Impression materials

by

Bibin bhaskaran

Impression materials

Definition :- (GPT):

1) A negative likeness or copy in reverse of the surface or object.

2) An imprint of the teeth and adjacent structures for use in dentistry

Impression material:- Any substance or combination of

substances used for making an impression or negative reproduction.

Impression technique:- A method and manner used in

making a negative likeness.

inelastic or rigid

elastic

material use material use

Chemical reaction (irreversible)

plaster of Paris Edentulous ridge

Alginate hydrocolloid

Teeth and soft tissues

zinc oxide-eugenol

Interocclusal records

Non aqueous elastomers Polysulfide,polyether Condensation silicone Addition silicones

classification

Thermally induced Physical reaction(reversible)

Compound wax

Preliminary impression

Agar TEETH & SOFT TISSUES

Classification

Based on rigidity : Rigid

eg Plaster,Zincoxide eugenol

impression compound

Elastic

eg Alginate,polyether,silicone

Based on setting of the material: 1.) Chemical reaction(irreversible)

eg plaster of paris,zincoxide eugenol

alginate,additon and condensation silicones

2 ) Physical change of state(reversible)

eg agar

Based on viscosity : Mucostatic

eg impression plaster,agar, light body elastomer

Mucocompressive

eg Impression compound,alginates Pseudoplastic

eg addition silicones

Based on interaction with saliva and water : Hydrophobic eg polysulfide ,condensation silicones Hydrophilic eg putty,impression plasterBased on use : Primary impression material eg impression compound,alginate

Secondary Impression material eg Zoe,medium bodied elastomers Duplicating material eg agar

Based on

Chemical composition : impression plaster

impression compound

metal oxide(zinc oxide eugenol)

pastes

agar hydrocolloid

alginate hydrocolloid

polysulfides

condensation silicones

addition silicones

polythers

light curing polyether

(urethane dimethacrylate)

Desirable qualities

Pleasant odor taste and color Absence of toxic irritants Adequate shelf life Economical Easy to use Setting that meet clinical

requirements Satisfactory consistency

Readily wet oral tissues Elastic Adequate strenght Dimensional stability Compatiblity with cast and die

materials Accuracy Disinfection

Impression plasterADAspecification

Composition

Uses Mixing time

Working time

Setting time

Advantages

Disadvantages

No 25 •Calcined caso4•Anti – expansion agents k2so4•Accelerators k2so4•Retarder borax•Gelatin •Gum tragnath•Starch•Alizarin red

•Primary impression material•Secondary impression material

60 sec Altered by use of additives

same •Good deatail reproduction•Inexpensive •Easy to handle•Non toxic•Increased shelf life•Setting time can be controlled.

•Requires separating medium•Dry sensation to patients mouth

Impression plaster

The impressions are very accurate Being hydrophilic it has got intimate contact with

oral tissues by absorbing surface moisture

Impression compoundADAspecification

Composition

Uses Flow Advantages

Disadvantages

Disinfection

No 3•Type 1-Impression(low fusing)•Type 2-Tray(high fusing)

•Rosin •Copal resin•Carnauba wax•Stearic acid•Talc•Coloring agent

•Type 1-primary impression,peripheral tracing•Type 2-As a tray to support other materials

•Type 1 flow at mouth temp is 6%•Type 2 flow at mouth temp is 2%

•Non toxic and non irritant•Hardens in reasonably acceptable time•Compatible with gypsum products•No separating medium required

•Although plastic not fluid enough to record fine detail•Distorts over undercuts•Shrinkage on cooling•Dimensional change on storage

2%alkaline glutarldehyde

Impression compound

Fusion temperature of impression compound is 43.5 degree celesius

Zinc oxide eugenol impression materialADAspecification

Composition

Uses Mixing time

Setting time

Advantages

Disadvantages

Disinfection

No 16•Type1 (hard)Type 2 (soft)

2 tubesTube 1-•ZnO•Veg or mineral oilTube 2-•Clove oil or eugenol•Gum/polymerised rosin•Filler silica•Lanolin•Accelerators –cacl2,mgcl2

•Impression pastes•Cement•Temporary filling•Root canal filling•Bite registration paste•Temporarly reline material•Surgical dressing

1 min/30-40 sec

Type 1-Initial –3-6minFinal-10 minType 2-Initial-3-6minFinal –15 min

•Adheres well to tray•Sufficiently fluid to record fine detail•No dimensional change in setting process•Hard when set•No separating medium required•Non toxic

•Burning of eugenol•Persistent taste•Adheres to tissue•Rigid material cant be used

2% glutarldehyde

Zincoxide eugenol impression material

Non eugenol pastes-

One of the chief disadvantages of Zoe pastes is the possible burning sensation caused by eugenol.orthoethoxybenzoic acid (EBA) is a valuable substitute for eugenol in this regard.

