Impression MaterialsImpression Materials
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Impr
essi
on
Mat
eria
lsNon-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
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Elastic
Aqueous Hydrocolloids
Non-aqueous Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
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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
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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
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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 processPhillip’s Science of Dental Materials 1996
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Aqueous Hydrocolloids• Semi-permeable membranes
– poor dimensional stability• Evaporation• Syneresis
– fibril cross linking continues• contracts with time• exudes water
• Imbibition– water absorption
• swells
Phillip’s Science of Dental Materials 1996
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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%)
agar hydrocolloid (hot) agar hydrocolloid (cold)
(sol) (gel)
cool to 43 C
heat to 100 C
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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 gelO’Brien Dental Materials & their Selection 1997
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Advantages
• Dimensionally accurate• Hydrophilic
– displace moisture, blood, fluids• Inexpensive
– after initial equipment• No custom tray or adhesives• Pleasant• No mixing required
Phillip’s Science of Dental Materials 1996
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Disadvantages
• Initial expense– special equipment
• Material prepared in advanced• Tears easily• Dimensionally unstable
– immediate pour– single cast
• Difficult to disinfect
Phillip’s Science of Dental Materials 1996
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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)
Phillip’s Science of Dental Materials 1996
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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
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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
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Advantages
• Inexpensive• Easy to use• Hydrophilic
– displace moisture, blood, fluids• Stock trays
Phillip’s Science of Dental Materials 1996
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Disadvantages• Tears easily• Dimensionally unstable
– immediate pour – single cast
• Lower detail reproduction– unacceptable for fixed pros
• High permanent deformation• Difficult to disinfect
Phillip’s Science of Dental Materials 1996
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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
Phillip’s Science of Dental Materials 1996
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Elastic
Aqueous Hydrocolloids
Non-aqueous Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
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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
Phillip’s Science of Dental Materials 1996
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--SH HS---------------------SH HS--
S H
O
=
Pb
=
O
O
=
Pb
=
OO = Pb = OHS
-S-S---------------S-S-
S
S + 3PbO + H2O
mercaptan + lead dioxide polysulfide rubber + lead oxide + water
Polysulfide Reaction
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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
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Advantages
• Lower cost– compared to silicones and polyethers
• Long working time• High tear strength• High flexibility• Good detail reproduction
Phillip’s 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
Phillip’s Science of Dental Materials 1996
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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
Phillip’s 1996
Phillip’s Science of Dental Materials 1996
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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
Phillip’s 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 materialwww.indiandentalacademy.com
Advantages
• Better elastic properties• Clean, pleasant• Stock tray
– putty-wash• Good working and setting time
Phillip’s 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
Phillip’s Science of Dental Materials 1996
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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
Phillip’s 1996
Phillip’s Science of Dental Materials 1996
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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
Phillip’s 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
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Advantages
• Highly accurate• High dimensional stability
– pour up to one week• Stock or custom trays• Multiple casts• Easy to mix• Pleasant odor
Phillip’s Science of Dental Materials 1996
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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
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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
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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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• Base– difunctional epimine-terminated prepolymer– fillers– plasticizers
• Catalyst– aromatic sulfonic acid ester– fillers
• Cationic polymerization– ring opening and chain extension
Composition
Phillip’s Science of Dental Materials 1996
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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
Phillip’s 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
Phillip’s Science of Dental Materials 1996
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Disadvantages• Expensive• Short working time• Rigid
– difficult to remove from undercuts• Bitter taste• Low tear strength• Absorbs water
– changes dimension
Phillip’s Science of Dental Materials 1996
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Handling Properties
Agar Alginate Polysulfide Condensation Silicone
Addition Silicone Polyether
PreparationBoil,
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
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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
castabilityExcellent Excellent Fair Fair Fair to
good Good
Cost Low Very low Low Moderate High to very high Very high
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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 < 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
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Comparison of Properties
• Working time– longest to shortest
• agar > polysulfide > silicones > alginate = polyether
• Setting time– shortest to longest
• alginate < polyether < agar < silicones < polysulfide
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Comparison of Properties
• Stiffness– most to least
• polyether > addition silicone > condensation silicone > polysulfide = hydrocolloids
• Tear strength– greatest to least
• polysulfide > addition silicone > polyether > condensation silicone >> hydrocolloids
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Comparison of Properties• 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
O’Brien Dental Materials & their Selection 1997
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Comparison of Properties• 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
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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
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• 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.”
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• 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.
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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.
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• 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
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• 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.
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• . (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.
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• . (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.
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• 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.
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• [B] 1. Open or• 2. Closed mouth
• [C] 1. Hand-manipulation or• 2. Functional movements
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• [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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