Denture base materials, heat cured

Heat-cured denture base materials were introduced into dental use in 1937. These materials are prepared from a powder-liquid slurry. The liquid is methyl methacrylate to which are added a plasticizer, crosslinking agent and inhibitor. The powder is poly(methyl methacrylate) containing approximately one percent initiator, usually benzoyl peroxide. By subjecting this slurry to elevated temperature (about 75°C to 100°C) for one or more hours depending on the temperature employed, sufficient free radicals are produced from the initiator to yield a satisfactory denture. Other initiators have been proposed. 

Heat-cured denture base materials were introduced to dentistry in 1937. The liquid portion of the monomer-polymer slurry consists of methyl methacrylate monomer containing 0.006% or less inhibitor, plasticizer and crosslinking agent. The solid contains a modified suspension-polymerized methyl methacrylate and 0.5% to 1% of initiator, usually benzoyl peroxide. This compound has a 10 hour half-life temperature of 72°C (1). Since the polymerization rate is increased with increase in temperature and is directly proportional to the square root of the initiator concentration, the customary denture base curing cycles of 90 min. at 65followed by heating to 100°C for 60 min., or heating to 74 C for 9 hrs. will release sufficient free radicals to yield a denture that shows minimum porosity and is fully cured in both the thick portions as well as the thin palate areas. Other peroxides employed for the polymerization of acrylic resins such as diacetyl-di(2,4-dichlorobenzoyl)-or... 

In conclusion, the porosity, hardness, and strength of microwave cured acrylic resins that are processed for less than 5 min exhibited no significant differences in properties when compared with conventionally polymerized resins [60-63]. However, the investigation of color stability of several commercially available heat-cured, quick heat-cured denture and microwave cured denture base resins (tested exclusively under microwave conditions) revealed that the materials demonstrated differences in color stability, but the standard heat-cured materials treated under microwave irradiation exhibited color changes that were negligible [64]. 

Silicone liners are similar in composition to the previously described elastomeric impression materials, which are produced by condensation pol5mieriza-tion. Systems for the relining application may be either a one-component system, which cures in the presence of moisture or heat, or a two-component system, containing base and catalyst. Both types generally have poor adhesion to the denture surface, and can readily support bacterial growth. 

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