Explains how injection-moulded denture resins are made: a pre-polymerised thermoplastic is softened by heat, forced under pressure into a plaster mould, then cooled, cut and polished. Shows a step-by-step diagram of the process, then compares acrylic, polycarbonate, polyamide and polyoxymethylene in a table covering their properties and uses. Closes with the advantages of low residual monomer and factory-made consistency, and the need for special equipment as a drawback.
Topic 24 of 52 in the MU Sofia syllabus for Dental Materials (Dental Medicine, Year 1). The free AceMed note covers it in 4 sections, about 159 words (2 min of reading), with 15 flashcards.
In this note
Introduction
The process
Materials
Why it is useful
Introduction
In the injection technique, a resin that is already polymerized is softened by heat and forced into a plaster mold under pressure. There is no mixing of powder and liquid, so almost no residual monomer is left in the finished denture.
The process
Pack the wax denture in plaster in a special two-part flask that has an opening, and attach injection sprue pins.
When the plaster has set, open the flask and remove the wax with hot water.
Close the flask. Heat the resin in the apparatus until it softens.
Inject the warm, flowing resin under pressure through the channels until the mold is full.
Cool the flask, unpack the denture, cut off the sprues, then grind and polish.
Materials
Injection resins are polymerized thermoplastic materials supplied as granules or cylindrical blocks.
Why it is useful
Fewer allergy and toxicity problems: there is little or no residual monomer.
Consistent quality: the polymer is made in the factory, not in the laboratory.
Drawback: it needs special equipment.
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