Polyethers And Polysulfides
Polysulphide Rubber-base Impression Material:
- This was the first elastomeric impression material.
- It is also known as “Mercaptan” and “Thioko”
Composition of Polysulphide Rubber-base Impression Material:
- Base Paste
- Liquid polysulphide polymer – 80 – 85%
- Inert filer (titanium dioxide, zinc sulphate, copper carbonate, and silica) -16 – 18%
- Reactor Paste
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- Lead oxide – 60 – 68%
- Dibutyl phthalate – 30 – 35%
- Sulfur – 03%
- Other substances like (magnesium stearate (retarder) and deodorants) – 02%
Manipulation Polysulphide Rubber-base Impression Material:
- High viscosity material, i.e. Put is usually supplied in small tubs with different colored scoops for identification and dispensing.
- Equal quantities of both the 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 polysulphide, 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. - Mixing is done in a large area to dissipate the heat.
Advantages of Polysulphide
- Excellent reproduction of surface detail as fie as 0.025 mm wide
- Polysulphide can be electroplated more with silver than copper
- The shelf-life is good (2 years)
- Polysulphide has good flexibility (7%)
- Polysulphide 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 Polysulphide:
- Unpleasant odor and color.
- These materials are extremely viscous and sticky. Mixing is difficult.
- Polysulphide has long setting time which adds to the patient 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.
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