Impression Materials

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Impression Materials
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Impression Materials

• Non-elastic
• Elastic
• Aqueous hydrocolloids
• Agar
• Alginate
• Non-aqueous elastomers
• Polysulfide
• Silicones
• Condensation
• Addition
• Polyether

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Indications

• Diagnostic casts
• preliminary
• opposing
• Indirect reconstruction
• fixed
• removable
• Bite registration

Giordano, Gen Dent 2000
4
Elastomeric Impression Materials

• Viscoelastic
• physical properties vary
• rate of loading
• Rapidly remove
• decreases permanent deformation
• chains recoil from a recoverable distance
• increases tear strength

Phillips Science of Dental Materials 1996
5
Non-elastic
Impression Materials
Agar (reversible)
Aqueous Hydrocolloids
Alginate (irreversible)
Elastic
Condensation
Non-aqueous Elastomers
Addition
OBrien, Dental Materials their Selection 1997
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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

Phillips Science of Dental Materials 1996
7
Aqueous Hydrocolloids

• Semi-permeable membranes
• poor dimensional stability
• Evaporation
• Syneresis
• fibril cross linking continues
• contracts with time
• exudes water
• Imbibition
• water absorption
• swells

Phillips Science of Dental Materials 1996
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OBrien, Dental Materials their Selection 1997
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Reversible Hydrocolloid (Agar)

• Indications
• crown and bridge
• high accuracy
• Example
• Slate Hydrocolloid (Van R)

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Composition

• Agar
• complex polysaccharide
• seaweed
• gelling agent
• Borax
• strength

• Potassium sulfate
• improves gypsum surface
• Water (85)

OBrien, Dental Materials their Selection 1997
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Manipulation

• Gel in tubes
• syringe and tray material

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Manipulation

• 3-chamber conditioning unit
• (1) liquefy at 100C for 10 minutes
• converts gel to sol
• (2) store at 65C
• place in tray
• (3) temper at 46C for 3 minutes
• seat tray
• cool with water at 13C for 3 minutes
• converts sol to gel

OBrien, Dental Materials their Selection 1997
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Advantages

• Dimensionally accurate
• Hydrophilic
• displaces moisture, blood, fluids
• Inexpensive
• after initial equipment
• No custom tray or adhesives
• Pleasant flavor
• No mixing required

Phillips Science of Dental Materials 1996
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Disadvantages

• Initial expense
• special equipment
• Material must be prepared in advanced
• Tears easily
• Dimensionally unstable
• Must be poured immediately
• Can only be used for a single cast
• Difficult to disinfect

Phillips Science of Dental Materials 1996
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OBrien, Dental Materials their Selection 1997
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Irreversible Hydrocolloid (Alginate)

• Most widely used impression material
• Indications
• study models
• removable fixed partial dentures
• framework
• Examples
• Jeltrate (Dentsply/Caulk)
• Coe Alginate (GC America)

Phillips Science of Dental Materials 1996
17
Composition

• Sodium phosphate
• retarder
• Filler
• Potassium fluoride
• improves gypsum surface

• Sodium alginate
• salt of alginic acid
• mucous extraction of seaweed (algae)
• Calcium sulfate
• reactor

OBrien Dental Materials their Selection 1997
18
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
19
Advantages

• Inexpensive
• Easy to use
• Hydrophilic
• displace moisture, blood, fluids
• Stock trays

Phillips Science of Dental Materials 1996
20
Disadvantages

• Tears easily
• Dimensionally unstable
• immediate pour
• single cast
• Lower detail reproduction
• unacceptable for fixed pros
• High permanent deformation
• Difficult to disinfect

Phillips Science of Dental Materials 1996
21
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

Phillips Science of Dental Materials 1996
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OBrien Dental Materials their Selection 1997
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Polysulfide

• First dental elastomers
• Indications
• complete denture
• removable fixed partial denture
• tissue
• crown and bridge
• Examples
• Permlastic (Kerr)
• Omni-Flex (GC America)

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Composition

• Base
• polysulfide polymers
• fillers
• plasticizers
• Catalyst
• lead dioxide (or copper)
• fillers
• By-product
• water

Phillips Science of Dental Materials 1996
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Polysulfide Reaction
--SH
HS---------------------SH
HS--
-S-S---------------S-S-
S
S
3PbO H2O
H
S
O Pb O
H
S
OBrien Dental Materials their Selection 1997
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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

27
Advantages

• Lower cost
• compared to silicones and polyethers
• Long working time
• High tear strength
• High flexibility
• Good detail reproduction

Phillips Science of Dental Materials 1996
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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

Phillips Science of Dental Materials 1996
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OBrien Dental Materials their Selection 1997
30
Condensation Silicone

• Indications
• complete dentures
• crown and bridge
• Examples
• Speedex (Coltene/Whaledent)
• Primasil (TISS Dental)

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Composition

• Base
• poly(dimethylsiloxane)
• tetraethylorthosilicate
• filler
• Catalyst
• metal organic ester
• By-product
• ethyl alcohol

Phillips 1996
Phillips Science of Dental Materials 1996
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Condensation Silicone Reaction
metal organic ester
ethanol
Phillips Science of Dental Materials 1996
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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

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Advantages

• Better elastic properties
• Clean, pleasant
• Stock tray
• putty-wash
• Good working and setting time

Phillips Science of Dental Materials 1996
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Disadvantages

