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.
Cool 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.