Impression materials /certified fixed orthodontic courses by Indian dental academy

IMPRESSION
MATERIALS
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

Contents
• Introduction
• History
• Definition and classifications
• Ideal requirements
• Impression materials and techniques
- Elastomeric materials
- Hydrocolloids
- Inelastic or rigid
• Latest advances
• Conclusions
• Referenceswww.indiandentalacademy.com

History:
• 18th
and 19th
century bees wax.
• 1782 William Rae – used wax with POP.
• 1842 Montgomery discovered GP.
• 1848 Colburn and Black-GP impression.
• 1925-28 Development of Hydrocolloids.
• 1930 – A W Ward and E B Kelly introduced ZOE
• 1936-40 Alginate by S.William Wilding.
• 1950 introduction of elastomers.
• 1960 Introduction of polyether in Germany.
• 1988 Latest addition and light cured elastomers.
• 1990-2000 New auto devices and delivery systems.
• Research continues….

DEFINITIONwww.indiandentalacademy.com

“An impression is essentially a negative or reverse
replica of any entity. In dentistry, this replica is of the
teeth and its supporting and surrounding structures.”

1. By generic chemical name: Silicone material or ZOE or
commercial brand names.
2. By the manner in which they harden or set
Chemical / irreversible Temp / reversible
• Plaster of Paris
• ZOE
• Alginate
• Elastomers
Thermoplastic Non-thermoplastic
• Impression
compound
• Wax
Agar

3. According to the ability of the set material to be
withdraw over undercuts :Elastic
impression materials
Non-elastic or Rigid
impression materials
 Agar
 Alginate
 Impression compound
 ZOE
Hydrocolloid Rubbers
 Polysulfide.
 Poly
silicones.
 Polyether.

4. According to the use of the materials in dentistry
A) Materials used for obtaining impression of dentulous
mouth

Alginate

Agar

Non-aqueous Elastomers
B) Materials used for obtaining Impression of edentulous
mouth:
• Impression Compound
• Impression Plaster
• Zinc Oxide eugenol
• Wax

MucocompressiveMucostatic
5. According to the viscosity or tissue displacement:
- Impression plaster - Impression
- Agar Compound
- Alginate - Putty elastomers

Ideal Requirements of DentalIdeal Requirements of Dental
Impression MaterialsImpression Materials

1. Pleasant taste, odor and esthetic colour
2. Not contain any toxic or irritating ingredients
3. Have adequate shelf life for storage and distribution
4. Be economical
5. Be easy to use with the minimum equipments
6. Have adequate strength so that it will not break or tear
while removing from the mouth

7. Exhibit dimensional stability
8. Faithfully reproduce the tissues of mouth
9. Be able to be electroplated
10. Accuracy and faithful reproduction of details
11. Readily disinfected
12. No release of gas during setting of impression or
cast and die materials

Elastomers
or
Rubber base Impression materials

• Soft and rubber-like & are known as
elastomers or synthetic rubbers.
• As per ADA Sp. No. 19 - non-aqueous
elastomeric dental impression materials.
• Liquid polymers which are converted into
solid rubber at room temperature

Types:
I. According to chemistry
1) Polysulfides
2) Polysilicones – condensation & addition
3) Polyether
II. According to Viscosity
1) Light body or syringe consistency
2) Medium or regular body
3) Heavy body or tray consistency
4) Very heavy body or putty consistency
III. ADA Classification
Based on selected elastic properties & dimensional changes
1) Type I
2) Type II
3) Type III www.indiandentalacademy.com

General Properties:
 Excellent reproduction of surface details
 Generally hydrophobic (except poly ether)
 Good elastic properties (repeated pouring is possible)
 Dimensional inaccuracies are lower but exist due to
various reasons
 Excellent tear strength.
 Electroplatable
 Extended shelf-life
 Generally higher cost
 Requires tray adhesive or mechanical interlockingwww.indiandentalacademy.com

Uses:
1. Impression material for all applications including
- Fixed partial dentures
- Dentures and edentulous impressions
2. Border moulding of special trays (poly ether)
3. Bite registration
4. As duplicating material for refractory casts
• All elastomers - two paste systems (base & catalyst)
• Putty consistency – supplied in jars
Supplied as:

POLY SULFIDES:
Ist
elastomer to be introduced
mercaptan/Thiokol

Composition:
Base Paste:
Liquid Polysulfide Polymer - 80 to 85 %
Inert fillers
(Titanium dioxide, zinc sulfate - 16 to 18 %
copper carbonate or silica)
Reactor Paste
Lead dioxide - 60 to 68 %
Dibutyl phthalate - 30 to 35 %
Sulfur - 3 %
Other substances like Magnesium
stearate (retarder) & deodorants - 2 %

Available as 2 systems - Base and accelerator
3 viscosities - light, medium and heavy bodies.
Tray adhesive:
Butyl rubber or styrene/acrylonitrile dissolved in a volatile
solvent such as chloroform or a ketone.

