Various types of impression materials, their compositions, uses, advantages and disadvantages along with recent advances explained.

1. IMPRESSION
MATERIALS
1126
PRESENTED BY,
DR. PRAGATI AGRAWAL

2. CONTENTS
■ INTRODUCTION
■ DEFINITION
■ IDEAL REQUIREMENTS OF IMPRESSION MATERIALS
■ CLASSIFICATION OF IMPRESSION MATERIALS
■ RIGID IMPRESSION MATERIALS
■ HYDROCOLLOIDS
■ DUPLICATING MATERIALS
■ ELASTOMERIC IMPRESSION MATERIALS
■ RECENT ADVANCES
■ DIGITAL IMPRESSIONS
■ REVIEW OF LITERATURE
■ CONCLUSION
■ REFERENCES
■ CROSS REFERANCES
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3. INTRODUCTION
■ Construction of model or casts is an important step in numerous
dental procedures.
■ This requires an impression mold or negative likeness of a dental
structure.
■ Thus, an accurate impression plays an important role for the
reproduction of an accurate cast which represents the oral
structures for designing and constructing various oral prosthesis.
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4. DEFINITION
IMPRESSION:-
An exact negative replica of the teeth and its associated
oral tissues with accurate reproduction of all finer details,
maintaining correct spatial dimensions.
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5. IDEAL REQUIREMENTS OF
IMPRESSION MATERIALS
■ Sufficiently fluid to adapt to the oral tissues
■ Viscous enough to be contained in the tray
■ Able to set into rubbery or rigid solid in mouth in a reasonable time (< 7 min).
■ Resistant to distortion or tearing when removed from the mouth
■ Dimensionally stable long enough to allow one or more casts to be poured
■ Very low or zero coefficient of thermal expansion
■ Good colour stability and colour contrast
■ Hydrophilic
■ Insoluble in oral fluids
■ Biocompatible
■ Cost effective
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6. CLASSIFICATION
SETTING MECHANISM MECHANICAL
PROPERTIES
INELASTIC ELASTIC
CHEMICAL REACTION
(IRREVERSIBLE)
PLASTER OF PARIS
ZINC OXIDE
EUGENOL
ALGINATE
POLYSULFIDE
POLYETHER
CONDENSATION
SILICONE
ADDITION
SILICONE
THERMALLY INDUCED
PHYSICAL REACTION
(REVERSIBLE)
IMPRESSION
COMPOUND
AGAR
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7. FORCE GENERATED IMPRESSION MATERIAL
MUCOSTATIC Impression plaster
Agar agar
Light body elastomer
Zinc oxide eugenol paste
MUCOCOMPRESSIVE Impression compound
Alginate
Regular, heavy, putty elastomers
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8. 8
DISPENSING SYSTEM MATERIALS
POWDER Impression plaster
alginate
2 PASTE ZnOE impression paste
Polysulfide
Polysilicone
3 PASTE Chemically activated
polyether
SINGLE PASTE Light activated polyether
GELS Agar agar
CAKES, CYLINDERS.
STICKS, SHEETS,
CONES
Impression compound
Impression wax
126

9. 9
CLINICALAPPLICATION MATERIALS
PRIMARY/ PRELIMINARY
IMPRESSION
Impression compound
Impression wax
Alginate
Heavy & regular body elastomer
SECONDARY/CORRECTIVE
WASH IMPRESSION
Impression plaster
ZnOE paste
Light body elastomers
BORDER MOULDING
IMPRESSION
Green stick compound
CAVITY IMPRESSION OF
INLAYS AND ONLAYS
elastomers
CROWN & BRIDGE
IMPRESSION
Hydrocolloids
elastomers
PARTIAL DENTURE
IMPRESSION
Hydrocolloids
Elastomers
126

10. IMPRESSION TRAYS
10126

11. IMPRESSION
PLASTER
ADA SPECIFICATION NO. 25
11126

12. ■ COMPOSITION:-
12
INGREDIENTS FUNCTION
Dental plaster
(β- calcium sulfate
hemihydrate)
Potassium sulfate Anti- setting expansion
agent
Borax Retarder
Colouring agent (alizarin
red)
Distinguish between cast
and impression.
Flavouring agent Patient acceptance
Potato starch Easy removal of cast from
impression
126

13. ■ MANIPULATION:-
■ requires custom tray of acrylic resin or shellac with 1- 1.5 mm spacer.
■ PUDDLING of the impression into place.
13126
Water : powder 0.5 or 0.6

14. ■ PROPERTIES:-
• Low setting expansion.
• Working time 2-3 min.
• Setting time is 4- 5 min.
• Low strength (4-5 Mpa)
• Mucostatic
• Disinfection: 10 min soak in
sodium hypochlorite solution.
USES:-
• Preliminary impressions
• Wash impression on preliminary impression with impression
compound.
• Splinting transfer coping for implant- supported prosthesis
• Bite registration
14126

15. ■ ADVANTAGES:-
• Mucostatic
• Accurate fine details
• Negligible dimensional
change.
■ DISADVANATGES:-
• Non elastic
• Bad taste
• Messy working
• Brittle
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16. IMPRESSION WAX
[ BEES WAX, PARAFFIN WAX AND CERESIN WAX]
16126

17. ■ TYPES:-
17
CORRECTIVE BITE
REGISTRATION
• Flow is 100% at 37 ℃
• Functional impression in
partial dentures and
obturators.
• Record PPS
• Used as wax veneer over
original impression to
register details of soft
tissues.
• Flow is 2.5% to 22% at
37℃
• U shaped thin sheets,
sometimes metallized or
foil laminated.
• Record occlusal
relationship.
126

