Impression materials and techniques

Impression materials & Techniques

1. PRESENTED BY Dr EKTA GARG
MDS 1st YEAR
DEPARTMENT OF CONSERVATIVE
DENTISTRY & ENDODONTICS

2. •Introduction
•Definition
•History
•Ideal Requirements
•Classification
•Impression materials
- Elastomeric materials
- Hydrocolloids
•Latest advances
•Impression Techniques

3. Introduction

4. Impression materials are used to produce the accurate replicas
of intraoral tissues.
There are a wide variety of impression materials available
each with their own properties, advantages and disadvantages.
Materials in common use can be classified as elastic or non-
elastic according to the ability of the set material to be
withdrawn over undercuts.

5. Definition

6. “Any substance or combination of
substances used for making an
impression or negative reproduction.”

- GPT

7. “An impression is an “imprint” or negative
likeness of the teeth and/or edentulous areas,
made in plastic material which becomes
hardened or set while in contact with the
tissue.”
-Hartwell 1992

8. “An impression is the perpetual
preservation of what already exists and not
the meticulous replacement of what is
missing.”

-M.M.Devan 1995

10. •1782 : William Rae used wax with Plaster of Paris.
•1940s: American dentists used Plaster OF Paris for impression & the technique
was presented to the profession at large by Chaplin Harris in 1953.
•1925 : Alphous Poller of Vienna was granted a British Patent for a totally
different type of impression material which was later described by Skinner as
Colloidal Sols of Emulsoid type. The possibility of using colloidal substance for
dental impression became apparent when Poller’s Negacoll was modified &
introduced into the dental profession as Dentacol in 1928. Agar hydrocolloid
was introduced to the dental impression.
•1930 : JD Hart of Oklahoma began to use Agar for fabrication of cast
restoration.

11. 1930 : AW Ward and EB Kelly introduced ZnO Eugenol.
1890s : A chemist from Scotland noticed that Brown Seaweed yielded peculiar
mucous extraction. He named it ‘Algin’.
1936-40 : S William Wilding used Algin as a dental impression material
1950s : Development of Rubber base impression materials (Polysulphides and
Condensation Silicones)
1960s : Polyether impression material developed in Germany
1970s : Addition silicone was introduced as a dental impression material
1988 : Latest addition and light cure elastomers
1990-2000 : New auto devices and delivery systems

12. Ideal Requirements

13. •Fluid enough to adapt to the oral tissues
•Viscous enough to be contained in the tray
•Setting time - less than 7 minutes
•Adequate tear resistance
•Dimensionally stable
•Biocompatible
•Cost effective

14. Classification

15. I. Based on the degree of tissue compression/
amount of pressure applied
•Mucostatic
Ex: Impression plaster

•Mucocompressive
Ex: Impression Compound

16. II. Based on Mode Of Setting &
Elasticity
A. Chemical
reaction
(irreversible)
By elasticity and use
Inelastic or rigid Elastic
Materials Use Material Use
1.Plaster of
Paris
2.Zinc-oxide
eugenol
Edentulous
ridge
Interocclusal

records
1. Alginate
2. Non-aqueous
elastomers
-Polysulfide
- Polyether
- Condensation silicone
- Addition silicone
Teeth
and soft
tissue
B. Physical reaction
(reversible)
3.Impression
Compound
Preliminary
impression
3.Agar hydrocolloid Teeth
and soft
tissue

17. III. Based on the chemical composition

18. IV. Based on type of impression & area of use

19. V. According to the use of the materials in
dentistry
A) Materials used for obtaining impression of dentulous mouth

Alginate

Agar

Non-aqueous Elastomers
B) Materials used for obtaining Impression of edentulous
mouth:
• Impression Compound
• Impression Plaster
• Zinc Oxide eugenol
• Wax

20. VI. Based on Manipulation

21. VII According to their method of use

22. VIII. Based on the
tray used for impression

23. Hydrocolloids

24. Colloids
 often classed as fourth state of matter as colloidal state.
 can be considered as a compromise between the very
small molecules in solution & very large particles in
suspension.
 Two phases
• Dispersed phase or dispersed particles
• Dispersion phase or dispersion medium
 All colloidal dispersions are termed as sols.

