SEMINAR :INELASTIC IMPRESSION MATERIALSUNDER THE ABLE GUIDANCE OF

DR.RAVI DWIVEDI.DR.N.K GUPTA.DR.AMRIT TANDAN.DR.SWATI GUPTA.DR.GARIMA AGGRAWAL. PRESENTED BY:DR.MANOJ UPADHYAY. VIRENDRA.V.SINGHDR.SULABH (JUNIOUR RESIDENT1)

INELASTIC IMPRESSION MATERIALINTRODUCTION- In the field of dentistry constructing

a cast is an important step in numerous dental procedures .An impression is a negative replica of a

dental structure which helps in construction of a cast which produces the accurate oral structure. To obtain

an accurate impression , a suitable impression material is required.There are many materials available now for making impression of oral

tissues.Before the mid of 20th century dentist used to make impression with softened wax, impression

plaster & I.C

IMPRESSION-

• Definition:It is defined as an imprint or negative likeness of the teeth and /or edentulous areas where the teeth have been removed, made in a plastic material which becomes relatively hard or or set while in contact with these tissues.Impressions may be made of full compliments of teeth, areas where some teeth have been removed or in mouth from which all teeth have been removed .

• A negative likeness or copy in reverse of the surface of an object;an imprint of the teeth and adjacent structures for use in dentistry.(GPT8)

IMPRESSION MATERIALS – PURPOSE & REQUIREMENTS

• Materials used to produce accurate replicas of intraoral & extraoral tissues should fulfill the following criteria –(Chiayi Shen)

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

• The impression made from these materials should remain dimensionally stable,atleast until the cast can be poured.6) The impression should maintain 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 biocompatible.8)The material associated processing equipment & processing time should be cost effective.

• TYPES OF CLASSIFICATION • Based upon the type of reaction needed for heat or chemical

reaction:• THERMOPLASTIC-COMPOUND & WAXES• STRICTLY THERMOPLASTIC-REVERSIBLE HYDROCOLLOIDS• THERMOSET-IMPRESSION PLASTER & ZOE PASTE.• BASED UPON THE REUSABLE OF MATERIAL• REVERSIBLE,IRREVERSIBLE• BASED ON SETTING CHARACTERISTICS• RIGID- DENTAL IMPRESSION PLASTER.• SEMI RIGID- IMPRESSION COMPOUND ,ZOE PASTE.• PLASTIC-IMPRESSION WAX &SOFT RESIN.• ELASTIC-HYDROCOLLOID IMPRESSION MATERIAL &RUBBER

BASE IMPRESSION

• BASED UPON THEIR APPLICATION• EDENTULOUS- IMPRESSION PLASTER,IMPRESSION

COMPOUND,AGAR .• DENTULOUS-PLASTIC & ELASTIC IMPRESSION MATERIAL.• CLASSIFICATION 2nd •

• 1)ACCORDING TO PROPERTIES• RIGID OR INELASTIC IMPRESSION MATERIALS• IRREVERSIBLE- IMPRESSION PLASTER ,ZOE.• REVERSIBLE- IMPRESSION COMPOUND• • ELASTIC IMPRESSION MATERIALS• HYDROCOLLOID IMPRESSION MATERIALS• IRREVERSIBLE-ALGINATE• REVERSIBLE-AGAR.• NON AQOUEOUS ELASTOMERIC IMPRESSION MATERIALS• POLYSULPHIDE,CONDENSATION SILICONE,ADDITION

SILICONE,POLYETHER.

