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6. 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
www.indiandentalacademy.com
7. 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
Phillip’s Science of Dental Materials 1996
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8. 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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12. 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
O’Brien Dental Materials & their Selection 1997
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13. 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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14. 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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15. 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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17. 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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18. Advantages
• Inexpensive
• Easy to use
• Hydrophilic
– displace moisture, blood, fluids
• Stock trays
Phillip’s Science of Dental Materials 1996
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19. 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
www.indiandentalacademy.com
20. 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
www.indiandentalacademy.com
23. 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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24. --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
O’Brien Dental Materials & their Selection 1997
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25. 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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26. 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
www.indiandentalacademy.com
27. 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
www.indiandentalacademy.com
29. 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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30. 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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32. 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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33. 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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35. 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
www.indiandentalacademy.com
36. 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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37. 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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38. 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
www.indiandentalacademy.com
39. 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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40. 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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42. • 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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43. 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
www.indiandentalacademy.com
44. 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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45. 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
www.indiandentalacademy.com
46. 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
www.indiandentalacademy.com
47. 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
O’Brien Dental Materials & their Selection 1997
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48. 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
O’Brien Dental Materials & their Selection 1997
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50. Comparison of Properties
• Working time
– longest to shortest
• agar > polysulfide > silicones > alginate = polyether
• Setting time
– shortest to longest
• alginate < polyether < agar < silicones < polysulfide
O’Brien Dental Materials & their Selection 1997
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51. 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
O’Brien Dental Materials & their Selection 1997
www.indiandentalacademy.com
52. 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
www.indiandentalacademy.com
53. 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
O’Brien Dental Materials & their Selection 1997
www.indiandentalacademy.com
54. Summary
• Study models
– Alginate most widely used
• inexpensive
• displaces moisture
• lower detail reproduction
• dimensionally unstable
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55. Summary
• Prosthodontics
– Addition silicones most popular
• accurate
• dimensionally stable
• user friendly
• expensive
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56. • 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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57. • 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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58. 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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59. • 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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60. • 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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61. • . (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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62. • . (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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63. • 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
64. • 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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65. • [B] 1. Open or
• 2. Closed mouth
• [C] 1. Hand-manipulation or
• 2. Functional movements
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66. • [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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67. Thank you
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