25. Types Of ColloidsTypes Of Colloids
The only exception is the gaseous state, i.e. two gases.

26. Hydrocolloids
 If the dispersion medium is water, the material is
known as hydrocolloid.
 Particles larger than those in solution.
 Particle size ranges from 1-200 nm.
 There is no clear line of demarcation among the
solutions, colloids & suspensions.
Gels
 Colloids with a liquid as a dispersion medium can
exist in two different forms known as Sol & Gel.

27.  Sol- has a appearance & many characteristics of a
viscous liquid.
 Gel- is a semisolid & produced from a sol by the
process of gelation.
Gelation
It is a process of conversion of sol to gel, to form
fibrils, micelles of the dispersed phase which become
interlocked to give characteristic jelly like consistency.
Within the gel, the fibrils branch & intermesh to give a
brush heap structure.

28. micellesmicellesbrush-heap brush-heap
structurestructure

29. Gelation Temperature
 The temperature at which gelation occurs is known as
gelation temperature.
• Agar - secondary bonds (weak) hold the fibrils together-
break at slightly elevated temperatures and become re-
established as it cools to room temperature - reversible
•Alginate - the fibrils are formed by chemical action -
irreversible

30.  The Gel may lose water by evaporation from its surface or by
exuding fluid onto the surface by a process known as SYNERESIS.
The gel shrinks as a result of evaporation & syneresis.
 If a gel is placed in water, it absorbs water by a process known as
IMBIBITION. The gel swells during imbibition, thereby altering the
original dimensions.
 The effects of syneresis, evaporation & imbibition on the
dimensional changes are of considerable importance in dentistry,
since any change in dimension that occurs after the impressions are
removed from the mouth will lead to inaccurate casts & models.

31. AGAR
(REVERSIBLE HYDROCOLLOID)

32.  Reversible hydrocolloids undergo transition from gel to
sol on heating.
 On cooling they return back to the original state.
The hydrocolloid supplied as the gel is heated above its
liquefaction temperature, cooled to a temperature
compatible with the oral tissues & placed in the mouth.
Gelation occurs as the tray continues to cool, after which
the impression is removed & poured.

33. Agar
 It is a sulphuric ester of a linear polymer of galactose.
• Gelation Temperature of agar is approx- 37˚-50˚c.
• The temperature at which the gel changes to sol i.e.
liquefaction temperature is 70˚-100˚c.
 Although it is an excellent impression material & yields
accurate impressions, it has been largely replaced by
alginates & rubber impressions because-
• Of the minimum equipment required
• Possibility of obtaining metal dies from rubber
impression.

34. Component Function Composition
Agar Brush – heap structure13 – 17%
Borates Strength 0.2 – 0.5%
Sulfates Gypsum hardener 1.0 – 2.0%
Wax Filler 0.5 – 1.0%
Thixotropic
materials
Thickener 0.3 – 0.5%
Water Reaction medium Balance 84%
Alkyl Benzoates Preservatives 0.1%
Color and FlavorsTaste & appearance Trace

35. Mode of supply :
Gel in collapsible tubes (for impressions)
A number of cylinders in a glass jar (syringe material)
In bulk containers (for duplication)

36. •Full mouth impressions without deep undercuts
•Quadrant impressions without deep undercuts
•Single impressions
•Can be used for crown and bridge impressions because of their
accuracy
•Cast duplication
•Tissue conditioner

37. Manipulation
Preparation, conditioning and tempering of the agar
material:
Before use the material is subjected to a controlled regimen in
three water baths.
Liquefying bath -100°C for 10 min.
Storage bath – 63-66°C
Tempering bath- 44-46°C for 3-10 min.

38. Conditioning unit

39. Making the Agar
impression

40. •Syringe material, directly taken from storage compartment -
applied on to the prepared tooth.
•Water-soaked outer layer of tray hydrocolloid is removed from the
tempering basin, outer layer removed and impression made.
•Gelation is accelerated by circulating cool water (18-21
o
C) through
the tray for 3-5 min.