• 2ndACCORDING TO SETTING MECHANISM• CHEMICAL REACTION(IRREVERSIBLE)• RIGID- IMPRESSION PLASTER,ZOE PASTE• ELASTIC-ALGINATE HYDROCOLLOID• NONAQUEOUS ELLASTOMERS• 1)POLYSULPHIDES 2)POLYETHERS 3)ADDITION SILICONE

• 4) CONDENSATION SILICONE • PHYSICAL REACTION(REVERSIBLE)• RIGID( FOR EDENTULOUS PATIENT)-IMPRESSION

COMPOUND.• ELASTIC( FOR TOOTH FORM CAN TAKE IMPRESSION OF

SLIGHT UNDERCUTS)-AGAR HYDROCOLLOID

• 3RD)ACCORDING TO USE-• FOR EDENTULOUS RIDGE-WITHOUT ANY

UNDERCUT.• REVERSIBLE-IMPRESSION COMPOUND.• IRREVERSIBLE-IMPRESSION PLASTER,ZOE• FOR DENTULOUS RIDGE-• REVERSIBLE-AGAR HYDROCOLLOID.• IRREVERSIBLE-ALGINATE HYDROCOLLOID &

ELASTOMERS.

• BY SETTING RXN.

RIGID/INELASTIC(EDENTULOUS RIDGE FORM)

ELASTIC( TOOTH FORM)

CHEMICAL RXN.IRREVERSIBLE)

PLASTER OF PARISZOE IMPRESSION PASTE.

ALGINATE HYDROCOLLOIDNON AQUEOUS-ELASTOMERS

TEMPERATURE CHANGES(REVERSIBLE)

IMPRESSION COMPOUNDIMPRESSION WAXES

AGAR HYDROCOLLOID

RIM LOCK TRAYS

• IMPRESSION TRAY-• DEFINITION- It is defined as a receptacle in to which suitable

impression material is placed to make a negative likeness.or• It is also defined as a device that is used to carry,confine & control

impression material while making impression.(GPT-8) IMPRESSION TRAYS –CLASSIFIED 1) STOCK TRAY 2) CUSTOM TRAY1)SHELLAC OR SIMILAR THERMOPLASTIC MATERIAL

2)ACRYLIC RESIN,EITHER HEAT OR COLD CURED.3)THERMO- FORMED OR SWAGED POLYMER SHEET.

4)TIN-LEAD ALLOY( POURED IN TO A PLASTER MOULD MADE FROM A WAX PATTERN,SOMETIME REFERRED TO AS ‘CHEMOPLASTIC CASTING PROCESS); THIS TYPE OF TRAY IS NOT POPULAR NOWDAYS.

• The design of trays must be related to the impression to be made.If we use impression compound ,there should be sufficient space between the tray & soft tissues to allow for adequate bulk of material & to allow the sluggish flowing material to move in to the desired relationship with the basal seat & border tissues.

• If we used ZOE paste which flows readily, the tray must fit more accurately than for dental plaster which is free flowing but more viscid .Consequently these free flowing materials must be used in trays made especially for each patient.

• These custom trays control the movable soft tissues around the impression but do not distort them, at the same time space is provided inside the tray so that the shape of tissues covering the residual alveolar ridge may be recorded with minimal or selective displacement.

• There should be atleast 2-3 mm clearance between the stock tray & the ridge. It should have 5-6 mm clearance for impression compound.

• The second most important part of the impression ‘is the proper positioning of the final impression tray on the basal seat on the basal seat in the mouth’.

HISTORY• PHILIP PFAFF- 1756- 1st described making

impression with softened wax.• CHRISTOPHE FRANCOIS DELABARRE-1820-

Introduced the Metal impression tray.• CHAPIN HARIS-1853-First used Plaster of Paris

for making impressions.• CHARLES STENT-1857- Introduced the 1st

Impression compound.

IMPRESSION MATERIALS

• One or combination of impression materials is not the panacea for making acceptable impressions in different situations .The character & position of the tissues to be reproduced in the impression , the technique employed & the purpose for which the impression is made dictate the choice of the material.

• Inelastic impression material’s exhibit an insignificant amount of elastic deformation when subjected to bending or tensile stresses .In addition ,they tend to fracture without exhibiting any plastic deformation,if the stress from applied pressure exceeds their tensile,shear or compressive strength values.

