10. Composition and preparation of addition silicone impression material - cream form
Covers the thin, medium- or light-bodied cream form of addition silicone impression material, starting with its accuracy and then its composition: base, catalyst and optional surfactants that make some types hydrophilic. It compares automatic cartridge mixing with hand mixing, then gives handling conditions, working and setting times, a table of shrinkage, permanent deformation and contact angle, and a short note on related bite-registration and duplication products.
Topic 10 of 52 in the MU Sofia syllabus for Dental Materials (Dental Medicine, Year 1). The free AceMed note covers it in 6 sections, about 255 words (2 min of reading), with 15 flashcards.
In this note
Introduction
Composition
Preparation
Working with it
Properties
Related products
Introduction
Addition silicone cream is the thin, medium-bodied or light-bodied form of A-silicone. It is among the most accurate impression materials: "hydrophilic" types can register details of 1 to 2 µm.
Composition
The composition is the same as that of the putty, with less filler:
Base: VPDMS, fillers, and small amounts of platinum and palladium, which absorbs hydrogen.
Catalyst: PMHS, fillers in a contrasting color, and a platinum salt as initiator.
Surfactants: some makers add these to reduce hydrophobicity. Such silicones are called hydrophilic.
It comes in tubes for hand mixing, or in cartridges with mixing tips.
Preparation
Automatic mixing
Load the cartridge into the gun and fit a new mixing tip.
Press the trigger. Two pistons push equal amounts of both pastes through the tip.
Apply the material straight onto the prosthetic field or into the tray, through the nozzle.
Hand mixing
Put equal lengths of the two pastes on a paper pad.
Mix with a spatula until the color is even.
Automatic mixing is better: it gives the best dosing and mixing, and it avoids the air that is nearly always trapped by hand.
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