1. Prof. Amal EZZ ELDIN DentaL biomaterials 2012
Elastomeric Impression Materials
Prof. Amal EZZ ELDIN DentaL biomaterials 2012

2. 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
Poor tear strength
Poor dimensional stability
Uses:
.Impression for crown and bridge.
Impression for Partial and complete denture.

3. Classification Elastic Polysulfides Polyethers -Hydrocolloids
Non-aqueous
elastomers
Condensation
silicone
Addition
silicone

4. Characteristics or Elastomeric Impression Materials
Base
Packaged as a paste in a tube, as a cartridge, or as putty in a jar.
Catalyst
Also 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.

5. Forms of Elastomeric Materials
Light-bodied
Also 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.
Light body
Heavy body

6. Forms of Elastomeric Materials- cont’d
Regular and heavy-bodied
Often 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.

7. Elastomers
Setting reaction: Polymerization for Chain-lengthening & Cross-linking
Condensation polymerization
Polysulphide
Condensation silicone
Additional polymerization
Additional silicone
Cationic polymerization
Polyether

8. Polysulfide

9. Polysulphides BASE CATALYST Lead dioxide(PbO2) Dibutyl pthalate
Polysulphide polymer
Copper carbonate
Titanium carbonate
Or silica as filler materials.
BASE
CATALYST
Lead dioxide(PbO2)
Dibutyl pthalate
Sulphur

10. 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

11. 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.

12. As % filler increase viscosity increases
Base: three consistencies
low: syringe light body
Medium regular
High: tray Heavy body
As % filler increase viscosity increases

13. Lead dioxide: is dark brown to gray brown in colour and toxic.
So substituted by hydrated Cu(OH)2  green mix

15. light body
heavy body

17. 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

18. Important notice To help you study go to the following web site
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