Three-five Minutes Ultrasonic Cleaning Reduce Residual Monomers in Acrylic Resin

Objectives: Residual monomers in acrylic resins decrease their mechanical properties and are toxic to the oral tissues. The current methods of reducing residual monomer are not clinically practical due to the extensive chair-side time required. The aim of this study was to determine the effect of ultrasonic cleaning time on the amount of residual methyl methacrylate monomer in three auto-polymerized acrylic resins. Methods: Thirty six disc-shaped auto-polymerized acrylic resin specimens of each brand (Unifast Trad Ivory, Unifast Trad Pink, and Unifast III A2) were randomly divided into six groups: Control, Positive control (immersion in 50^oC water for 1 hour) and Ultrasonic treatment in 50^oC water for 3, 5, 10, or 15 minutes. The residual monomer extraction procedure was performed per ISO 20795-1:2013. High performance liquid chromatography (HPLC) was used to determine the amount of residual monomer. The data were analyzed by one-way ANOVA and Tukey’s HSD. Results: The amount of residual monomer in the positive control group and ultrasonic treatment groups were significantly lower than that of the control group for each brand. The reduction in residual monomers was not significantly different between the ultrasonic treatment in 50^oC water (3 minutes for Unifast Pink and 5 minutes for Unifast Ivory and Unifast III) groups and the positive control group. Conclusion: Ultrasonic treatment for 3–5 minutes reduced the amount of residual monomer in auto-polymerized acrylic resin similar to immersion in 50^oC for 1 hour; however less chair-time was required.