impression materialsplay an important role in dentistry so here is the basic information about various materials used in dentistry

1. Impression materials
By
Dr Vijyanta suman
I MDS

2. contents
Introduction
Definition
History
Classification
Properties
Impression making
Prosthodontic considerations
Review of literature
Conclusion
Reference 2

3. Introduction
Impression materials are used to register or reproduce the form and
relationship of the teeth and oral tissues.
Hydrocolloids and synthetic elastomeric polymers are most commonly
used to make impressions of various areas of the dental arch.
Each of these classes of materials has certain advantages and
disadvantages.
3

4. PURPOSE OF IMPRESSION MATERIALS
• Impression materials are used to make an accurate replica or mold of the
hard and soft oral tissues.
• The impression is a negative reproduction of the tissues, and by filling
the impression with dental stone or other model material, a positive cast
is made that can be removed after the model material has set
• It is used to make models, cast, die or as duplicating materials
• The accuracy, detail, and quality of this final replica are of greatest
importance 4

5. • Impression material : any substance or combination of substances
used for making an impression or negative reproduction
• Impression tray : A receptacle into which suitable impression material
is placed to make a negative likeness
A device that is used to carry, confine, and control impression material
while making an impression
• Impression : 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
GPT-9 5

6. • Die : the positive reproduction of the form of a prepared tooth in
any suitable substance
• Model : a facsimile used for display purposes; a miniature
representation of something
• Cast : a life-size likeness of some desired form; it is formed from a
material poured into a matrix or impression or from a CAM printed
replica; Dental Cast, Diagnostic Cast, Preliminary cast, Refractory
cast, Remount cast
GPT-9
6

7. 7

8. 8

9. Chronology of events in the history of impression materials
1756 : Phillip Pfaff made first impression using Wax
1782 : William Rae made cast using plaster of paris
1848 : Guttapercha was introduced as impression material (colburn/Blake)
1844 : Plaster of paris introduced for impression of teeth (Dunning)
1857 : Charles stent develops Impression compound
1915 : Plastic-plaster impression technique (Rupert Hall)
1925 : Reversible hydrocolloid impression materials introduced
1930s : ZoE as impression material (Ward and Kelly)
1941 : Irreversible hydrocolloids introduced
1953 : Polysulfide Impression material introduced
1960s : Polyether was introduced in Germany
1970s : silicones were introduced
9
Starcke EN.A historical review of complete denture impression materials. Journal of the American Dental
Association. 01 Nov 1975;91(5):1037-1041

10. 10
DESIRABLE QUALITIES
• A pleasant odor, taste, and acceptable color
• Absence of toxic or irritant constituents
• Adequate shelf life for requirements of storage and distribution
• Economically commensurate with the results obtained
• Easy to use with the minimum of equipment
• Setting characteristics that meet clinical requirements
• Satisfactory consistency and texture
• Readily wets oral tissues

11. 11
• Elastic properties that allow easy removal
• Adequate strength to avoid breaking or tearing
• Dimensional stability over temperature and humidity ranges normally
found in clinical and laboratory procedures for a period long enough
to permit the production of a cast or die
• Compatibility with cast and die materials
• Accuracy in clinical use
• Readily disinfected without loss of accuracy
• No release of gas or other byproducts during the setting

12. classification

13. 13
According to their composition, mechanism of setting,
mechanical properties
SET BY CHEMICAL REACTION (IRREVERSIBLE)
• Inelastic : Plaster of Paris, Zinc oxide–eugenol
• Elastic : Alginate, Polysulfide, Polyether Condensation Silicone,
Addition silicone
SET BY TEMPERATURE CHANGE
(REVERSIBLE/THERMOPLASTIC)
• Inelastic : Impression compound
• Elastic : Agar

14. 14
According to tissue displacement
Mucostatic : Plaster, ZOE, Low viscosity
Alginates, low viscosity elastomeric
materials
Mucocompressive : (Mucodisplacive)
Impression compound, high viscosity
Alginates and Elastomers

15. 15
According to uses in dentistry
IMPRESSION MATERIALS
USED IN EDENTULOUS
PATIENTS (COMPLETE
DENTURE)
Impression plaster
Impression compound
IMPRESSION MATERIALS
USED IN DENTULOUS
MOUTH
Alginates
rubber base impression
materials