Chemistry and Setting Reactions
The lead dioxide reacts with the poly sulfide polymer
 Chain lengthening by oxidation of the terminal -SH groups
 Cross-linking by oxidation of the pendant -SH groups
Exothermic reaction - 3 to 40
C rise in temp.
It is accelerated by heat and moisture
PbO2 + S
HS - R- SH HS - R-S-S-R-SH + H2O
Mercaptan + Lead dioxide Poly sulfide + Water
T-butyl hydro peroxide – alternative to PbO2www.indiandentalacademy.com

1. Unpleasant odor and colour - stains linen & messy to work with
2. Extremely viscous and sticky - mixing is difficult
3. Mixing time is 45 seconds
4. Long setting time of 12.5 (at 370
C) - Patient discomfort
5. Excellent reproduction of surface detail
6. Dimensional stability:
- Curing shrinkage is high 0.45%.
- It has the highest permanent deformation (3 to 5%)
among the elastomers
7. It is hydrophobic - so the mouth should be dried thoroughly before making an
impression
8. It can be electroplated (with silver than copper)
9. The shelf life is good (2 years)
Properties:

Silicone Rubber
Impression Material:
Developed to over come some of the
disadvantages of poly sulfide

Based on the type of polymerization reaction
1) Condensation silicones
2) Addition silicones
Types

• Also known as conventional silicone.
• Available in light, medium and putty consistency
CONDENSATION SILICONE:
Base Accelerators
Polydimethyl siloxane
(hydroxy-terminated)
Orthoethyl silicate – cross
linking agent
Colloidal silica or microsized
metal oxide (filler) 35-75%
Stannous octoate - catalyst
Color pigments
COMPOSITION:

CH3 OC2H5
Sn
OH-Si-OH + C2H5O-Si- OC2H5 Silicone + CH3CH2OH
octoate
CH3 OC2H5
Dimethyl + orthoethyl Silicone + ethyl
siloxane silicate rubber alcohol
 Ethyl alcohol - byproduct - evaporate - shrinkage &
dimensional instability
 Tray adhesive – Polydimethyl siloxane & Ethyl silicate
SETTING REACTION:

Properties:
• Pleasant odor and color.
• Mixing time of 45sec & setting time of 8-9mins.
• Excellent reproduction of surface details and highly elastic.
• Lesser dimensional stability
- high curing shrinkage (0.4 - 0.6%)
- permanent deformation due to shrinkage caused by the
evaporation of ethyl alcohol is also high (1-3%).
• Hydrophobic - needs a dry field.
• Electroplatable (silver / copper) and has adequate shelf life.
• Biologically inert.
• Compatible with all gypsum products.www.indiandentalacademy.com

Addition silicones:
Also called as polyvinyl siloxanes
Better properties than condensation silicones.

Base:
Poly (methyl hydrogen siloxane)
Other siloxane prepolymers
Fillers
Accelerator:
Divinyl poly siloxane
Other siloxane pre polymers
Platinum salt: Catalyst (chloroplatinic acid)
Palladium (Hydrogen absorber)
Retarders
Fillers
Composition:

CH3 CH3 CH3 CH3
Pt salt
Si-H + CH2=CH-Si Si-CH2-CH2-Si
activator
CH3 CH3 CH3 CH3
Vinyl + Silane Silicone
siloxane siloxane rubber
SETTING REACTION:
• No by product, but imbalance  hydrogen gas  air bubbles in
the stone models
• To avoid this palladium is added.

