting by
gypsum
Disposable tray
Disadvantages:
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Not enough detail
for final impression
Must be poured
immediately
Hydrocolloids:
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SYNERESIS – shrinkage in impression due to loss
of water from heat or exposure to air.
IMBIBITION – swelling of impression due to
taking up moisture
To avoid these conditions (dimensional distortion),
pour-up immediately!
Elastomers:
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Two-paste systems:
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Two tubes – pastes mixed by hand
Two putties – mixed/kneaded by hand
Cartridge & Extruder Gun – automix tips used
Cartridge & Motor-driven Mixer – automix tips used
Set by chemical reaction
Warmth and moisture may slow setting
Must use a tray adhesive (if tray not perforated)
Latex may inhibit set of polyvinylsiloxanes
Elastomers:
Elastomers are used in a two-step process:
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Preliminary Impression - the material used to
form the base or the “tray” material used in an
impression; usually more viscous or heavy-body
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Secondary or “Wash” Impression – the material
applied through a syringe around the prep site
for detail; usually less viscous;
light or medium -body.
Elastomers:
POLYSULFIDE:
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Oldest elastomeric used in dentistry
Two pastes – mix base with catalyst
Liquid polymer with “sulfhydryl” group –
contains sulfur
“rubber-base” impression material
Used best with custom trays
Other materials have replaced this one
Elastomers:
Handling Polysulfides:
1. Equal lengths of pastes on pad
2. Pastes are “swirled” together, then stropped
3. Material placed in custom tray
4. Take impression – hold in place for up to 15 min.
5. Remove from pt’s mouth slow & steady force
6. Rinse & disinfect
7. Pour-up impression within several hours
Polysulfides:
Advantages:
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Economical
Good tear resistance
Good compatibility
with gypsum
Disadvantages:
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Malodor
Stains clothing
Long setting time
Fair stability
Less accurate
Elastomers:
Condensation Silicones:
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Similar to silicone rubber products (but non-toxic)
Setting by-product of alcohol
“Hydrophobic” – results in voids in stone
Shrinkage occurs as it sets
Must be poured immediately
Accurate, but slow setting time
Replaced by improved products
Elastomers:
POLYETHERS:
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Developed in 1960’s
No reaction by-product produced
Shorter working and setting time
Only come in a single viscosity
Stiff material – can use a triple tray
Very popular – “Impregum”
No need to pour-up immediately
Elastomers:
Handling Polyether:
1. Mix equal lengths of paste; or extrude
through the automix cartridge tip
2. Load syringe and apply to tooth thru tip
3. Load tray and invert over area for
impression
4. Allow to set; 4 – 5 minutes
5. Remove from mouth
6. Rinse & disinfect
Polyether: Impregum
Polyether:
Advantages:
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Short setting time
Single viscosity
Good stability
Good tear strength
Clean & easy to use
Disadvantages:
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Bad taste
Most difficult to
remove from mouth
Elastomers:
ADDITION SILICONES:
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“Polyvinylsiloxanes” – silicone polymer
Two pastes or two putties
Hydrophobic by nature – manufacturers
adding components to increase wettability
Very accurate & fast setting
Avoid contact with latex (gloves, rubber dams)
Low setting shrinkage & very stable
Elastomers:
Handling Addition Silicone:
 Mix equal lengths of
pastes, or automix
 Apply light-body material
to tooth thru syringe
 Load tray with heavy-body
 Set tray over prep site
 Set in 4 – 5 minutes
 Rinse & disinfect
Addition Silicone: Polyvinylsiloxane
Advantages:
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Very stable
Short setting time
Good tear resistance
Great accuracy
No bad taste
Disadvantages:
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May have poor
wettability
Two pastes to mix