There are many impression materials used in prosthetic
dentistry and there are many different techniques employed to
obtain a true replica of the teeth and mucosa
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
2
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
1. Non toxic and non irritant
2. Acceptability to the patient:
3. Accuracy:
4. Use of material:
5. Compatible with
model materials
6. Economics of material
3
(a)Setting time,
(b)Taste,
(c)Consistency
(a) Surface reproducibility
(b) Dimensional stability
(a) Ease of mixing
(b) Working time
(c) Setting time
(d) Handling of the material (a) Cheap
(b) Long shelf life
(c) Accuracy (save redoing impression)
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
Mucodisplacive : compound, high viscosity alginates, high
viscosity elastomers - these record an impression of the mucosa
under load.
This results in a wider distribution of load during function, making
it more stable it also compensates for the differing
compressibility of the denture bearing area reducing the risk of a
fracture due to flexion.
4
The retention of the dentures may be
compromised as the soft tissues wish to
return to their original position at rest.
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
Mucostatic : plaster, zinc oxide eugenol, low viscosity
alginates – since they are more fluid displace the tissues less.
These essentially record an impression of the undisplaced
mucosa. This results in better retention of the denture because
of closer adaptation to the mucosa at rest.
5
Instability of the denture may occur during
function as the tissues distort
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
6
Non-elastic impression materials
Impression compound
Impression Plaster
Zinc Oxide Eugenol
Impression Waxes
Elastic impression materials
Hydrocolloids
Agars
Alginates
Elastomers
Polysulphides
Silicones
Polyethers
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
7
These materials are rigid and
therefore exhibit little or no elasticity.
Any significant deformation
produces a permanent deformation.
Used where there are no undercuts
and are mainly used for edentulous
patient cases.
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
8
Characteristics
• Thermoplastic
• Poor surface detail
• High coefficient of
thermal expansion
(contraction of up to
0.3%)
• Distorts wen removed
over undercut areas
• Mucocodisplacive
• Poor dimensional
stability
• Can be modified by re-
heating
• Non toxic and non irritant
• Good shelf life
Advantages
• Non irritant and non toxic
• Reusable (but with re-
use the constituents are
leached out)
• Can be reheated and
readapted
• Can support other
materials for wash
impressions
• Mucocompressive
Disadvantages
• Poor dimensional
stability
• Poor surface detail
• Expansion coefficient
• Will distort if removed
from undercuts
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
9
Characteristics
• Excellent at recording
fine detail
• Dimensionally stable if
anti expansion solution
used
• Fractures if undercuts
present
• Mucostatic
• Needs to be treated with
a separating medium
before being cast in
stone or plaster
• Exothermic reaction
• 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
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
10
Characteristics
• Used for recording
edentulous ridges in a
close fitting special tray
or the patients existing
dentures
• Non toxic
• Adherence to tissues
• Mucostatic or
mucocodisplacive
• Good surface detail in
thin section
• Good dimensional
stability
• Can be added to with
fresh zinc oxide eugenol
• Stable on storage and
good shelf life
Advantages
• Dimensional stability
• Good surface detail
• Can be added to
• Mucostatic or
mucocodisplacive
Disadvantages
• Cannot be used in very
deep undercuts
• Only sets quickly in thin
section
• Eugenol allergy in some
patients
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
11
Not commonly used thermoplastic materials, which flow at
mouth temperature and are soft a room temperature.
Normally used to correct small imperfection (e.g. airblows) in
other impressions, especial zinc oxide impressions.
Combination of a low melting paraffin wax and beeswax in a
ratio of approximately 3:1 to ensure the wax flows at room
temperature.
A cast should be poured up immediately after taking the
impression to avoid distortion which readily occurs in wax.
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
12
Can be stretched and bent to a fairly
large degree without suffering any
deformation.
Used for recording the patient's mouth
where undercuts are present.
Usually used for partial dentures,
overdentures, implants and crown and
bridge work.
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
13
Relatively fluid materials when
the solute particles present are
dispersed throughout the liquid.
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.
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
14
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.
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
15
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.
Hydrocolloid materials especially the alginates, may
display a lack of incompatibility with some makes of dental
stones. The resultant model may show reduced surface
hardness and possibly surface irregularities and
roughness.
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
16
Characteristics
• Good surface detail –
can be used for crowns
and bridges
• Can be used on
undercuts, but liable to
tear on deep undercuts
• Evaporation or imbibition
• Non toxic and non irritant
• Slow setting time
• Poor tear resistance
• Adequate shelf life
• Can be sterilised by an
aqueous solution of
hypochlorite.
Advantages
• Good surface detail
• Reusable and easily
sterilised
Disadvantages
• Need special equipment
(water bath) and special
technique
• Dimensional instability
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
17
Characteristics
• Good surface detail –
used for study models
and for removable partial
dentures
• 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
Advantages
• Non toxic and non irritant
• Good surface detail
• Ease of use and mix
• Cheap and good shelf
life
• Setting time can be
controlled with
temperature of water
used
Disadvantages
• Poor dimensional
stability
• Incompatibility with some
dental stones
• Setting time very
dependent on operator
handling
• Messy to work with
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
18
On mixing the powder with water a sol is formed, a chemical
reaction takes place and a gel is formed. The powder contains
1. Alginate salt (e.g. sodium alginate)
2. Calcium salt (e.g. calcium sulphate)
3. Trisodium phosphate
SODIUM
ALGINATE
SODIUM
SULPHATE
+ +
CALCIUM
SULPHATE
CALCIUM
ALGINATE
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
19
Clinical considerations: Powder and water should be measured to manufactures
instructions.
Water at room temperature should be used, this gives a
reasonable working time of a couple of minutes. Faster or slower
setting times can be achieved by using warm or cold water
respectively.