18. IMPRESSION COMPOUND
[DENTAL/ MODEL/
MODELLING COMPOUND]
ADA SPECIFICATION NO. 03
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19. TYPES:-
19
TYPE I (LOW
FUSING)
>45℃
TYPE II (HIGH
FUSING)
>70℃
IMPRESSION
COMPOUND
GREENSTICK
COMPOUND
TRAY
COMPOUND
126

20. ■ SETTING:-
Softenend by heating and hardened by cooling (physical set)
COMPOSITION:-
20
PERCENTAGE FUNCTION
Natural / synthetic resin
• Copal resin
• Rosin 20%
20%
Thermoplasticity
Flow
Cohesion
Waxes
(bees, carnauba, paraffin
wax)
7% Thermoplasticity
(smooth surface)
Oils & fats
(stearic acid, shellac,
gutta purcha)
3% Plasticizer
(flow, plasticity,
workability, hardener)
French chalk, talc,
diatomaceous earth
50% Filler
(strength, less thermal
expansion & contraction)
Rouge (Fe2O3) trace Reddish brown colour
126

21. ■ PROPERTIES:-
• Non toxic, non irritant, non poisonous to oral tissues
• Highly viscous and muco-compressive.
• Fusion temperature 43.5 degree C
• Poor conductor of heat
• Coefficient of thermal expansion 200- 500 ppm/℃
• Warpage / distortion if not poured within 1 hour.
DISINFECTION:-
Immersion in 2% alkaline glutaraldehyde solution.
21126

22. ■ MANIPULATION:-
22
WET KNEADING DRY KNEADING
126

23. ■ PRECAUTIONS:-
Direct flame – ignite, boil
prolonged immersing or heating in hot water
(brittle, grainy, sticky surface)
 60- 65 ℃water
 A gauze or napkin placed in water to avoid sticking of
compound.
23126

24. ADVANTAGES:-
■ Reusable and economical.
■ Long shelf life (5 yrs).
■ Non- toxic.
DISADVANTAGES:-
■ Non – elastic
■ Contraindicated in
dentulous cases and in the
presence of undercuts.
■ Can’t be sterilized.
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25. 25
USES:-
Primary impression of
edentulous patients
Border moulding
126

26. ZINC OXIDE
EUGENOL
IMPRESSION PASTE
ADA SPECIFDICATION NO. 16
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27. ■ COMPOSITION:-
27
BASE PASTE PERCENTAGE FUNCTIONS
Zinc oxide 87% Reactor
Fixed vegetable/
mineral oil (linseed/
olive)
13% Plasticizer, paste
former, retarder, masks
eugenol action
CaCl2 2% accelerator
126

28. 28
REACTOR PASTE
Clove/ eugenol oil 12% • Reactor
CaCl2 or MgCl2 5% • Accelerator
Gum/ polymerized
resin
50% • Speed of reaction,
smooth
homogeneous mix
• Gives body &
coherence to mix
material
• Thermoplasticity to
set material
Fillers
(silica, kaolin, etc.)
20% • Paste former
• Increase strength
Lanolin 3% • Plasticizer
Resinous balsom
(Canada/ peru balsam)
10% • Increases flow
Colour pigments Trace • Thorough mixing
126

29. ■ MANIPULATION:-
29
SAME LENGTH
OF BOTH PASTES
REACTOR PASTE
APPLIED OVER THE
BASE PASTE
126
GLASS SLAB OR
OIL IMPERVIOUS
PAPER
FLEXIBLE
STAINLESS STEEL
SPATULA

30. ■ SETTING REACTION:-
• Acid- base reaction, called as chelation.
i. Hydrolysis of ZnO to Zn(OH)2
ii. The phenol –OH of eugenol act as weak acid and reacts with
Zn(OH)2 to form a salt, Zn eugenolate.
iii. The chelate, zinc eugenolate forms an amorphous gel and
crystallizes to form a strong mass. It is a matrix surrounding a
core of ZnO.
30
ZnO + H2O → Zn (OH)2
Zn (OH)2 + eugenol → ZnE2 + 2H2O
(Base) (Zinc eugenolate)
126

31. ■ MIXING TIME:-
1 min
■ SETTING TIME:-
Initial set: 3- 6 min (both type 1, 2)
Final set: 10 min (type 1)
15 min (type 2)
31
FACTORS INCREASING SETTING
TIME:-
• Low temperature (cool glass slab and
spatula)
• Low humidity
• More ZnO paste
• Slower and shorter mixing time
• Retarders (boroglycerin, inert oils,
waxes)
126
DECREASING SETTING
TIME:-
• Zinc acetate or acetic acid
• Adding a drop of water to
paste before mixing.
• Increased mixing time.

32. ■ PROPERTIES:-
• Non toxic but eugenol can give tingling or burning sensation to the patient.
• Hardness penetration depth ( kreb’s penetrometer):
<0.5 mm (type 1)
0.8- 1.5 mm (type 2)
• Consistency:-
30- 50mm (type 1)
20- 45mm (type 2)
• Good dimensional stability
• Inelastic (can’t be used in undercut areas)
• Compatible with stone and die materials
• Shelf life upto 1 year.
■ DISINFECTION:-
Immersion in 2% glutaraldehyde solution.
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33. ■ USES:-
33
Secondary/wash
impression
Surgical pack
Bite registration
126

