Impression materials / dentistry jobs

Impression materials II
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INDIAN DENTAL ACADEMY
Leader in continuing dental education

 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.
 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to be withdrawn over undercuts.

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

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.

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

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 stone
 autoclave → α-hemihydrate - more perfect crystals
model stone, die stone

β-hemihydrate
α-hemihydrate

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 → 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

 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
„History „: exothermic, breaks, non
convenient…

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)

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

 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 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 undercutswww.indiandentalacademy.com

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 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

 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

WaxesWaxes
 Origin of waxesOrigin of waxes::
 mineral wax –mineral wax –
obtained from petroleum distillationobtained from petroleum distillation
paraffin wax –paraffin wax –
brittle at room temperaturebrittle at room temperature
melting temperature: 48-70 °Cmelting temperature: 48-70 °C
microcrystalline wax - less brittlemicrocrystalline wax - less brittle
melting temperature: 65-90 °Cmelting temperature: 65-90 °C
 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

 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 andwhich flow at mouth temperature and
are soft a room temperature. They doare soft a room temperature. They do
not set by chemical reaction. Normallynot set by chemical reaction. Normally
used to correct small imperfection (e.g.used to correct small imperfection (e.g.
airblows) in other impressions, especialairblows) in other impressions, especial
zinc oxide impressions.zinc oxide 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!

Impression materials after setting
Rigid
Non undercut areas
 Impression Plaster
 Compound
 Zinc-oxide eugenol paste
 Wax
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.
 Hydrocolloid:
Alginate
 Synthetic elastomers:
Polysulphide
Polyether
Silicone

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. The colloid
is relatively fluid when the solute particles present are dispersed throughout
the liquid. This is called a sol. Alternatively, the particles can become
attached to each other, forming a loose network which restricts movement of
the solute molecules. The colloid becomes viscous and jelly like, and is
called a gel. Some colloids have the 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.

AlginateAlginate
 CompositionComposition
sodium or potassium alginatesodium or potassium alginate 20%20%
salts of alginic acid, preparedsalts of alginic acid, prepared
ffrom various speciesrom various species
of seaweedof seaweed
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

 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 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

 PROPERTIES
 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
 Setting time can depend on technique
 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 www.indiandentalacademy.com

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.
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.

 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 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.

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 bodied
very low viscosityvery low viscosity -- light bodiedlight bodied

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!
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

 PROPERTIES
 Hydrophobic
 Hydrogen gas evolution on setting
 Moderate shelf life
 Moderate tear strength
 Shrinking of impression over time
 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

--
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,
medium, heavy and verymedium, heavy and very
heavy bodied.heavy 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
6-8 minutes.6-8 minutes.
do not adhere todo not adhere to impressionimpression
traytray-adhesive solutions!-adhesive solutions!
expensiveexpensive
during setting, additionduring setting, addition reaction occursreaction occurs
Platinic compound catalyst presentPlatinic compound catalyst present
no byproductno byproduct
no polymerizationno polymerization contractioncontraction

 PROPERTIES
 Good shelf life
 Dimensionally stable
 Moderate tear strength
 Excellent surface detail
 No gas evolution
 ADVANTAGES
 Accurate
 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)

Polyether elastomersPolyether elastomers
 CompositionComposition::
supplied as two pastessupplied as two pastes
base paste:base paste:
liquid polyetherliquid polyether
fillersfillers
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
rubber-likerubber-like polymerpolymer www.indiandentalacademy.com

 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.
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.

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 by-setting which has no reaction by-
product resulting in a materialproduct resulting in a material
with very good dimensionalwith very good dimensional
stability.stability.
High force when removing fromHigh force when removing from
mouth.mouth.
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!

 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)

•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%
activator paste: lead-dioxideactivator paste: lead-dioxide 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
Polysulphide elastomersPolysulphide elastomers

do not adhere to impression traydo not adhere to impression tray-adhesives:rubber solution in-adhesives:rubber solution in
acetoneacetone
lead dioxide may have toxic effect-alternative oxidizing systemslead dioxide may have toxic effect-alternative oxidizing systems
ttypes:ypes: heavy bodiedheavy bodied
regularregular
light bodiedlight bodied
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

 These are now relatively unpopular materials. The
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).
They are also messy to handle and have an
objectionable odour.
 Dies resulting from polysulphide impressions are
generally wider and shorter than the tooth preparation.
This distortion, which worsens the longer the delay in
pouring up, 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

 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 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

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