MODELLING PLASTIC

IMPRESSION COMPOUND(MODELING PLASTIC, KERR’S,STENTS

IMPRESSION COMPOUND)• One of the oldest dental impression material is the impression

compound.IC is supplied as sheets, sticks, cakes &cones

• COMPOSITION OF AN IMPRESSION COMPOUND• Ingredient Parts • Rosin 30• Copal resin 30• Carnauba wax 10• Stearic acid 5• Talc 75• Coloring agent Appropriate amount

ROLE OF PLASTICIZERS & FILLERS

• PLASTICIZERS-Shellac stearic acid & gutta-percha are added to improve plasticity & workability.

• FILLERS- Are inert materials.Strengthen or improve the physical propeties.As waxes and resins in impression compound (non crystalline character)cause high flow of the I.C & low strength.Fillers like Talc, Diatomaceous earth, soap stone, french chalk are added to reduce the plasticity of matrix by frictional action.

PROPERTIES OF IMPRESSION COMPOUND

• GLASS TRANSITION TEMPERATURE & FUSION TEMPERATURE-

• When impression compound is heated in a hot water bath the material looses its hardness at approx.39°C however at this stage it is still not plastic or soft enough for making an impression.This temperature at which the material loses its hardness or brittleness on heating or forms a rigid mass on cooling is called GLASS TRANSITION TEMPERATURE.

SIGNIFICANCE OF GLASS TRANSITION TEMPERATURE

• Once the impression tray is seated,it should be held firmly in position until first fusion temperature & later GTT is reached , thus the impression is made above the fusion temperature where as it is removed from the mouth only after it cools down to its Glass Transition Temperature.

• FUSION TEMPERATURE-On further heating at approx.43.5°C the material softens to a plastic mass that can be manipulated .This is called fusion temperature.It is the temperature at which crystalline fatty acid melts (or solidify).

• SIGNIFICANCE OF FUSION TEMPERATURE-• Above this temperature 43.5°C the fatty acids are

liquid & lubricate the softened material to form a smooth plastic mass, while the impression is being obtained.Thus all impressions with compound should be made above this temperature.Below this temperature an accurate impression can’t be expected.

THERMAL PROPERTIES-• Impression compound has very low thermal

conductivity i.e they are poor conductors of heat.• SIGNIFICANCE-• During softening of the material the outside will

soften first & the inside last,so to ensure uniform softening IC be kept for sufficiently long time in a water bath.Kneading of the material ensures further uniform softening. Due to poor thermal conductivity, the layer adjacent to the mouth tissues will remain soft ,removal of which will cause distortion.Thus it is important to cool the compound thoroughly before removing it from the mouth.

COEFICIENT OF LINEAR EXPANSION (CTE)

• CTE of a IC is comparatively high due to presence of resins & waxes .The linear contraction from mouth temperature to room temperature is 0.3% ,this error can be reduced by 1) By making an impression as usual & then passing the impression over a flame until the surface is softened & then obtaining a second impression.During the second impression shrinkage is relatively slight since only the surface layer has been softened completely.

• FLOW- • Good flow is desirable in impression making. The

softened material should flow in to all the details of the tissue contour.Once the I.C hardens it should have minimum flow lest it gets distorted.

• According to ADA specification no 4• Type 1:IMPRESSION COMPOUND-flow not more than

3% at 37°(oral temp.)• Flow not less than 80% & not more than 85% at

45°C.• Type 2: TRAY COMPOUND-Flow not more than 2% at

37°C.• Flow not less than 70% and not more than 85%

at 45°C.

DIMENSIONAL STABILITY

• Since the release of strains is unavoidable, the safestway to prevent distortion is to pour the cast immediately or at least with in the hour.Another cause of warpage is the removal of the impression too early before it is thoroughly cooled in the mouth.

