IMPRESSION MATERIALS

AND TECHNIQUES IN

ORTHODONTICS

By,

Dr.Karan Purohit

M.S.R.D.C

CONTENTSCONTENTS• INTRODUCTION.

• HISTORY

• IDEAL REQUISITES OF AN IMPRESSION MATERIAL

• CLASSIFICATION OF IMPRESSION MATERIALS AND TRAYS

• IMPRESSION MATERIALS- ALGINATE,AGAR AND SILICONES

• IMPRESSION TECHNIQUE

• IMPRESSION FOR CLEFT PALATE PATIENT

• IMPRESSION FOR MYOFUNCTIONAL APPLIANCES

• ORA SCANNER

• CONCLUSION

• REFERENCES

INTRODUCTION •Impression materials are used to make an accurate replica of oral tissues.

•The area involved may vary from a single tooth to the whole dentition or an impression of an edentulous mouth. •Usually the impression material is carried to the mouth in a plastic state on a tray and removed from the mouth when the material has set. •The accuracy, detail and quality of the final replica is of greatest importance.

• There are a wide range of impression materials having its own advantages and disadvantages.

• When making impressions for orthodontic cast the hard and soft tissues should be accurately reproduced.

• The casts should include the teeth, palate and the alveolar process to the base of vestibule and to the floor of the mouth.

DENTAL IMPRESSION?

An imprint or a negative likeliness of the teeth and or edentulous areas where the teeth have been removed, made in a plastic material which becomes relatively hard or set when it comes in contact with these tissues.

IMPRESSION MATERIAL ?

Any substance or combination of substances used for making a negative reproduction or a replica of the oral tissues

HISTORY PHILIP PFAFFS (1756) WAS THE FIRST TO DESCRIBE TAKING AN IMPRESSION OF THE JAW .

DELABARRE (1820) INTRODUCED THE IMPRESSION TRAY

HARLES STENT (1857) A LONDON DENTIST TESTED A COMBINATION OF DIFFERENT KINDS OF WAXES HARDENED AT ORAL TEMPERATURES, WHICH IS STILL USED TODAY UNDER THE NAME OF STENTS COMPOSITION.

JOSEPH RICHARDSON (1860) SUGGESTED THE EARLY USE OF GUTTA PERCHA FOR OBTAINING IMPRESSION BECAUSE OF ITS ELASTICITY

S. WILLIAM WILDING (1940) USED ALGIN AS DENTAL IMPRESSION MATERIAL

S. L. PEARSON, (1955) LIVERPOOL UNIVERSITY DEVELOPED ELASTIC IMPRESSION MATERIALS FROM SYNTHETIC RUBBER AND RESIN BASES.

  In orthodontics, impression gives a negative reproduction of

the tissues and by filling it with dental stone or other model material

a positive cast is made that can be removed after model material has

set., which in turn are used for;

 

1.   STUDY PURPOSE

2.   FABRICATION OF APPLIANCES

3.   MAINTAINING RECORDS

 

IDEAL REQUISITES OF AN IMPRESSION MATERIAL

• BE NON TOXIC TO THE TISSUES.

• SHOULD HAVE AN ADEQUATE SHELF LIFE .

• BE SUFFICIENTLY FLUID ON INSERTION TO GIVE

ACCURATE SURFACE DETAIL.

• HAVE PLEASANT TASTE, SMELL AND APPEARANCE .

• HAVE NO DIMENSIONSAL CHANGES EITHER IN OR OUT OF THE

MOUTH AT ALL NORMAL DEGREES OF TEMPERATURE AND HUMIDITY.

• SET OR HARDEN, AT OR NEAR MOUTH TEMPERATURE .

• IT SHOULD HAVE SUITABLE WORKING AND SETTING TIME.

•BE COMPATIBLE WITH DIE AND MODEL MATERIALS

• BE INEXPENSIVE

No impression material fulfills all these requirements

And the selection of the material best suited for a

particular Clinical situation and technique rests with

Dentists.

