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
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
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
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