Alginate ADAspecification

Composition

Uses Mixing time

Working time

Setting time

Advantages

Disadvantages

Disinfection

No 18Type 1(Fast)Type 2(Slow)

•Soluble alginatesNa,K,Ammonia•Calcium sulphate dihydrate•Trisodium phosphate•Diatomaceous earth•Potassium titanium fluoride•Flavourin agent.

•To record impressions of dental arches•Premilinary impression•Duplicating cast and models

Type 1-45secType 2-1min

Type 1-1.25-2minType 2-3-4.5min

Type 1-1-2minType2 –2-4.5min

•Non toxicand non irritant•Acceptable odor•Compatible with gypsum•Elastic •Sufficiently fluid

•Dimensionally unstable•Tears if undercuts severe•Difficult to sterilize•Poor shelf life

•10 min in sodium hypochlorite solution•10 min in iodophor solution •10 min in glutaraldehyde solution

Alginate

Gelation reaction-

2Na3P04 + 3CaSo4----- Ca3(Po4)2+3 Na2SO4

Recent advances in alginates

Dust free alginates-

De-dusting agent (glycerin or glycol)

Siliconized alginates-

silicon polymers are added to strengthen the material

Alginates containing disinfectants-

eg quaternary ammonium salts or chlorohexamine are added to alginate powder.

Hard and soft set alginates-

by adjusting the amount of fillers

Reversible hydrocolloid-AGARADAspecification

Composition

Gelation temperature

Liquefaction temperature

Advantages

Disadvantages

Disinfection

No 11 •Agar•Sulfates (k2so4)•Borax •Alkyl benzoate•Water •Fillers(silica)•Plasticizer(glycerine)•Bactericide (thymol)colors

37 degree celesiusTo45 degree celesius

60 to 70Degree celesius

•No custom tray required•Clean and pleasant•Easy to pour•Inexpensive•Good shelf life•High accuracy•Re-usable

•Requires conditioning unit•Decreased dimensional stability•Weak inn deep sulcus

Iodophor /bleach/glutarldehyde

Agar

Gelation-

Gelation is accomplished by circulating cold water of approximately 18-23 degree for not less than 5 min.

Elastomeric impression materials

Classification :-Based on viscosity-

Class 1 heavy body heavy viscosity

Class 2 regular body or medium body

Class 3 light body or low viscosity

Based on chemistry-

Polysulfides

Condensation silicones

Additional slilicones

Polythers

Visible light curable polyether

POLYSULFIDESADASpecification

Composition

Mixing time

Working time

Setting time

Advantages

Disadvantages

Disinfection

No 19

1,Base paste –•Liquid polymer containing thiol,mercaptan or polysulfide polymer.•Filler –titanium dioxide•Plasticizer-DI-n-butyl phthalate•Sulfur

2,Reactor paste-•Pbo2 or organic hydroperoxides or inorganic hydroxides•Inert oil/plasticizer•Filler -silica •Stearic acid

45 sec-1min

5-7min 8min •No special equipment•Superior strength•Pouring can be delayed to 1 hr•Can be electroplated•Adequate shelf life

•Custom trays required•Hydrophobic•Sensitive to heat•Long setting time•High shrinkage•High permanent deformation

2% glutarldehyde

polysulfides

Polysulfide is one of the least stiff or highly flexible of elastomeric material

For accurate polysulfide impressions- The cast should be poured immediately after taking

impression Minimise the amount of material used to take impression

by using custom made acrylic trays

ADASpecification

Composition

Mixing itime

Working time

Setting time

Advantages

Disadvantages

Disinfection

No 19

2 types- 1,Double mix type 2,Putty type

Base paste-•Polydimethyl siloxane/liquid silicone polymer•Filler –silicaReactor paste-•Tetra functional silicates•Tin compound

45 sec Upto 5 min

10 – 12 min

•No special equipment required•Moderate strenth in deep sulcus•Adequate shelf life•Pleasant odor

•Custom tray required•Difficult to electroplated•hydrophobic

2% glutaldehyde

Condensation silicones(Double mix type)

Condensation silicones

It is also called room temperature vulcanising silicones(RTV)

