This document discusses different types of impression materials used in dentistry, including their properties and uses. It covers elastic materials like alginate, polyether, polysulfide, and silicone impressions that can record undercuts, as well as rigid materials like plaster, wax, and zinc oxide eugenol. Key properties discussed include accuracy, elasticity, dimensional stability, and setting characteristics. Hydrocolloids like alginate provide good detail but poor stability, while synthetic elastomers offer improved tear resistance and stability at the cost of potential allergic reactions or toxicity. Mixture, properties, advantages, and disadvantages are described for each major material type.

1. Impression materials

2. Chairside Impression
- negative likeness of the denture
bearing tissues
Laboratory Cast
- positive likeness of the denture
bearing tissues

5. Placing some soft, semi fluid material in the mouth
and allowing the material to set…

7. Impression materials after setting
Rigid
Non undercut areas
Plaster of Paris
Elastic
Undercut areas allowed
AlginatePlaster of Paris
Compound
Zinc-oxide
eugenol paste
Wax
Alginate
Polysulphide
Polyether
Silicone

8. Impressions trays
Stock tray
prefabricated
range of sizes and
Special tray
constructed onto the
primary castrange of sizes and
shapes,
metal or plastic,
perforated or
nonperforated
primary impressions
preliminary or anatomic
primary cast
spaced trays
close fitting trays
aluminium filled shellac
acrylic resins
secondary impressions

12. Basic properties of impression materials
Fluid
obtained by - mixing the components
- heating- heating
→ until it exhibits plastic flow
Setting period
changing from fluid to solid
Set
end form of the material

13. Certain properties
I. Consistency of the
fluid material
high viscosity
heavy bodied, puttyheavy bodied, putty
regular viscosity
intermediate flow
low viscosity
light bodied
very low viscosity
light bodied

14. Certain properties
II. Setting characteristics of the material
Inital setting time
- beginning of the setting process- beginning of the setting process
- for manipulating the material (working time)
- the impression material should be inserted
Final setting time
- the material is completely set, it can be
removed from the mouth

15. Certain properties
III. Properties of the set material
Dimensional stability (shape and size
changing)changing)
a) more than 0,2% in six hours → dimensionally
unstable
alginates - shrinkage !
b) less than 0,2 % in six hours → dimensionally
stable
Elastic recovery

16. Impression materials: required propertiesImpression materials: required properties
Non toxic
Accurate
Easy to handle
Easy to manipulateEasy to manipulate
Consistency
Setting time
Elasticity
Dimensionstability
Wettability
Thixotropic
Economy
Disinfection
Flavour

17. Impression materials after setting
Elastic
These materials can be stretched and bent to a fairly large degree without
suffering any deformation. These are used for recording the patient's
mouth where undercuts are present. Usually used for partial dentures,
overdentures, implants and crown and bridge work
The elastic impression materials can be divided into two groups: the
hydrocolloids and the synthetic elastomers.
Rigid
Non undercut areas
Impression Plaster
Compound
Zinc-oxide eugenol paste
Wax
hydrocolloids and the synthetic elastomers.
Hydrocolloid:
Alginate
Synthetic elastomers:
Polysulphide
Polyether
Silicone

18. Hydrocolloides
A colloid is a state of matter in which individual particles of
one substance, are uniformly distributed in a dispersion
medium of another substance. When the dispersion
medium is water it is termed a hydrocolloid.
Fluid: when the solute particles present are dispersed
throughout the liquid, this is called a sol.
particles attached to each other, forming a loose network:
the colloid becomes viscous and jelly like, and is called a
gel.gel.
ability to change reversibly from the sol state to the gel
state.
A sol can be converted into a gel in one of two ways :
1. Reduction in temperature, reversible because sol is
formed again on heating (eg agar).
2. Chemical reaction which is irreversible (eg alginates). A
gel can lose (syneresis which results in shrinkage) or take
up (imbibition which results in expansion) water or other
fluids.
Hydrocolloids are placed in the mouth in the sol state when
it can record sufficient detail, then removed when it has
reached the gel state.