CLINICAL SIGNIFICANCE:
Sulfur compounds retard the setting of silicones
One source of sulfur contamination is from latex gloves
Vinyl gloves should be used

Properties:
• Pleasant odor and color
• Excellent reproduction of surface details
• Mixing time of 45 secs ,setting time of 5-9 mins.
• Best dimensional stability
- low curing shrinkage (0.17 %)
- lowest permanent deformation (0.05 – 0.3 %)
• Stone pouring delayed by 1-2 hours
• Extremely hydrophobic, some manufacturers add a surfactant
(detergent) to make it more hydrophilic
• Can be electroplated with silver and copper
• Good shelf life of 1-2 yrs
• Good tear strength (3000gm / cm2
)www.indiandentalacademy.com

Poly ether Rubber
Impression material
• Introduced in Germany in late 1960’s
• Good mechanical properties and dimensional stability, but
short working time, very stiff material and expensive

Composition:
Base Paste
Poly ether polymer
Colloidal silica (filler)
Glycol ether or phthalate (plasticizer)
Accelerator paste
Aromatic sulfonate ester (cross-linking agent)
Colloidal silica (filler)
Phthalate or glycol ether (plasticizer)
Available as 3 viscosities: light, medium & heavy bodied.

CHEMISTRY & SETTING REACTION
H O O H
CH3– C - CH2– C – O – R – O – C - CH2– C - CH +  Crosslinked
rubber
N N
CH2-CH2 CH2-CH2
Polyether + Sulfonic ester  Crosslinked rubber
Exothermic reaction  4-50
C

Properties:
1. Pleasant odor and taste
2. Mixing time is 30 secs, setting time of 8 mins
3. Dimensional stability is very good.
Curing shrinkage is low (0.24%)
The permanent deformation is also low (1-2%).
4. Very stiff (flexibility of 3%), needs extra space,
around 4 mm is given.
4. Hydrophilic (moisture control not critical)
5. Electroplatable with silver & copper
6. Shelf life extends upto 2 years

Property Polysulfide Condesn
. Addn
. Polyether
Working time (min) 4-7 2.5-4 2-4 3
Setting time (min) 7-10 6-8 4-6.5 6
Tear strength (N/m) 2500-7000 2300-2600 1500-4300 1800-4800
By product H2O Ethanol - -
Custom tray YES NO NO NO
Unpleasant odour YES NO NO NO
Multiple casts NO NO YES YES
% contraction (24hr) 0.40 – 0.45 0.38 – 0.60 0.14 – 0.17 0.19 – 0.24
Stiffness (1= > stiff) 3 2 2 1
Distortion (1= > Dist) 1 2 4 3www.indiandentalacademy.com

RECOMMENDED DISINFECTANTS
MATERIAL DISINFECTANTS
Polysulfide Glutaraldehyde, Cl compounds,
Iodophors & Phenolics
Silicones ------ do --------
Polyether Cl compounds or Iodophors
Alginate ------ do --------
ZOE Glutaraldehyde or Iodophors
Impression compound Cl compounds or Iodophors

AUTOMATIC DISPENSING & MIXING DEVICES
ADVANTAGES:
- More uniform mix
- Less air bubbles
- Reduced working time

Different methods of making impressions
1. Single mix or mono-phase technique:
- Regular viscosity elastomer is used (addition silicone/polyether)
- Paste is mixed, part of it is loaded on to the tray & the
remaining onto the syringe
- Syringe material is injected onto the prepared area & tray
material is seated over it.

Multiple
mix
technique
DISADV:
Higher viscosity
material may displace
more fluid wash
material

RELINE OR 2-STAGE PUTTY
WASH TECHNIQUE
• Preliminary impression is made with a putty consistency
using a thin plastic sheet or spacer over it (acts as a spacer)
• Light body is injected around the prepared tooth
• The plastic sheet is removed & putty impression is seated
back

RECENT ADVANCES
IN
ELASTOMERS

Visible light cured impression material:
• Polyether urethane dimethacrylate.
• Introduced in early 1988 by GENESIS and L D
CAULK.
• Two viscosities: Light and heavy.

Composition:
- Polyether urethane dimethacrylate
- Photo initiators
- Photo accelerators
- Silicon dioxide (Filler)
Chemistry: Similar to light cured composites

Properties:
• Long working time and short setting time.
• Blue light is used for curing with transparent
impression trays.
• Tear strength – 6000 to 7500 gm/cm2
(Highest among elastomers)
• Other properties are similar to addition silicone.