34. ■ ADVANTAGES:-
• Accurate reproduction of
fine details.
• Good dimensional
stability.
• Can be added and
readapted.
• No tray adhesive required.
• Easy to manipulate.
• Not expensive.
■ DISADVANTAGES:-
• Can’t be used in undercut
areas.
• Eugenol can cause burning
sensation.
• Requires special trays.
• Instruments difficult to
clean.
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35. ■ MODIFICATIONS:-
1. Surgical paste -- increased filler, eugenol, plasticizer and
addition of antibiotic.
2. Bite registration paste – increased plasticizer (petroleum jelly)
3. Non- eugenol paste – eugenol replaced by an organic acid like
ortho ethoxy benzoic acid (EBA) along with bactericides and
other medicaments.
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36. HYDROCOLLOIDS
36126

37. GENERAL PROPERTIES
■ Syneresis
■ Imbibition
■ Dimensionally unstable
■ Gels are relatively weak elastic solids.
37
INCREASE GEL STRENGTH:
• Increased density of concentration of dispersed
phase in sol.
• Low temperature
• Appropriate amount of fillers
• Faster loading or pressing
• Impression removed with a single, sudden jerk.
126

38. ■ Gypsum hardener added because polysaccharide inhibits the gypsum
setting.
■ Impression surface should be shiny but with no visible water during
pouring of cast.
Dry surface – adherence of impression to cast, resulting in tear.
Wet surface – rough stone surface
■ Removal of cast after 30-60 min of pouring to prevent dessication of
hydrocolloid.
126 38

39. AGAR AGAR
[Reversible hydrocolloid]
ADA SPECIFICATION NO. 11
■ An organic, hydrophilic (polysaccharide) extracted from certain
seaweeds.
■ Sulfuric ester of a linear polymer of galactose.
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40. 40
■ COMPOSITION:-
INGREDIENTS % FUNCTIONS
Agar 13-17 Brush heap structure
Borax 0.2-0.5 Viscosity of sol, strength of gel, retarder
K2SO4 1-2 Gypsum hardener, accelerator
Alkyl benzoate 0.1 Preservative
Diatomaceous
earth
0.3-0.5 Filler
Water 85.5 Reaction medium
Thymol Trace Bactericide
Glycerin Trace Plasticizer
Colour and
flavouring agents
Trace appearance and taste
126

41. ■ PROPERTIES:-
• Non- toxic and non- irritant.
• Gelation time 5 minutes.
• Gelation temperature 32℃- 45℃
• Compressive strength 0.4- 0.7 MPa
• Tear strength 715g/cm
• Muco-static due to low viscosity.
• Permanent deformation of 1% (permanent set) due to viscoelastic nature.
• Dimensionally unstable.
• Compatible with gypsum products.
• Cannot be electroplated.
DISINFECTION:-
Iodophor, bleach, 2% glutaraldehyde
41126
STORAGE MEDIUM:
2% potassium sulfate solution
100% relative humidity

42. ■ MANIPULATION:-
42
LIQUEFACTION
10-15 min
STORAGE
TEMPERING/
CONDITIONING
3-10 min
Syringe material never tempered
Syringe material applied to the prepared
teeth from the base
Tray material seated with light pressure
Cool water circulated at 18℃ - 21℃ for 3-5
min
126

43. 43
GELATION MECHANISM:-
• GEL IS HEATED
• INCREASE IN
KINETIC ENERGY
OF FIBRILS
• GEL CONVERTED
TO SOL
• DECREASE OF SOL
TEMPERATURE
• BRUSH HEAP
STRUCTURE OF
FIBRILS
• WEAK VANDER
WAALS FORCES
HYSTERESIS:-
• THE TEMPERATURE LAG OR
DIFFERENCE BETWEEN
LIQUEFACTION AND
GELATION.
70℃
GEL SOL
37℃
126

44. 44
Increased permanent deformation:-
• More compression or strain
• Longer time of compression
• Thicker sample
• Lower rate of loading
• Repeated cyclic loading
SINGLE SUDDEN JERK
REMOVAL OF
IMPRESSION
126

45. ■ WET FIELD TECHNIQUE:-
• The tooth surface and tissues are flooded with warm water and left wet.
• This improves the flow of material in the mouth.
■ USES:-
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46. ADVANTAGES
■ Reproduce finer details.
■ Used for model
duplication.
■ Sufficiently flexible.
■ High elastic recovery.
■ Can be reused.
DISADVANTAGES
■ Dimensionally unstable.
■ Cannot be electroplated.
■ Low tear strength.
■ Elaborate and expensive
equipment required.
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47. ALGINATE
(IRREVERSIBLE HYDROCOLLOID)
ADA SPECIFICATION NO. 18
■ Based on alginic acid which is prepared from brown seaweed,
algae.
■ Linear polymer of anhydro b- D- mannuronic acid of high
molecular weight.
47126

48. 48
SUPPLY:-
TYPE I: Fast set; 1.5-3 min
TYPE II: Normal set; 3-4.5 min
126

49. 49
COMPOSITION:-
INGREDIENTS % FUNCTION
Soluble alginate
(Na, K, ammonium or
tri- ethanol amine)
1.5 Forms sol with water.
Forms gel of calcium alginate.
Calcium sulfate
dihydrate
16 Reactor
Trisodium phosphate 2 Retarder
Diatomaceous earth 60 Filler
Zinc oxide 4 Filler
Potassium titanium
fluoride
3 Gypsum hardener
Flavouring agent Trace Pleasant taste
Colour pigments Trace
126

50. ■ PROPERTIES:-
• Non toxic and non – irritant to oral tissues.
(silica from diatomaceous earth can be a health hazard if inhaled)
• Pleasant taste and odour.
• 3% permanent set due to viscoelasticity.
• Gel strength 0.5 – 0.8 Mpa
• Tear strength 300-700 g/cm
(3-5 mm thick impression required)
• Flexibility 12-14%
• Dimensionally unstable
• Compatible with gypsum products.
• Cannot be electroplated.
• Perforated trays used for mechanical retention.
• Shorter shelf life (not >1 year) and stored in cool dry environment.
50126