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

COLLOIDS

• They are the fourth state of matter because of their differences in

structure, constitution, and reactions .

•Particles size ranging from 1 to 200 nanometers.

• Colloid are Suspension of 2 phases

• Colloidal materials used for making impressions are either algin or

agar dissolved in water.

•Hence the name “HYDROCOLLOIDS”

Colloids , have two distinct phases

A dispersed phase + dispersion phase

LIQUID COLLOIDS ARE CALLED SOL

SOLID COLLOIDS ARE CALLED GEL

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.

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 hydrocolloids may absorb water

by a process, which is opposite of synerisis that will cause the

separation of the polysaccharide chains and thus causes the

swelling of the impression.

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’. Later S William wilding used this algin as

dental impression. 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 OR FAST SETTING

TYPE II – NORMAL SETTING

APPLICATIOS OF ALGINATE

1.Most communally used for making impression for orthodontic study models.

2.For duplicating models.

COMPOSITIONNO 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 REACTION.

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

Properties

WORKING TIME ;-

for fast setting materials -1.25 to 2 min (mixing time-45 sec)

for regular setting times is - 2 to 4.5 min (m.t.-60 sec)

• Flexibility

A D A specification permits a range of 5% to 20% at a stress of 1000 gms\cm2 and most alginate have a typical value of 14%.

• Strength

The compressive strengths range from 5000 – 9000 gms\cm². The Tear strength vary from 380- 700 gms\cm.

• Elasticity

highly elastic but less when compared to agar and about 97.3% elastic recovery occurs. The amount of permanent deformation is more as compare to agar.

ACCURACY

• Alginates are sufficiently flexible to record fine detail in the mouth..

• During setting of the material it is important that the impression should not be moved.

• The reaction is faster at higher temperature and so the material is contact with the tissues sets first.

• Any pressure on the gel due to movement of the tray will set up stresses within the materials which will distort the alginate after its removal from the mouth.

• The material is sufficiently elastic to be withdrawn over undercuts; occasionally tearing of the impression materials may occur with serious undercuts.

• Alginate are not stable on storage because of evaporation

• Compatibility with plaster and stone can be good. Some alginates give powdery surface on casts from dental stones.

• SHELF LIFE;-

• Short shelf life.Alginate impression material deteriorates rapidly at elevated temperature and The material should be stored in cool dry place.(not above 37c)

DIMENSION STABILITY

Alginate impression loses water by evaporation and shrinks on standing in air

If it is placed in water it absorbs water and swells .Therefore, cast should be poured immediately after making the impression.

If storage is unavoidable keeping in a humid temperature of 100% results in least dimensional changes.

BIOLOGICAL PROPERTIES

Some of silica particles present in dust are of possible health hazards.

Presently some manufacturers supply “Dust free” alginate.

• Inexpensive and hydrophillic (contact angle 37°)

• Easy to manipulate

• Displace blood and saliva and pour well with gypsum stone)

• Minimum requirement of equipments

• Accurate if proprely handled

Disadvantages of alginate

Low tear strength

Poorer reproduction of surface detail as compare to agar

Not as dimensionally acccurate as medium and light body silicone.

Not dimensionally stable on storage due to syneresis and poured immediately.(triethanolamine modified alginates more stable in long life hermetically sealed bags impressions can be stored for 48 hrs)

Zelgan (densply)

W:P 57 ml : 22 g

Mixing time 45 sec

Manipulation time 60 sec

Time in mouth 45 sec

Dustless alginates:- Many materials have now been formulated which gives off little or no dust particles, so avoiding dust inhalation. This can be achieved by coating the material with a glycol

Siliconised alginates:- Two pastes alginates have been developed, which incorporate silicon polymer component. These materials have superior resistance to tearing compared to unmodified alginates. However dimensional stability is reported to be poor

A combination reversible hydrocolloid / alginate impression technique has been improved.