Uses – It is widely used in recording dentulous impressions in

preparation of crowns,bridges,inlays,onlays and to some extent for partial dentures

It is also used to record edentulous impressions in preparation of complete denture

Putty type

Advantages – No custom tray required No special equipment required Moderate strength in deep sulcus Pleasant odor Adequate shelf life

Disadvantages – Should be poured shortly after removal Hydrophobic Difficult to electroplate Easily distorted

Addition silicones(Double mix type)

ADASpecification

Composition

Mixing itime

Working time

Setting time

Advantages

Disadvantages

No 19

2 types1,Double mix type2, Putty type

•Polymer –polyvinyl siloxane,vinyl polysiloxane,vinyl silicones•Cross linking agent-hydride silicone•Catalyst –chloroplatinic acid

30- 45 sec

Is greater than silicones

10-12min

•No special equipment•Dimensionaly stable•Good shelf life•Pleasant odor

•Custom tray•Hydrophobic •Expensive

Addition silicones

Addition polysilicones are the most stable of all the existing materials

It has an excellent recovery of 99.93% It exhibits pseudoplastic properties.it can be used both

as syringe and tray materials

Putty type

Advantages –

No custom tray No special equipment Good shelf life Can be poured more than once

Disadvantages –

Extremely hydrophilic More difficult to pour Most expensive

Polyether materialsADASpecification

Composition

Mixing itime

Working time

Setting time

Advantages

Disadvantages

No 19Base plate tube-•Pre polymer-ethylene amine•Inert filler-silica•Plasticiser –glycoletherCatalyst paste-•Ester derivatives of aromatic sulphonic acid•Plasticiszer –phthalate•Thinner-octyl phthalate•Methyl cellulose

30-45 sec

2-3min 5-6 min•No special equipment•Finish line easily read•Pleasant odor•Can be poured more than once•Hydrophilic•Good shelf life•Fast setting

•Custom tray•Very stiff•Least tear strength•More expensive

Polythers

Uses- For recording impression in preparation of

crowns and bridges Cavity preparation for inlays and onlays For construction of partial and complete

dentures

Visible light cured polyether

ADASpecification

Composition AdvantagesDisadvantages

No 19Introduced in 1988

Light bodied material=syringeHeavy body=tubes Contains•Polyurethane dimethacrylate resin with sio2 +plasticizer•Polymerises in light

•Complete control over W.T/S.T•Curing time relatively short•Excellent physical/mechanical/clinical properties

•Need for transparent trays•If delay in placement material to be stored in dark place•Difficult to cure remote areas•Should not be used in patients allergic to methacrylates

Light cured polyether

It has excellent elasticity It has infinite working time and short setting

time The impression can be stored upto two weeks

Disinfection

Most manufacturers recommend a specific

disinfectant,such as iodophor,bleach,or glutaldehyde,for disinfection.

Certain disinfectants may result in gypsum casts that have a lower surface hardness or diminished surface detail.

The current protocol for disinfecting hydrocolloid impressions recommended by the centre for disease control is to use house hold bleach(1 to 10 dilutions),iodophor or synthetic phenols as disinfectants

An alternate disinfection method is by immersion,but this should not exceed 10 min.

Duplicating is required for two reasons:-

1, The cast on which the wax pattern of the metal frame work is to be formed must be made from refractory investment because it must withstand the casting temperatures required for gold or base metal alloys

2, The original cast is needed for checking the accuracy of the metal frame work and for processing the denture base portion of the partial denture

The most common duplicating materials are agar hydrocolloid compounds, The primary advantage of agar is their set is reversible.the disadvantage is it is subject to dimensional change.The best storage condition is 100% humidity.

Duplicating materials

Tissue conditoners are soft elastomers used to treat an irritated mucosa supporting a denture.it is used to provide time for healing of soft tissues

Tissue conditioners are composed of powder containing poly(ethyl methacrylate)and a liquid containing an aromatic ester – ethyl alcohol.

The properties that make tissue conditioners effective are-

1,viscous behavior which allows adaptation to irritated denture bearing mucosa

2,viscoelastic behavior which cushions the cyclic forces of mastication and bruxism

Tissue conditioners

Zardiackas.L.D , Dental materials,Dentla clinics of morth america,July 2007,vol 51,pg 629-643 .

O’Brien.W.J, Dental materials and their selection, 3rd edition, Quintessence publications.

Craig.R.G, Dental Materials, 12th edition, Elsevier publications.

Anusavice, Phillip’s Science of Dental Materials, 11th edition, Saunders publications. Impression materials.

References