51. 51
Increase in gelation time:-
Decrease the water temperature
(18-20 degrees or less)
Decrease in permanent deformation:-
Less percentage compression.
Removal of impression in a single sudden jerk.
Longer recovery time (removal of impression
from mouth after 8 min)
Gel strength:-
Decrease in w/p ratio in limits, increase
strength.
Over or under spatulation, decreases
strength.
126

52. 52
MANIPULATION:-
126

53. 53
MAXILLARY: 2 Scoops of powder
(15g) + 1 measure of water (48 ml)
MANDIBULAR: 1 Scoop of powder
(7.5g) + ½ measure of water (24ml)
Powder is incorporated into water
and mixed with vigorous figure 8
motion or stropped between the
blade of spatula and sides of bowl.
MIXING TIME 45 sec – 1 min.
Final mix is smooth and creamy that
does not drip off the spatula.
UNDER SPATULATION:-
• Inadequate wetting and
lack of homogeneity.
• Grainy mix and poor
recording of details.
OVER SPATULATION:-
• Inadequate working time.
• Reduced gel strength.
126

54. ■ IMPRESSION MAKING:-
• Mixed alginate loaded onto perforated tray from posterior
portion and pushed towards anterior.
• The tray is seated first posteriorly and then anteriorly in the
mouth and held gently.
• Removed with sudden single jerk.
• Washed under tap water, disinfected and poured immediately.
54126

55. ■ GELATION:-
55
The set material is an intermeshed brush heap structure of
fibrils of calcium alginate enclosing unreacted
sodium/potassium alginate, excess water, filler particles and
reaction by products.
126

56. ■ PRECAUTIONS:-
 Clean instruments (gypsum impurities may accelerate the reaction).
 Dust should not be inhaled after tumbling the powder container.
 Correct water powder ratio as per manufacturer’s instructions.
 No air incorporation during mixing.
 Over and under spatulation avoided.
 Water temperature 18-23℃.
 Impression thickness 3-5 mm.
 No tray disturbance during gelation.
 Impression held in mouth for 2-3 min after gelation for better strength
and elasticity.
 Removal of impression with single sudden jerk.
 Immediate pouring of cast. For shorter periods, it can be stored in 100%
humidity or covered with damp napkin or wet cotton.
56126

57. ADVANTAGES
■ Reproduces excellent surface
details.
■ High elastic recovery.
■ Records undercuts.
■ Comfortable to patient.
■ Hygienic.
■ Economical and easy
manipulation.
DISADVANTAGES
■ Dimensionally unstable.
■ Low tear strength.
■ Cannot be electroplated.
■ No proper storage medium.
■ Cannot be corrected.
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58. 58
USES:-
• Primary impression for
complete dentures, partial
dentures and crowns and
bridges.
• Impression for study model
in orthodontics.
• Impression for athletic
mouth guards.
• For duplicating casts and
models.
126

59. MODIFIED ALGINATES
59
1. DUST FREE ALGINATE (DFA):-
■ A de- dusting agent incorporated into powder,
glycerin or glycol.
2. SILICONIZED ALGINATE:-
■ Silicone polymers added.
■ Tray and syringe viscosities.
■ Superior resistance to tearing.
3. 2 PASTE ALGINATE:-
■ One paste– sol of alginate, filler, retarder, and
other ingredients.
■ Other paste– gypsum dihydrate, filler, retarder,
glycerol or glycol, gypsum surface modifier
and silicone oil.
126

60. 4. CHROMATIC/ COLOUR INDICATOR ALGINATE:-
■ Shows different stages of reaction during manipulation.
5. HARD AND SOFT ALGINATE:-
■ Different percentage of fillers to control the flexibility of set
material.
■ Hard set alginate has flexibility of 5-8%.
6. ALGINATE WITH DISINFECTANTS:-
■ Quarternary ammonium salts, chlorhexamine added to alginate
powder.
■ Patients strictly informed not to swallow the impression material.
60126

61. 126 61
MECHANICAL MIXING DEVICES
ROTATING MIXING
BOWL VACUUM MIXER
DYNAMIC MECHANICAL
MIXER FOR 2 PASTE
SYSTEM

62. LAMINATE TECHNIQUE
(AGAR-ALGINATE
COMBINATION)
62126

63. ADVANTAGES
■ Lesser equipment cost.
■ Lesser preparation time.
■ Eliminates water cooled trays.
■ Good record of surface details
by agar.
■ Cost effective.
DISADVANTAGES
■ Poor dimensional stability.
■ Bond between agar and
alginate not strong.
■ High viscosity displaces agar
during seating.
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64. FAILURES
FAILURES AGAR AGAR ALGINATE
Grainy surface • Inadequate boiling
• Too low storage
temperature
• Too long storage time.
• Non homogeneous mix
• Prolonged mixing
• Excessive gelation
• Less w/p ratio
Seperation of tray
and syringe material
• Water left on surface of
tray material.
• Premature gelation.
Tearing • Inadequate thickness.
• Premature removal
• Delay in seating
• Prolonged mixing
• Inadequate mixing
• Moisture contamination
• Premature removal
External bubbles • Gelation of syringe
material
• Pre gelation before seating
• Air trapped while mixing.
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65. 65
FAILURES AGAR AGAR ALGINATE
Irregular voids • Too cold material • Water or debris on
tissue
Distortion • Movement of tray
during gelation
• Removal before
completion of gelation
• Improper removal from
mouth
• Delayed cast pouring.
• Movement of tray
during gelation
• Removal before
completion of gelation
• Improper removal from
mouth
• Delayed cast pouring.
Rough and chalky stone
model surface
• Inadequate cleaning
• Excess water or surface
hardener left.
• Incomplete gelation
• Improper mixing or
high w/p of cast or die
stone.
• Too cold water
circulation.
• Inadequate cleaning
• Excess water or surface
hardener left.
• Incomplete gelation
• Improper mixing or
high w/p of cast or die
stone.
126