16. INELASTIC IMPRESSION MATERIALS
16

17. 17
Inelastic impression materials exhibit an insignificant amount of elastic deformation
when they are subjected to bending or tensile stresses.
they fracture without exhibiting any plastic deformation if the stress from applied
pressure exceeds their tensile, shear, or compressive strength values.
These materials include :-
impression plaster
impression compound
ZOE impression paste
inability to sustain a substantial amount of elastic deformation without fracture : use
in dental impression making is limited

18. 18
IMPRESSION PLASTER
• Impression plaster is a β-calcium sulfate hemihydrate used at a water/powder ratio of approximately
0.5 to 0.6.
• Its fluidity makes it suitable for making impressions of soft tissues in the uncompressed state
• Because of its rigidity, the use of impression plaster has been suggested for making preliminary
impressions or splinting transfer coping utilized to produce long-span implant-supported prostheses.
Composition
To make plaster a suitable impression material, the expansion and the setting times should be controlled
Potassium sulfate : anti-setting expansion agent to reduce the setting expansion
Borax : retarder - to balance the setting acceleration caused by the potassium
Alizarin red : A pigment, make a clear distinction between the impression and the model after casting of
the model.

19. 19
Manipulation
• A custom tray (1- to 1.5-mm spacer ) is preferred over stock tray as it is too fluid
• Preliminary impressions can be made with dental compound, and impression plaster can be used as
the wash material
• The technique for inserting the impression into the mouth involves “puddling” the impression into
place. With the remaining plaster in the tray, the tray is seated in a single movement. Then the tray is
gently moved from side to side and anteroposteriorly
• When the impression involves an undercut area, it is necessary to fracture the impression to facilitate
removal from the mouth.
• Long, narrow strips of wax can be adapted around the periphery of the impression (Beading) : clear
indication of where the impression ends, preventing overtrimming and overextension
• The impression is then coated with a thin layer of separating medium and cast in fresh plaster

20. 20
Impression making associated with implants requires the use of square direct or tapered
indirect transfer copings for the transfer of implant positions before fabrication of the
prosthesis.
For multiple-unit impressions, the direct technique may use splinted or nonsplinted
implant transfer copings. The materials used to splint copings can be resin composite,
plaster, or acrylic resin with or without reinforcement
Disinfection of a plaster impression can be achieved with a 10-min soak in sodium
hypochlorite solution

21. 21
Advantages:
Good surface detail
Excellent dimensional stability
Disadvantages:
Cannot be added to (add another layer)
Properties affected by operator handling technique
Taste and roughness may cause the patient to vomit
Heat evolved during setting

22. 22
IMPRESSION COMPOUND (Modeling plastic)
thermoplastic material supplied in the form of sheets and sticks.
There are two types of impression compounds available.
Type I : lower-fusing material for making impressions in the oral cavity
supplied in either sheet or stick form
Type II : higher-fusing material, called tray compound, used for forming trays to be
used in the oral cavity.
An impression of soft tissue is obtained with tray compound
It is then used as a tray to support a thin layer of a second impression material,
Secondary impressions may also be made with a ZOE wash paste, hydrocolloid,
impression plaster, or elastomer.

23. 23
Composition
• composed of a mixture of waxes, thermoplastic resins, filler, and a coloring agent.
• Shellac, stearic acid, and gutta-percha are added to improve plasticity and workability.
• The waxes or resins in the impression compound are the principal ingredients of the matrix.
• Filler is added to increase the viscosity at temperatures above that of the mouth and to increase
the rigidity of the compound at room temperature.
INGREDIENTS
• Resin
• Copal resin
• Carnauba wax
• Stearic acid
(Plasticizer)
• Talc
• Coloring agent
PARTS
•30
•30
•10
•5
•25

24. 24
Manipulation
• Softening by heat :-
• The fusion temperature : Above this temperature, the material remains plastic while the
impression is being made. Once the impression tray is seated, it should be held gently in position
until it cools below the fusion temperature.
• The thermal conductivity is very low : allow an extended time to achieve thorough cooling and
heating of the compound.
• A compound stick may be softened over a flame : When a direct flame is used, the compound
should not be allowed to boil or ignite so that the constituents are volatilized.
• sheet should be immersed in warm water : to ensure uniform softening of the material.
• Prolonged immersion or overheating in the water bath is not indicated; the com- pound may
become brittle and grainy

25. 25
ZINC OXIDE–EUGENOL (ZOE) IMPRESSION PASTE
 The reaction between zinc oxide and eugenol yields a relatively hard
 Applications in dentistry :-
• Impression material for edentulous mouths
• Surgical dressing
• Bite registration paste
• Temporary filling material
• Root canal filling material
• Cementing medium
• Temporary relining material for dentures.

