This document provides an introduction and overview of various dental impression materials, including their classification, desirable qualities, and properties. It discusses impression compounds, zinc oxide eugenol paste, reversible hydrocolloids like agar, irreversible hydrocolloids like alginate, and elastic impression materials. For each material, it describes composition, manipulation, advantages, and disadvantages. The document aims to provide an understanding of different impression materials for successful use in clinical dentistry.

2. Introduction
Terminology
Desirable qualities
classification
Impression compound
Impression plaster
Zinc oxide eugenol
Elastic impression material
elastomeric impression material
Review of literature
CONTENT
2

3. INTRODUCTION
Impression material are used to register or reproduce the
form and the relationship of the teeth and the oral tissue, the
area involved may vary from a single tooth to the whole
dentition, or an impression may be made of an edentulous
mouth.
Hydrocolloids and synthetic elastomeric polymer are among
the materials most commonly used to make impressions of
various areas of the dental arch.
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4. Each of these classes of material has certain
advantages and disadvantages .
An understanding of physical characterstics and the
limitation of each material is necessary for their
successful use in clinical dentistry
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5. TERMINOLOGY
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6. 6

7. DESIRABLE QUALITIES
 A pleasant odor, taste, and acceptable color
 Absence of toxic or irritant constituents
 Adequate shelf life for recquirement of storage
and distribution
 Economically commensurate with the result
obtained
 Easy to use with the minimum of equipment
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8.  Setting characteristics that meet clinical
requirements
 Satisfactory consistency and texture
 Readily wets oral tissue
 Elastic properties with freedom from permanent
deformation after strain
 Adequate strength so it will not break or tear on
removal from the mouth
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9.  Dementiosal 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
 Compatibiliyu with cast and die material
 Accuracu in clinical use
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10.  Readily disinfected without loss of accuracy
 No release of gas or other byproducts during the
setting of the impression or cast and the die
material
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11. 11
CLASSIFICATION
Impression materials
High viscosity
Impression
compound
Putty
elastomers
Medium
viscosity
Regular
elastomers
Low viscosity
Impression
plaster
Impression
paste
hydrocolloid
Light body
elastomers
Irreversible
hydrocolloid
Reversible
hydrocolloid

12. Impression compound
• One of the oldest dental impression matrial
• Rigid, reversible impression material which can
sets by physical change
SYNONYMS
modeling compound and modeling plastic
12

13. classification
o Type 1 – impression compound
o Type2 – tray compound
SUPPLIED AS
sheets, sticks, cakes and cones
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14. Application
• Preliminary impression in an edentulous mouth
• Impression of full crown preparartion where
gingival tisues must be displaced
• Peripheral tracing or border molding
• To check undercuts in inlay preparation
• To make a special tray
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15. Composition
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16. Manipulation
STICKS
Small amount of compound can be softened over a
flame. When adirect flame is used, the compound
should not be allowed to boil or ignite, otherwise the
plasticizers are volatilized
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17. CAKES
Larger amount of compound are softneded in warm
water in a thermostatically controlled water bath
usally in the range of 65 to 75degree. After the
compound is removed from the watr bath, it is usally
kneaded with fingers in order to obtain uniform
plasticity throughout the mass.
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18. ZINC OXIDE EUGENOL
MPRESSION PASTE
• Cementing and insulating medium
• Temporary filling material
• Root canal filling material
• Surgical pack in periodontal surgical procedure
• Bite registration paste
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19. • Temporary relining material for denture
• Impression for edentulous patients
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20. Classification
ADA specification no. 16
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Type 1 or hard Type 2 or soft

21. Available as
In paste form in two tube
• Base paste
• Accelerator or reactor or catalyst paste
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22. Composition
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23. Setting reaction
Is a typical acid-base reaction to form a chelate. This
reaction is also known as chelation and the product
is called zinc eugenolate.
• ZnO+H2O Zn(OH)2
• Zn(OH)2+2HE ZnE2+2H2O
(base) (acid eugenol) (zinc eugenolate)
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24. Setting time
Initial setting time
Is the period from the beginning of the mixing until
the material ceases topull away or string outwhen
its surface is touched with a metal rod. The material
should be seated in the mouth before the initial set.
The final set
When a needle of specified dimension fails to
penetrate the surface of the specimen more than
0.2mm under a load of 50gm.
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25. Setting time
Initial setting
time=3-6min
Final setting
time=10min
Type
1 Initial setting
time=3-6min
Final setting
time=15min
Type
2
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26. 26
Factors controlling setting time
o Particle size ; if small and acid coated, the setting
time is less
o By varying the length of two pastes
o By adding zinc acetate or drop of water or acetic
acid (acetic acid is more effective than water. It
increses speed of formation of zinc hydroxide)

27. 27
o Longer the mixing time, shorter is the setting time
o High atmospheric temperature and humidity
accelerate setting
o Setting can be delayed by cooling the mixing
slab. Spatula or adding small amount of retarder
or oils or waxes