41. According to ADA specification no.11 :-
•Compressive strength : 8000 gm/cm2
•Tear strength : 700 gm/cm2
•Viscosity : Sufficient fluid to allow detailed reproduction of hard and
soft tissues
•Flexibility: 11% when a stress of 14.2 psi applied
•Elastic recovery : 98.8%
•Accuracy : 25µm
•Working time : 7-15 min.
•Setting time : 5 min.
•Gelation temperature : 37-50°C
•Liquefaction temperature : 70-100°C

42. •Hydrophilic
•Good elastic properties
•Can be re-used as a duplicating material
•Long working time and low material cost
•No mixing technique, the potential for errors are eliminated
•Palatable and well tolerated by patients
•High accuracy and fine detail recording
•Compatible with die and cast materials

43. •Low tear resistance
•Low dimensional stability
•Only one model can be used
•Extensive and expensive equipment required
•It can not be elecroplated
•Impossible to sterilize for re-use

44. ALGINATE
(IRREVERSIBLE
HYDROCOLLOID)

45. •Developed as a substitute for the agar impression
material when its supply became scarce during World
War II.
•Based on a natural substance extracted from certain
brown seaweed. This substance is called as-
anhydro-ß-d-mannuronic acid or
alginic acid (sodium or potassium or
triethanolamine acid) (insoluble in water)

46. Currently, alginate is more popular than agar because-
• easy to manipulate
• comfortable for the patient.
• relatively inexpensive
• does not require elaborate equipment

47. Component Function Weight
percentage
Potassium alginateSoluble alginate 15
Calcium sulfate Reactor 16
Potassium titanium
Fluoride
Accelerator 3
Zinc oxide Filler particles 4
Diatomaceous
earth
Filler particles 60
Sodium phosphate Retarder 2
Composition

48. SETTING REACTION :-
Two main reactions occurs during setting :
i) 2Na
3
PO
4
+ 3 Ca SO
4
 Ca
3
(PO
4
)
2
+ 3 Na
2
SO
4
(Sodium phosphate) (Calcium sulphate)
(Retarder) (Reactor)
i)Sodium Alginate + CaSO
4
+ H
2
O  Ca Alginate + Na
2
SO
4
(Powder) (Reactor) (Gel)

49. •I. According to concentration of sodium
phosphate
•Fast set
•Regular set
•II. According to concentration of filler
•Soft set
•Hard set
Classification of alginate Classification of alginate
((Robert Robert
G. CraigG. Craig))

50. Types Mixing time Working time Setting time
I- Fast set 45 sec 1.25 mins 1-2 mins
II- Normal set 60 sec 2 mins 2-4.5 mins
MANIPULATION :-
Prepare a proper mixture of water & powder.
The measured powder is sifted into the premeasured water.
Water added first to ensure complete wetting of powder particles.
Clean equipment is important.
Avoid incorporating air into the mix.
Figure –of-eight motion is best, with the mix being swiped or stropped against
the sides of the bowl with intermittent rotations (180˚) of the spatula to
press out air bubbles.
 All of the powder must be dissolved.

52. PROPERTIES :-
According to ADA specification No 18:
Flexibility : 14% at a stress of 1000gm/cm2
Elastic recovery : 97.3%
Tissue detail reproduction : 0.075mm
Compressive strength : 5000-8000/cm2
Tear strength : 350-700gm/cm2
Poor dimensional stability
USES :-
Impression making in complete denture prosthesis and orthodontics
In undercuts and in excessive salivary flow
For impressions for mouth protectors
For impression in study models and working cast.

53. ADVANTAGES :-
Easy to mix and manipulate
Minimum requirement of equipment
Flexibility of set impression
Accuracy if properly handled
Low cost
Hygienic, fresh material for each impression
Good surface details even in saliva
Comfortable to the patient
DISADVANTAGES :-
Cannot be electroplated
Distortion occurs easily
Poor dimensional stability
Poor tear strength

54. RECENT ADVANCES IN ALGINATES
Sol containing water but no source of calcium ions .A reactor of Plaster
of Paris can be added to the sol later.
The two component system may be in the form of two pastes- One
contains the alginate sol and the other contains the calcium reactor
Siliconised alginates
Chromatic alginates eg. Integra & KromaFaze (Dux dental) ,Take one
alginate(Kerr)
Dustless alginates( glycerin is added on the alginate powder to
agglomerate the particles) eg.Identic dust free alginate (Dux
dental),Jeltrate Dustless(Dentsply Caulk) , Integra dustfree
alginate(Kerr)
Alginot
Alginator 2

56. Laminate technique (Alginate – Agar
Method)
•The hydrocolloid in the tray is replaced with a mix of chilled
alginate that bonds to the syringe agar.
•Alginate gels by a chemical reaction whereas agar gels by
means of contact with the cool alginate rather than with the
water circulating in the tray.
•Since the agar, not the alginate is in contact with the prepared
tooth, maximum detail is produced.

