Impression Materials (Dental)

Impression Materials
Dr. Md. Arifur Rahman
Assistant Professor & Head
Dental Unit
Northeast Medical College, Sylhet
E-mail: arahman@neub.edu.bd
1

Impression Materials
 Impression : It is the negative imprints of the
natural teeth & their supporting tissue.
2Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC

Types of Impression
A . Full mouth or full arch impression.
1. For edentulous arch : a. Upper & Lower.b. Primary or
initial. c. Secondary or final.
2. For dentulous arch : a. Upper. b. Lower.
B. copper band or matrix band impression: It is used to
take impression of a single tooth.
C. Impression of a quadrant of the mouth (Sectional
impression)
D. Wash impression: It is done in the case of edentulous
patient after taking primary impression. It can records
more appropriate
3
Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC

Impression Tray
The metallic or plastic carrier, which
are use to take impression of natural
teeth & their supporting oral tissues
by the impression materials, are
known as Impression Tray.
4

Types of Impression Tray :
 1. Stock Tray:
a. Full tray : 1. Upper or lower. 2. metallic or nonmetallic. 3.
Plane or perforated. 4. Rim lock. 5. Small, medium & large. 6.
Special double chamber perforated with cooling arrangement.
7. Disposable.
b. Half tray: 1. Upper or lower. 2 Metallic or non metallic. 3.
Plane or perforated. 4. Disposable.
c. Sectional tray: 1. Upper or lower. 2. Metallic or nonmetallic.
3. Plane or perforated. 4. Rim lock. 5. Disposable.
 2. Individual or close fitting or Special tray or custom built
tray or hand made tray : a. Upper or lower . b. Dental
plastic. C Base plate. D. Impression compound. E. Plane or
perforated. F. Disposable.
 3. Copper band or matrix band tray: This tray is for taking
the impression of a single tooth. 5

Impression materials
The materials which are used to take impression of
natural teeth and their supporting tissue they are
called as Impression materials.
 Classification of impression materials:
According to the elasticity of the materials.
1 Non elastic : a. Rigid impression materials.
Example- Plaster of Paris.
b. Plastic impression materials:
i. Thermoplastic impression materials. Example-
Compo, Wax, Gutta-percha.
ii. Paste impression materials. Example-ZOEpaste
im.
6

Classification of impression
materials:(Cont..)
 2. Elastic : A. Hydrocolloid :
1. Reversible hydrocolloid (agar).
2. Irreversible hydrocolloid (alginate).
B. Elastomer: a. Polysulphide. b. Silicones
(1.Condensation Silicone. 2. Addition silicone.).
c. Polyether.
 According to the mode of setting (hardening)
 Set by chemical setting. Example:- Alginate, Elastomers.
 Set by physical setting. Example:- Agar, Wax, Compo.7

Ideal Properties of Impression
Materials
1. It should be nontoxic & non irritant.
2. It should be elastic in nature.
3. It should have good flow.
4. Manipulation should be easy.
5. It should be dimensionally stable after
setting.
6. It should be cheap and available.
7. Setting should be less than 5 minutes.
8. Its shelf life should be good.

8 Ideal requirements of
 (1) They should be fluid enough to adapt to oral
tissues;
 (2) They should be viscous enough to be contained in
the tray that is seated in the mouth;
 (3) While in the mouth, they should transform (set)
into a rubbery or rigid solid in reasonable amount of
time. Ideally the total setting time should be less than 7
minutes;
 (4) The set impression should not distort or tear when
removed from the mouth.
9

8 Ideal requirements of
 (5) The impressions made from these materials should
remain dimensionally stable at least until the cast can be
poured.
 (6) The impression should maintain its dimensional
stability after removal of a cast so that a second or third
cast can be made from the same impression;
 (7) The materials should be bio-compatible; and
 (8) The materials, associated processing equipment and
processing time should be cost-effective.
10

Thermoplastic impression materials
These are those materials which are
when heated become soft and plastic
again on cooling they become hard.
Compo, Wax, Gutta-percha and zinc
oxide eugenol paste these are the most
commonly used thermoplastic impression
materials
11

Properties
 They are thermoplastic in nature.
 It can use again and again.
 It is not hygienic.
 It is cheap and available .
 It does not have sufficient flow and may cause
internal compression.
12

Internal compression
If we use thermoplastic / non elastic
impression materials for taking impression , it
has a limited flow. To make the materials flow
we have to give an extra amount of pressure,
which will compress the oral mucous
membrane and it will set in this compress
position. After preparation of model followed
by any appliance, during supply the appliance
will give same amount of constant pressure to
the patient. This unwanted extra amount of
pressure is known as Internal Compression.