66. DUPLICATING
MATERIALS
ADA SPECIFICATION NO. 20
66126

67. ■ Duplicating materials used to make accurate replica of model or cast.
■ It is required for 2 reasons:-
i. The cast on which wax pattern of metal framework is to be formed
must be made from refractory investment to withstand high casting
temperature.
ii. Original cast is required for checking the accuracy of metal framework
and for processing denture.
TYPES:-
67
TYPE I: thermo reversible
(agar agar, PVC gel
TYPE II: Non reversible
(alginate, elastomer)
CLASS I: Aqueous
(agar agar, alginate)
CLASS II: Non aqueous
(PVC gel, elastomer)
126

68. 68
IDEAL REQUIREMENTS:-
• Maximum permanent deformation 3%.
• Strain in compression 4-25%.
• Minimum compressive strength
0.215MPa (type 1)
0.255MPa (type 2)
• Minimum tear strength 900g/cm.
126

69. 69
AGAR AGAR
• Excellent reproduction
of fine details.
• Sufficient strength,
flexibility and tear
strength to duplicate
undercuts.
• Dimensionally unstable.
PVC GEL
• Sufficient strength,
flexibility and chemical
stability which permits
large numbers of
duplications.
ALGINATE
• Simpler
• Dimensionally unstable
• Not reusable
ELASTOMERS
(POLYSILICONE & POLYETHER)
• Excellent reproduction of fine
details.
• Good dimensional stability.
• Many duplications possible.
• Compatible with duplicating die
materials.
• Expensive
• Cannot be reused.
126

70. ELASTOMERIC/
RUBBER BASED
IMPRESSION
MATERIALS
70126

71. ■ A group of synthetic polymer- based
impression materials that are chemically
cross-linked when set and that can be
stretched and yet rapidly recover to their
original dimensions when the stress is
released.
71126

72. CLASSIFICATION
■ ACCORDING TO
CHEMICAL NATURE/
NAME:-
1. Polysulfide
2. Polysilicone
a) addition
b) condensation
3. Polyether
a) Light activated
b) Chemically activated
■ ACCORDING TO
VISCOSITY:-
1. Very high viscosity – putty
2. High viscosity – heavy body
3. Medium viscosity – regular
body
4. Low viscosity – light body/
syringe consistency
72126

73. ■ ACCORDING TO
POLYMERIZATION:-
1. Addition polymerization –
polyether, addition silicone
2. Condensation polymerization –
polysulfide, condensation
silicone
■ ACCORDING TO
DISPENSING:-
1. Single paste system – light
activated polyether
2. 2 paste system (base + reactor) –
polysulfide, addition and
condensation silicone
3. 2 paste system with
pseudoplastic property (single
tray and syringe monophase
material) – addition silicone
4. Single paste (base) with reactor
liquid – condensation silicone
5. 3 paste system (base + reactor +
thinner/ body modifier) –
chemically activated polyether
73126

74. 74
ACCORDING TO USE:-
IMPRESSION TYPE IMPRESSION
OBJECT
IMPRESSION
MATERIAL
Double mix single
impression
• Cavity impression for
inlays and onlays
• Light + heavy body
Double mix double
impression (reline
technique)
• Cavity impression of
inlays, onlays, etc.
• Impression of crowns
and partial denture.
• Putty + light body
• Putty + regular body
Individual tray method
(tube impression)
• Impression of a
crown (single tooth)
• Regular body
• Light body
Single mix single
impression
• Cavity impression of
inlays and onlays
• Impression of partial
denture
• Regular or heavy
body with
pseudoplastic
property
• Light or regular body
126

75. 75
ACCORDING TO DIMENSIONAL STABILITY, FLOW AND
PERMANENT DEFORMATION:-
TYPES MAX.
PERMANENT
DEFORMATION
%
MAX. FLOW IN
COMPRESSION
%
MAX.
DIMENSIONAL
CHANGE IN 24
HRS %
I 2.5 0.5 0.5
II 2.5 0.5 1.0
III 2.5 2.0 0.5
126

76. POLYSULFIDE
76
THIOKOL
MERCAPTAN
VULCANIZING
2 PASTE SYSTEM
LIGHT BODY
MEDIUM BODY
HEAVY BODY
126

77. 77
COMPOSITION
BASE PASTE CATALYST PASTE
• Low molecular weight polysulfide
with 2 terminal & 1 pendant SH
group
• TiO2 or lithopone (filler)
• Dibutyl phthalate (plasticizer)
• 0.5% sulfur (accelerator)
• PbO2 or organic peroxide (reactor)
• TiO2 (filler)
• Dibutyl phthalate (plasticizer)
• Oleic or stearic acid (retarder)
126
Permalastic, coe-flex, omni
flex (copper oxysulfate
activator)

78. ■ SETTING REACTION:-
• Condensation polymerization
• Water byproduct
• A series of oxidation reaction.
• Oxidation of terminal SH group –
polymer chains
• Oxidation of pendant SH group –
cross linking and elasticity
• Hot and humid conditions
accelerate the setting
78
Working time 3-6 min at 25℃
Setting time 10-20 min.
126

79. CONDENSATION
SILICONE
79
ROOM TEMPERATURE
VULCANIZING (RTV) SILICONE
2 PASTE SYSTEM
BASE PASTE AND REACTOR
LIQUID
LIGHT, REGULAR, HEAVY,
PUTTY
126

