Impression materials and techniques in orthodontics

IMPRESSION MATERIALS
AND TECHNIQUES IN
ORTHODONTICS
www.indiandentalacademy.com

CONTENTSCONTENTS
• INTRODUCTION
• IMPRESSION REQUISTS & OBJECTIVES
• STEPS IN MAKING AN IMPRESSION
• VARIOUS IMPRESSION MATERIALS
• IMPRESSION FOR MYOFUNCTIONAL
APPLIANCES
• ORA SCANNER

Many dental appliances are constructed outside the patient’s
mouth on the models of the hard and soft tissue. The accuracy of the
fit and efficiency of the appliance depends on how accurately the
model replicates the natural oral tissues and the accuracy of the model
in turn depends on the accuracy of the impression in which it was
cast.
Thus the function of the impression material is to :
“ACCURATELY RECORD THE DIMENSION OF THE
ORAL TISSUES AND THEIR SPATIAL RELATIONSHIP”
INTRODUCTION

Basically the process of making an impression involves
placement of a suitable impression material in the plastic state
against the oral tissues and allowing it to set…..
After setting the impression is removed and thus the negative
replica of the oral tissue is obtained this is then used to obtain a
positive replica of the oral tissues i.e MODEL or CAST (in case of a
single tooth it is termed as a DIE)

In orthodontics impression are primarily made to obtain
CASTS, which in turn are used for
1. STUDY PURPOSE
2. FABRICATION OF APPLIANCES
3. MAINTAINING RECORDS
In dentistry various types of materials are used for making an
impression. NO ONE MATERIAL will be used in all the scenarios
rather based on the properties, ease of use, accuracy and economy.
Various material will be used according to the particular need of the
practitioner. www.indiandentalacademy.com

IDEAL REQUISITS OF AN IMPRESSION MATERIAL
• Ease of manipulation
• Adequate flow
• Appropriate working time and setting time
• Adequate mechanical strength to resist permanent deformation
during removal of the impression
• Dimensional accuracy and faithful reproduction of details.

• Acceptability to the patient & biocompatibility
• No significant degradation of properties following disinfection of
the impression
• Compatibility with the die or cast material
• Good shelf life
• Economical & should not require elaborate armamentarium.

OBJECTIVES OF MAKING AN IMPRESSION.
To record
 All the teeth in the upper and lower arch
 The entire alveolar process
 The retromolar pad in the lower arch
 The hamular notch in the maxillary arch
 A detail, undistorted & bubble free reproduction of the oral
tissues.

STEPS IN MAKING IMPRESSION
• Selection of the tray
• Preparation of the patient
• Seating of the tray
• Disinfection of the impression
Impression trays
They are used to carry the impression material to the mouth in

TRAYS
STOCK CUSTOM
EDENTULOUS DENTULOUS
PARTIAL COMPLETE
OTHER TRAYS
E.g – TRIPLE TRAY FOR BITE REGISTRATIONwww.indiandentalacademy.com

 MAXILLARY TRAY
• The tray must completely cover the tuberosity
• Must be 4mm wider than the most apical portion of the alveolar
process at the molar region.
• The tray must cover the anteriors with the incisors contacting the flat
portion of the tray about 4 mm from the raised palatal part of the
tray.
SELECTION OF IMPRESSION TRAY

 MANDIBULAR TRAY
• The tray should cover all the teeth as well as the retromolar pad
• The tray should be 4 mm wider than the buccal and lingual
portion of the anterior teeth
• It must be possible to center the tray and yet comply with the
above mentioned points.