Manipulation:
• Both light body and heavy body are cured with
visible light having larger diameter probe.
• Curing time approx 3 min.
Adv: - Controlled working time
- Excellent properties
Disadv: - Special transparent trays
- Difficult to cure in remote area

Hydrocolloids:
• Kola - ‘glue’ and ‘oid’- like, a ‘glue-like’ character.
• Colloids are classified as the fourth state of matter , they
lie between suspension and solutions.
• Characterized by their unique dispersion of particles held
together by primary or secondary forces.
• The size of the particles larger than solutions & range from
1 to 200nm

• The colloidal materials that are dissolved in water are termed
hydrocolloids
• If the change of sol to gel is thermal and reversible –
reversible hydrocolloid (agar)
• If the change of sol to gel is chemical and irreversible -
irreversible hydrocolloid (alginate)
• An important characteristic of gels is the processes of syneresis
and imbibition.
• These both alter the original dimensions of the gel

Reversible Hydrocolloid – AGAR
 Introduced by “Alphous poller of Vienna” in 1925
 Adopted commercially as “Dentacol” in 1928
 It was the first successful elastic impression material
 Agar is an organic hydrophilic colloid extracted from certain
“Seaweed”
 It is a sulphuric ester of a linear polymer of galactose
 Though highly accurate, it has been largely replaced by
alginates and elastomers due to its cumbersome manipulation

ComponentComponent FunctionFunction CompositionComposition
(%)(%)
AgarAgar Brush Heap structureBrush Heap structure 13 – 1713 – 17
BorateBorate StrengthStrength 0.2 – 0.50.2 – 0.5
Pot. SulfatePot. Sulfate Gypsum hardenerGypsum hardener 1.0 – 2.01.0 – 2.0
Wax, ZO, Silica, DM,Wax, ZO, Silica, DM,
etc.etc.
FillerFiller 0.5 – 1.00.5 – 1.0
Thixotropic materialsThixotropic materials ThickenerThickener 0.3 – 0.50.3 – 0.5
WaterWater Reaction mediumReaction medium Balance 84%Balance 84%
AlkylbenzoatesAlkylbenzoates PerservativePerservative 0.10.1
Composition:

The Material is supplied as:
 Gel in collapsible tubes (for impressions)
 A number of cylinders in a glass jar (syringe material)
 In bulk containers (for duplication)
Manipulation:
Agar hydrocolloid requires special equipments
- Hydro colloid conditioner
- Water cooled rim lock trays

Conditioner Consists of:Conditioner Consists of:
a. Boiling or liquefaction section: 10 mins in boiling water (1000
C).
b. Storage section: 65-680
C is ideal it can be stored till needed
c. Tempering section: 460
C for about 2mins

WATER COOLED RIM LOCK TRAYS

FINAL IMPRESSION WITH AGAR

Advantages:
1. Hydrophilic Impression material
2. Good elastic properties, Good recovery from distortion
3. Can be re-used as a duplicating material
4. Long working time and low material cost
5. No mixing technique
6. High accuracy and fine detail recording
Disadvantages:
1. Only one model can be used
2. Extensive and expensive equipment required
3. It can not be electroplated
4. Impossible to sterilize for reuse
5. Low dimensional stability & tear resistancewww.indiandentalacademy.com

Uses of Agar:
1. Widely used at present for cast duplication
2. For full mouth impression without deep undercuts
3. As tissue conditioner
4. Was used for crown & bridge before the advent of elastomers

Laminate technique or agar-alginate
combination technique
• Injecting syringe agar material onto the prepared tooth
• Placing an impression tray with alginate over the
injected syringe agar
Wet field technique
• Area to be recorded is flooded with warm water
• Syringe agar material – quickly & liberally over prepared tooth
• Immediately, tray agar placed over the syringe agar
• Hydraulic pressure www.indiandentalacademy.com

Irreversible HydrocolloidIrreversible Hydrocolloid
oror
AlginateAlginate

• ‘Algin’ - a peculiar mucous extract yielded by Algae (brown
seaweed).
• In England, 40 yrs later, “S. William Wilding” received the
patent for alginate as impression material.
• Alginate was developed as a substitute for agar when it
became scarce due to II world war.
• Currently, alginate is more popular than agar because,
 It is easy to manipulate
 It is comfortable for the Patient
 It is relatively inexpensive and does not require
elaborate equipmentwww.indiandentalacademy.com