26. 26
Composition
ZOE impression pastes are dispensed as two separate pastes.
Zinc oxide
Fixed vegetable
or mineral oil
87%
13%
Tube 1
(Base)
Oil of cloves or eugenol
Gum or polymerized rosin
Filler
Lanolin
Balsam
12
50
20
3
10
Tube 2
(Accelerator)
Oil of cloves(70% to 85% eugenol) produces less of a burning sensation
The addition of rosin facilitates the speed of the reaction and yields a smoother product.
Canada balsam and Peru balsam are used to increase flow and improve mixing properties

27. 27
setting reaction
• When the two pastes are mixed, the phenol –OH of the eugenol acts as a weak acid and undergoes
an acid-base reaction with zinc hydroxide to form zinc eugenolate
• Acetic acid or zinc acetate : accelerate the reaction.
• Disadvantages : stinging or burning sensation caused by the eugenol as it leaches out and contacts
soft tissues. Orthoethoxybenzoic acid (EBA) is a valuable substitute for eugenol in this regard

28. 28
Manipulation
• Mixing of the two pastes is accomplished on an oil-impervious paper or glass mixing slab.
• The proper proportion of the two pastes is generally obtained by squeezing two strips of paste of the
same length
• A flexible stainless steel spatula is typically used for the mixing procedure.
• The two strips of contrasting colors are combined with the first stroke of the spatula, and the mixing
is continued for approximately 1 min
• These materials are classified as
Type I : hard paste - final set occur within 10 min
Type II : soft paste - final set occur within 15 min
• setting time can be shorten by :
Adding a small amount of zinc acetate or additional accelerator
drop of water in the paste before mixing
extending the mixing time.
• Prolonging the setting time. : cool spatula and mixing slab

29. HYDROCOLLOID IMPRESSION
MATERIALS
29

30. 30
• A colloid is a substance that is microscopically dispersed uniformly throughout
another substance
• If the dispersion phase of a colloidal system is water, it is called a hydrocolloid
• CHARACTERISTICS OF HYDROCOLLOIDS Impression materials
• During impression making, the material sets from a flowable state to a solid state.
This change of state associated with hydrocolloids is called the sol-gel
transformation.
• A sol is a colloidal dispersion of very small particles in a continuous liquid
medium an
• gel is a suspension that behaves like an elastic solid.

31. 31
AGAR (REVERSIBLE HYDROCOLLOID)
The physical change of agar from sol to gel is induced by lowering the temperature.
The gel liquefies to a sol when it is heated to liquefaction temperature (70 °C to 100 °C)
When sol is cooled, it becomes a gel at a gelation temperature (between 37 °C and 50 °C).
Composition : component function Composition (%)
Agar
Borate
Sulfate
Wax, diatomaceous earth, clay
Thixotropic materials
Water
Thymol
glycerin
Brush-heap structure
Strength
Gypsum hardener
Filler
Thickener
Reaction medium
Bactericidal
Plasticizer
13−17
0.2−0.5
1.0−2.0
0.5−1.0
0.3−0.5
Balance
borax is a potent retarder for the setting of gypsum

32. 32
Making the Agar Impression
This process requires a three-compartment conditioning unit
The first step in impression making is to liquefy the hydrocolloid gel in the tube in boiling water(100 °C)
for a minimum of 10 minutes.
Place it in a storage bath at 65 °C to retain the sol condition until it is needed
The tempering time is 3 to 10 min, just sufficient to ensure that all the material has reached a lower
temperature
Gelation is accelerated by circulating cool water through the tray for 3 to 5 min.
the tray must be held in the mouth until gelation has completed
it is necessary to remove the impression with a snap and not to tease it out.