Modified alginates

Fluorides or silicofluorides to improve surface of stone model(hexafluoro titanate in alginoplast and xantalgin)

Chlorhexidine added to alginate powder (hydrogum plus chlorhexidine) inactive bacterial microorganism.

Mint and vanilla flavour (orthoprint, formula 1) flavoured drops available(TOC) Zhermack vanilla flavored orthoprint is antinausea.

ALGINATE KROMOPAN

• This material has ability to eliminate gagging.

• It is dimensionally stable upto 100 hrs.

• Unique three color change determines time for spatulating ,loading tray and insertion of impression.

• Colour change to indicate different stages of manipulation e.g violet during spatulation, pink when loaded into tray and white when ready to load in mouth .(kromopan 100,kromogel)

• The only one with physical working time adjustment.

• For every Personal Krono drop, added to a water measure (water used to obtain the mixing), working time is lengthened of 20 seconds.

• Personal Krono is not a chemical retarder and therefore does not alter Kromopan components' balance.

• The in-mouth setting speed remains unaltered.

• Personal Krono can be used in summer when the working time is shorter due to high temperatures.

• The colour timing guide ensures that Kromopan is perfectly mixed and that the insertion is perfectly timed.The in-mouth setting time is 30 seconds.

Orthoprint

5 Year Guarantee

Highly Elastic

Vanilla Flavor, that Works with Alginate Flavors too

Dust Free

Alginate Flavorings

•Creates great tasting alginate at an economical low price•Sugar free•20 different flavors

Flavour Codes:

Banana (BAN), Blueberr y (BB), Bubble Gum (BG)Cherr y (C), Cinnamon (CIN), Cola (COLA)Fruit Punch (FP) ,Grape (G), Lemon (L)Orange (O), Pina Colada (PC), Peppermint (PEP)Pineapple (PIN), Raspberr y (R), Root Beer (RB)Strawberr y (S), Chocolate (CHOC) ,Crème Caramel (CC)Jamaica Java Cof fee (JJC), Watermelon (WM)

It is essential that impression materials adhere firmly to the impression trays.

This can be achieved by either perforations or by the use of adhesives. Adhesive solutions are needed for alginates, polysulphides and silicones.

Adhesives for alginates are solutions of resins in alcohol, they are supplied in a bottle with a brush or an aerosol spray.

Polysulphide adhesives are rubber solutions in acetone. Examples of silicone adhesives are isopropylalcohol or amylacetone.

Tray adhesive for alginates

Come in liquid or aerosol presentation. Solvent is also available for cleaning metal trays after use.

INDICATIONSFix Adhesive – Liquid and Fix Adhesive – Spray are tray adhesives for alginate impression materials.

Fix Solvent is used to remove Fix Adhesives from the impression tray after impression taking and casting.

CONTRAINDICATIONSUse in patients or by persons with a known allergy to diethylenetriamine or any other components of the products.

Kerr adhesive for silicones

IMPRESSION TRAYS  

They are used to carry the impression material to the mouth in its plastic state till it sets.

TRAYS

STOCK CUSTOM

PERFORATED NONPERFORTED

OTHER TRAYS

E.g – TRIPLE TRAY FOR BITE REGISTRATION

Disposable impression trays

Tuff Lock™ Disposable Impression Tray

A unique mechanical locking system eliminates the need for spray adhesives

A clean, complete impression is assured

High sides provide excellent margin and gingival detail

Econo Lock™ Disposable Impression Tray

Specifically designed for Orthodontic use

Made from sturdy plastic that will insure an accurate, distortion free impression

Prestige Rimlock Impression Trays

Prestige 'Rimlock' Impression Trays offer dentists the chance to produce ideal impressions in a solid, non-flexible tray, without the need to use impression adhesives.

Rimlock trays incorporate a unique 'beaded' edge that retains the impression material securely.

