Polysulphide Impression Material In Dentistry

Polysulfide is also known as mercaptan or Thiokol

Composition of Polysulfide:

Composition of Polysulfide

Setting Reaction of Polysulfide:

As base and accelerator pastes are mixed, they undergo both polymerization by oxidation of terminal SH groups and the cross-linking of pendant SH groups. Reaction occurs between polymer with free mercaptan, i.e.–SH groups, and the oxidizing agent lead dioxide, which lengthens and cross–links the chain through the reaction of terminal and pendant –SH group. The whole reaction is exothermic which increases the temperature from 3°C to 5°C and the formation of water as a by-product.

Mercaptan + Lead dioxide → Polysulfie + Water

Polysulphide Impression Material In Dentistry

Properties of Polysulfide

Polysulfide has unpleasant odor and color. It stains linen and is messy to work with.
These materials are extremely viscous and sticky. Mixing is difficult.
Polysulfide has a long setting time of 12.5 minutes.
Excellent reproduction of surface detail.
Dimensional stability: The curing shrinkage is high and continuous even after settling. It has the highest permanent deformation among the elastomers, i.e. 3 to 5%.
Polysulfide has high tear strength (4,000 g/cm).
Polysulfide has good flexibility (7%) and low hardness.
Polysulfide is hydrophobic so the mouth should be dried before making an impression.
Polysulfide can be electroplated more with silver than copper.
Shelf-life is good, i.e. 2 years.

Advantages of Polysulfide

Excellent reproduction of surface detail as fine as 0.025 mm wide
Polysulfide can be electroplated more with silver than copper
The shelf-life is good (2 years)
Polysulfide has good flexibility (7%)
Polysulfide has high tear strength (4,000 g/cm) thus making it more resistant to tearing even when the impression is in thin section.

Disadvantages of Polysulfide

Unpleasant odor and color.
These materials are extremely viscous and sticky. Mixing is difficult.
Polysulfide has long setting time which adds to the patient’s discomfort.
Dimensional unstability: It has high permanent deformation. The curing shrinkage is high, and loss of byproduct (water) also causes shrinkage.
Staining is present due to lead dioxide.

Manipulation of Polysulfide

High-viscosity material, i.e. putt is usually supplied in small tubs with different colored scoops for identification and dispensing.
Equal quantities of both pastes are taken.
Mixing is done by hand by kneading the material together to obtain a uniform mix without any streaks.
Manufacturers also supply base and catalyst in separate tubes with a much smaller diameter opening for a catalyst to enable dispensing equal lengths of base and catalyst, though the volume is different.
For polysulphides mixing of low-viscosity material is accomplished by taking equal lengths of base and catalyst on a paper pad and manipulating by stiff bladed spatula in a circular motion for 45 seconds till the mix is free from streaks.