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.