MODIFICATION OF THE TRAY MAY BE DONE USING
SOFT OR MODELING WAX
• Around the periphery of the tray, wax will protect the soft tissue
• Allows extension of the tray to enable accurate sulcus depth
recording
• In case where patients have high arched palates it is advisable to
place wax in relation to the palatal aspect of the tray to ensure
accurate recording of the palate and minimal wastage of the
material. www.indiandentalacademy.com

PREPRATION OF THE PATIENT
• Explain the procedure to the patient in the simplest of
terms so that the patient is aware of the procedure and therefore
the fear of the unknown is over come. This is especially
important in young individuals and those who seem
apprehensive of the treatment that they are about to receive.
• Seat the patient upright so as to prevent the gagging due
to the backward flow of the excess material into the throat.www.indiandentalacademy.com

• Advice the patient to breath through the nose and in case
of gagging try and distract the patient’s attention and ask the
patient to look down wards.
• Prior to making the impression it is advisable to ask the
patient to rinse the mouth with water as this will
 Reduce the amount of bacteria in the mouth
 Reduce the amount of saliva in the mouth there by reducing
the chances of voids being formed.

• Practice the placement of the empty tray into the patient’s mouth
• Assume the correct operator positioning
 Maxillary impression - 11 o’ clock
 Mandibular impression - 7 o’ clock

SEQUENCES OF IMPRESSION MAKING
It is advisable to make mandibular impression
first as there is less chance of the patient to gag .This
allows the patient to become accustomed to the taste and
the feeling of the material in the mouth which in turn
reduces the chances of gagging while making an
impression of the maxillary arch.

SEATING THE IMPRESSION TRAY
MANDIBULAR IMPRESSION
• Operator position at 7 O’clock
• Patient seated such a way that the occlusal plane placed
parallel to the floor.
• Use the thumb and the index finger of the free hand to
retract the cheek.
• Grasp the handle of the tray and rotate the tray into the
mouth by using the front of the tray to deflect the other
cheek. www.indiandentalacademy.com

• Once inserted straighten the tray so that the tray is in line with the
patient’s midface .
• Note the position of the tray in relation to the anteriors.
• Using the index finger of both the hands press the tray downwards
lightly and evenly over the mandibular arch until resistance
is felt.

• Manipulate the patients cheeks and lips to create a more detailed
anatomy of the facial and vestibular area.
• Ask the patient to raise the tongue and then move it from side to side.
• Allow the material to set and then remove. Using a firm grip on the
tray handle, use a side ways lifting motion to remove the tray.

MAXILLARY IMPRESSION.
• Operator position at 11 O’clock position
• Patient seated such a way that the occlusal plane placed parallel
to the floor.
• Ask the patient to open the mouth.
• Use the thumb and the index finger of the free hand to retract the
cheek.

• The tray is rotated into the mouth once again using the front of
the
tray to deflect the other cheek.
• Once inserted straighten the tray so that the tray is in line with the
patient’s mid face .
• Begin to apply light pressure upwards till the light resistance is
felt

• Initially seating the posterior region of the tray and subsequently the
anterior part of the tray allowing the material to flow over the molars.
• Retract the upper lip as the tray is seated. This allows the material to
flow and displace any air which might otherwise cause voids.
• Hold the tray in place till the material is set.
• Remove the tray with the firm grip of the handle using a downwards
and sideways flipping action.

DISINFECTING THE IMPRESSION
• Gently rinse the impression under the tap water to remove any
debris that may be retained in the impression.
• Gently shake the excess water.
• Spray the entire impression with an O.S.H.A. (occupational health
and safety administration) approved disinfecting solution.
OR

• May immerse the impression in a disinfectant such as :
gluteraldehyde solution
iodophors
1:10 dilution of sodium hypochlorite
synthetic phenols
• Rinse again

CRITERIA FOR ACCESSING THE IMPRESSION
• Lack of voids.
• No distortion , clear and distinct impression
• Adequately extended.
• Free of debris and extraneous material.
• Adequate details and all structure must be recorded.
• Stable material which is sufficiently attached to the tray.