33. 33
ALGINATE (IRREVERSIBLE HYDROCOLLOID)
The setting of alginate hydrocolloid is a process of cross- linking alginic acids with
calcium ions
Composition :
component Function Weight (%)
Potassium alginate
Calcium sulfate
Zinc oxide
Potassium titanium
fluoride
Diatomaceous earth
Sodium phosphate
Soluble alginate
Reactor
Filler particles
Gypsum hardener
Filler particles
Retarder
15
16
4
3
60
2

34. 34
Potassium alginate
K2n _ Alginate
Calcium alginate
Can _ (Alginate)2
Calcium sulfate
n Ca SO4
Potassium sulfate
n K2SO4
Sodium phosphate
2 Na3PO4
Calcium sulfate
3 CaSO4
Calcium phosphate
Ca3(PO4)2
Sodium sulfate
3 Na2SO4
Setting reaction
Controlling Setting Time
• A slight modification in the W/P ratio or the mixing time
• The setting time is best regulated by the amount of retarder added during the
manufacturing process.
• Fast-setting alginate : 1.5 to 3 min
• Normal-setting alginate (3 to 4.5 min)

35. 35
Making the Alginate Impression
• For impression to be retained on the tray, a perforated metal tray is preferred.
• If a plastic tray or a metal rim-lock tray is selected, a thin layer of alginate tray adhesive should be
applied and allowed to dry completely
• The thickness of the alginate impression between the tray and the tissues should be at least 3 mm.
• Alginate impression should not be removed from the mouth for at least 3 min after gelation has
occurred
• it is best to avoid torquing or twisting the impression in an effort to remove it

36. 36
PROPERTIES OF HYDROCOLLOID IMPRESSION MATERIALS
syneresis : Once the hydrocolloid impression is removed from the mouth and exposed
to air at room temperature, some shrinkage will occur.
imbibition : if the impression is immersed in water, swelling occurs
The storage medium, such as 2% potassium sulfate solution, or 100% relative humidity in
a storage chamber to reduce the dimensional change of agar impressions
Agar is among the most accurate of impression materials.
Most alginate impressions are not capable of reproducing the finer details observed in
impressions with other elastomeric impression materials.

37. 37
LAMINATE TECHNIQUE (ALGINATE-AGAR METHOD)
combined agar-alginate technique : tray of chilled alginate that bonds to the agar
expressed from a syringe.
The alginate gels by a chemical reaction, whereas the agar gels by means of contact
with the cool alginate rather than with the water circulating through the tray.
Advantages : it is the agar, not the alginate, that contacts the prepared teeth,
maximal detail is reproduced.
equipment cost is lower and less preparation time is required.
Disadvantages : the bond between the agar and alginate is not always sound
the higher viscosity of the alginate material displaces the agar hydrocolloid during
seating
the dimensional inaccuracy of the alginate hydrocolloid limits its use to single units.

38. 38
DUPLICATING MATERIALS
• ANSI/ADA Specification No. 20
• Both types of hydrocolloids are used in the dental laboratory to duplicate dental
casts or models for the construction of prosthetic appliances
• Agar hydrocolloid is more popular in the lab because it can be used many times.
• with intermittent stirring, agar hydrocolloid can be kept in a liquid form for 1 or 2
weeks at a constant pouring temperature.
• The hydrocolloid type duplicating materials have the same composition as the
impression materials but their water content is higher, the agar or alginate content
is lower, which influences their compressive strength and percent permanent set.

39. ELASTOMERIC IMPRESSION
MATERIALS
39

40. 40
o Elastomers comprise 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
o They are supplied in two components, a base paste and a catalyst
paste that are mixed before making impressions
o Formulated in several consistencies, including extra low, low, medium,
heavy, and putty (increasing order of filler content)
o there are three elastomers based on the backbone of polymer chains :
• Polysulfide
• Silicone (condensation and addition)
• Polyether.

