Polysulfide Elastomeric Impression materials

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.

 

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