Heavy bodied
COMPOSITION
BASE PASTE | FUNCTION |
Polysulfide polymer – 80-85% | This is further polymerized and cross linked to form rubber |
Filler (Titanium dioxide zinc sulfate) – 16-18% | To provide required strength |
Plasticizer (Dibutyl Phthalate) | To provide appropriate viscosity |
Small quantity of sulphur – 0.5% | To accelerate the reaction |
Accelerator paste
Lead dioxide – 60-68% | To react with thiol group causing setting and give brown colour |
Filler and plasticizer | To provide strength and to give adequate viscosity |
Oleic / stearic acid | Act as retarder to control rate of setting reaction |
CHEMISTRY AND SETTING REACTION
The main component of polysulfide is a multifunctional mercaptan (-SH) or polysulfide polymer. These linear polymer contains pendent –SH groups
Reaction yields water as by product
PROPERTIES
Unpleasant odour and colour
It has a long Setting time of 8 to 12minutes
Mixing time is 45 seconds
Excellent reproduction of surface detail
Dimensional stability:
The curing shrinkage is high (0.45%)
Has the highest permanent deformation (3.5%)
This improves with time. So pouring of model should be delayed by half an hour
Tear strength is 4000 gms/cm2
It has good flexibility. A 2mm spacing in the tray is sufficient to make the impression.
It is hydrophobic. So impression area should be dry
Shelf life is good i.e. 2 years
SILICONE RUBBER IMPRESSION MATERIALS
Types:
Two types of silicone impression materials are available based on the type of polymerization reaction occurring during setting
Condensation silicone
Addition silicone
MODE OF SUPPLY
Available as base and catalyst in paste form. The condensation silicone catalyst can also be supplied as a liquid. The putty is supplied in jars.
Condensation silicone is available in three viscosities.
Light bodied
Medium bodied
Putty
CONDENSATION SILICONES
BASE PASTE
Hydroxyl terminated polydimethyl siloxane | Undergoes cross linking to form rubber |
Colloidal silica | Filler |