8. Composition and preparation of condensation silicone impression material - cream form
Covers the composition of condensation silicone cream, a thin C-silicone sold in medium-bodied and light-bodied forms, with its base paste and catalyst. Walks through the mixing steps, the setting reaction and how filler content changes shrinkage and hardness. A comparison table sets medium- and light-bodied materials side by side, and the note closes with the two-phase impression technique using putty and light-bodied layers.
Topic 8 of 52 in the MU Sofia syllabus for Dental Materials (Dental Medicine, Year 1). The free AceMed note covers it in 5 sections, about 190 words (2 min of reading), with 15 flashcards.
In this note
Introduction
Composition
Preparation
Setting
Two-phase impression
Introduction
Condensation silicone cream is the thin form of C-silicone, supplied as medium-bodied or light-bodied paste. It has less filler than putty, so it flows better and records finer detail, but it shrinks more.
Preparation
Squeeze out a measured length of base paste.
Add the catalyst: a set number of drops, or a fixed length of paste. Pastes usually need equal lengths, but follow the maker's directions.
Mix with a metal spatula in lengthwise strokes for about 30 seconds, keeping out air.
Check the color: contrasting pastes show when mixing is complete.
Apply the mix with a spatula onto the putty, or with a special syringe onto the prosthetic field.
Setting
Setting is the same polycondensation as in putty, with ethanol as the by-product. Pure HPDMS shrinks by 0.8%, and the fillers reduce this.
Working time is 1.5 to 3 minutes and setting time is 3 to 7 minutes. The contact angle is 98°, so the material is hydrophobic and the field must be thoroughly dry.
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