Impression compound
It is a non elastic type of
thermoplastic impression materials.
Which has a limited uses in dentistry
now a days. It is only used to take
primary impression of edentulous
patient.
14

Composition of impression compound
 Stearic acid -20 P/W ( It gives the plasticity and flow
to the compo) ,
 Oleic acid-4 P/W ( It gives also plasticity and flow to
the compo) ,
 Gum copal-19 P/W ( It gives the bulk to the compo it
also increase the hardness),
 Kauri resin-17 P/W ( It gives hardness to the compo)
 Powder soapstone or French Chalk -40 P/W ( It
gives hardness plasticity and hardness).
15

Properties of Impression
compound
 They are thermoplastic in nature.
Advantages:
1. Can be reused, easy to use
2. Non-irritant and non-toxic
3.It is cheap and available .
Disadvantages
1. Poor dimensional stability
2. Easy to distort when withdrawn from the mouth
3. It don’t have sufficient flow and may cause internal
compression.
16

Impression compound (Cont..)
 Types of compo : According to the fusing temperature
compo are of three types:
 (1) Low fusing (Type-I) : The compo which become soft at 55-
60C they are called low fusing compo. Uses: (a) To take primary
impression of edentulous patient. (b) For making occlusal rim.
(c) Making tampoon.
 (2) High fusing (Type-II) : The compo which become soft at
above 70C they are called high fusing compo. Uses: (a) Taking
im for partial dentures with moderate undercuts. (b) For making
special tray.
 (3) Medium fusing (Type-III) : The compo which become
soft at 60-70C they are called medium fusing compo. Uses: (a)
To take primary impression of edentulous patient. (b) For
making special tray. (c) Taking im for partial dentures with
moderate undercuts 17

Impression compound (Cont..)
 According to the supplied form compo are of three
types:
 Sheet Form : Uses: (1) To take primary impression of
edentulous patient. (2) Tampon can be made for arrest of
bleeding. (3) For making occlusal rim.(4) For making special tray.
 Stick form : Uses: (1) It is used as a copper band impression
materials.(2) Used for marginal addition of special tray, primary
im.(3) To build up the post dam area. (4) Checked the undercut
areas in the cavity.
 Cone form: Uses: (1) Checked the undercut areas in the cavity
(2) It is used as a copper band impression materials.
(3) To build up the post dam area.
18

disadvantages of compound impression
material while it is in the mouth
1. Its specific heat is low. So, it takes more time to
harden.
2. The impression because of gravity may fall
down.
3. It is viscid and it may not evenly flow all over
the tissues and tooth surface. So, fine details
may not be recorded.
19

Clinician’s responsibility:
 1. The clinicians should hold impression tightly
with tissues and tooth surface. The impression
should be chilled with cool water inside mouth
until it hardens.
 2. The impression should be kept outside the
mouth in the room temperature. As the
dimensional stability of compo is less die/
model should be made as soon as possible after
removal from mouth.
20

 3. The compound has dimensional change. It has
linear contraction of 1.5% when it is cooled from
its mouth temperature to room temperature. So,
the compound should be uniform and low
thickness to reduce the contraction.
21

Hydrocolloid Impression
Materials
 Hydro means water.
 Colloid means gelatin substance.
 Material used to obtain preliminary and
final impressions.
22

Irreversible Hydrocolloid
 Material that cannot return to a
solution state after it becomes a gel.
 Alginate is the irreversible
hydrocolloid most widely used for
preliminary impressions.
23

Makeup of Alginate
 Potassium alginate (15% by wt)
 Comes from seaweed; is also used in foods such
as ice cream as a thickening agent. It soluble
alginate
 Calcium sulfate (16% by wt)
 Reacts with the potassium alginate to form the
gel.
 Sodium phosphate (2% by wt)
 Added to slow down the reaction time for
mixing.
24

 Diatomaceous earth (60% by wt)
 A filler that adds bulk to the material.
 Zinc oxide (4% by wt)
 Filler particles. Adds bulk to the material.
 Potassium titanium fluoride 3%
 Accelerator. Added so as not to interfere with the
setting and surface strength.
Makeup of Alginate- cont’d
25