CLASSIFICATION OF THE IMPRESSION
MATERIALS BASED ON:
SETTING
REACTION
THERMOPLASTIC THERMOSET
ELASTICITY ELASTIC INELASTIC
NATURE OF
THE SETTING
REACTION
REVERSIBLE IRREVERSIBLE
PRESSURE
EXERTED ON
THE TISSUE
MUCOCOMPRESSIVE MUCOSTATIC
DENTITION
STATUS
EDENTULOUS DENTULOUS

In orthodontics we require impression materials that are elastic
since we deal with dentulous patients
The most commonly employed materials include
I. Hydrocolloid – Agar Agar (reversible)
- Alginate (irreversible)
II. Elastomeric impression materials.www.indiandentalacademy.com

COLLOIDS
They are the fourth state of matter with particular size ranging
from 1 to 200 nanometers.
They are an intermediate phase between a true solution and a
suspension / emulsion where a suspension is solid in liquid and
emulsion is a liquid in liquid these suspended particles do not
readily diffuse and tend to fall out of the suspension medium.
True solution on the other hand consists of a single phase no
separation between the solute and the solvent.

Colloids , emmulsion and suspensions have two distinct
phases
A dispersed phase + dispersion phase
LIQUID COLLOIDS ARE CALLED SOL
SOLID COLLOIDS ARE CALLED GEL

Sol to gel transformation
In the gel state, the dispersed phase agglomerates,
forming chains or fibrils called “MICELLES”. The
fibrils may branch and intermesh to form a brush
heap structure
Water being entrapped between the fibrils
SOL GEL
GELATION TEMPERATURE (370
– 500
C)
Fibrils are held together by secondary
molecular forces

This process may also occur through a chemical
reaction the structure of the fibrils formed is very similar
but the process is very different and is irreversible
The fibrils of the gel formed are chemically bonded
by primary forces and therefore they are not affected by
the temperature.

IRREVERSIBLE HYDROCOLLOID
ALGINATE (ADA no 18)
At the end of 19th
century the chemist from Scotland noticed
that certain brown seaweed produced a mucous extraction that he
termed as ‘ALGIN’. This became the chief ingredient in our
popularly used dental ALGINATE, which is
A SODIUM SALT ANHYDRO-ß-D-MANURONIC ACID/
ALGINIC ACID

The factors causing its successful use as an impression material
include:
• Ease of manipulation
• Comfortable to the patients
• Relatively inexpensive not requiring elaborate armamentarium.
TYPES
TYPE I – RAPID SETTING
TYPE II – NORMAL SETTINGwww.indiandentalacademy.com

COMPOSITION
NO COMPOSITION FUNCTION %
I. Salt of Alginic acid Dissolves in water & reacts
with calcium ions
15%
II. Calcium sulphate Reacts with pottasium
alginate to form calcium
alginate
16%
III. Tri sodium phosphate Reacts in preference with
calcium sulphate - retarder
2%
IV. Pottasium Titanium Gypsum hardener 3%
V. Zinc oxide Filler 4%
VI. Diatomaceous earth Filler 60%
VII. Flavouring & coloring
agents
Makes the material more
palatable
TRACES

SETTING REACION.
Soluble alginate reacts with the calcium sulphate resulting in the
formation of an insoluble calcium alginate.
This process occurs quite rapidly and thus would not allow sufficient
working time so to compensate for this problem a water soluble salt
namely Tri-sodium phosphate is added to prolong the working time.
The basic idea behind adding this salt is to allow calcium sulphate to
initially react with tri-sodium phosphate in preference to the soluble
alginate
K2nAlg + CaSO4 nK2SO4 + CanAlgwww.indiandentalacademy.com

The insoluble calcium alginate forms gel with the water
molecules interspersed between its molecules.
Controlling the gelation should not be attempted by altering
the water powder ratio as this will result in impairment of the
characteristics of the final gel.
Rather cooling the reaction procured by using the cold water
can increase the working time the inverse also holds good.

MANIPULATION
The recommended water powder ratio should be used. In
general it is 40 ml of water per 15 gms of powder but slight variation
can be present depending on the manufacturer. The weighed power
is incorporated into the water by carefully mixing with the spatula.
Care should be taken to ensure that air is not incorporated into the
mix by spatulating the mix against the side of the bowl while using
the vigorous figure of 8 motion till a smooth creamy mix is obtained.