19. AlginateAlginate
CompositionComposition
sodium or potassium alginatesodium or potassium alginate 20%20%
salts of alginic acid, preparedsalts of alginic acid, prepared
ffrom various species of seaweedrom various species of seaweed
fillers: diatomaceous earthfillers: diatomaceous earth 44%44%fillers: diatomaceous earthfillers: diatomaceous earth 44%44%
gives body to the impressiongives body to the impression
CaSO4 · 2 H2OCaSO4 · 2 H2O 15%15%
sodium tripolyphosphatesodium tripolyphosphate 8%8%
retardantretardant
modifiersmodifiers magnesium oxide, sodiummagnesium oxide, sodium
fluoride 11fluoride 11%%
good setting, good surfacegood setting, good surface

20. MixingMixing
PowderPowder : W: Waterater = 1 : 3 in a flexible bowl with a curved, rigid spatula= 1 : 3 in a flexible bowl with a curved, rigid spatula
Container of powder should be shaken before use to get an even distribution ofContainer of powder should be shaken before use to get an even distribution of
constituents. Powder and water should be measured to manufactures instructions.constituents. Powder and water should be measured to manufactures instructions.
Water at room temperature should be used, this gives a reasonable working time of aWater at room temperature should be used, this gives a reasonable working time of a
couple of minutes.couple of minutes.
On mixing the powder with water a sol is formed, a chemical reaction takes place and aOn mixing the powder with water a sol is formed, a chemical reaction takes place and a
gel is formed.gel is formed.
ddimensionally unstableimensionally unstable
syneresis (Hsyneresis (H22O loss from the surface)O loss from the surface)
shrinkage → impression should be cast in 15 minutes, or stored in hygroforshrinkage → impression should be cast in 15 minutes, or stored in hygroforshrinkage → impression should be cast in 15 minutes, or stored in hygroforshrinkage → impression should be cast in 15 minutes, or stored in hygrofor
do not adhere to the impression traydo not adhere to the impression tray –– adhesiveadhesives, or perforateds, or perforated traystrays
pH changes during settingpH changes during setting -- chromaticchromatic alginatesalginates

22. PROPERTIES
Good surface detail
Reaction is faster at higher temperatures
Elastic enough to be drawn over the undercuts, but tears over the
deep undercuts
Not dimensionally stable on storing due to evaporation
Non toxic and non irritant
Setting time can depend on technique
Alginate powder is unstable on storage in presence of moisture or in
warm temperatures
Alginate powder is unstable on storage in presence of moisture or in
warm temperatures
ADVANTAGES
1. Non toxic and non irritant
2. Good surface detail
3. Ease of use and mix
4. Cheap and good shelf life
5. Setting time can be controlled with temperature of water used
DISADVANTAGES
1. Poor dimensional stability
2. Incompatibility with some dental stones
3. Setting time very dependent on operator handling
4. Messy to work with

23. Impression materials II
Dr. Judit Borbély 2012

24. Last week

25. Impression materials are used to
record the shape of the teeth
and alveolar ridges. There are a
wide variety of impression
materials available each with
their own properties, advantages
and disadvantages.and disadvantages.
Materials in common use can be
classified as elastic or
rigid (non-elastic) according to
the ability of the set material to
be withdrawn over undercuts.

26. Impression materials: required propertiesImpression materials: required properties
Non toxic
Accurate
Easy to handle
Easy to manipulateEasy to manipulate
Consistency
Setting time
Elasticity
Dimensionstability
Wettability
Thixotropic
Economy
Disinfection
Flavour

27. Impression materials after setting
Elastic
These materials can be stretched and bent to a fairly large degree without
suffering any deformation. These are used for recording the patient's
mouth where undercuts are present. Usually used for partial dentures,
overdentures, implants and crown and bridge work
The elastic impression materials can be divided into two groups: the
hydrocolloids and the synthetic elastomers.
Rigid
Non undercut areas
Impression Plaster
Compound
Zinc-oxide eugenol paste
Wax
hydrocolloids and the synthetic elastomers.
Hydrocolloid:
Alginate
Synthetic elastomers:
Polysulphide
Polyether
Silicone

28. The synthetic elastomers
First introduced in the late 1950s, synthetic elastomeric impression
materials quickly became popular as dental materials because they
significantly reduced the two main problems associated with the
hydrocolloids, namely poor dimensional stability and inadequate tear
resistance. These are used where a high degree of accuracy is needed,
especially in crown and bridge work.
Albert Einstein in Princeton, ca. 1950
They have two main advantages
over the Hydrocolloids - good tear
resistance and dimensional
stability.They are mainly hydrophobic
rubber based materials. All of these
materials come in different viscosity's
ranging from low to high viscosity.
The light bodied material maybe used
as a wash impression over a medium
or heavy-bodied material.