Physical Phases of Alginate
 The first phase is a sol (as in solution). In the
sol phase, the material is in a liquid or
semiliquid form.
 The second phase is a gel. In the gel phase,
the material is semisolid, similar to a gelatin
dessert.
26

Packaging and Storing of Alginate
 Containers about the size of a coffee can are
the most commonly used form of packaging.
 Premeasured packages are more expensive,
but save time by eliminating the need for
measurement of the powder.
 Shelf life of alginate is approximately 1 year.
27

Fig. 46-7 Examples of packaging for alginate.
28

Advantages of Alginate
1. It is cheap and easily available
2. It is easy to mix and manipulate
3. Elaborate arrangement does not require
4. It is sufficiently elastic and impression of
moderate undercut area can be take.
5. Comfortable to the patient
6. It is hygienic
7. It gives good surface details
29

Disadvantages of Alginate
1. It can not be corrected if there is inaccuracy of the
impression
2. It is elastic but not so adhesive. So, it should be held
tightly against the tissue surface until it sets
3. On storage after impression it loses its dimension (it
suffers from syneresis and imbibition).
4. Poor tear strength .
30

Causes for Distortion and Dimensional
Change of Alginate
 If an alginate impression is stored in water or in
a very wet paper towel, the alginate will absorb
additional water and expand. This condition is
called imbibitions.
 If an alginate impression remains in the open
air, moisture will evaporate from the material,
causing it to shrink and distort. This condition
is called syneresis.
31

Alginate Settings
 Normal set alginate
 Working time of 2 minutes and a setting time of up
to 41/2 minutes after mixing.
 Fast set alginate
 Working time of 11/4 minutes and a setting time of 1
to 2 minutes.
 Working time
 The time allowed for mixing the alginate, loading the
tray, and positioning the tray in the patient's mouth.
 Setting time
 The time required for the chemical action to be
completed.
32

Altering the Setting Times of
Alginate
 Cooler water can increase the setting time if
additional time is needed for the procedure.
 Warmer water can reduce or shorten the
setting time of the procedure.
33

Water-to-Powder Ratio
 An adult mandibular impression generally
requires two scoops of powder and two
measures of water.
 An adult maxillary impression generally
requires three scoops of powder and three
measures of water.
34

Fig. 46-8 Scoop and water measure for alginate.
35

Taking an Alginate Impression
 Explain the procedure to the patient:
 The material will feel cold, there is no unpleasant
taste, and the material will set quickly.
 Breathe deeply through your nose to help you relax
and be more comfortable.
 Use hand signals to communicate any discomfort.
36

An Acceptable Alginate Impression
 The impression tray is centered over the central and
lateral incisors.
 There is a complete "peripheral roll," which includes all of
the vestibular areas.
 The tray is not "overseated," which would result in
exposure of areas of the impression tray.
 The impression is free from tears or voids.
 There is sharp anatomic detail of all teeth and soft tissues.
 The retromolar area, lingual frenum, tongue space, and
mylohyoid ridge are reproduced in the mandibular
impression.
 The hard palate and tuberosities are recorded in the
maxillary impression.
37

Fig. 46-12 An alginate impression.
38

composition of zinc oxide eugenol paste
Components Percentage
Tube No. 1 (Base)
Zinc oxide 87
Fixed vegetable or mineral oil 13
Tube No. 2 (Accelerator)
Oil of cloves or eugenol 12
Gum or polymerized rosin 50
Filler(silica type) 20
Lanolin 03
Resinous balsam 10
Accelerator solution (CaCl2) and colour 05

Role of different ingradient
1. The vegetables or mineral oil acts as a plasticizer that
aids in reducing irritating effect eugenol.
2. Oil of cloves: Use in preference to eugenol because it
produces less burning sensation for patients when it comes
in contact with soft tissues.
3. Rosin: It facilitates the speed of reaction and yields a
smoother, more homogenous product.
5. Filler (wax) or an inert powder (such as kaolin, talc or
diatomaceous earth). They are added to provide strength
and smoothness.
40

Give the composition agar and its
effects
Agar Brush-sheap structure 13-17
Borate Strength 0.2-0.
Sulfate Gypsum hardener 1.0-2.
Wax, hard Filler 0.5-1.0
Thixotropic
materials Thickener 0.3-0.5
Water Reaction medium Balance
41

Role of different ingredients
Agar : is an organic hydrophilic colloid extracted from
certain types of seaweed.
Water : It is the principle ingredient.
Borax : Borax in small percentage. It strengthens the gel.
Potassium sulfate : Acts as an accelerator. It is added to
counter act the retarding effect of borax.
Diatomaceous earth, clay, silica, wax, rubber and similar
inert powder acts as filler to control strength, viscosity and
rigidity.
Thymol and glycerine : These are added to act as a
bacteriocidal agent and plasticizer.
Pigment and flavor are also included.