• Poor dimensional stability
• high shrinkage
• polymerization
• evaporation of ethanol
• pour immediately
• within 30 minutes
• Hydrophobic
• poor wettability

Phillips Science of Dental Materials 1996
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OBrien Dental Materials their Selection 1997
37
Addition Silicones

• AKA Vinyl polysiloxane
• Indications
• crown and bridge
• denture
• bite registration
• Examples
• Extrude (Kerr)
• Express (3M/ESPE)
• Aquasil (Dentsply Caulk)
• Genie (Sultan Chemists)
• Virtual (Ivoclar Vivadent)

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Composition

• Improvement over condensation silicones
• no by-product
• First paste
• vinyl poly(dimethylsiloxane)prepolymer
• Second paste
• siloxane prepolymer
• Catalyst
• chloroplatinic acid

Phillips 1996
Phillips Science of Dental Materials 1996
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Addition Silicone Reaction
Chloroplatinic Acid Catalyst
Phillips Science of Dental Materials 1996
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Manipulation

• Adhesive to tray
• Double mix
• custom tray
• heavy-body
• light-body to prep
• Putty-wash
• stock tray

Craig Adv Dent Res 1988
41
Advantages

• Highly accurate
• High dimensional stability
• pour up to one week
• Stock or custom trays
• Multiple casts
• Easy to mix
• Pleasant odor

Phillips Science of Dental Materials 1996
42
Disadvantages

• Expensive
• Sulfur inhibits set
• latex gloves
• ferric and Al sulfateretraction solution
• Pumice teeth beforeimpressing
• Short working time
• Lower tear strength
• Possible hydrogen gas release
• bubbles on die
• palladium added to absorb

Manikos Aust Dent J 1998
43
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
44
OBrien Dental Materials their Selection 1997
45
Polyether

• Indications
• crown and bridge
• bite registration
• Examples
• Impregum F (3M/ESPE)
• Permadyne (3M/ESPE)
• Pentamix (3M/ESPE)
• P2 (Heraeus Kulzer)
• Polygel (Dentsply Caulk)

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Composition

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

Phillips Science of Dental Materials 1996
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Polyether Reaction
base
catalyst
ring opening
Phillips Science of Dental Materials 1996
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Manipulation

• Adhesive to tray
• stock or custom tray
• very stiff
• Paste-paste mix
• Auto-mixing
• hand-held
• low viscosity
• mechanical dispenser
• high viscosity

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Advantages

• Highly accurate
• Good dimensional stability
• Stock or dual-arch trays
• Good surface detail
• Pour within one week
• kept dry
• Multiple casts
• Good wettability

Phillips Science of Dental Materials 1996
50
Disadvantages

• Expensive
• Short working time
• Rigid
• difficult to remove from undercuts
• Bitter taste
• Low tear strength
• Absorbs water
• changes dimension

Phillips Science of Dental Materials 1996
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Impression Material UsageCivilian General
Dentists

• Crown Bridge
• vinylpolysiloxane 81
• alginate 38
• polyether 28
• Inlays and Onlays
• vinylpolysiloxane 71
• polyether 22
• alginate 20

Multiple responses
DPR 2001
52
Impression Material UsageCivilian General
Dentists

• Complete dentures
• alginate 58
• vinylpolysiloxane 55
• polyether 27
• Partial dentures
• alginate 78
• vinylpolysiloxane 43
• polyether 15

Multiple responses
DPR 2002
53
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
OBrien Dental Materials their Selection 1997
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Handling Properties
Agar Alginate Polysulfide 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
OBrien Dental Materials their Selection 1997
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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 lt 0.10 lt 0.05 lt 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
OBrien Dental Materials their Selection 1997
56
Comparison of Properties

• Working time
• longest to shortest
• agar gt polysulfide gt silicones gt alginate
  polyether
• Setting time
• shortest to longest
• alginate lt polyether lt agar lt silicones lt
  polysulfide

OBrien Dental Materials their Selection 1997
57
Comparison of Properties

• Stiffness
• most to least
• polyether gt addition silicone gt condensation
  silicone gt polysulfide hydrocolloids
• Tear strength
• greatest to least
• polysulfide gt addition silicone gt polyether gt
  condensation silicone gtgt hydrocolloids

OBrien Dental Materials their Selection 1997
58
Comparison of Properties

• Cost
• lowest to highest
• alginate lt agar polysulfide ltcondensation
  silicone lt addition silicone lt polyether
• Dimensional stability
• best to worst
• addition silicone gt polyether gt polysulfide gt
  condensation silicone gt hydrocolloid

Phillips 1996
OBrien Dental Materials their Selection 1997
59
Comparison of Properties

• Wettability
• best to worst
• hydrocolloids gt polyether gt hydrophilic addition
  silicone gt polysulfide gt hydrophobic addition
  silicone condensation silicone
• Castability
• best to worst
• hydrocolloids gt hydrophilic addition silicone gt
  polyether gt polysulfide gt hydrophobic addition
  silicone condensation silicone

OBrien Dental Materials their Selection 1997
60
Regularly-Used Impression MaterialsCivilian
Practitioners

• Alginate 88
• Polyvinyl Siloxane 85
• Polyether 27
• Other 6

Multiple Responses
DPR 2005
61
Summary

• Study models
• Alginate most widely used
• inexpensive
• displaces moisture
• lower detail reproduction
• dimensionally unstable

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Summary

• Prosthodontics
• Addition silicones most popular
• accurate
• dimensionally stable
• user friendly
• expensive