29. ONE STAGE IMPRESSION
Light bodied impression material is placed in a syringe, and
placed over the areas where high detail is required (e.g.
over a crown preparation). Some is then squirted over
the heavy-bodied impression material which has been
loaded into an impression tray. The impression is then
taken as normal. This technique saves time, but it can be
very labour intensive because the two need to mixed atvery labour intensive because the two need to mixed at
the same time.
TWO STAGE IMPRESSION
An impression is taken with the heavy-bodied material. This
is then removed from the mouth and inspected. The light
bodied material is then prepared and again placed in a
syringe. This is then squirted over heavy-bodied material
and then impression relocated.

30. Silicone elastomersSilicone elastomers
Polymers of silicone and oxygen atoms → polysiloxanePolymers of silicone and oxygen atoms → polysiloxane
Elastic properties can be obtained by cross linking andElastic properties can be obtained by cross linking and
additionaddition of the long chainsof the long chains
Viscosity types: high viscosityViscosity types: high viscosity -- heavy bodied,heavy bodied, puttyputty
regular viscosityregular viscosity -- intermediate flowintermediate flow
low viscositylow viscosity -- light bodiedlight bodiedlow viscositylow viscosity -- light bodiedlight bodied
very low viscosityvery low viscosity -- light bodiedlight bodied

31. Supplied as a paste andSupplied as a paste and
Condensation cured siliconesCondensation cured silicones
polysiloxane chains are terminated withpolysiloxane chains are terminated with
silanolsilanol, dibutilyn dilaurate catalyst present, dibutilyn dilaurate catalyst present
during setting, condensation reaction occursduring setting, condensation reaction occurs
and theand the byproduct is alcoholbyproduct is alcohol
Supplied as a paste andSupplied as a paste and
liquid or two pastes, inliquid or two pastes, in
light, medium, heavy orlight, medium, heavy or
very heavy bodied (putty).very heavy bodied (putty).
do not adhere todo not adhere to impressionimpression
traytray--adhesive solutions!adhesive solutions!

33. PROPERTIES
Hydrophobic
Hydrogen gas evolution on setting
Moderate shelf life
Moderate tear strength
Good surface detail
Shrinking of impression over time
Non toxic and non irritant
Very elastic (near ideal)
ADVANTAGES
Accurate
Ease of use
Can be used on severe undercuts
DISADVANTAGES
Hydrogen evolution
Liquid component of paste/liquid system may cause irritation

34. Addition cured siliconesAddition cured silicones
Supplied in 2 pastes or in aSupplied in 2 pastes or in a
gun and cartridge form as light,gun and cartridge form as light,
during setting, additionduring setting, addition reaction occursreaction occurs
Platinic compound catalyst presentPlatinic compound catalyst present
no byproductno byproduct
no polymerizationno polymerization contractioncontraction
--
gun and cartridge form as light,gun and cartridge form as light,
medium, heavy and very heavymedium, heavy and very heavy
bodied.bodied.
On mixing, in equalOn mixing, in equal
proportions, crosslinkingproportions, crosslinking
occurs to form a siliconeoccurs to form a silicone
rubber. Setting occurs in aboutrubber. Setting occurs in about
66--8 minutes.8 minutes.
do not adhere todo not adhere to impressionimpression
traytray--adhesive solutions!adhesive solutions!
expensiveexpensive

36. PROPERTIES
Good shelf life
Dimensionally stable
Moderate tear strength
Excellent surface detail
No gas evolution
Non toxic and non irritant
ADVANTAGES
AccurateAccurate
Ease of use
Fast setting
Wide range of viscosity's
DISADVANTAGES
Hard to mix
Sometimes difficult to remove the impression from the mouth
Too accurate in some circumstances (cast produced is not
sufficiently oversized)