41. 41
POLYSULFIDE
Base paste :
polysulfide polymer - multi- functional mercaptan (-SH)
filler -lithopone or titanium dioxide
Plasticizer - dibutyl phthalate
Sulfur - approx 0.5%
Accelerator paste (liquid) :
Lead dioxide
Filler
Plasticizer
Retarder - Oleic or stearic acid

42. 42
The reaction starts at the beginning
of mixing and reaches its maximum
rate soon after spatulation is
complete
hot and humid conditions will
accelerate the setting of polysulfide
impression

43. 43
CONDENSATION SILICONE
supplied as a base paste and a low-viscosity liquid catalyst, a two-paste system, or a
two-putty system.
Base :
α-ω-hydroxyl-terminated polydimethyl siloxane
Filler – metal oxide/silica
Color pigments
Accelerator :
Cross linking agent - Orthoethyl silicate
Catalyst – stannous octoate

44. 44
Condensation polymerization of poly dimethyl siloxane with tetraethyl
orthosilicate in the presence of stannous octoate (catalyst)

45. 45
ADDITION SILICONE
This material is often called a polyvinyl siloxane (PVS) or vinyl polysiloxane
Base :
Polymethylhydrosiloxane
divinylpolysiloxane.
Fillers
Accelerator :
Divinylpolysiloxane
Platinum salt
Fillers
Retarders

46. 46
• No reaction by-products are formed as long as the correct proportions of
divinylpolysiloxane and polymethyl- hydrosiloxane are used and there are no impurities
• The residual polymethylhydrosiloxane in the material can lead to a secondary reaction
with each other or with moisture, to produce hydrogen gas

47. 47
• These impression materials require a dry field for impression making.
• One of the disadvantages of the silicone impression materials is their inherent
hydrophobic nature.
• A nonionic surfactant can be added to the paste in the manufacturing process to
render a degree of hydrophilicity to the surface of the material.
• Sulfur contamination from natural latex gloves inhibits the setting of addition
silicone
• Medium-body addition silicone, as a substitute for alginate impression material
been formulated for making impressions for diagnostic purposes,. The advantage
is the ability to make multiple, accurate diagnostic casts from one impression

48. 48
POLYETHER
Base :
Polyether polymer
Filler - Colloidal silica
Plasticizer – Glycolether or Phthalate
Acceleratoe paste :
Cross linking agent – Aromatic sulfonate ester
Filler – colloidal silica
Plasticizer - pthalate

49. 49
polyether
Sulfonic
ester
Crosslinked
rubber
There are two types of polyether impression materials. The first is based
on the ring-opening polymerization of
aziridine rings
The second type is based on an acid-catalyzed condensation
polymerization of polyether prepolymer with alkoxysilane terminal
groups

50. 50
Properties of Elastomeric Impression materials
Hydrophobic : except Polyether
Elastic properties : repeated pouring is possible
High coefficient of thermal expansion
Excellent reproduction of surface details
Dimensional change and inaccuracies can occur : curing shrinkage
Excellent tear strength
Can be electroplated with cu/Ag
Each elastomers has specific adhesive because they do not adhere to tray

51. 51
• The working time : begins at the start of mixing and ends just before the elastic
properties have developed
• The 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

52. 52Craig’s Restorative Dental materials – Mosby; 13 edition

53. 53
Physical & Mechanical properties of Elastomeric materials
Craig’s Restorative Dental materials – Mosby; 13 edition

54. 54
Type of material Advantages Disadvantages
Polysulfide
Long working time
High tear resistance
Margins easily seen
Moderate cost
Requires custom tray
Stretching leads to distortion Compatible
only with dental stone
Stains clothing
Obnoxious odor
Pour within 1 hour
Condensation silicone (putty wash)
Clean and pleasant
Good working time
Margins easily seen
High polymerization
shrinkage
Volatile by-product
Low tear strength Hydrophobic
Pour immediately
Vinyl polysiloxane Clean and pleasant Margins easily seen
Ideally elastic
Pour repeatedly Stable: delay pour
Hydrophobic
No flow if sulcus is moist Low tear
strength
Polyether
Least hydrophobic of all elastomers
Margins easily seen, Good stability Delay
pour, Shelf life: 2 y
Stiff, high modulus, Bitter taste
Need to block undercuts, Absorbs water
Leaches components, High cost

55. 55
MAKING IMPRESSSIONS WITH ELASTOMERIC MATERIALS
 The use of elastomeric impression material to fabricate gypsum models, casts, and dies
involves six major steps:
• preparing a tray
• managing tissue
• preparing the material
• making an impression
• removing the impression
• preparing stone casts and dies.

