Introduction
Heat-cured polymers are acrylic resins in which heat activates the initiator. Careful temperature control gives long polymer chains, little residual monomer and the best properties among basic denture resins.
Why the temperature schedule matters
- About 60 °C: benzoyl peroxide decomposes at the best rate, which gives the longest chains. Higher temperatures break it down too quickly.
- Heat from the reaction: chain growth is exothermic and heats the dough 20 to 30 °C above the water. If the total reaches 100.3 °C, the monomer boils and forms gas pores.
- Final stage at 100 °C: after about 90 minutes the initiator runs out. The hotter water then polymerizes the unreacted monomer.
If the water is heated too fast, the resin can pass 120 °C. It becomes porous and poorly colored, with a degree of polymerization of about 1800 and over 3% residual monomer. A correct schedule gives a degree of about 2500, a molecular weight of about 250,000 and 0.3 to 0.5% residual monomer.