37. Polyether elastomersPolyether elastomers
CompositionComposition::
supplied as two pastessupplied as two pastes
base paste:base paste:
liquid polyetherliquid polyether
fillersfillersfillersfillers
inert oilsinert oils
activator paste:activator paste:
sulphonic acid esulphonic acid esstherther inin hydrocarbonshydrocarbons
fillersfillers
During setting reaction cross linking reaction occurs withDuring setting reaction cross linking reaction occurs with
thethe aziazirirididinno groups of the base and the end product is ao groups of the base and the end product is a
rubberrubber--likelike polymerpolymer

38. A popular polyether impression material,
Impregum (Espe GmbH, Germany), was
the first elastomer to be developed
specifically for use in dentistry and
introduced in the
late 1970s.late 1970s.

39. Impregum™ Penta™ Soft Heavy
Body/Light Body Impression Material
Polyether precision impression material
that is accurate and hydrophilic,
resulting in outstanding detail even in
a moist environment
Impregum™ Penta™ Soft Medium
Body Impression Material,
Polyether precision impression material
medium viscosity and is intended for
use in the monophase technique.

40. Polyether impression materials tendPolyether impression materials tend
to have a fast setting time of lessto have a fast setting time of less
than 5 minutesthan 5 minutes
In contrast to polysulphides, theyIn contrast to polysulphides, they
undergo an addition curedundergo an addition cured
polymerisation reaction onpolymerisation reaction on
setting which has no reaction bysetting which has no reaction by--
product resulting in a materialproduct resulting in a material
with very good dimensionalwith very good dimensionalwith very good dimensionalwith very good dimensional
stability.stability.
The set material may however swellThe set material may however swell
and distort because of theand distort because of the
absorption of water on storage inabsorption of water on storage in
conditions of high humidity.conditions of high humidity.
Impressions should therefore beImpressions should therefore be
stored dry.stored dry.
DDo not adhere to impressiono not adhere to impression
traytray--special adhesives!special adhesives!

41. PROPERTIES
Hydrophillic (ie absorbs water)
Good shelf life of up to 2 years
Good elastic recovery
Non toxic
Low setting contraction
Low tear strength
Excellent surface detail
Good dimensional stability
ADVANTAGES
Accuracy
Good on undercuts
Ease of use
DISADVANTAGES
May cause allergic reaction due to the sulphonic acid ester
Poor tear strength
Rapid setting time (ie short working time)
Stiff set material (sometimes hard to remove from mouth)

42. ••CompositioComposition :n :
supplied as two pastessupplied as two pastes
base paste: liquid polysulphidebase paste: liquid polysulphide 55%55%
fillers (ZnSO4, TiO2)fillers (ZnSO4, TiO2) 44%44%
perfumeperfume 1%1%
Polysulphide elastomersPolysulphide elastomers
activator paste: leadactivator paste: lead--dioxidedioxide 10%10% causescauses
colloidal sulfurcolloidal sulfur 1%1% polymerizationpolymerization
oleic and stearic acidoleic and stearic acid 2%2% stabilizesstabilizes
fillers (ZnSO4, TiO2)fillers (ZnSO4, TiO2) 50%50% settingsetting
inert oilinert oil 37%37% characteristicscharacteristics
Mixing should continue until a streak-free mass is obtained

43. do not adhere to impression traydo not adhere to impression tray--adhesives:rubber solution inadhesives:rubber solution in
acetoneacetone
During setting reactionDuring setting reaction terminal hydrogen atoms of the liquidterminal hydrogen atoms of the liquid
polisulfide arepolisulfide are oxidizoxidized by the lead dioxideed by the lead dioxide with a resultantwith a resultant
increase in the degree of polymerizationincrease in the degree of polymerization
acetoneacetone
lead dioxide may have toxic effectlead dioxide may have toxic effect--alternative oxidizing systemsalternative oxidizing systems
ttypes:ypes: heavy bodiedheavy bodied
regularregular
light bodiedlight bodied