56. 56
• The use of a custom tray is recommended to reduce the quantity of material required to make
impressions : any dimensional changes attributed to the materials are minimized.
• A custom tray allows a uniform distribution of impression material
• The use of custom trays for polyether and addition silicone impressions is not critical, since these
materials are stiffer and have less polymerization shrinkage than the polysulfide material.
• The stock tray should be rigid, thereby minimizing flexure of the tray during impression making.
• Disposable stock trays are also used to support the putty when the putty-wash technique is used for
making impressions.
• Prior to making an impression, a uniform thickness of tray adhesive is applied on the tray surface,
extending over its edge, and it is allowed to dry

57. 57
TISSUE MANAGEMENT
The margins of tooth preparations for fixed prostheses often
extend to or below the free margin of the gingiva. To ensure
access for the tooth preparation and for making the impression,
it is necessary to displace the gingival tissues, control gingival
hemorrhage, and control sulcular fluids.
The most popular methods of gingival displacement is the use of
gingival retraction cord.
An electrosurgical unit or a soft tissue laser can also be used.

58. 58
MANIPULATION OF IMPRESSION MATERIALS
elastomeric impression materials are supplied for three modes of mixing : hand mixing,
static mixing, and dynamic mechanical mixing
Hand Mixing :
If one of the components is in liquid form, such as the catalyst for condensation silicones,
a length of the base is dispensed from the tube onto a graduated mixing pad and drops of
the liquid catalyst corresponding to the length of the base are added.
The two-putty systems available for condensation and addition silicone are dispensed by
volume using an equal number of scoops of each material.
The best mixing technique is to knead the material with one’s fingers until a uniform color
is obtained.

59. 59
Static mixing :
This technique transforms two fluid materials into a homogeneous mixture without mechanical
mixing.
The device used to accomplish this mixing is a gun for compressing materials in a two-cylinder
cartridge which contains the base and catalyst separately, as well as a mixing tip
When the trigger is pulled, the plunger is driven forward so that the base and catalyst pastes are
forced from the cartridge into the mixing tip
The pastes pass through the bore and exit the nozzle as a uniform mixed paste.
Four different sizes of mixing tips : the more viscous the material, the larger is the mixing tip that
should be used.

60. 60
Syringe tips can be fit to the nozzle to deliver the mixed paste directly to the prepared teeth.
These syringes fit the cartridge, as the mixing tips.
The base and catalyst are first injected into the respective barrel.
A plunger then forces the material through a smaller static mixing tip.
It can deliver the light body material directly onto the abutments
Dynamic mechanical mixing : The motor-driving mechanism
forces the material into the mixing tip and makes the
impeller (insert) inside the tip rotate.
The function of the impeller is only to mix the material.

61. 61
MAKING AN IMPRESSION
Multiple-Mix Technique
Monophase Technique
Putty-Wash Technique

62. 62
Multiple-Mix Technique
A syringe material (light body) and a tray material (heavy body) are used in this technique
The lighter material is injected from the filled syringe or directly from a static mixing gun within and around the
tooth preparation.
The filled tray with heavy body is then inserted in the mouth and seated over the syringe material, which has been
extruded on hard and/or soft tissue. The tray material will force the syringe material to adapt to the prepared
tissues.

63. 63
Monophase Technique or single-viscosity technique
Medium-body polyether and addition silicone are often used
only one mixture is made, and part of the material is placed in the tray, and another portion is placed
in the
syringe for injection in the cavity preparation, prepared teeth, or soft tissue.
The success of this technique depends on the pseudo- plastic properties of the materials.

64. 64
Putty-Wash Technique
This method was originally developed for condensation silicone.
The thick putty material is placed in a stock tray and a preliminary impression is made which serves as
custom made tray
Space for the light-body “wash” material is provided either by cutting away some of the “tray” putty or
by using a thin polyethylene sheet as a spacer between the putty and the prepared teeth during
preliminary impression making
A mixture of the thin-consistency wash material is placed into the putty impression and on the
preparation; then the tray is reseated in the mouth to make the final impression.
An alternative approach is to inject the wash material around the preparation and then immediately seat
the tray with freshly mixed putty over the wash material.