The material nearer the tissues sets first
Retention is needed to the impression tray and is provided by
perforations in the tray and/or adhesives.
Once removed, it should be covered in a damp gauze/napkin to
prevent syneresis (not placed in water which would cause
imbibition-expansion).
The impression should be soaked in hypochlorite for 60 seconds
and then cast as soon as possible.
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
20
Used where a high degree of accuracy is needed,
especially in crown and bridge work.
Two main advantages over the Hydrocolloids - good
tear resistance and dimensional stability.
Hydrophobic rubber based 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.
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
21
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 in its original impression.
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
22
Characteristics
• Used for complete
denture, crown and
bridge work mainly, but
also used for partial
dentures, overdentures
and implants
• Dimensional stability
• Excellent surface detail
• Varying viscosity
• Very small setting
contraction
• Contraction on cooling
from mouth to room
temperature
• Very good tear
resistance
• 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
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
23
Characteristics
• Used for crown, bridge
and bite registration
• Hydrophillic
• 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 (short
working time)
• Stiff set material
(sometimes hard to
remove from mouth)
• Bad taste
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
24
Two kinds, depending on the chemical reaction: Addition Silicones
Excellent dimensional stability
Cannot be manipulated with latex gloves
The cast can be done up to a week after the impression
Condensation Silicones Releases ethanol molecules upon setting
Contraction after ethanol's evaporation
Inlays, partial fixed prosthesis
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
25
Characteristics
• Used for complete
dentures, crown and
bridge work mainly, but
also for partial dentures,
implants and
overdenture
• Hydrophobic
• Ethenol release
• 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
• Ethenol release
• Liquid component of
paste/liquid system may
cause irritation
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
26
Characteristics
• Used for crown and
bridge, denture, bite
registration
• Good shelf life
• Dimensionally stable
• Moderate tear strength
• Excellent surface detail
• No gas evolution
• Non toxic and non irritant
Advantages
• Accurate
• Ease of use
• Fast setting
• Wide range of viscosities
Disadvantages
• Hard to mix
• Sometimes difficult to
remove the impression
from the mouth
• Cannot be manipulated
with latex gloves (may
prevent setting)
• Hidrogen release
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
27
Impression Material Usage by General Dentists
Crown & Bridge
–addition silicone 81%
–alginate 38%
–polyether 28%
Inlays and Onlays
–addition silicone 71%
–polyether 22%
–alginate 20%
DPR 2001
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
28
Impression Material Usage by General Dentists
Complete dentures
–alginate 58%
–addition silicone 55%
–polyether 27%
Partial dentures
–alginate 78%
–addition silicone 43%
–polyether 15%
DPR 2002
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
29
Handling Properties
Agar Alginate Polysulfide Condensation
Silicone
Addition
Silicone Polyether
Preparation Boil, temper,
store Powder, water 2 pastes
2 pastes or
paste/liquid 2 pastes 2 pastes
Ease of use Technique
sensitive Good Fair Fair Excellent Good
Patient
Reaction Thermal Shock Pleasant, clean
Unpleasant,
stains Pleasant, clean Pleasant
Unpleasant
clean
Ease of
Removal Very easy Very easy Easy Moderate Moderate
Moderate to
difficult
Disinfection Poor Poor Fair Fair Excellent Fair
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
30
Handling Properties
Agar Alginate Polysulfide Condensation
Silicone
Addition
Silicone Polyether
Working
Time (min) 7 – 15 2.5 5 – 7 3 2 –4.5 2.5
Setting
Time
(min)
5 3.5 8 – 12 6 – 8 3 – 7 4.5
Stability 1 hour Immediate pour 1 hour Immediate pour 1 week 1 week kept dry
Wettability
and
castability
Excellent Excellent Fair Fair Fair to good Good
Cost Low Very low Low Moderate High to very
high Very high
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
31
Comparison of proprieties
Working time
–longest to shortest
agar > polysulfide > silicones > alginate = polyether
Setting time
–shortest to longest
alginate < polyether < agar < silicones < polysulfide
Stiffness
–most to least
polyether > addition silicone > condensation silicone > polysulfide = hydrocolloids
Tear strength
–greatest to least
polysulfide > addition silicone > polyether > condensation silicone >> hydrocolloids
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
32
Comparison of proprieties
Cost
–lowest to highest
alginate < agar = polysulfide <condensation silicone < addition silicone < polyether
Dimensional stability
–best to worst
addition silicone > polyether > polysulfide > condensation silicone > hydrocolloid
Wettability
–best to worst
hydrocolloids > polyether > hydrophilic addition silicone > polysulfide > hydrophobic
addition silicone = condensation silicone
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
33
Materials for Study Models
Alginate most widely used
•inexpensive
•displaces moisture
•lower detail reproduction
•dimensionally unstable
Materials for Prosthodontics
Addition silicones most popular
•accurate
•dimensionally stable
•user friendly
•expensive
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References
• Phillips’ Science of Dental Materials, edited by K Anusavice, 11th ed., 2008,
Saunders Publishing.
• Dental Materials and their Selection, edited by WJ O’Brien, 4th ed., 2008,
Quintessence Publishing.
• Dental Products Report, 2001, 2002, 2005.
• CW Caswell, AS von Gonten, and TR Meng, Volumetric proportioning techniques for
irreversible hydrocolloids: a comparative study, J Am Dent Assoc 1986 112:859-861.
• MN Mandikos, Polyvinyl Siloxane Impression Materials: An Update on Clinical Use,
Australian Dental Journal, Dec 1998, 43(5): 428-434.
• RG Craig, Review of Impression Materials, Advance in Dental Research, Aug 1988,
2,51-64.
Introduction
Properties
Mucostatic vs
Mucodisplasive
Classification
Non-elastic
Elastic
Summary
References