POLYSULFIDE ELASTOMERIC IMPRESSION MATERIAL:
First elastomeric impression material to be introduced, also known as mercaptan / thymol, it is a type of Rubber based impression material
Supplied as
* Base paste (white)
* Accelerator (brown/grey)
Available in 3 viscosities:
* Light bodied
* Medium bodied
* Heavy bodied
Composition:
Base paste:
* Liquid polysulfide polymer 80-85%
* Inert fillers (titanium oxide, zinc sulfate, silica) 16-18%
Reactor Paste:
* Lead dioxide 60-69%
* Dibutyl phthalate 30-35%
* Sulfur 3%
* Other substances (like magnesium stearate) 2%
* and deodorants
Setting reaction:
HS – R – SH ———-PbO2 + S—-> HS – R- S – S – R – SH + H2O
Properties:
1) Setting time – 5-8 min.
* colder climate increases setting time.
* Drop of water accelerates the reaction.
2) Excellent detail reproduction.
3) Dimensional stability
* curing shrinkage – 0.45% due to continued reaction.
* Shrinkage due to loss of byproduct.
4) Permanent deformation – 3-5%
* highest amongst elastomers.
5) High tear strength – 7000gm/cm2
6) Good flexibility of 7%, allows elastic recovery of the material.
7) Hydrophobic- tissue should be thoroughly dried before making the impression.
8) Can be electroplated with copper.
Advantages:
1. long working time.
2. proven accuracy
3. high tear resistance.
4. inexpensive to use
5. less hydrophobic
6. longer shelf life.
Disadvantages:
1. must be poured with dental stone immediately.
2. potential for significant distortion.
3. odor is offensive.
4. messy & stains clothes.
5. second pour is less accurate.