They are of high quality stainless steel that is fully autoclavable

 

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 4-6 mm wider than the buccal and lingual

portion of the anterior teeth

• It must be possible to center the tray

.

 

MODIFICATION OF THE TRAY MAY BE DONE USING SOFT

OR MODELING WAX

• When the teeth are in extreme malposition or the arch is

abnormally shaped, soft wax may be added to the impression tray.

For example: to carry the impression material well up into the vestibule in Class II

Division 1

• 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.

Upper and lower extend impression trays with motite

The wax has the added advantage of reducing the pressure of the impression tray metal rim on the displaced tissue during the Impression taking technique

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.

•Seat the patient upright so as to prevent the gagging due to the

backward flow of the excess material into the throat. 

• 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 pre-impression mouth wash

cocktail

Removes the debris

Reduce the surface tension of the teeth and tissues.

• 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

MANIPULATION

The recommended water powder ratio should be used. In general it is 38 ml

of water per 16 gms of powder but slight variation can be presented

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.

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.

• 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.

• A blob of material may be placed in the palatal vault of the patient

just behind the incisors, to eliminate the trapped air and to ensure the

faithful reproduction of palatal tissue

• Use the thumb and the index finger of the free hand to retract the

cheek.

Maxillary impression taking technique

• 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.

• To remove the impression , lift lips and cheek away with fingers to

break the seal ,grasp handle pull tray away from teeth with quick motion

Making impression for cleft palate patients(for combined Prosthesis and orthodontic appliances)

Preliminary impression

If the registration of the entire cleft is desirable the stock tray modified with modeling compound wax. extending posteriorly to the post pharyngeal wall.

Fast setting irreversible hydrocolloid is used.

1.If the patient is a child, he\she should be given the opportunity to

examine the tray.

2. The patient should have an early morning appointment.

3. The patient should have an empty stomach.

4. Topical anesthetic should be used on a child who has a severe gag

Reflex.

5. The tray should not be over loaded with the impression material. excess material in the naso pharynx will increase the difficulty of removing the impression without fracture.

6. All oral perforations should be packed with the gauze that has Been saturated with petroleum jelly.

Final impression- an acrylic resin tray is constructed over the Diagnostic cast,

The patient is prepared in the same manner as for the

Preliminary impression , the final is then made with the irreversible

Hydrocolloid impression material.

IMPRESSION FOR A FUNCTIONAL APPLIANCE

Impression for functional appliance fabrication differ some what from

those for orthodontic diagnostic cast

1] Areas where appliance components will contact soft tissue must be clearly

delineated. Most appliances use contact with lingual mucosa to stimulate

forward posturing,The impression must include the alveolar process below the

lower molars if long lingual flanges are employed.

The impression must not stretch and excessively displace the soft

tissues in an area of contact with appliance.This is critical when

lip pads and buccal shields are planned. To much extension

of impression will result in pads and shield are too long and will

cause soft tissue irritation and ulceration when the appliance is

worn

DISINFECTING THE IMPRESSION

Disinfection of impression is a concern due to viral diseases such as Hepatitis B,A I D S and herpes simplex

• 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.

CAUSES OF FAILURE

1. Grainy material •Improper mixing •Prolong mixing •Undue gelation•Water : powder ratio too low

2. Tearing •Inadequate bulk•Moisture contamination•Premature removal from mouth•Prolong mixing

3. External bubbles •Undue gelation, preventing flow•Air incorporated during mixing

4. Irregularly shaped voids •Moisture or debris on tissue

5. Rough and chalky stone model

•Inadequate cleansing of impression•Excess water or potassium sulfate solution left in impression•Premature removal of model

6. Distortion •Impression not poured immediately •Movement of tray during gelation•Premature removal from mouth

REVERSIBILE HYDROCOLLOIDS

AGAR-AGAR(ADA NO:-11)