44. relatively unpopular materials, setting
reaction of polysulphides tends to be
long with setting times often in excess of
10 minutes (acceleration is possible by
adding a small drop of water to the mix)
messy to handle
objectionable odour
Dies wider and shorter than the tooth
preparation. This distortion, which
worsens the longer the delay in pouring
up, is the result of impression shrinkageup, is the result of impression shrinkage
which is directed towards the impression
tray - hence the wider die. Shrinkage
occurs firstly as a result of a continued
setting reaction after the apparent setting
time, and secondly through the
evaporation of water produced as a by-
product of the setting reaction.
A special tray, providing a 4 mm uniform
space, is needed to reduce distortion
from the shrinkage of a large bulk of
material. The recommended maximum
storage time of the set impression is
about 48 hours

45. PROPERTIES
Dimensional stability
Excellent surface detail (is only used in special trays)
Viscosity depends on the brand used
Very small setting contraction (0.3-0.4% over the first 24 hrs)
Contraction on cooling from mouth to room temperature
Very good tear resistance
Good shelf life
Viscoelastic
ADVANTAGES
Dimensional stabilityDimensional stability
Accuracy
Comes in a number of different viscosity's
Long working time (although this may be a disadvantage in some clinical situations)
Long shelf life
DISADVANTAGES
Lead oxide in base paste may have toxic effects
Staining of clothes due to the Lead oxide
Messy to work with - unpleasant rubbery smell
Can only be used in a special tray

46. Impression materials after setting
Rigid
Non undercut areas
Impression PlasterImpression Plaster
Compound
Zinc-oxide eugenol paste
Wax
Elastic
Undercut areas allowed
Alginate
Polysulphide
Polyether
Silicone

47. Rigid materials
These materials are rigid and therefore exhibit little or no
elasticity. Any significant deformation produces a
permanent deformation. They are used where there are
no undercuts and are mainly used for edentulous patient
cases.
Non-elastic impression materials are generally not used
for obtaining impressions of crown preparations
because of their inability to accurately record undercuts.because of their inability to accurately record undercuts.

48. Impression Plaster „History „History „History „History „
Composition – CaSO4 . ½ H2O
Potassium-SO4 or salts of strong
acids (2,5%)
→ accelerators
→ reduce of the setting expansion→ reduce of the setting expansion
Salts of weak acids or borax
(0,25%)
→ retarders
Coloring agent

50. Manufacturing
CaSO4 · 2 H2O CaSO4 · ½ H2O + 1 ½ H2O
Mineral gypsum: CaSO4 · 2 H2O - heating 110-130 °C
dry → β-hemihydrate - irregular particles
plaster of Paris, model stoneplaster of Paris, model stone
autoclave → α-hemihydrate - more perfect crystals
model stone, die stone

51. β-hemihydrate
α-hemihydrate

52. Setting reaction
hydration reaction
quick, exothermic, setting expansion
CaSO4 · ½ H2O + 1 ½ H2O crystallization CaSO4 · 2 H2O
100g powder + 60 ml water - mixed in a flexible bowl with a spatula
Visible signs:
1. Dissolution - light surface → fluid
2. Colloidal state - matt surface → paste2. Colloidal state - matt surface → paste
3. Crystal formation - solid → hardening
4. Breaks with a special sound
Influence on the setting time
and expansion:
water/powder ratio
spatulation time
Temperature

53. PROPERTIES
Excellent at recording fine detail (because very fluid when inserted in mouth)
Dimensionally stable if anti expansion solution used
Fractures if undercuts present
Mucostatic
Needs to be treated with a separating medium (e.g. varnish or soap solution)
before being cast in stone or plaster
Exothermic setting reaction
On storage dimensionally stable but a small amount of shrinkage may occur
Non toxic but may be unpleasant due to dryness and heat evolved during
setting
ADVANTAGES
Good surface detail
Excellent dimensional stability
Rate of the setting reaction can be controlled by the clinician
DISADVANTAGES
Cannot be used for mucocdisplacive impressions
Cannot be added to
Properties affected by operator handling technique
Taste and roughness may cause the patient to vomit

54. Impression compound
Composition:
mixture of thermoplastic resins and waxes 47%
with fillers (talcum) and pigments 53%
becomes soft between 55 °C and
60 °C in water bath
at mouth temperature reverts to a
solid state
(slow reaction because of poor
heat conduction)