Component Function Wt%
Potassium alginate Soluble alginate 15
Calcium sulfate Reactor 16
Zinc oxide Filler particles 4
Potassium Titanium fluoride Accelerator 3
Diatomaceous earth Filler Particles 60
Sodium phosphate Retarder 2
COMPOSITION OF ALGINATE

SETTING REACTION:
Alginic acid is a linear polymer of Anhydro- B-D mannuronic
acid of high molecular weight
Two main reactions occurs during setting:
i) 2 Na3 PO4 + 3 Ca SO4 Ca3 (PO4)2 + 3 Na2 SO4
(Sodium phosphate) (Calcium sulphate)
(Retarder) (Reactor)
ii) Sodium Alginate + Ca SO4 + H2O Ca Alginate + Na2 SO4
(Powder) (Reactor) (Gel)

Types: Type I - Fast Setting
Type II - Normal Setting
Latest advances - Modified Alginates:
1. In the form of a sol, containing the water. A reactor of plaster
of Paris is supplied separately.
2. 2 paste system, one containing the alginate sol, the second the
calcium reactor. These materials are said to contain silicone
and have superior tear resistance.www.indiandentalacademy.com

3. Chromatic alginates: contain acid/base indicator that change
colour at different critical points, indicating mixing time,
loading into mouths & setting.
4. Dustless Alginate:
To avoid dust inhalation - coating the material with a glycol.
5. Siliconised Alginates:
Alginates modified by the incorporation of silicone polymers
which improve the physical properties.www.indiandentalacademy.com

Manipulation: - 15 gm. Powder : 40 ml of water
- figure-of-eight motion, swipe & strop
Control of gelation time:
1. By manufacturers : by adding retarders
2. By Dentist - Cold water : Longer is the geln
. time
- Warm water : Shorter is the geln
. time
Types Mixing time Working time Setting time
I- Fast set 45 sec 1.25 mins 1-2 mins
II- Normal
set
60 sec 2 mins 2 - 4.5 mins

Advantages:
1. Easy to mix and manipulate.
2. Minimum requirement of equipment.
3. Accuracy (if properly handled)
4. Low cost
5. Comfortable to the patient
6. Hygienic (as fresh material is used for each impression)
Disadvantages:
1. Cannot be electroplated.
2. Distortion occurs easily
3. Poor dimensional stability (poured within 15 min.)
4. Poor tear strength

Uses:
1. Complete denture prosthesis & orthodontics
2. Mouth protectors
3. Study models and working casts
4. Duplicating models

COMPARISON BETWEEN HYDROCOLLOIDS
Properties Agar Alginate
Flexibility 20 % 14 %
Elasticity &
elastic recovery
98.8 % 97.3 %
Reprodn
. of
details
25 um < agar
Tear strength 715 gm/cm2
350-700 gm/cm2
Comp. strength 8000 gm/cm2
500-8000 gm/cm2
Diml
. Stability Better Poor
Reuse Possible Not possible
Manipulation Conditioner & rim
lock trays
Normal trays

INELASTIC IMPRESSION
MATERIALS:
- Limited use in operative dentistry.

Impression plaster:
• Type-1 Gypsum: Calcium sulfate dihydrate with
modifiers
• Was used as a final or wash impression in
complete denture.
Impression compound:
• Rigid reversible impression material sets by
temp change.
• Primary impression in edentulous mouth.

Types: ADA specification No. 3
• TYPE – I IMPRESSION COMPOUND
- Primary impression
- individual tooth impression
• TYPE - II TRAY COMPOUND
- Border moulding
- Check undercuts in inlay
- Make a special tray
Tube impression / Single tooth impressionwww.indiandentalacademy.com

ZINC OXIDE EUGENOL PASTE:
Composition:
• Base - Zinc oxide 87 %
- Mineral oil 13 %
• Catalyst - Eugenol 12 %
- Poly rosin 50 %
- Filler (Silica) 20 %
- Lanolin 3 %
- Resinous balsam 10 %
- CaCl2 5 %

Setting reaction: Acid-base reaction
ZnO + H2O → Zn (OH)2
Zn (OH)2 + 2HE → ZnE2 + 2H2O
(Base) (Acid) (Zinc eugenolate)
Working time - 1 min
Setting time - 10-15 mins
Non-Eugenol pastes:Non-Eugenol pastes:
Zinc oxide reacts with carbolic acidwww.indiandentalacademy.com

Impression materials /certified fixed orthodontic courses by Indian dental academy

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