Release of methyl methacrylate from heat-cured and autopolymerized resins: cytotoxicity testing related to residual monomer.

Three heat-cured and three autopolymerized acrylic denture bases with different mixing proportions and/or processing methods were investigated for the amount of residual monomer content and methyl methacrylate (MMA) released into saliva after incubation during the first and second 24 hours after processing. A corresponding range of concentrations of MMA was also used to test for cell cytotoxicity using a culture of human oral fibroblasts. The results showed that the amount of residual monomer was dependent not only on the type of polymerization but also on the amount of liquid in the mixture ratio and the processing method. The acrylic resin that had the lowest residual monomer also released the smallest amount of MMA but resins which have higher residual monomer may not necessarily release higher amounts of MMA. MMA, tested in the same range of concentration as the MMA found leached from acrylic resin in this study, was found to be toxic in the cell culture. Therefore, it is recommended that dentists attempt to reduce the amount of leachable substances before insertion of new dentures. In addition, it is recommended that dentists advise their patients not to wear newly made dentures overnight, as this may cause mucosal irritation from the potential accumulation of leachable substances.