MUCOCOMPRESSIVE TECHNIQUE vs REPRODUCTION OF DETAIL

• Mucocompressive technique records the oral tissues in a functional & displaced form. The material used for this technique include I.C ,waxes & softliner.The oral soft tissues are resilient & thus tend to return to their anatomical position once the forces are relieved .

• Dentures made by this technique tend to get displaced due to tissue rebound at rest.During function ,the constant pressure exerted on to soft tissues limit the blood circulation leading to residual ridge resorption.

MANIPULATION

• The fusion temperature of the compound indicates a definite reduction in plasticity of the material during cooling. Above this temperature, the softened material remains plastic while the impression is being made. Once the impression tray is seated, it should be held gently (passively) in position until the impression cools below the fusion temperature. Under no circumstances should the impression be disturbed or removed until it reaches oral temperature. Compound may be softened over a flame or by immersion in a warm water bath when a large amount is needed.

• Once the impression tray is seated, it should be held gently (passively) in position until the impression cools below the fusion temperature. Under no circumstances should the impression be disturbed or removed until it reaches oral temperature. Compound may be softened over a flame or by immersion in a warm water bath when a large amount is needed.

• When a direct flame is used , the compound should not be allowed to boil or ignite so that the constituents are volatilized. prolonged immersion or overheating in the water bath is not indicated; the compound may become brittle and grainy if some of the low molecular weight ingredients leach out of the material. Softening of the compound in a warm water bath is the method recommended for separating the cast from a compound impression .

Advantages of Impression Compound • Non irritant & nontoxic• Reusable.• Can be reheated & readapted• Can support other materials for wash Impressions.• Easy manipulation.• Low cost• Good dimensional stability but excessive water

incorporation during wet kneading can cause dimensional change.

• In making of TUBE IMPRESSIONS.• DISADVANTAGES• Highly viscous • Can displace tissue surface• It does not record surface details very accurately

due to poor dimensional stability.• Will distort if removed from undercuts.

ZINC OXIDE EUGENOL(ZOE) IMPRESSION PASTE

• Zinc oxide & eugenol are widely used in dentistry.Under proper conditions the reaction between ZnO & Eugenol yields a relatively hard mass that has certain medicinal advantages as well as mechanical property benefits ,for some dental operations.

• ZnO eugenol is used as an impression material for edentulous mouth ,a surgical dressing, bite registration paste,temporary filling material,rootcanal filling material ,cementing medium,& temporary relining material for dentures.

According to ADA specification no:16

• Type 1 HARD PASTE - Final setting should occur with in 10 min.Initial setting time 3-6 min.

• TYPE 2nd SOFT PASTE- Final setting should occur with in 15 min.Initial setting time 3-6 min.

• INITIAL SETTING TIME- Period from the beginning of mixing until the material ceases to pull away or string out when its surface is touched with a metal rod.

• FINAL SETTING TIME: When a needle of specified dimension fails to penetrate the surface more than 0.2mm,under a load of 50 gms. to be precise.

Composition of a Zinc Oxide-Eugenol Impression Paste

• COMPONENTS PERCENTAGE

• TUBE NO. 1 (BASE)• Zinc oxide (French-processed or U.S.P.) 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 3%• Resinous balsam 10%• Accelerator Solution (CaCl₂,) and color 5%

ROLE OF INDIVIDUAL COMPONENTS

• Vegetable or mineral oil acts as plasticizer and also aids in masking the action of eugenol as an irritant.

• Oil of clove contains 70-85% eugenol.It is sometimes used in preference to eugenol because it reduces burning sensation.

• Addition of rosin to the second tube speeds up the reaction.• Canada & Peru balsam used to increase flow & mixing

properties.• Other accelarators are: Zinc acetate,Primary Alcohals,Glacial

acetic acid.