80. 80
COMPOSITION:-
BASE PASTE CATALYST PASTE
• Low molecular weight
silicone polymer with
terminal OH group
(α-ω-hydroxyl-terminated
polydimethyl siloxane)
• Colloidal silica or TiO2
(filler)
• Alkyl silicate (cross
linking)
• Tin dilaurate or stannous
octoate (activator)
126
Multiphase – acusil, coltex
Monophase – xantropen, lastic

81. ■ SETTING REACTION:-
• Condensation polymerization
• Ethyl alcohol byproduct
• A series of cross linking of siloxane polymer to alkyl silicate in
the presence of activator to form a a3D polymer network.
81126

82. ADDITION SILICONE
82
POLYVINYL SILOXANE (PVS)
VINYL POLYSILOXANE (VPS)
2 PASTE SYSTEM
SINGLE PHASE/ MONOPHASE
EXTRA LOW, LIGHT, REGULAR,
HEAVY, PUTTY
126

83. 83
COMPOSITION:-
BASE PASTE CATALYST PASTE
• Polymethyl hydrogen siloxane
(hydride or silane terminated
silicone)
• Other siloxane pre-polymer
• Fillers
• Divinyl poly dimethyl siloxane
• Platinum salt (activator)
• Siloxane pre-polymer
• Fillers
126
Multiphase – reprosil
(dentsply), provil, president
Monophase – imprint,
bluemousse

84. ■ SETTING REACTION:-
• Addition polymerization
• No byproduct
• A series of cross linkage between vinyl terminated silicone and silane
terminated (hydried) silicone molecules in the presence of catalyst to form
a 3D polymer network.
• A side reaction (release of hydrogen gas) may occur if:
- no balance between vinyl siloxane & hydried silicone
- moisture reacts with hydrides of base polymer
• Adding noble metal (Pt, Pd) act as hydrogen absorber.
• Latex gloves retard the setting due to presence of dithiocarbamate
compounds.
• Aluminium sulfate and ferric sulfate in gingival retraction cords also
retards setting reaction.
84126

85. POLYETHER
85
2 paste system
A diluent oil to produce light body.
Earlier only regular body
Recently Light, Medium, heavy body
126
Impregnum F (premier)
Permadyne (2 viscosity
system)

86. 86
COMPOSITION:-
BASE PASTE CATALYST PASTE
• LMW polyether with
terminal imine group
• Colloidal silica (filler)
• Dibutyl phthalate or
glycoether (plasticizer)
• Sulfonic acid ester
(alkyl-aromatic
sulfonate reactor)
• Filler
• Plasticizer
126

87. ■ SETTING REACTION:-
87
Ring opening addition
polymerization of aziridine
rings at the end of branched
polyether molecules
Acid-catalysed
condensation
polymerization of
polyether pre-polymer
with alkoxysilane terminal
groups
126

88. PROPERTIES
WORKING & SETTING TIME:-
 Working time – begins at the start of mixing and ends just before
the elastic properties have developed.
 Setting time – time that has elapsed from the beginning of
mixing until the curing process has advanced sufficiently that the
impression can be removed from the mouth with no distortion.
88
W.T. & S.T.
• Filler
• Base material
MEAN WORKING
TIME (MIN)
MEAN SETTING
TIME (MIN)
IMPRESSION MATERIAL 23℃ 37℃ 23℃ 37℃
POLYSULFIDE 6.0 4.3 16.0 12.5
CONDENSATION SILICONE 3.3 2.5 11.0 8.9
ADDITION SILICONE 3.1 1.8 8.9 5.9
POLYETHER 3.3 2.3 9.0 8.3
126

89. RHEOLOGICAL PROPERTIES:-
 All elastomeric materials exhibit shear thinning property before
setting.
 Monophase impression making
 More stable and resistant to distortion than a light viscosity material.
 Addition silicone, polyether.
89
Shear thinning is the tendency for viscosity to decrease as the
shearing rate increases.
Pseudoplasticity
Tendency to become less
viscous as the shear rate
increases and to recover
viscosity immediately upon the
elimination of shear stress.
Thixotropy
property to become less viscous
when sufficient energy in the form
of impact force or vibration is
applied to overcome its yield stress;
at rest they require specific time to
return to the previous viscous state.
126

90. ELASTICITY & VISCOELASTICITY:-
 Demonstrated by Maxwell- Voigt Model.
90
Viscoelasticity is the ability of a material to strain instantaneously like
an elastic solid during rapid stretching or to shear flow and to retain
linearly over time (like honey) when a stress is applied slowly.
PERMANENT
DEFORMATION IN
COMPRESSION FOLLOWING
STRAIN INDUCED DURING
REMOVAL:-
Addition silicone < condensation
silicone < polyether <
polysulfide
ELASTIC RECOVERY:-
Addition silicone > condensation
silicone > polyether > polysulfide
ELASTIC MODULUS
(STIFFNESS):-
Polysulfide < condensation
silicone < addition silicone <
polyether
126

91. TEAR STRENGTH:-
 Measures the resistance of an elastomeric impression materials
to fracture when subjected to a tensile force acting perpendicular
to a surface flaw.
91
The amount of force needed to tear a specific test specimen divided
by the thickness of the specimen.
Addition & condensation silicone
< polyether < polysulfide
Consistency Tear strength
Addition of thinning agent, tear strength
Removal of impression in a quick snap, tear strength
126

