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What is Addition Silicone?
Addition silicone, often shortened to “a-silicone”, is the most used impression material in restorative dentistry. It is widely regarded as the best impression material due to the advantages it holds over alternative materials. Also known as PVS (polyvinyl siloxane) or VPS (vinyl polysiloxane), addition silicone is an elastomeric impression material typically used for creating crowns, bridges, partial dentures and implants. A-silicone can take several different forms but will always follow the same chemical reaction of polymerisation and be presented as either a one-stage or two-stage paste-to-paste system.
Addition Silicone Composition
A-silicone Base Paste:
- Polymethylhydrosiloxane (PMHS)
undergoes cross-linking - Fillers (colloidal silica)
controls viscosity
A-silicone Accelerator:
- Polyvinyl siloxane cross-linking agent
- Platinum salt catalyst
- Fillers controls viscosity
What Are the Different Types of A-Silicone?
There are a few different types of addition silicone. These are based on their differing amounts of filler content. Filler content dictates the flow properties (viscosity) of each. The more filler, the thicker and less flowable the material will be.
Addition silicone materials come in as many five viscosities. Starting from the lowest viscosity to the highest, these are extra light body, light body, medium body (universal), heavy body and putty. The most used are medium body (35%-75% viscosity), heavy body (60%-70% viscosity) and light body (5%-15% viscosity), commonly referred to as wash.
Different types of addition silicones come with different setting (polymerisation) times. Addition silicones can be presented in double-barreled cartridges for use in an automix gun or as a base and catalyst putty.
How is A-Silicone Used?
An a-silicone impression can be done using either a one-stage or two-stage paste-to-paste technique.
- One-stage impression: Heavy-bodied a-silicone or putty is placed onto an impression tray. A layer of light-bodied a-silicone (wash) is then placed over it or directly onto the relevant teeth or both. The impression tray is then placed back into the patient’s mouth for the material to set.
- Two-stage impression: A putty impression is recorded first, and after it has set it is relined with a thin layer of wash material. Two-stage impressions can be taken with or without a spacer.
Disadvantages of A-Silicone
- Cost
- Inhibited by the sulphur in latex gloves and rubber dam, so non-latex gloves and dams should be used if necessary
- Hydrophobic so requires excellent moisture control
Kent Express’ bestselling a-silicones
Cyber Silicone Putty Soft Fast 800g/500ml
Impression material based on Vinyl polysiloxane. Excellent detailed reproduction. High tear strength. Hydrophillic. Total working time 2 minutes including 30 second mixing time. Total setting time 4 minutes.
Cyber Silicone Putty Soft Regular 800g/500ml
Impression material based on Vinyl polysiloxane. Excellent detailed reproduction. High tear strength. Hydrophillic. Total working time 2 minutes including 30 second mixing time. Total setting time 5 minutes 30 seconds.
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