Manipulation

• The mixing of the two pastes is generally accomplished on an oil-impervious paper or a glass mixing slab. The proper proportion of the two pastes is generally obtained by squeezing two strips of paste of the same length, one from each tube, onto the mixing slab. A flexible stainless steel spatula is typically used for the mixing procedure. The two strips of contrasting colors are combined with the first stroke of the spatula, and the mixing is continued for approximately 1 min, or as directed by the manufacturer, until a uniform color is achieved.

• . A flexible stainless steel spatula is typically used for the mixing procedure. The two strips of contrasting colors are combined with the first stroke of the spatula, and the mixing is continued for approximately 1 min, or as directed by the manufacturer, until a uniform color is achieved.

SETTING REACTIONThe setting reaction is a typical AcidBase reaction to form a chelate.The reaction is called chelation & the product is Zinc

Eugenolate.ZnO + H₂O→Zn(OH)₂

Zn(OH)₂ + 2HE→ZnE₂ +2H₂O.

-OH and methoxy group of Acid Eugenol

chelate structure of salt Zinc Eugenolate

Factors controlling the setting time

• Particle size of ZnO powder- If the particle size is small & if it is acid coated,the setting time is less.

• By varying the lengths of the two pastes.(not recommended)

• Setting time can be decreased by adding zinc acetate or a drop of water or acetic acid.(acetic acid is more effective than water.It increases speed of formation of the zinc hydroxide.

• Longer the mixing time ,shorter is the setting time .

• High atmospheric temperature & humidity accelerates setting.

• Setting can be delayed by cooling the mixing slab(slab not be used if its temperature is below the dew point),spatula,or adding small amounts of retarder.

Dimensional Stability &Disinfection• The dimensional stability of the impression pastes is

quite satisfactory. A negligible shrinkage (less than 0.1%) may occur during hardening. No significant dimensional change subsequent to hardening should occur with high-quality commercial products

• The recommended disinfectant solution for ZOE impression paste is 2% alkaline glutaraldehyde solution.It is not compatible with chlorine compound unlike I.C, Phenolic spray can be used(as in I.C)

• Noneugenol Pastes• One of the chief disadvantages of the ZOE

pastes is the possible stinging or burning sensation caused by the eugenol that leaches out and contacts soft tissues Zinc oxide can react with various carboxylic acids and form ZOE like materials Orthoethoxybenzoic acid, commonly abbreviated as EBA, is a valuable substitute for eugenol in this regard.

• Surgical Pastes• After a gingivectomy (i.e., the surgical removal

of diseased or redundant gingival tissues), a zinc oxide-eugenol paste may be placed over the wound to aid in the ‘retention of a medicament’ and to promote healing. These pastes are generally softer and slower in their setting reaction in comparison with impression pastes.

• The mixture being formed in to a rope i.e packed in to the wounds and the interproximal spaces to provide retention of the dressing. The final product should be strong enough to resist displacement during mastication, but not so brittle that it shears readily under localized stresses.

• Bite Registration Pastes• The materials used for recording the occlusal relationships

between natural or arlificial teeth include impression plaster, compound, wax, resin, and metal oxide paste. Zinc oxide-eugenol pastes are often used as recording materials in the construction of complete dentures and fixed or removable partial dentures. The ZOE impression paste offers almost no resistance to closing of the mandible, thus allowing a more accurate interocclusal relationship record to be formed. furthermore, the ZnO Eugenol interocclusal record is more stable than one made in wax.

• Advantages• Sufficient body to make up for any minor

underextensions in tray itself during impression making.

• Enough working time to complete border moulding.• Registers accurate surface details.• Dimensionally stable• Not requires separating media.• Disadvantages• Sticky in nature and adheres to tissues.• Eugenol can cause burning sensation & tissue irritation

since free eugenol leeches out.

Powder particles of plaster of paris.The crystals are spongy & irregular in shape.

IMPRESSION PLASTER

• Impression Plaster (Type 1 gypsum Product) Is based on calcined Calcium sulphate hemihydrate, which reacts with water to form a hard mass of calcium sulphate dihydrate.

