Dental Materials · MU Sofia

9. Composition and preparation of addition silicone impression material - putty form

Covers the composition of addition silicone putty, with a table of the base and catalyst components and their roles, including the platinum initiator, PMHS cross-linker and palladium hydrogen absorber. Walks through hand-mixing preparation with equal masses, the glove and field precautions that stop setting, the addition setting reaction with its low shrinkage, and a property table giving working and setting times, shrinkage, permanent deformation and contact angle.

Inside: 5 sections · 1 labelled picture · 2 tables · 15 flashcards · 2 min

Topic 9 of 52 in the MU Sofia syllabus for Dental Materials (Dental Medicine, Year 1). The free AceMed note covers it in 5 sections, about 163 words (2 min of reading), with 15 flashcards.

In this note

  1. Introduction
  2. Composition
  3. Preparation
  4. Setting
  5. Properties

Introduction

Addition silicone putty (heavy-bodied A-silicone, or vinylsiloxane) is a very stable impression material. It sets without a by-product, so it shrinks less than condensation silicone. The price is a higher cost and some sensitivity to contaminants.

Composition

It comes as two equal, identical-looking masses in boxes, labeled base and catalyst.

Preparation

  1. Take equal amounts of both masses with the dosing spoons.
  2. Knead them together by hand, in vinyl or nitrile gloves, until the color is even.
  3. Place the putty in the tray.
  4. Seat it on a very dry or slightly moist prosthetic field.

Never mix A-silicone putty in latex gloves: traces of sulfur stop it setting.

Astringent drugs used on the field and acrylate traces from temporary restorations have the same effect.

Setting

Vinyl groups on VPDMS react with PMHS in an addition polymerization and no by-product is released. Unfilled material shrinks by only about 0.2%, and fillers reduce this further.

Properties

Cooling the material lengthens working time. The drawbacks are high cost and limited shelf life.

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