Properties of Agar
•Accuracy: Fine detail of the tissues and prepared tooth can be
recorded.
•Impression of the undercut areas can be taken.
•It also suffers from shrinkage and imbibitions
•Compatible with stone because of the presence of counter part of
Borax (K2SO4)
•Non-toxic, non-irritant
•Can be re-used
•Can be sterilized
•Manipulation is not so easy
•Best material for duplication of the model
•Cheap

Differentiate reversible and
irreversible hydrocolloids.
44

Differentiate reversible and
irreversible hydrocolloids. (con.)
45

Elastomers
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.

Elastomers
Silicone
Condensation Addition
Polysulphide Polyether

Polysulphides
Used for crown and bridge work mainly, but also used for
partial dentures, and implants. Two equal lengths are mixed
together with a spatula for about a minute. The tray needs to
be treated with an adhesive (rubber solution in acetone) to
provide retention for the polysulphide. Taking the
impression is delayed by 5 minutes before the impression is
placed in the patients mouth - the final setting time is usually
about 10 minutes from the start of mixing - this delay
therefore decreases the amount of time the impression tray
is in the patients mouth. A one or two stage impression
technique may be used. Although dimensionally stable, the
impression should be cast within 24 hours.

Composition
Supplied as two pastes mixed in a 1:1 ratio.
BASE PASTE
Polysulphide (forms rubber on polymerization)
Filler (to give body)
Plasticizer (control viscosity)
ACTIVATOR PASTE
Inert oil (forms a paste)
Sulphur (facilitates the reaction)
Lead oxide (causes polymerization and cross-linking)

PROPERTIES of Polysulphides
 Dimensionally stable.
 Excellent surface detail
 Viscosity depends on the brand used
 Very small setting contraction (0.3-0.4% over
the first 24 hrs)
 Very good tear resistance
 Good shelf life
50

Polysulphide
ADVANTAGES
 Dimensional stable.
 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.

Polyether
Supplied in two pastes
BASE PASTE
Polyether
Filler
CATALYST PASTE
Sulphonic acid ester (enhances further polymerization and
crosslinking) ,
Inert oils (forms a paste)
When mixed the polymer and sulphonic acid ester react to
form a stiff polether rubber. Setting time occurs in
about 6 minutes.

PROPERTIES
of Polyether
 Hydrophilic (i.e. absorbs water)
 Good shelf life of up to 2 years
 Good elastic recovery
 Non toxic
 Low setting contraction
 Poor tear strength
 Good dimensional stability
53

Polyether
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)

Condensation Silicones
CLINICALLY Used for crown and bridge work
mainly, but also for partial dentures, implants
and over dentures. Used in stock trays or special
trays. One or two stage impression stage.
Although dimensionally stable the impression
should be cast within 24 hours.
55

Supplied as a paste and liquid or two pastes, in light,
medium, heavy or very heavy bodied (putty).
BASE PASTE
Silicone polymer with terminal hydroxy groups
Filler
CATALYST PASTE
Crosslinking agent (organohydrogen siloxane)
Activator (dibutyl-tin dilaurate)
On mixing the two pastes react, cross linking occurs and
setting takes about 7 minutes.
56
Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC

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

Addition Silicones
CHEMISTRY
Supplied in 2 pastes or in a gun and cartridge form as
light, medium, heavy and very heavy bodied.
One paste contains a poly dimethyl siloxane polymer in
which some methyl groups are replaced by hydrogen.
The other paste contains a pre-polymer in which some
methyl groups are replaced by vinyl groups, this paste
also contains a Chloroplatinic acid catalyst.
On mixing, in equal proportions, cross linking occurs
to form a silicone rubber. Setting occurs in about 6-8
minutes.

Addition Silicones
PROPERTIES
 Good shelf life
 Dimensionally stable
 Moderate tear strength
 No gas evolution
 Non toxic and non irritant
59

Addition Silicones
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
60

Thank you

Impression Materials (Dental)

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