57. ADVANTAGES :-
Most cost effective way of producing an impression with adequate
detail.
 less preparation time required.
DISADVANTAGES :-
The bond between the agar & alginate is not always sound.
The higher viscosity of the alginate material displaces the agar
hydrocolloid during seating.
Dimensional inaccuracy of the alginate hydrocolloid limits its use to
single units.

58. Elastomeric
Impression Materials

59. •Soft and rubber-like & known as elastomers or synthetic rubbers
•As per ADA Sp. No.19- non-aqueous elastomeric dental impression
materials
•Liquid polymers when mixed with a suitable catalyst are converted into
solid rubber at room temperature.
TYPES :-
I. According to chemistry –
 Polysulphides
Condensation polymerizing silicone
Addition polymerizing silicone
Polyether
Visible light curable polyether urethane dimethacrylate ( a new class
added recently)

60. II.ADA Classification
Based on selected elastic properties & dimensional changes(sp no.19)
Maximum permanent Maximum flow Maximum dimensional
deformation in compression change in 24 hrs
Type I 2.5 0.5 -0.5
Type II 2.5 0.5 -1
Type III 5.5 2.0 -0.5
Each type is further divided into four viscosity classes;
III. According to Viscosity(ISO 4823)
1) Light body or syringe consistency
2) Medium or regular body
3) Heavy body or tray consistency
4) Very heavy body or putty consistency

61. Excellent reproduction of details
Generally hydrophobic
Good elastic properties
Excellent tear strength
High coefficient of thermal expansion
Electroplatable :-silver or copper plated
Extended shelf-life : 2 years
Generally higher cost
Requires tray adhesive and mechanical interlocking.

62. Dimensional changes occur due to :-

- Curing shrinkage
- Loss of by products of reaction
- Condensation silicone lose alcohol
- Polysulphide lose volatile accelerators(Hydroperoxide type)
- Polyethers absorb water and loses soluble plasticizers
- Thermal contraction when transferred from mouth to room
temperature.
- Incomplete elastic recovery after removal
- Increased filler content reduces the shrinkage
- Uniform thickness of the material : shrinkage more uniform
- Good adhesion of tray : Shrinkage is directed towards outer
surface of the tray
- Time of pouring : after elastic recovery

63. SUPPLIED AS :-
All elastomers –two paste systems(base and catalyst)
Putty consistency – supplied in jars
USES :-
1) Impression material for all applications including
- Fixed partial dentures
- Dentulous and edentulous impressions
2) Border moulding of special trays(polyether)
3) Bite registration
4) As duplicating material for refractory casts

64. Polysulfide
(Synonyms : Rubber base, Mercaptan,
Thiokol rubber)

65. •First elastomeric impression to be introduced
•Composition :
Base paste :
Liquid Polysulphide Polymer - 80-85%
Inert fillers( Titanium dioxide, Zinc sulfate , - 16-18%
copper carbonate or silica)
Plasticizers
Reactor Paste
Lead dioxide - 60-68%
Dibutyl phthalate - 30-35%
Sulfur - 3%
Other substances like Magnesium
Stearate(retarder) & deodorants - 2%

66. Tray adhesive :-

Butyl rubber or styrene/acrylonitrile dissolved in a volatile
solvent such as chloroform or a ketone is used with
polysulphides
Mode of supply:
-
Available as 2 systems : Base and accelerator
- 3 viscosities: light, medium and heavy bodies
Chemistry and Setting Reactions :-
-On mixing base and accelerator pastes the liquid polymer sets
to form a solid, but flexible and elastic rubber like material.