• Chemical reaction• CaSO 2H₂O→(110-130°C)→CaSO₄.1/2 ₄̇�

H₂O)130-200°C→CaSO₄(Hexagonal anhydrite)

• Composition: CaSO4 . 0.5H2O β-hemihydrate+K₂SO₄+Borax+Coloring & Flavouring Agent.

• Potassium sulfate – to reduce expansion but accelerates setting.

• Borax – a retarder to prolonge setting time.• Diatomaceous earth, quartz, lime - to make the

plaster more brittle.• POTATO STARCH-Impression plaster containing

potato starch to make it soluble(SOLUBLE PLASTER) after cast has hardened on putting in hot water starch swell making cast separation easy.

• Main indication:Primarily restricted to use as a final impression (Wash impression) in construction of Complete dentures,Bite registration material.

• Setting reaction: CaSO4.0.5H2O + 1.5H2O CaSO4.2H2O + heat

+expansion• The setting reaction is associated with expansion of 0.3-0.6%

when this is with in the confines of an impression tray will lead to significant reduction in accuracy.Mixing the plaster with anti expansion solution (4% K₂SO₄ &0.4% Borax) will reduce this.

• K₂so₄ reduces expansion to 0.05% but this also acclerates the setting reaction & borax is added as a retarder which gives more time for making impression.

•

A quick setting, type I, reliable impression plaster. Commonly used for impression, soldering transfers, labial and occlusal indexes, and fabrication of temporaries. It has a compressive strength of 350psi, an initial setting time of 3-5 minutes.

PROPORTIONING, MIXING, AND CARING FOR IMPRESSION PLASTER

• The water and powder should be measured by using an accurate graduated cylinder for the water volume and a weighing balance for the powder.

• The powder should not be measured volume (use of a scoop), because powder varies from product to product and does not pack uniformly. Powder will pack harder as the container remains unused. If the container is shaken, the volume increases as a result ot entrapment of air.

• Preweighed envelopes have become popular, because they promote accuracy,reduce waste, and save time.

Mixing• If mixing is performed by hand, the bowl

should be parabolic in shape, smooth, andresistant to abrasion. The spatula should have a

stiff blade and a handle that is convenientto hold.• Entrapment of air in the mix must be avoided

to prevent porosity,leading to weak spots and surface inaccuracies,

2) Plaster impression 3) A plaster impression with wax beading around it's periphery

Section through a cast of a set plaster that was improperly mixed, Air voids weaken the plaster and impair its appearance .

.

• Section through a cast of set plaster that was properly proportioned & mixed .

• The use of an automatic vibrator of high frequency and low amplitude is helpful.

• P lace a measured amount of water in the bowl, and sift the weighed powder into the water as initial hand mixing is performed.

• Then stir the mixture vigorously, periodically wiping the inside of the bowl with the spatula to ensure the wetting of all of the powder and the breaking up of any agglomerates, or lumps Continue mixing until a smooth mix is obtained, usually within a minute .

• 'I'he guesswork of repeatedly adding water and powder to achieve the proper consistency

must be avoided, because this yields a lower strength and it may cause distortion, & is

one of the main causes of inaccuracy in the use of gypsum products.

• The preferred method of mixing of impression plaster is to add the measured water first, followed by gradual addition of the preweighed powder 'I'he powder is incorporated during approximately 15 sec of mixing with a hand spatula, followed by 20 to 30 sec of mechanical mixing under vacuum.

Caring for the Cast• If the surface of the cast is not hard and smooth when it

is removed from the impression, its accuracy is questionable. 'The cast should be an accurate reproductionof the oral tissues, & any departure from the expected inaccuracy will probably result in a poorly fitting prosthesis. 'I'herefore the cast should be handled carefully.

• Once the setting reactions in the cast have been completed, its dimensions will be relatively constant thereafter under ordinary condition of room temperature and humidity.