This is a organic , hydrophilic colloid (polysaccharide)

extracted from certain type of sea weed. It is a sulfuric ester of a

linear polymer of galactose

The temperature at which the

LIQUIFACATION TEMPERATURE (700 – 1000C) GEL SOL GELATION TEMPERATURE (370 – 500C)

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%

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

AGAR

WATER COOLED TRAYS

Properties Permanent deformation-A D A specification requires that the recovery from deformation be greater than 96.5% after the material is compressed 20% for 1 sec

FLEXIBILITY- 4-15%

STRENGTH- 8000gm\cm²TEAR STRENGTH- 800-900gm\cmCompatibility with gypsum-more compatible with gypsum materialAGAR impression are best stored in 100% relative humidity if models cannot prepared immediately

BIOCOMPATIBILITY Thermal injury from reversible hydrocolloid as a result of impropertempering or faulty equipment during impression making

DUPLICATING MATERIAL

Alginate and 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

•Premature removal from mouth•Material partially gelled 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•Premature removal from mouth

NON AQUEOUS ELASTOMERIC IMPRESSION

MATERIAL (ADA no 19)

These materials are classified as synthetic

rubbers, developed to mimic natural rubber when it became

difficult to obtain during WORLD WAR II .They are liquid

polymers and can be converted to rubber at room temperature by

mixing with a suitable catalyst.

They undergo polymerization or cross linking by condensation/addition reactions to produce a firm elastic solid.

CLASSIFICATION

• POLYSULFIDES

• SILICON POLYSILOXANES

CONDENSATION SILICON

ADDITION SILICON (VINYL

POLYSILOXANE)

• POLYETHER

•RECENTLY INTRODUCES LIGHT CURE POLYERHER

URETHANE DIMETHACRYLATE.

THEY ARE SUPPLIED IN FOUR CONSISTENCY

• LOW (SYRINGE/WASH)

• MEDIUM (REGULAR)

• HIGH (TRAY)

• PUTTY (VERY HIGH)

HIGH, MEDIUM AND LOW CONSISTENCIES ARE

SUPPLIED AS A PASTE IN TWO FORMS

• BASE

• ACCELARATOR / CATALYST

CATALYST SOME TIMES ALSO AVAILABLE AS LIQUID

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 system

ADVANTAGES :-

HIGHLY ACCURATE IMPRESSION

PLEASANT ODOUR AND TASTE

GOOD DIMENSIONAL STABILTY

TEAR STRENGHT IS GOOD

GOOD SHELF LIFE

DISADVANTAGES

SETTING TIMES IS SHORT MIXING SHOULD BE DONE RAPIDLYHIGHLY EXPENSIVE

FOR MAKING DIGITAL ORTHODONTIC STUDY MODELS

The impression can be taken in a high quality ALGINATE or POLYVINYL SILICONE or POLYETHER material

High quality alginate such as ORTHOPRINT is taken in a rigid plastic impression tray.

The alginate impressions are sanitized, wrapped in a paper towel and Packaged in sealed plastic bags. This ensures that impression will remain stable for 5 days

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

CONCLUSION

• One must not depend on a material to provide good impressions.

• Any material is good and should be used till the operator is familiar with its characteristics

• Selecting the impression material depends on the convenience of the dentist and clinical situation.

ALL WE NEED IS AN ACCURATE IMPRESSION.

REFERENCES

I Anusavice Philips science of dental materials XI Edition

2 Restorative dental materials X EDITION By Robert G. Craig 3 Contemporary Orthodontics III Edition By William R. Proffit

4 Removable appliance Fabrication By Emil Witt, Dr Med. Dent

5 Hand book of Orthodontics IV Edition By Robert E. Moyers

7 Orthodontics for dental students By T.C. White and J.H. Gardiner

8 Journal of Orthodontics Vol 31 Nov 4 Dec 2004 ISSN 1465-3125 (AJODO)