The Level of Residual Monomer in Rapid Heat-cured Acrylic Resin

Methods: The circular specimens, of 50 mm in diameter and 3 mm in thickness, were prepared according to ISO 20795-1:2008. For rapid heat-cured acrylic resins (Vertex Rapid Simplified and QC-20), three groups of specimens (n=6) were cured at 100ºC for 10, 20 (as manufacturer’s recommendation) and 30 minute. The control group   (conventional heat-cured acrylic resin, Vertex Regular) was prepared and cured according to manufacturer’s recommendation. All specimens were wet-grinded, stored in the dark chamber for 24 h and drilled to get small fragments. These fractions were dissolved and residual monomer was determined by gas chromatography (GC). One-way ANOVA and Dunnett T3 test were performed to determine significant differences of the mean residual monomer at α=0.05.

Results: When acrylic resins were processed according to manufacturer’s recommendations, the mean residual monomer of QC-20 (2.06%) was the highest, followed by Vertex Rapid Simplified (1.26%) and Vertex Regular (0.61%) and they were significantly different from each other. For the effect of different curing times in rapid heat-cured acrylic resins, the significantly higher residual monomer was observed in less curing time group (10-min) compared with those of 20-min and 30-min-groups. No significant difference in the amount of residual monomer was observed between 20-min and 30-min curing groups.

Conclusion: Rapid heat-cured acrylic resin released significantly higher residual monomer than a conventional heat-cured acrylic resin. Reduction of curing time (less than 20 min) for rapid heat-cured acrylic resin would produce significantly higher residual monomer than acrylic resin that processed under the recommended curing time (20 min).