• The gypsum cast is slightly soluble in water. When a dry cast is immersed in water, negligible expansion may occur, provided that the water is saturated with calcium sulfate. If it is not so saturated, gypsum may be dissolved.

• If the stone cast is immersed in running water; its linear dimension may decrease approximately 0.1% for every 20 min of immersion. The safest method for soaking the cast is to place it in a water bath made for the purpose, in which plaster debris is allowed to remain constantly on the bottom of the container to provide a saturated solution of calcium sulfate.

• if the storage temperature is raised to between 30° and 110° , shrinkage occurs as the water of crystallization is removed and the dihydrate reverts to the hemihydrate.

The contraction of plaster at high temperature is greater than that of the stone, and it also loses strength.

• It is not safe to store or heat a stone cast in air at a [emperature higher than 55°C ( I 30°F).

• Gypsum surfaces made with thinner mixes appear to be affected more than those with a low W/P ratio.

• The best means of storage is to seal the product in a moisture-proof metal container, When gypsum products are stored in closed containers, the setting time is generally retarded only slightly, apploximately 1 or 2 min, per year. This may be counteracted by a slight increase in the mixing time if necessary.

• TYPICAL PROPERTIES OF PLASTER IMPRESSION• 2Hr SettingExp. 1HrComp.St• TYPE 1 W/P SETTING TIME Min. Max. Mpa Psi • IMPRESSION 0.4-0.75 4±1 min. 0.0 0.15 4.0 580

• PLASTER•

• MIXING TIME WORKING TIME SETTING TIME

• HandMixing 1 min. 3 min. 4±1min.• Mechanical mixing• 20-30sec.

• Advantages:• 1. Cheap and long shelf life, easy to prepare• 2. Excellent surface detail reproduction• 3. Excellent dimensional stability• 4.Rate of setting reaction can be controlled by the clinician.• 5. Mucostatic.• Disadvantages:• Can not be used for mucodisplacive impression materials.• Very rigid – often need to be fractured when• removed from the mouth• Fractures if undercuts are present• Non-toxic but may dry soft tissues - unpleasant to• patients

IMPRESSION WAXES • (BITE WAXES or CORRECTIVE WAXES)

• DENTAL IMPRESSION WAX- According to Kenneth J. Anusavice Dental impression wax is a thermoplastic wax used to make a type of dental impression.

BITE REGISTRATION WAX

IMPRESSION WAXES TYPES

• TYPES-

CORRECTIVE IMPRESSION WAX.

BITEREGISTRATION WAX.

CORRECTIVE IMPRESSION WAX:

• CORRECTIVE IMPRESSION WAX:• • COMPOSITION & PROPERTIES: They consist of Paraffin,Ceresin

& Beeswax.It may also contain metal particles.• Flow at 37°C is 100%. These waxes are subjected to distortion

during removal from the mouth.They should be poured immediately.

• USES-• It is used as a wax venner over an original impression to contact

& register the details of the soft tissues.• To make functional impression of free end saddles.(Class 1 &2)

R.P.D.• To record posterior palatal seal in dentures.• Functional impression for obturators.

MOUTH TEMPERATURE WAX

BITE REGISTRATION WAX

• COMPOSITION- Beeswax,paraffin, ceresin,aluminium or copper particles

• SUPPLIED AS: U shaped rods on wafers. One side of the wax is usually covered with foil

• MANIPULATION: The wax is softened in warm water.The soft wax is then placed between the teeth & the patient is asked to bite.The wax is then taken out & placed in chilled water.the cast of the patient is placed in the indentation formed by the teeth.It is then mounted with plaster on the articulator.

• USES- It is used to record the relationship between the upper & lower teeth.This is necessary in order to mount the casts correctly in the articulator.

REFERENCES

• KENNETH J. ANUSAVICE• CRAIG RESTORATIVE DENTAL MATERIAL.• INTERNET.