Freezing for Better Biocompatibility: Residual Monomer Reduction in High-Impact vs. Conventional PMMA Acrylic Resins

Abstract Introduction: Residual monomer content (RMC) in denture base acrylic resins is a recognized factor contributing to oral mucosal irritation and allergic reactions. Objective: This in vitro study aimed to evaluate and compare the RMC in conventional and deep-frozen high-impact, as well as conventional heat-cure polymethylmethacrylate (PMMA) acrylic resins, following immersion in water for 24 and 48 hours. Materials and Methods: A total of 120 disc-shaped specimens were fabricated from two heat-cure acrylic resins – a conventional PMMA (DPI) and a high-impact PMMA (Trevalon HI) – using the compression molding technique. Group I (n=60) specimens were prepared using conventional resin mixing, packing, and a long curing cycle. For Group II (n=60), specimens were prepared by deep-freezing the mixed acrylic, followed by thawing, packing, and a long curing cycle. Each group was further subdivided based on storage duration in distilled water (24 hours and 48 hours). The pulverized form of each specimen was subsequently analyzed for RMC using High-Performance Liquid Chromatography (HPLC). The acquired data were subjected to appropriate statistical analysis. Results: The mean RMC was highest in Group I conventional heat-cure PMMA (DPI) specimens stored for 24 hours. Conversely, the lowest mean RMC was observed in Group II high-impact PMMA (Trevalon HI) specimens after 48 hours of water storage. A paired t-test revealed a statistically significant difference among all comparison groups (p < 0.001). Conclusion: Deep-freezing the mixed high-impact Trevalon HI PMMA acrylic resin, followed by storage in water for 48 hours, significantly reduced the residual monomer content. This technique could potentially enhance the biocompatibility of denture base resins.