28. Properties
• Consistency and flow
ADA specification No. 16, the spread is
Type 1 pastes – 30 to 50mm
Type 2 pastes – 20 to 45mm
• Detail reproduction
It register surface details quite accurately due to
good flow
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29. • Rigidity and strength
The compressive strength of hardened ZOE is
approximately 7mpa two hours after mixing
• Dimensional stability
A negligible shrinkage less than 0.1%
• Biological consideration
Burning sensation
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30. • Enough working time to
complete border molding
• Register accurate detail
• Dimensionally stable
• Does not require separating
media since it does not stick
to the cast material
• Minor defect can be
corrected locally without
discarding a good
impression
• Special tray fabrication
• Sticky in nature adhere to
tissue
• Burning sensation
• Not used for making
impression of teeth and
undercuts as it is inelastic
In nature
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31. ELASTIC IMPRESSON
MATERIAL
DEFINATION; An elastic impression material is one
that can transform from a semisolid, nonelastic state
to a highly elastic solid state
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32. Hydrocolloid
COLLOID
Is a substance that is microscopically dispersed
uniformly throughout another substances.
• Dispersed phase/dispersed particle(the suspended
particle)
• Dispersion phase/dispersion medium(the
substance in which it is suspended)
If a dispersion phase of a colloidal system is water,
called as hydrocolloid.
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33. REVERSIBLE
HYDROCOLLOID-AGAR
First successful elastic impression material to be
used in dentistry
๏ It is an organic hydrophilic colloid (polysaccharide)
extracted from a type of seaweed (Gelidium,
Gracilaria, etc. China and South America are major
sources of farmed seaweed.
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34. ๏ Agar is a sulfuric ester of a linear polymer of
galactose. Although it is an excellent impression
material and yields accurate impressions, presently it
has been largely replaced by alginate hydrocolloid
and rubber impression materials.
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35. Classification
๏ Type I – High consistency (for use as tray material)
๏ Type II – Medium consistency (for use as tray or
syringe material)
๏ Type III – Low consistency (for syringe use only)
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36. Usess
๏ Widely used at present for cast duplication (e.g.,
during the fabrication of cast metal removable partial
dentures, etc.).
๏ For full mouth impressions without deep undercuts.
๏ It was used extensively for FPD impressions prior to
elastomers.
๏ As a tissue conditioner.
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37. Supplied as
๏ Gel in collapsible tubes (for impressions).
๏ As cartridges or gel sticks.
๏ In bulk containers -for duplication.
๏ Commercial names Syringe materials include—
Herculloid, Cartriloids (Van R), etc. Duplicating
materials include Wirogel (Bego), Dubliform
(Dentaurum).
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38. Composition
38

39. Functions of the ingredients
๏ Agar Basic constituent 13-17% for tray material 6-8%
for syringe material.
๏ Borates Improves the strength of the gel, (it also
retards the setting of plaster or stone cast when
poured into the finished impression - a
disadvantage).
๏ Potassium sulphate It counters retarding effect of
borates, thereby ensures proper setting of the cast or
die.
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40. ๏ Hard Wax It acts as a filler. Fillers affect the strength,
viscosity and rigidity of the gel. Other fillers are zinc
oxide, diatomaceous earth, silica, rubber, etc.
๏ Thixotropic materials It acts as plasticizer. Examples
are: Glycerine, and Thymol. Thymol acts as
bactericide also.
๏ Alkylbenzoates It acts as preservative.
๏ Coloring and flavoring For patient comfort and
acceptance.
๏ Water It acts as the dispersion medium.
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41. Gelation or setting of Agar
๏ Agar changes from the sol to the gel state (and vice
versa) by a physical process.
๏ As the agar sol cools the dispersed phase groups to
form fibrils called micelles.
๏ The fibrils branch and intermesh together to form a
brush-heap structure.
๏ The fibrils form weak covalent bonds with each other
which break easily at higher temperatures resulting
in gel turning to sol.
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42. ๏ The process of converting gel to sol is known as
liquefaction which occurs at a temperature between
70 and 100° C. On cooling agar reverses to the gel
state and the process is called gelation.
๏ Gelation occurs at or near mouth temperature which
is necessary to avoid injury to oral tissues.
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43. Manipulation
๏ Hydrocolloid conditioner
๏ Water cooled rim lock trays
๏ Impression syringes
๏ Connecting water
๏ Agar tray material in tubes
๏ Agar syringe material
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44. The hydrocolloid
conditioner
๏ Boiling section or Liquefaction section- Ten minutes
in boiling water (100°C). The sol should be
homogeneous and free of lumps. After every use the
agar brush heap structure gets more difficult to
break.
๏ Storage section - 65-68°C temperature is ideal. It
can be stored in the sol condition.
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45. ๏ Tempering section - 46°C for about two minutes with
the material loaded in the tray. This reduces the
temperature so that it is tolerated by the sensitive
oral tissues. It also makes the material viscous.
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46. Impression tray
๏ Rim lock trays with water
circulating devices are used. The
rim lock is a beading on the inside
edge of the tray which helps to
retain the material (as agar does
not adhere to the tray). It also has
an inlet and outlet for connecting
the water tubes. The tray should
allow a space of 3 mm occlusally
and laterally and extend distally to
cover all teeth. 46