55. Dental application
Type I. -used for impression
taking
sheet (black, brown, red)
primary impressions for
complete dentures
green stick
border trimming materialborder trimming material

56. PROPERTIES
Poor surface detail
High coefficient of thermal expansion (contraction of up to 0.3% when removed from
mouth to room temperature)
Distorts wen removed over undercut areas
Hardens in the mouth in suitable time
Mucodisplacive
Poor dimensional stability
Can be modified by re-heating
Tray borders can be progressively developed with greenstick
During manipulation internal stresses can be set up
Non toxic and non irritantNon toxic and non irritant
Good shelf life
ADVANTAGES
1. Non irritant and non toxic
2. Reusable (but with re-use the constituents are leached out)
3. Can be reheated and readapted
4. Can support other materials for wash impressions
5. Mucocompressive
DISADVANTAGES
1. Poor dimensional stability
2. Poor surface detail
3. Expansion coefficient
4. Will distort if removed from undercuts

57. Zinc-oxide eugenol paste
Composition:
supplied as two pastes
base paste activator paste
white brownish, transparent
ZnO eugenol
Hydrogenated resin fillers: talc, diatomaceous earth
inert oil
MgCl as acceleratorMgCl as accelerator
Some pastes contain a substitute for eugenol e.g. a
carboxylic acid.
The 2 pastes come in contrasting colours and mixed
to give a paste of even colour.
The material is mixed in a 1:1 paste ratio and used in thin
sections only (2-3mm) as a wash impression.
Dental application:
secondary impression for complete dentures
temporary luting of fixed appliances

58. PROPERTIES
Non toxic
Adherence to tissues
Mucostatic or mucocodisplacive (depending on brand used)
Good surface detail in thin section
Good dimensional stability (little or no dimensional change on
setting, 0.1% dimensional change during setting)
Can be added to with fresh zinc oxide eugenol
Stable on storage and good shelf life
ADVANTAGES
1. Dimensional stability
2. Good surface detail
3. Can be added to
4. Mucostatic or mucocodisplacive
DISADVANTAGES
1. Cannot be used in very deep undercuts
2. Only sets quickly in thin section
3. Eugenol allergy in some patients

59. WaxesWaxes
Origin of waxesOrigin of waxes::
mineral waxmineral wax ––
obtained from petroleum distillationobtained from petroleum distillation
paraffin waxparaffin wax ––
brittle at room temperaturebrittle at room temperature
melting temperature: 48melting temperature: 48--7070 °° CCmelting temperature: 48melting temperature: 48--7070 °° CC
microcrystalline waxmicrocrystalline wax -- less brittleless brittle
melting temperature: 65melting temperature: 65--9090 °°CC
animal wax (beeswax)animal wax (beeswax)
adding to paraffin wax → less brittleadding to paraffin wax → less brittle
vegetable waxvegetable wax
carnauba wax: derived from palm treecarnauba wax: derived from palm tree
candenilla wax: derived from plantscandenilla wax: derived from plants

60. Dental applicationDental application
modeling wax (rose)modeling wax (rose)
inlay wax (blue, green)inlay wax (blue, green)
sticky wax (yellow)sticky wax (yellow)
baseplate waxbaseplate wax
border trimming impression waxborder trimming impression wax
undercut waxundercut wax
PropertiesProperties::
Waxes are thermoplastic materials,Waxes are thermoplastic materials,
which flow at mouth temperature and arewhich flow at mouth temperature and arewhich flow at mouth temperature and arewhich flow at mouth temperature and are
soft a room temperature. They do not setsoft a room temperature. They do not set
by chemical reaction. Normally used toby chemical reaction. Normally used to
correct small imperfection (e.g. airblows)correct small imperfection (e.g. airblows)
in other impressions, especial zinc oxidein other impressions, especial zinc oxide
impressions.impressions.
A cast should be poured up immediately
after taking the impression to avoid
distortion which readily occurs in wax.
Because of easy deformationBecause of easy deformation
not widely used as impressionot widely used as impressionn
material!material!

61. Thank You for Your Attention!