65. 65

66. 66
REMOVAL OF THE IMPRESSION
• The impression should not be removed until the curing has progressed sufficiently
• One method for determining the time of removal is to inject some of the syringe
material onto a space that is not in the field of operation
• When a multiple mix technique is used, test both the syringe and the tray materials.
• Typically, the impression should be ready for removal within at least 10 minutes from
the time of mixing
• The first step is to break the physical adhesion between the tissue and the
impression
• The second step stretches the impression enough to pass under the height of
contour of the hard tissue to remove the impression

67. 67
PREPARATION OF STONE CASTS AND DIES
• The hydrophobic characteristics of silicone impression materials make them
suitable for pouring of epoxy resin to produce dies
• pouring with gypsum products challenging, as it increases the potential of
forming voids in gypsum dies and casts.
• surfactant sprays(debubblizers) : improve the surface wettability of the silicone
impression material for the stone slurry (thin layer is applied)
• A dilute solution of soap is also an effective surfactant
• An alternative to the surfactant is to select a hydrophilized addition silicone

68. 68
Common failures occurring with the use of Elastomeric Impression Materials
Type of failure
• Rough or uneven impression surface
• Bubbles
• Irregularly shaped voids
• Rough or chalky stone cast
• Distortion
Causes for failure
• Incomplete polymerization
• Too rapid polymerization from high humidity or
temperature
• Excessively high accelerator/base ratio
• Air incorporated during mixing
• Moisture or debris on surface of teeth
• Inadequate cleaning of impression
• Excess water that is not blown off
• Lack of mechanical retention to the tray
• Excessive bulk of material
• Insufficient relief for the reline material
• Movement of tray during polymerization
• Premature removal of impression from mouth

69. 69
DISINFECTION
Condensation silicones, addition silicones, and polysulfides can be disinfected with all EPA-registered
disinfectants without the loss of surface quality or accuracy if the disinfection time is short.
The impressions should be immersed for the time specified for each disinfectant. After disinfection, the
impression should be removed, rinsed, and poured with the gypsum product as soon as possible.
long immersion time may cause the surfactant in the hydrophilic polyvinyl siloxane to leach out and render
the impression less hydrophilic.
The current protocol for disinfecting hydrocolloid impressions recommended by the CDCP is to use
household bleach (1:10 dilution), iodophors, or synthetic phenols as disinfectants.
Can be either sprayed or immersed (not more than 10 min)

70. 70
Material Method Recommended
Disinfectant
comments
Alginate
Agar
Polysulfide & silicone
Polyether
ZOE impression paste
Impression compound
Use only disinfectant for a
short-term exposure time
(<10 min for alginate)
Immersion
Use disinfectant only for a
short time (<10 min)
Immersion preferred; spraying
can be used for bite
registrations
Chlorine compounds or
iodophors
Glutaraldehydes, chlorine
compounds, iodophors,
phenolics
Chlorine compounds or
iodophors
Glutaraldehydes or
iodophors
Iodophors or chlorine
compounds (2%
Glutaraldehyde)
Short-term glutaraldehyde has
been shown to be acceptable
Do not immerse in alkaline
glutaraldehyde
Disinfectants requiring more than
30-min exposure times are not
recommended.
ADA recommends any of the
disinfectant classes;
Not compatible with chlorine
compounds! Phenolic spray can be
used.

71. RECENT ADVANCES
71

72. 72
Digitial Impressions
• After the tooth preparation is complete and the tissues are retracted to visualize the tooth margins,
the tooth is dried and readied for scanning
• scanning systems : use an oxide powder on the tooth to remove optical highlights from the surface
of the preparation and to enhance the scan quality.
• Scanners use either a series of static images or a stream of video images to capture the geometry
of the tooth preparation.
• Laser utilization allows scanning of a variety of different surface types and colors without the
need for a contrast agent (powder). These scans are registered together to form a single 3-D
model

73. 73

74. 74
Advantages of Digital Impressions
• Provide a clean and streamlined impression method
• Simplify impression making without the complexity of the many materials required for conventional
impressions with an elastomeric material
• Reduces the environmental impact of disposing the materials required for conventional impressions
• Digital scanning takes less time than conventional impression, which increases the efficiency and
productivity of dental office.
• The on screen image can be checked for margin visibility, preparation from and interocclusal clearance.
• Adjustment and isolated scanning is possible.
• Results are instantly visible and can be enlarged
• Scanning takes 3 to 4 minutes, no material restriction, no risk of error due to distortion
Craig’s Restorative Dental Materials – Mosby 13th edition p362-364

