Introduction
Cold-cured polymers, also known as self-curing, quick-curing or auto-curing resins, polymerize when a chemical activator splits the initiator. No heat is needed, which makes them convenient for repairing broken or defective dentures.
How they differ in composition
- Liquid: the same as in heat-cured resin, plus an activator. The most common is dimethyl-para-toluidine, at up to 0.75%. Tertiary amines, sulfonic acids and salts of sulfinic acids can also act as activators.
- Powder: the same as in heat-cured resin, but with more initiator, up to 1.5%.
Setting
The activator rapidly breaks down the initiator. Chains stop growing after 10 to 20 minutes. Temperature has a large effect: the reaction almost stops at 5 °C, and above 30 °C it speeds up, with the mix reaching up to 90 °C. The resin is usually cured in the open air without pressure.
Properties
Because the reaction is fast, the chains are shorter. Cold-cured resin therefore has lower density and weaker mechanical and biological properties than heat-cured resin.
- Higher solubility, water uptake and toxicity: more monomer remains free.
- More porosity: there is no pressure during curing.
- Color change: nitrogen compounds in the activator oxidize, and the products stain the resin yellow-brown.
- Allergy: oxidized activator can cause allergic reactions.