92. DIMENSIONAL STABILITY:-
 6 sources:-
i. Polymerization shrinkage
ii. Loss of condensation reaction byproduct (water or alcohol) –
polysulfide & condensation silicone
iii. Thermal contraction from oral temperature to room temperature
iv. Absorption of water or disinfectant over time -- polyether
v. Incomplete recovery of deformation because of viscolelastic
behaviour
vi. Incomplete recovery because of plastic deformation
92
DIMENSIONAL ACCURACY – lack of dimensional change during
curing and shortly after removal from mouth.
DIMENSIONAL STABILITY – lack of dimensional change over
time.
126

93. DISINFECTION:-
93
MATERIAL METHOD DISINFECTANT
POLYSULFIDE
& SILICONE
Immersion
Not > 30 min
• Glutaraldehyde
• Chlorine compounds
• Iodophors
• phenolics
POLYETHER Immerse with
caution
Only for <10 min
• Chlorine compounds
• phenolics
126

94. WETTABILITY & HYDROPHILIZATION:-
 Contact angle of distilled water on set silicone impressions are
100 degree i.e. most hydrophobic. This leads to voids in cast.
 To increase wettability:
• Spray a surfactant on impressions prior to pouring of cast.
• Adding a non-ionic surfactant to impression material during
manufacturing. This is called as hydrophilization.
94126

95. BIOCOMPATIBILITY:-
 Polysulfide – lowest cell death count
-- lead compound present is questioned to be harmful
-- radiopaque
 Polyether – highest cell cytotoxicity score
-- hypersensitivity to catalyst system
-- contact dermatitis
95126

96. SHELF LIFE:-
 Should be stored in cool, dry environment.
 If clear liquid is expressed out with the material, it indicated
plasticizer segregation due to manufacturing error or excessive
temperature extremes during storage.
96126

97. 126 97
POLYSULFIDE CONDENSA
TION
SILICONE
ADDITION
SILICONE
POLYETHER
ELASTIC
RECOVERY %
97.9 99.5 99.8 98.5
FLEXIBILITY % 7 5 4 3
FLOW % 0.5 0.10 0.03 0.03
REPRODUCTION
LIMIT µm
25 25 25 25
SHRINKAGE, 24
HOURS %
0.25 0.6 0.05 0.10

98. 126 98

99. EFFECT OF MISHANDLING:-
99
TYPE OF
FAILURE
CAUSES
Rough or uneven
impression surface
• Incomplete polymerization
• Latex contamination in addition silicone
• High humidity or temperature causing rapid polymerization
• High accelerator/ base ration in condensation silicone
Bubbles • Air incorporated during mixing
Irregularly shaped
voids
• Moisture or debris on teeth surface
Rough or chalky
stone cast
• Inadequate cleaning of impression
• Excess water or wetting agent on impression
• Premature removal of cast
• Improper powder/ water ratio of stone
• Failure to delay pour of addition silicone with no Pd salt for
atleast 20 min
126

100. 100
FAILURE CAUSES
Distortion • Resin tray still undergoing polymerization shrinkage
• Lack of adhesion of elastomer to tray due to insufficient adhesive,
adhesive not dried or using incorrect adhesive.
• Lack of mechanical retention to impression tray.
• Excessive bulk of material.
• Insufficient relief for the reline material.
• Development of elastic properties of material before tray is fully
seated.
• Continued pressure against impression material that has
developed elastic properties.
• Movement of tray during polymerization.
• Premature removal of impression from mouth.
• Improper removal of impression from mouth.
• Delayed pouring of polysulfide or condensation silicone.
126

101. 101
CHARACTERISTICS
GENERIC TYPE ADVANTAGES DISADVANTAGES
POLYSULFIDE • Long working time.
• High tear resistance
• Margins easily seen
• Moderate cost
• Requires custom tray
• Stretching leads to distortion
• Compatible with stone
• Stains clothing
• Obnoxious odour
• Pour within 1 hr
CONDENSATIO
N SILICONE
• Putty for custom tray
• Clean and pleasant
• Good working time
• Margins easily seen
• High polymerization shrinkage
• Volatile byproduct
• Low tear strength
• Hydrophobic
• Pour immediately (within 30 min)
ADDITION
SILICONE
• putty for custom tray
• Automix dispense
• Ideally elastic
• Margins easily seen
• Pour repeatedly and delayed
• Hydrophobic
• Low tear strength
• Putty displaces wash
POLYETHER • Fast setting
• Automix dispense
• Least hydrophobic
• Delayed pour; good stability
• Bitter taste
• Stiff
• Absorbs water & leaches
components
• expensive126

102. MAKING IMPRESSIONS
102
1. IMPRESSION TRAYS
CUSTOM TRAY
• Less material
• Less dimensional changes
• Better accuracy and
uniform distribution of
material.
• Avoided in undercut area
due to difficult removal.
• polysulfide
STOCK
TRAY
TRAY ADHESIVE
• Polysulfide – butyl rubber
or styrene/ acrylonitrile
dissolved in volatile
solvent, chloroform or
ketone
• Condensation silicone –
polydimethyl siloxane,
ethyl silicate
126

103. 103
2. TISSUE MANAGEMENT
Single gingival retraction
cord
Double cord technique
For atleast 5
min
126

104. 104
3. MANIPUILATION OF IMPRESSION MATERIALS
HAND
MIXING
126

105. 105
CONDENSATION
SILICONE
BASE
CATALYST
126

106. 106
PVS LIGHT BODY
CONDENSATION SILICONE
LIGHT BODY
126

107. 107
STATIC
MIXING
GUN SYRINGE
MIXING TIP
126

108. 108
DYNAMIC
MECHANICAL
MIXING
MOTOR DRIVEN
126

109. 109
4. TECHNIQUES
MULTIPLE
MIX
SYRINGE MATERIAL (LIGHT BODY)
+
TRAY MATERIAL (HEAVY BODY)
126

110. 110
MONOPHASE/
SINGLE
VISCOSITY
• MEDIUM BODY ELASTOMER
• POLYETHER
126

111. 111
1 STEP PUTTY
WASH
PUTTY + LIGHT BODY
126

112. 112
2 STEP PUTTY
WASH
PUTTY + LIGHT BODY
126

113. 5. REMOVAL OF IMPRESSION
■ Within at least 10 minutes from the time of mixing, allowing 6-8 minutes
for the impression to remain in mouth.
1. Break the physical adhesion between tissues and impression.
2. Stretching impression enough to pass under the height of contour and
removal in a quick snap.
113126