PROPERTIES:-
• Setting time FAST setting 1 to 2 minutes
REGULAR setting 2 to 4.5 minutes
Range being from 1 to 5 minutes
• FLEXIBILITY 14% at stress of 1000 gm/cm2
• ELASTICITY RECOVERY 97.3% , less than Agar Agar.
• STRENGTH
Compressive strength 5000-8000 gm/cm2
Tear strength 350 – 700 gm/cm2
• The shelf life of the material is short so it should be stored in a
cool dry area to ensure against any moisture contamination

MODIFIED ALGINATE
• Dust free alginate - glycerin
• A new system in which the SOL contains water but not calcium ion
so that the second component added is actually Plaster of Paris.
• A two component paste system
(I) Alginate Sol
(II) calcium reactor
• Chromatic alginate actually changes the color once set.
• Alginates modified with silicon/polymers for fine detail but these
have the disadvantage of having a very poor dimensional stability.

CAUSES OF FAILURE
1. Grainy material •Improper mixing
•Prolong mixing
•Undue gelation
•Water : powder ratio too low
3. Tearing •Inadequate bulk
•Moisture contamination
•Premature removal from mouth
•Prolong mixing
4. External bubbles •Undue gelation, preventing flow
•Air incorporated during mixing

5. Irregularly shaped voids •Moisture or debris on tissue
6. Rough and chalky stone
model
•Inadequate cleansing of
impression
•Excess water or potassium sulfate
solution left in impression
•Premature removal of model
7. Distortion •Impression not poured
immediately
•Movement of tray during gelation

REVERSIBILE HYDROCOLLOIDS
AGAR-AGAR
A hydrophilic colloid (polysaccharide) extracted from certain
type of sea weed
The temperature at which the
LIQUIFACATION TEMPERATURE (700
– 1000
C)
GEL SOL
GELATION TEMPERATURE (370
– 500
C)

INGREDIENTS FUNCTION COMPOSITION %
1. AGAR BASIC
CONSTITUENT
13-17
2. BORATES STRENGTH 0.2-0.5
3. SULPHATES GYPSUM HARDNER 1.0-2.0
4. WAX FILLER 0.5-1.0
5. THIXOTROPHIC
MATERIAL
THICKNERS 0.3-0.5
6. WATER REACTION
MEDIUM
BALANCE
7. ALKYL
BENZOATE
PRESERVATIVE 0.1%www.indiandentalacademy.com

THE MATERIAL
TYPES AVILABLE
The hydrocolloid is supplied in two forms:-
The more fluid “cartridge form” available for use in syringes.
the more viscous type used in trays
Special water cooled trays are used to rapidly cool the
material in the patients mouth

1000
c 650
c 450
c
CONDITIONING BATH

At 1000
C – rapidly converts Gel to Sol and the contents of the
tube become very fluid.
At 650
c- transfer the material to second bath, this temperature
will maintain the material in its SOL form leave the material in this
temperature until the material is required for use
At 450
c a few minutes prior to the use the material is cooled
to this temperature before placing in the patients mouth.

High viscosity SOL can be transferred from the tempering bath
into the stock tray.
Low viscosity sol can be directly syringed out onto the teeth
surface.
The cooling of the material in the mouth to promote rapid gel
formation may be achieved by the spraying cold water on the tray or
by using special water cooling impression trays. These trays are stock
trays with a narrow bore metal tube attached to the outer surface, the
tube is connected to the cold water supply and circulatory water
reduces the temperature of the tray.

SYNERISIS
The process of synerisis may be explained as the squeezing
of water from between the polysaccharide chains. As a result of
which one may often observe a small droplets of water on the
surface of impression. Which results in shrinkage of the
impression.

IMBIBITION
In the presence of excess water the agar-agar may absorb
water by a process, which is opposite of synerisis that will cause the
separation of the polysaccharide chains and thus the swelling of the
impression.