67. -Lead dioxide reacts with the polysulfide polymer
-Chain lengthening by oxidation of the terminal –SH groups
-Cross-linking by oxidation of the pendant –SH groups

PbO
2
+ S
HS - R - SH HS - R-S-S-R-SH + H
2
O
OR
Mercaptan+ Lead dioxide Polysulphide + Water
Commercial products :
Permlastic (Lead dioxide system), Coeflex, Omniflex (Copper
hydroxide system)

68. Advantages Disadvantages
- High tear strength - Dimensionally unstable
- Long working time - Unacceptable odor
- Established precision- Untidy and stains clothing
- Economic - Long setting time
- Extensive shelf life- Least elastic recovery
- Less hydrophobic- Subsequent pours are less
accurate.

69. Silicones

70. These materials were developed to overcome some of the disadvantages of
polysulphide materials :-
•Objectionable odor
•Staining of linen by lead dioxide
•Amount of effort required to mix the base with the accelerator
•Long setting times
•Moderately high shrinkage on setting
•Fairly high permanent deformation
•Pouring should be within one hour
TYPES :-
- Condensation silicone
- Addition silicones

71. •Polymer chains grow simultaneously and a reaction byproduct is formed
with associated shrinkage
•Products available:-
- Accoe(GC)
- Cuttersil(Heraeus Kulzer)
- Silene(Bosworth)
- Speedex(Coltene Whaledent)
- Xantopren(Heraeus Kulzer)
•Advantages :-
-It is clean and pleasant
- Good working time
- Easily seen margins
CONDENSATION SILICONE

72. •DISADVANTAGES :-
- High polymerization shrinkage
- Volatile alcohol byproduct
- Low tear strength
- Hydrophobic
- Pour immediately
•COMPOSITION :-
Base Paste
- Polydimethylsiloxane (Hydroxy-terminated)
- Colloidal silica or microsized metal oxide(filler) 35-75%
- Colour pigments
Accelerator Paste
- Orthoethyl silicate - (cross linking agent)
- Stannous octoate - catalyst

73. •SETTING REACTION :-
CH
3
OC
2
H
5
OH-Si-OH +C
2
H
5
O-Si-
OC
2
H
5
Sn
Silicone +
CH
3
CH
2
OH
Octoate
CH
3
OC
2
H
5
Dimethyl
siloxane
Orthoeth
yl
silicate
Silicone
rubber
Ethyl
alcohol
+ +

74. •These reactions are effected at ambient temperatures and the
materials are therefore called RTV( Room Temperature
Vulcanization) silicones.
•The ethyl alcohol formed evaporates gradually leading to
shrinkage & instability. So a condensation silicone should be
poured as soon as possible after removal from the mouth.

75. •Also called as polyvinyl siloxanes
•Has better properties than condensation silicones
•MODE OF SUPPLY :-
Available in various viscosities and paste and jars with contrasting colors
Eg: - Impressiv( Cosmedent)
- Imprint 3 Penta (Putty impression material with automix)
- Aquasil/Reprosil/Hydrosil(Dentsply Caulk)
- Exaflex/ Examix/Exafast/Hydroflex(GC America)
- Express, Imprint/Imprint II(3M ESPE)
- Flexitime(Heraeus Kulzer)
ADDITION SILICONE

76. •Composition:-
Base :-
- Poly(methyl hydrogen siloxane)
- Other siloxane prepolymers
- Fillers
Accelerator :
- Divinyl polysiloxane
- Other siloxane prepolymers
- Platinum salt : Catalyst (chloroplatinic acid)
-Palladium (Hydrogen absorber)
- Retarders
- Fillers

77. •CHEMISTRY AND SETTING REACTION :-
CH
3
Si-H +
CH
3
CH
3
CH
2
= CH-Si
CH
3
CH
3
CH
3
Si-CH
2
-CH
2
-Si
CH
3
CH
3
Pt salt
activator
Vinyl siloxane + Silane siloxane Silicone rubber

78. Complications from latex gloves :-
•Contact of polyvinyl siloxanes with latex gloves should be avoided
•Especially true when handling and placing gingival cords
•Mechanism :-
- Migration of particulate sulfur and sulphur chloride compounds to the
surface and are transferred to prepared teeth and adjacent soft tissues
- When mixing by hand, mechanism of inhibition is thought to be
contamination of chlorplatinic acid catalyst with free sulfur left in
glove
- Residues from acrylics,methacrylates and petroleum jelly lubricants may
interfere with setting reaction of material
•Contact of internal surface of impression with gloved hands :-
- Failure of the material adjacent to the tray to polymerize
- Separation of the tray from the impression material