114. IDEAL IMPRESSION
■ No voids or air bubbles.
■ Intact uninterrupted cuff of the impression material should be
present beyond every margin.
■ Homogenous colour of the material. Presences of streaks
indicate poor mixing.
■ Good blend between heavy body and light body materials.
■ No part of custom tray shown in the impression.
■ The impression should not be separated from the tray.
114
FLASH
126

115. RECENT
ADVANCES
115126

116. 116
VINYLSILOXANETHER:-
• It is a chemical combination of a polyether material and a
polyvinylsiloxane, A-silicone.
• Similar mechanical and hydrophilic properties while achieving better
final hardness.
HYDROPHILIC ADDITION SILICONE:-
• Adding surfactant.
• Decrease surface tension.
• Increase surface energy.
• To reduce marginal voids and distortion in the impressions
and improve the quality of gypsum dies.
126

117. 117126
• Di- ketone is the photo initiator.
• Blue light used for curing.
• Commercial name : Genesis

118. DIGITAL
IMPRESSIONS
CAD-CAM
118126

119. 119126

120. ■ Digital impression is advantageous for:
i) patients who are gaggers and cannot tolerate impression material in mouth
for several minutes
ii) presence of tori or undercut which make removal of a traditional
impression difficult or impossible without causing the patient discomfort/ or
tearing the margins
iii) no need for infection control
iv) no concern about the compatibility of specific material with specific
disinfectants.
120126

121. 121126

122. REVIEW OF
LITERATURE
122126

123. Comparison of elastomeric impression materials used in
fixed prosthodontics
James N. Ciesco, D.D.S., M.S., William F. P. Malone, D.D.S., Ph.D.,*
James L. Sandrik, Ph.D.,** and Boleslaw Mazur, D.D.S., M.S.*
Loyola University Medical Center, School of Dentistry, Maywood, Ill.
123
• 5 elastomeric materials
2 polysulfides (1 lead-cure and 1 non- lead cure), 2 silicones (1 condensation
polymerization and 1 addition polymerization), and 1 polyether
• Dimensional accuracy and stability evaluated
custom tray and
manufacturers’
adhesive
without using the
tray system.
• Materials poured immediately and
evaluated using a custom tray and
adhesive.
• Polyether > addition silicone >
lead-cure polysulfide and the
condensation polymerization
silicone,
126

124. 126 124
• The alginate impression materials differing in gypsum pouring time
recommended by their manufactures and in color change properties, low-
viscosity addition and condensation silicone and polyether impression
materials in medium consistency.
• The alginate impression materials, compared to elastomeric materials were
found to be more sensitive to the disinfectants used.
• Loss of details, deterioration and change of morphology of gypsum surfaces,
subsurface porosity and exposed large particles were observed.
• Disinfectants used : Aseptoprint Liquid, Zeta 7 solution, Silosept and
Dentaclean Form

125. WETTABILITY OF A HYDROPHILIC ADDITION SILICONE
IMPRESSION MATERIAL
D. H. Pratten, D.M.D., M.S.,* and R. G. Craig, Ph.D.** Medical College
of Virginia, School of Dentistry, Richmond, Va., and University of
Michigan, School of Dentistry, Ann Arbor, Mich.
■ Four families of commercial elastomeric impression materials (polyether
[PE], polysulfide [PS], hydrophilic addition silicone [ASHY], and traditional
hydrophobic addition silicone [AS] were evaluated for their ability to be
wetted by an aqueous solution of CaSO. 2H2O.
126 125

126. REFERENCES
■ Philip’s Science of Dental Materials; Anusavice, Shen, Rawls;
12th edition
■ Science of dental materials; V Shamabhatt, B T Nandish
■ Craig’s restorative dental materials; John M. Powers, Ronald L.
Sakaguchi; 12th edition
■ Applied dental materials; John F. McCabe & Angus W.G. Walls;
8th edition
126126

127. CROSS REFERANCES
■ Digital Impression: A Review; City Dental College J. Volume-9, Number-2,
July-2012
■ Wettability of a hydrophilic addition silicone impression material; The journal
of prosthetic dentistry; february 1989 volume 61 number 2
■ Manipulation of elastomeric impression materials; Indian Dentist Research
and Review; Feb 15, 2018
■ Intraoral Digital Impression Technique: A Review; Journal of Prosthodontics
24 (2015) 313–321 ©2014 by the American College of Prosthodontists
■ Properties of a new polyether urethane dimethacrylate photoinitiated
elastomeric impression material; The journal of prosthetic dentistry; january
1990 volume 63 number 1
■ Vinylsiloxanether : A New Impression Material. Clinical Study of Implant
Impressions with Vinylsiloxanether versus Polyether Materials; Clinical
Implant Dentistry and Related Research, Volume 14, Number 1, 2012
■ Impressions in fixed prosthodontics; Indian Dentist Research and Review;
Nov 25, 2017
127126

128. ■ Comparison of elastomeric impression materials used in fixed
prosthodontics; THE JOURNAL OF PROSTHETIC
DENTISTRY; JANUARY 1981 VOLUME 45 NUMBER 1
128126