PROF. AMAL EZZ ELDIN DENTAL BIOMATERIALS

2012

Elastomeric Impression Materials

Rubber-like in nature *polymers (ADA No. 19: Non Aqueous

Elastomers).

They are synthetic rubber and formed by chemical reaction.

The process of changing the elastomeric base into final

rubber-like material known as polymerization

They offer potential solution to two main problems of hydrocolloids

1. Poor tear strength

2. Poor dimensional stability

Uses:

.Impression for crown and bridge.

• Impression for Partial and complete denture.

Non-aqueouselastomers

Non-aqueouselastomers

PolyethersPolyethers

Additionsilicone

Additionsilicone

Condensationsilicone

Condensationsilicone

PolysulfidesPolysulfides

ElasticElastic

-Hydrocolloids-HydrocolloidsClassification

Characteristics or Elastomeric Impression

MaterialsBase

Packaged as a paste in a tube, as a cartridge, or as putty in a jar.

CatalystAlso known as the accelerator, is packaged

as a paste in a tube, as a cartridge, or as a liquid in a bottle with a dropper top.

Forms of Elastomeric Materials

Light-bodiedAlso referred to as syringe type, or wash type.

This material is used because of its ability to flow in and about the details of the prepared tooth. A special syringe, or extruder, is used to place the light-bodied material on and immediately around the prepared teeth.

Heavy body

Light body

Forms of Elastomeric Materials- cont’d

Regular and heavy-bodiedOften referred to as tray‑type materials, they

are much thicker. As the names imply, they are used to fill the tray. Their stiffness helps to force the light‑bodied material into close contact with the prepared teeth and surrounding tissues to ensure a more accurate impression of the details of a preparation.

Elastomers Setting reaction: Polymerization for Chain-

lengthening & Cross-linking Condensation polymerization

Polysulphide Condensation silicone

Additional polymerization Additional silicone

Cationic polymerization Polyether

Polysulfide

I-

Polysulphides

•

Polysulphide polymer

· Copper carbonate

· Titanium carbonate

Or silica as filler materials.

BASE CATALYST

•

• Lead dioxide(PbO2)• Dibutyl pthalate• Sulphur

Polysulfide A polyfunctional

mercaptan or polysulfide polymer Terminal S-H

Chain-lengthening 1 mol% Pendent S-H

Cross-link Initiated by an

oxidizing agent such as lead dioxide.

By-product = H2O Exothermic reaction

Reaction: condensation polymerization

Terminal and pendant groups of polymer are

oxidized by lead dioxide chain extension of

terminal SH gp and cross linking of pendant

gp.

Polysulphide polymer + lead dioxide

polysulphide rubber + lead oxide + H2O …..

Exothermic 3-4°C.

in molecular weight

Paste rubber.

Base: three consistencies

low: syringe ------ light body

Medium ----------- regular

High: tray ----------- Heavy body

As % filler

increase

viscosity

increase

s

Lead dioxide: is dark brown to

gray brown in colour and toxic.

So substituted by hydrated

Cu(OH)2

green mix

light body

heavy body

Properties of clinical interest

Setting time: 8-14 minutes this is one of the problem that we don’t use it very much as it is annoying for the pt to put the impression inside the pt mouth for more than 10 min.

Higher tear strength than hydrocolloids Accuracy improves if impression is poured within

30 minutes (after 30min water can be produced and evaporate changing its shape.

very unpleasant taste and odor this is another reason why we don’t use if often.

Messy ( can stain clothes ) Can be irritant to oral mucosa

For all these reasons, Polysulfides have been largely replaced by other rubber materials

17

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