DUPLICATING MATERIAL
Agar –Agar may be used successfully as a duplicating
material. In this way multiple casts can be duplicated from a single
master cast, which may have been formed using some other material.
This process is essential in ones orthodontic practice as it enables the
use of one master cast to form several casts subsequently.

1. Grainy material •Inadequate boiling
•Storage temperature too low
•Storage time too long.
2. Separation of tray and material. •Water soaked layer of tray
material not removed
•Premature gelation
3. Tearing •Inadequate bulk
•Material partially geled when
tray seated
4. External bubbles •Gelation of syringe material
preventing flow
CAUSES FOR FAILURE OF IMPRESSION

5. Irregularly shaped voids • Material too cool or grainy
6. Rough and chalky stone model •Inadequate cleansing of
impression
•Excess water or potassium sulfate
solution left in impression
•Premature removal of die
7. Distortion •Impression not poured
immediately
•Movement of tray during gelation

NON AQUEOUS ELASTOMERIC IMPRESSION
MATERIAL (ADA no 19)
They are liquid polymers and can be converted to rubber at
room temperature by mixing with a suitable catalyst they undergo
polymerization and or cross linking by condensatation/addition
reactions to produce a firm elastic solid.

CLASSIFICATION
• POLYSULFIDES
• SILICON POLYSILOXANES
CONDENSATION SILICON
ADDITION SILICON (VINYL
POLYSILOXANE)
• POLYETHER
• VISIBLE LIGHT CURE

THEY ARE SUPPLIED IN FOUR CONSISTENCY
• LOW (SYRINGE/WASH)
• MEDIUM (REGULAR)
• HIGH (TRAY)
• PUTTY (VERY HIGH)

HIGH, MEDIUM AND LOW CONSISTENCIES ARE
SUPPLIED IN TWO FORMS
• BASE
• ACCELARATOR / CATALYST
CATALYST SOME TIMES AS LIQUID
PASTES ARE SUPPLIED IN COLLAPSABLE TUBE.

MANIPULATION
Equal lengths of two pastes are dispensed on a paper
pad for normal mixes. Initial mixing is accomplished with
circular motion and final mixing to produce a mix free from
streaks is done with broad stroke of spatula. Mixing is readily
accomplished in 45 seconds. When catalyst is supplied in liquid
form a specific number of drops per unit length is indicated in
the instructions and mixing is accomplished in the manner
similar to the two paste systemwww.indiandentalacademy.com

The putty system use scoops supplied by the
manufactures for dispensing and may be mixed with heavy
spatula or kneaded with hand until free from streaks.

VISIBLE LIGHT CURE
THESE MATERIALS ARE AVILABLE IN TWO
CONSISTENCIES
1. LIGHT BODY MATERIAL
2. HEAVY BODY MATERIAL
COMPOSITION
URETHENE DIMETHACRYLATE ELASTOMER RESIN.

MECHANICAL PROPERTY
• This material has a excellent elasticity and very low
dimensional shrinkage on storage.
• It may be poured immediately or upto two weeks later..

MANIPULATION
Light body material is syringed into the slucus, around
and over the preparation and position of the adjacent teeth. A
clean tray is loaded to the fill line with the heavy body
material. After the tray is seated in the mouth both viscosities
are cured simultaneously using a visible light cure unit.
Curing time approximately 3 minutes

IMPRESSION FOR A FUNCTIONAL APPLIANCE
Along with an accurate reproduction of the teeth the areas where
appliance contact the tissue must be recorded and clearly delineated.
Most appliances used contact with the lingual mucosa to stimulate
forward positioning of the mandible, so the area must be adequately
recorded. The impression should not be over extended.

ORASCANER
It is a revolutionary new process. The orthodontist uses 3-D
images taken by the OraScanner™
to build a computer model of the
teeth. The OraScanner functions much like a video camera, taking
pictures of the teeth and sending them to the computer to build a
complete 3-D model

Impression materials and techniques in orthodontics

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