79. •Prevention :-
- Use vinyl or nitrile gloves to eliminate the problem
- Preparations should be cleaned after temporary prosthesis before
making final impression
- Avoid handling retraction cords with latex gloves
TRAY ADHESIVE :-
Polydimethyl siloxane & Ethyl silicate

80. •Available in 4 consistencies
•Light body
•Medium body
•Heavy body
•Putty

81. Advantages Disadvantages
- Excellent dimensional accuracy - Hydrophobic
- Long term dimensional stability- Expensive
- Hydrogen gas evaluation
in some materials
- Pleasant to use
- Short setting time - Hydrophilic formulations
imbibe moisture
- Auto mix available
- If hydrophilic, good compatibility
with gypsum
- Sulfur contamination by
latex glove

82. Polyether
•Introduced in Germany in late 1960s
•Good mechanical properties and dimensional stability, but short
working time, very stiff material and expensive
•Commercial names:
- Impregnum(ESPE,Germany)
- Permadyne(ESPE,Germany)
•Available as 3 viscosities: light,medium & heavy bodied

83. •COMPOSITION :-
Base Paste
- Polyether polymer
- Colloidal silica(filler)
- Glcol ether or phthalate(plasticizer)
Accelerator paste
- Aromatic sulfonate ester (cross-linking agent)
- Colloidal silica (filler)
- Phthalate or glycol ether (plasticizer)
•CHEMISTRY & SETTING REACTION
Polyether + Sulfonic ester Crosslinked rubber

84. •PROPERTIES :-
- fast setting time of less than five minutes
-Undergo addition based polymerization reaction
- Have no reaction by product so are dimensionally stable
- Must be stored dry as they absorb water and swell under conditions of
high humidity
- Are relatively hydrophilic and hence more forgiving of inadequate
moisture control
- Have good tear resistance, but are rigid, hence considerable force may
be required when removing from mouth or cast

85. Advantages Disadvantages
Dimensional stability- Set material very stiff
Accuracy - Imbibition
Shorter setting time- Short working time.
Automix available- Allergic hypersensitivity in some cases.

86. PROPERTIES OF ELASTOMERIC IMPRESSION MATERIALS
•Accuracy :-
- According to ADA sp no 19, elastomeric impression materials must be
able to reproduce fine detail of 25µm.
• Differences in ability to record fine detail of various viscosities :-
-Lower the viscosity of impression materials , better it will record fine
details
•Elastic recovery :-
-No impression material has 100% elastic recovery
- Eliminate or block out any undercuts in the tooth preparation before
making impression
•Dimensional stability
- PVS materials possess ideal dimensional stability
- Hydrocolloids are subject to imbibation & syneresis

87. •Flow & flexibility
- Addition silicone and polyether are pseudoplastic impression materials
•Rigidity
- Polyether impression materials tend to be more rigid than the other
materials
- PVS materials are reasonably stiff, but fracture of the dies are
uncommon
- Reversible hydrocolloid is the least rigid of all impression materials
-With dual arch impressions, use a very rigid impression material.
•Workability
- Automix devices, electronic mixing devices, and simpler mixing guns
provide a standardized mix

88. •Hydrophilicity :-
- Reversible hydrocolloid impression materials are truly hydrophilic
- Polyether impression materials are also hydrophilic but require a dry
field for making impressions
- The original PVS were hydrophobic but wettability is improved in the
later formulations
•Shelf life :-
-No more than 6 months’ supply of impression material should be kept
on hand at any time
•Patient comfort :-
- Polysulphide & Agar is less patient friendly
•Economic factors :-
- Reversible hydrocolloid is less expensive than elastomeric impression
materials

91. RECENT ADVANCES
Visible light cured polyether urethane dimethacrylate
•In early 1988, a visible light cured impression was introduced(Genesis
L.D. caulk).
•Two viscosities :-Light and heavy bodied
•Composition :-
- Polyether urethane dimethacrylate
- Photoinitiators (camphoroquinone)
- Photoaccelerators (Diethyl amino ethyl methacrylate)
- Silicone dioxide (Filler)
•Chemistry :-
Similar to light cured composites

