IMPRESSION MATERIALS AND TECHNIQUES IN ORTHODONTICS By, Dr Analini.

CONTENTS INTRODUCTION. HISTORY CLASSIFICATION OF IMPRESSION MATERIALS AND TRAYS ALGINATE,AGAR AND SILICONES 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 casts 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

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 in contact with these tissues.

IMPRESSION MATERIAL Any substance or combination of substance 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 CHARLES 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. LEVI GILBERT AND W. H. DWINDLE (1843) DEVELOPMENT OF PLASTER OF PARIS IMPESSION JOSEPH RICHARDSON (1860) SUGGESTED THE EARLY USE OF GUTTA PERCHA FOR OBTAINING 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 PURPOSE2. FABRICATION OF APPLIANCES3. MAINTAINING RECORDS

IDEAL REQUISITES OF AN IMPRESSION MATERIAL BE NON INJURIOUS TO THE TISSUES. SHOULD HAVE AN INFINITE 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 HAVE SUITABLE WORKING AND SETTING TIME. BE CAPABLE OF HAVING ADDITIONS MADE AND OF REINSERTION IN THE MOUTH WITHOUT DISTORTION HAVE A SIMPLE TECHNIQUE AND NEED NO ELABORATE ARMAMENTARIUM 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:

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.

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: 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 phasesA dispersed phase + dispersion phase

LIQUID COLLOIDS ARE CALLED SOLSOLID COLLOIDS ARE CALLED GEL

Sol to gel transformationIn the gel state, the dispersed phase agglomerates, forming chains or fibrils called MICELLES. The fibrils may branch and intermesh to form a brush heap structureWater being entrapped between the fibrils

SOL GELGELATION TEMPERATURE (370 500C)

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.

SYNERISISThe 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.

IMBIBITIONIn 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 the swelling of the impression.

IRREVERSIBLE HYDROCOLLOIDALGINATE (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--D-MANURONIC ACID/ ALGINIC ACID

Structural formula of alginic acid with molecular wt of 32000-200000

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 SETTING

PropertiesWorking time-for fast setting materials-1.25-2 min (mixing time-45 sec) for regular set-3-4.5 min (m.t.-60 sec) Setting time-1-4.5min(regular) 1-2min(fast set) Permanent deformation- The A D A specification requires that the recovery from deformation be more than 95% when material is compressed 20% for 5sec

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

Strength

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

COMPOSITION

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 K2nAlg + CaSO4 nK2SO4 + CanAlg

Crosslinking of Na alginate molecules to form Ca alginate

STEPS IN MAKING IMPRESSION Selection of the tray Preparation of the patient Seating of the tray Disinfection of the impressionImpression trays They are used to carry the impression material to the mouth in its plastic state till it sets.

TRAYSSTOCKCUSTOMPERFORATEDNONPERFORTEDOTHER TRAYSE.g TRIPLE TRAY FOR BITE REGISTRATION

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 and yet comply with the above mentioned points.

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. 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.

Advice the patient to breath through the nose and in case of gagging try and distract the patients 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 patients mouth

Assume the correct operator positioning Maxillary impression - 11 o clock Mandibular impression - 7 o clock

MANIPULATIONThe 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 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.

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 Oclock 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 patients 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 Oclock 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 patients 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 extending posteriorly to the post pharyngeal wall. The added section is under extended about 4-5 mm in all directionsleaving adequate space for impression material.

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 APPLIANCEImpression 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.

DIMENSIONAL STABILITY For maximum accuracy the model material must should be poured into alginate impression as soon as possible. If it is delayed , the impression should be stored in 100% relative humidity in a plastic bag or wrapped in a damp paper towel It is satisfactory for some materials for periods up to 2 hours

BIOCOMPATIBILITY Inhaling fine airborne particles from alginate impression materials Can cause SILICOSIS and PULMONARY HYPERSENSITIVITY

MODIFIED ALGINATE Dust free alginate GLYCOL COATED particlesA 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.

