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DR.MARIAM AKHLAQUE

DEMONSTRATOR

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IRREVERSIBLE REVERSIBLE

INELASTIC / RIGID IMPRESSION WAXESIMPRESSION PLASTEZnO EUGENOL ( ZOE )

IMPRESSIONCOMPOUND

ELASTIC ALGINATEELASTOMERS

AGAR

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COMPOSITION:* β-calcium sulphate hemihydrate

higher water/powder ratio (approximately 0.60)than is normally used for modeling plaster.

* Anti-expansion agents - Potassium sulphatesecondary effect of accelerating the settingreaction.

* A retarder, borax to promote setting time.

* Diatomaceous earth, quartz, lime - to make theplaster more brittle* Pigment such as ALAZERIN RED

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SPECIAL TRAY : made of shellac or acrylicwith 1-1.5mm spacer

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Recording impressions of patients with excessively mobilesoft tissues overlying the residual alveolar bone (a ‘flabby’ridge).

A flabby ridge is one which becomes displaceable due tofibrous tissue deposition seen in the upper anterior region.Usually occurs when natural teeth oppose an edentulous

ridge. A flabby ridge causes instability of the denture.

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Two stage technique:

a special tray is made with appropriate spacing for

zinc oxide/ eugenol paste where the mucosa is well

supported and having a window overlying the‘flabby’ area.

BULK of the ridge is recorded - ZOE impression

(excess material remove from the window )

FLABBY RIDGE recorded – impression plaster

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Advantages:1. Cheap and long shelf life, easy to prepare2. Very good surface detail reproduction3. Excellent dimensional stability

Disadvantages:1. Very rigid – often need to be fractured when

removed from the mouth2. Fractures if undercuts are present

3. Non-toxic but may dry soft tissues – unpleasant

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Thermoplastic materials consisting of paraffinand bees wax in a ratio of 3:1

Used to correct imperfection / faults in otherimpression particularly with ZnO eugenolpastes.

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COMPONENTS EXAMPLES

THERMOPLASTIC MATERIAL synthetic resin n47% waxes

FILLERS 50% talc

LUBRICANT 3% stearic acid

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TYPE 1 – lower fusingimpression material

available in two forms :sheet formstick form

Type 2 – higher fusingused for constructing impression

trays

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The sheet material - used for recording impressions of edentulous ridges, using stock trays.The stick material - used for border extensions onimpression trays or for recording impressions of single

crown.

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Sheet form - ideally soften using a waterbath

having a temperature range 55-60ºC .ideal temperature and time of conditioning isimportant.

effects of temperature:low  – material doesn’t soften properly  

high - material become sticky and un manageable

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Effect of conditioning time:It should not be so long that constituents,such as stearic acid leached out.

STICK FORM: The stick material is generallysoftened using a flame. The material istempered in a water bath before placing inthe patient’s mouth 

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The stick material is used for border

extensions on impression trays. for recording impressions of single crowns

using the copper ring technique.

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full denture plaster of paris single stage special trayZnO EUGENOL single stage special tray

compo – ZnO eugenol two stage stock tray

Partial denture Alginate single stage stock trayelastomers single stage special tray

Fixed dentures compound imp single stage copper ring techelastomers single stage special tray

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Hi viscosity – it limits the degree of fine detail

recorded in an impression.

Muco- compressive impression material – 

displaces the lingual and buccal soft tissues viscosity is an advantage when recording

impressions of edentulous patients WHERE it is

necessary to record the full depth of the sulcus so

that a denture with adequate retention can be

designed. Fairly rigid

Poor elastic properties

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Internal stresses are produced within thecompound impression.

(1) hi value of coefficient of thermalexpansion.(2) The poor thermal conductivity.(3) The relatively large temperature drop

from the softening temperature to mouthtemperature

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Can be reused Non toxic

Non irritant

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Supplied as two pastes Mixed together on paper pad or glass slab

Pastes 1 - Zinc oxide Olive oil Zinc stearate Water Pastes 2 - Eugenol koalon or talc

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used to record the secondary impressions of edentulous arches. The impression is

normally recorded in a close-fitting ( specialtray) constructed on the model obtainedfrom the primary impression, or on patient’sexisting denture.

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The thickness of paste is normally around1 mm.

low viscosity allow fine details to be recordedminimum dimensional changeeugenol may cause allergic reaction.