75. 75
Digital impressions are advantageous in
• Patients who are gaggers and cannot tolerate impression material in mouth for several minutes
• Presence of tori or undercut which make removal of a traditional impression difficult or
impossible without causing the patient discomfort/ or tearing the margins
• No need for infection control
• No concern about the compatibility of specific material with specific disinfectants
A Begum. R Ahmed. Digital Impressions. City Dental College Journal, 2012

76. 76
• The tear strength of some alginates has been improved, and some have been formulated so that the
powder is dustless, thus reducing the health hazard as a result of patient inhalation of dust during
the dispensing process
• Polyether and silicone impression materials have been modified so that the working time, viscosity,
and flexibility of the polyethers have been improved
• Fluoride or silico fluorides can be added to Alginate
• A colour pH change to indicate different stages in manipulation (violet during spatulation, pink
when loaded and white on setting)
• Chlorhexidine & triethanolamine modified Alginates also have been introduced
R G Craig. Review of Dental Impression Materials.Advances in Dental Research.1988
Doubleday B.Impression Materials.British journal of orthodontics.May1988;25(2):8-10

77. 77
vinyl polyether siloxane (VPES)
newer elastomer that has been developed is called as vinyl polyether siloxane (VPES) combining
features of both addition silicone and polyether
This material has to be used only in a one step multiple mix technique
It is available in viscosities :-
medium (Monophase) : Transfer (implantology), Crown and bridge, Inlay/onlay, veneer
Heavy
Light : Precision impressions
Advantages
Excellent flowability
Remarkable hydrophilicity
Optimized elastomeric properties
Easy and fast, true-to-detail fabrication of casts
RM Shetty, GR Bhandar.Vinyl Polysiloxane Ether: A Breakthrough in Elastomeric Impression Material

78. REVIEW OF LITERATURE
78

79. 79
A systematic review was conduct to evaluate the evidence of possible benefits and
accuracy of digital impression techniques vs. conventional impression techniques
Digital impression accuracy is at the same level as conventional impression methods in
fabrication of crowns and short fixed dental prostheses (FDPs).
For fabrication of implant-supported crowns and FDPs, digital impression accuracy is
clinically
acceptable.
In full-arch impressions, conventional impression methods resulted in better accuracy
compared to digital impressions.
Ahlholm P, Sipilä K, Vallittu P, Jakonen M, Kotiranta U. Digital versus conventional Impressions in Fixed
Prosthodontics : A Review.J Prosthodont. 2018 Jan;27(1):35-41

80. 80
The different impression materials which can be used for an ocular impressions are Irreversible
Hydrocolloids, Opthalmic Alginates, tissue conditioners, polyvinyl siloxane and dental impression
waxes like Korecta wax no.4 and Iowa wax
Mix Alginate with excess water, fill in a disposable plastic syringe, eyelids are drawn gently apart and
impression material is introduced at inner side of plpebral opening
Tissue conditioner is applied on a trimmed stock acrylic resin prosthesis and inserted and kept for 20
minutes. After removing excess material prosthesis is worn for 24-48 hours and if esthetics and
adaptation is acceptable, it is relined with heat cure resin
A thin layer of korecta wax no 4 is added on intaglio surface and borders of already existing
prosthesis in order to reline it, dip it into 123 F water bath for five minutes and then place and check
for the adaptation
MF Mathews.The ocular impression: A review of the literature and presentation of an alternate
technique.journal of Prosthodontics Implant Esthetic & Reconstructive Dentistry. Aug 2004;9(4):210-216

81. 81
conclusion

82. 82
REFERENCES
• Phillips’ science of Dental Materials. Twelfth Edition.p181-196
• Craig’s Restorative Dental Materials – Mosby 13th edition p362-364
• A Begum. R Ahmed. Digital Impressions. City Dental College Journal, 2012
• R G Craig. Review of Dental Impression Materials.Advances in Dental
Research.1988
• Doubleday B.Impression Materials.British journal of orthodontics.May1988;25(2):8-
10
• RM Shetty, GR Bhandar.Vinyl Polysiloxane Ether: A Breakthrough in Elastomeric
Impression Material
• Ahlholm P, Sipilä K, Vallittu P, Jakonen M, Kotiranta U. Digital versus conventional Impressions in
Fixed Prosthodontics : A Review.J Prosthodont. 2018 Jan;27(1):35-41