Chromatic alginates: These exhibit colour signalling

When mixed with water it turns VOILET

When it turns PINK it has to be loaded on the tray

And when it turns WHITE it is ready for insertion

CAUSES OF FAILURE

AGAR ALGINATE COMBINATION IMPRESSIONS(LAMINATE TECHNIQUE)

The equipments needed for taking an agar impressioncan be minimized by use of an agar alginate syringe tray combination impression. The hydrocolloid is replaced with mix of chilled alginate .That will bond with with the syringe Agar

. The alginate gels by chemical reaction where as agar gels by means of contact with cool alginate rather than water circulation through the tray. Since the hydrocolloid , not the alginate , is in contact with the prepared teeth maximum detail will be reproduced

REVERSIBILE HYDROCOLLOIDS

AGAR-AGARThis is a organic , hydrophilic colloid (polysaccharide) extracted from certain type of sea weed. It is a sulfuric ester of a linear polymer of galactoseThe temperature at which the LIQUIFACATION TEMPERATURE (700 1000C) GEL SOL GELATION TEMPERATURE (370 500C)

THE MATERIALTYPES AVILABLEThe hydrocolloid is supplied in two forms:- The more fluid cartridge form available for use in syringes. the more viscous type used in traysSpecial water cooled trays are used to rapidly cool the material in the patients mouth

AGAR

At 1000C rapidly converts Gel to Sol and the contents of the tube become very fluid. At 650c- 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 useAt 450c a few minutes prior to the use the material is cooled to this temperature before placing in the patients mouth.

CONDITIONING UNIT

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 circulating 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.

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\cmTEAR 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 MATERIALAlginate 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.

CAUSES FOR FAILURE OF IMPRESSION

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 and or cross linking by condensation/addition reactions to produce a firm elastic solid.

CLASSIFICATION POLYSULFIDES SILICON POLYSILOXANES CONDENSATION SILICON ADDITION SILICON (VINYL POLYSILOXANE) POLYETHER

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 / CATALYSTCATALYST SOME TIMES AS LIQUIDPASTES ARE SUPPLIED IN COLLAPSABLE TUBE.

Condensation silicones Supplied in a low and putty type consistency. These are suppliedas a base and accelerator. The base contains poly dimethyl siloxane which have reactive terminal hydroxyl groups.Fillers may be CuCO3or silica(35-75%)for low to putty consistencies. The accelerator maybe liquid that consists of stannous octoate suspension and alkyl silicatesor it may be supplied as paste by addition of thickening agent The reaction proceeds producing 3 dimensional network rubber withethyl alcohol as a byproduct Stock trays are generally used

Addition silicones It is available in low,medium,heavy and putty consistencies and is also Poly siloxane. Base contains low molecular wt polymer with silane group and filler. The accelerator contains a moderately low molecular wt polymer with vinyl terminal groups and filler

Biocompatibility Comparing the cell cytotoxicity for different impression materials reveals that polysulfide results in the lowest cell count and set polyester impression material produces the highest cell cytotoxicity Foreign body of impression material can cause severe gingival inflammation if it is left in a gingival sulcus Contact dermatitis from polyester especially to the dental assistant has been reported due to polyester catalyst

MANIPULATIONEqual 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

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.

FOR MAKING DIGITAL ORTHODONTIC STUDY MODELS

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

High quality alginate such as ORTHOPRINT taken in a rigid plastic impression tray The alginate impressions are sanitized, wrapped in a damp paper towel and Packaged in seal able plastic bags This ensures that impression will remain stable for 5 daysIf the impression will not be delivered by the V day then we considerUsing a polyether such as IMPREGUM

ORASCANERIt 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 as good as the dentist using it and any material must be used for sometime before the operator is familiar with its characteristics Selecting the impression material depends on the convenience of the dentist

ALL 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

Cleft lip and palate Persectives in Management Vol II By SAMUEL BERKOVITZ

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

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

Seminar on impression materials and techniques By Dr Ashutosh Shetty

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