47. Setting time and working
time
๏ The working time ranges between 7-15 minutes and
the setting time is about 5 minutes. Both can be
controlled by regulating the flow of water through the
cooling tubes. Since the cooling tubes are on the
periphery, the material sets from the periphery
towards the teeth surfaces.
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48. Properties
GELATION, LIQUEFACTION AND HYSTERESIS
๏ Gelation (solidification) occurs at 37°C approximately,
whereas liquefaction (melting) occurs at a higher
temperature, i.e., 60 to 70°C higher than the gelation
temperature. This temperature lag between
liquefaction and gelation is known as hysteresis.
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49. SYNERESIS AND IMBIBITION (DIMENSIONAL STABILITY)
๏ If left in a dry atmosphere, water is lost by syneresis
and evaporation, and if it is immersed in water, it
absorbs water by a process known as imbibition.
๏ The exuding of fluid from the gel is known as
syneresis
Importance- Syneresis and imbibition can result in
dimensional changes and therefore inaccurate casts. To
avoid this hydrocolloid impressions should be poured
immediately.
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50. Laminate technique(AGAR-
ALGINATE COMBINATION
TECHNIQUE)
๏ After injecting the syringe agar on to the area to be
recorded, an impression tray containing a mix of
chilled alginate that will bond with the agar is
positioned over it. The alginate gels by a chemical
reaction, whereas the agar gels through contact with
the cool alginate rather than the water circulating
through the tray.
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51. Advantages of laminate
technique
๏ The syringe agar gives better details than alginate.
๏ Less air bubbles.
๏ Water cooled trays are not required and therefore
more convenient.
๏ It sets faster than the regular agar technique.
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52. Advantages
๏ Accurate dies can be prepared, if the material is
properly handled.
๏ Good elastic properties help reproduce most
undercut areas.
๏ It has good recovery from distortion.
๏ Hydrophilic, moist mouth not a problem. It also gives
a good model surface.
๏ It is palatable and well tolerated by the patient.
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53. ๏ It can be reused when used as a duplicating material
(reuse is not recommended when used as impression
material).
๏ Low cost because it can be reused.
๏ It is economical when compared to synthetic elastic
materials.
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54. Disadvantages
๏ Does not flow well when compared to newly available
materials.
๏ It cannot be electroplated.
๏ During insertion or gelation the patient may
experience thermal discomfort.
๏ Tears relatively easily. Greater gingival retraction is
required for providing adequate thickness of the
material.
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55. ๏ Only one model can be poured.
๏ Has to be poured immediately. Cannot be stored for
too long.
๏ Requires special and expensive equipment.
๏ A soft surface of the gypsum cast results unless a
plaster hardener is used.
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56. Alginate
๏ The word alginate comes from ‘alginic acid’
(anhydro-β-d-mannuronic acid) which is a mucous
extract yielded by species of brown seaweed
(Phaeophyceae). Alginic acid is a naturally occurring
hydrophilic colloidal polysaccharide.
๏ Alginate was developed as a substitute for agar when
it became scarce due to World War II (Japan was a
prime source of agar). Currently alginate is more
popular than agar for dental impressions, because it
is simpler to use. Alginate is perhaps the most widely
used impression material in the world.
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57. Types
๏ Type I — Fast setting.
๏ Type II — Normal setting.
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58. Supplied as
๏ Commonly in bulk packing (tins, bins or sachets)
๏ In preweighed packets for individual impression
๏ A plastic scoop is supplied for dispensing the bulk
powder and a plastic cylinder is supplied for
measuring the water.
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59. ๏ It is used for impression making
—When there are undercuts.
—In mouths with excessive flow of saliva.
—For partial dentures with clasps.
๏ For making preliminary impressions for complete
dentures.
๏ For impressions to make study models and working
casts.
๏ For duplicating models.
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60. Setting reaction
๏ Initially the sodium phosphate reacts with the
calcium sulphate to provide adequate working time.
Next after the sodium phosphate is used up, the
remaining calcium sulphate reacts with sodium
alginate to form insoluble calcium alginate which
forms a gel with water.
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61. Properties of alginate
๏ It is about 14% at a stress of 1000 gm/cm2. However,
some of the hard set materials have lower values (5
to 8%). Lower W/P ratio (thick mixes) results in lower
flexibility (ADA Sp. No. 18/ISO 1563:1990 for alginate
hydrocolloids).
๏ Alginate hydrocolloids are highly elastic (but less
when compared to agar) and about 98.2% elastic
recovery occurs. Permanent deformation is less if the
set impression is removed from the mouth quickly.
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