92. Properties :-
- Long working time and short setting time
- Blue light is used for curing with transparent
impression trays
- Tear strength-6000-7500 gm/cm
2
(Highest among
elastomers)
- Dimensional stability, flow, detail reproduction,
permanent deformation, wettability, compatibility with cast
and die materials and electroforming is similar to addition
silicone

93. Manipulation :-
- Light body is syringed into the sulcus and over the
preparation
-Heavy body is loaded onto a clear tray and seated over the
light body
- Both are simultaneously cured with a visible light curing unit
having an 8mm or larger diameter probe
- Curing time is approximately 3 mins

94. •Advantages :-
- Controlled working time
- Excellent properties

• Disadvantages :-
- Need special transparent trays
- Difficult to cure in remote area

95. Automatic dispensing and mixing devices
-This latest technique consists of a double barrel caulking gun with mixing
tip. The tip contains spirals on the inside. Forcing of the base &
accelerator results in its mixing.
e.g. Volume mixer (Kerr), Pentamix(3M ESPE)

96. -Advantages :-
More uniform mix
Less air bubbles
Reduced working time

97. Senn (GC America) :-
Hybrid polyether/polysiloxane material that has both hydrophilicity and
dimensional accuracy, before, during and after set.

98. MATERIALMATERIALADVANTAGESADVANTAGES DISADVANTAGESDISADVANTAGES
ALGINATEALGINATE Rapid set, HydrophilicRapid set, Hydrophilic
Low cost, No custom tray Low cost, No custom tray
requiredrequired
Poor accuracy & surface Poor accuracy & surface
details, Low tear résistancedetails, Low tear résistance
Low stability.Low stability.
AGAR-AGARAGAR-AGAR Long working timeLong working time
HydrophilicHydrophilic
Low tear résistanceLow tear résistance
Low stabilityLow stability
Equipment requiredEquipment required
POLYSULFIDEPOLYSULFIDE High tear resistanceHigh tear resistance Long setting timeLong setting time
Unpleasant odor, StickyUnpleasant odor, Sticky
ADDITION ADDITION
SILICONESILICONE
Dimensional stability, Dimensional stability,
excellent accuracy, Auto excellent accuracy, Auto
mix availablemix available
Hydrophobic, release of Hydrophobic, release of
hydrogen gas, hydrogen gas,
Most expensiveMost expensive
CONDENSATIOCONDENSATIO
N SILICONEN SILICONE
Fair accuracy, short setting Fair accuracy, short setting
timetime
Release of Alcohol Release of Alcohol
byproduct, Hydrophobic.byproduct, Hydrophobic.
POLYETHERPOLYETHER Dimensionally stable, Dimensionally stable,
accurate, Auto mix accurate, Auto mix
availableavailable
Rigid, imbibitionRigid, imbibition
short working time, short working time,

99. METHODS OF DISINFECTION OF IMPRESSIONS
Material Method Recommended
disinfectant
Comments
Irreversible
hydrocolloid
(alginate)
Less than ten
min. immersion
with caution
Chlorine
compounds or
iodophors
Short term
glutaraldehyde
also has to be
acceptable.
Reversible
hydrocolloid
Do not immerse
in alkaline
glutaraldehyde
PolysulfideImmersionGlutaraldehydes,
chlorine
compounds,
iodophors,
phenolics
Disinfectants
requiring more
than 30 min
exposure times
are not
recommended

100. Material Method Recommended
disinfectant
Comments
Polyether Immerse with
caution. Use
only
disinfectant
with a short
exposure time
(<10 min)
Chlorine
compounds or
iodophors
ADA
recommends any
of the
disinfectant
classes, however
short term
exposures are
essential to avoid
distortion.
ZOE impression
paste
Immersion
preferred,
spraying can be
use for bite
registration.
Glutaraldehydes or
iodophors
Not compatible
with chlorine
compounds!
Phenolic spray
can be used.
Impression
compound
Iodophors or
chlorine compounds
Phenolic spray
can be used

102. Classification
•Based on the position of the mouth
Open mouth technique
Closed mouth technique (functional impression )
•Based on the pressure applied
Positive pressure
Negative pressure
Selective pressure technique

103. •Based on the mixing technique
Double mix
 Heavy-light body technique
 Putty wash technique
•One stage – simultaneous
•Two stage – relief channel
- 2mm spacer technique
Single mix or monophase technique
•According to the tray used
Custom tray impressions
Stock tray impressions

104. Three most common methods for making
impressions for fixed restorations are-
Simultaneous dual-viscosity technique,
Single-viscosity or monophase technique,


 Putty-wash technique

105. Simultaneous dual-viscosity technique
• low-consistency material is injected with a syringe into
critical areas & the high-consistency material is mixed &
placed in an impression tray.
• After injecting the low viscosity material, the tray
containing the higher viscosity material is placed in the
mouth.
• Since both the materials are mixed together, they join,
bond & set together.
•After the materials have set, the tray & the impression
are removed.

107. •Advantages
Over comes the polymerization shrinkage of the light body
material
Margins duplicated in light body
• Disadvantages
Use of custom tray
An assistant required for mixing the material - tray/syringe
simultaneously
Margins duplicated in heavy body in case of excess pressure

108. Single viscosity or monophase technique
• Impressions often made with a medium viscosity impression
material.
• Addition silicone & polyether are well suited for this
technique because both have a capacity for shear thinning.
• When the medium viscosity material is forced through an
impression syringe, viscosity is reduced, whereas the
viscosity of the same material residing in the tray is
unaffected. This behavior of the materials is referred to as
PSEUDOPLASTIC.

109. •Advantages
 Reduced wastage of the material
 Less time consumption
 Avoids the time involved in fabrication of custom tray
•Disadvantages
 Relatively high viscosity and reduced flow of the
monophase materials, makes their injection onto the
preparation more difficult to control -increased incidence
of surface voids
- Stephen M. Dunne et al 1998

110. PUTTY -WASH
TECHNIQUE

111.  Two steps impression procedure whereby a preliminary impression
is taken in high or putty consistency material before the tooth
preparation is made.
 Space is provided for a low consistency material by a variety of
techniques, & after tooth preparation, a low consistency material is
syringed in to the area & the preliminary impression reinserted.
The low & high consistency materials bond, & after the low
consistency material sets, the impression is removed. This procedure
is sometimes called a WASH TECHNIQUE.
The Putty consistency materials & this technique were developed
for condensation silicones to minimize the effects of dimensional
change during polymerization. This technique was extended to
addition silicones after their introduction even though their
polymerization shrinkage is significantly lower.

112. Putty wash
simultaneously
technique (One
stage)
Light body material syringed on to the
preparation while the putty material loaded in a
stock tray is simultaneously inserted into the
mouth.

114. •Advantages
Reduced chair side time
•Disadvantages
Absolute lack of control in the bulk of wash material
By mixing putty, syringe material simultaneously, setting
distortion of putty included in over all distortion of impression
 - Chee and Donovan 1992
Possibility of margins duplicated in putty medium
Tendency of bubbles to be formed and occluded in the set
impression

115. Putty wash relief channel
technique
Pre-operative putty impression is made intra orally
In the area where the tooth is to be prepared,
impression material is removed or channels prepared
using putty cutter instrument
The impression is then relined with low viscosity
material

117. •Advantages
Impression can be captured with the wash materials
•Disadvantages
To confine the wash material to area of relieved impression
If entire area is washed - creates hydraulic displacement of
putty impression resulting in smaller dies
- Donovan TE 2004

118. Putty wash 2mm spacer
technique
2 mm thick wax spacer is prepared on a diagnostic
cast, occlusal stops are provided on non-functional
cusps.
A putty impression is made with a stock tray
resulting in a putty custom tray with 2mm space for
the wash material.
Putty custom tray is then washed with light body
material.

120. •Advantages
 Wash stage carried out after the putty has set and
contracted
 Controlled wash bulk compensates for this contraction
with minimal dimensional change
•Disadvantages
 Extra chair side time
 Extra material

121.  Clinicians have an excellent array of impression materials &
techniques for fabrication of tooth restorations.
 Based on the quality of impressions sent to the commercial
laboratories, it seems that many impressions fall short of the
quality made possible by current impression materials.
 Thus it is important to review the contemporary principles of
impression materials & to take impressions consistent with
those principles. It is thus important to familiarize with the
various specialty impression techniques available & use them
when indicated.