Comparison of residual monomer loss from cold-cure orthodontic acrylic resins processed by different polymerization techniques.

Introduction: This investigation aimed to assess and compare the amount of residual monomer (RM) released from removable orthodontic appliances constructed by sprinkle-on and dough techniques.
Materials and Methods: One hundred and twenty acrylic samples were prepared from orthodontic autopolymerized acrylic resins and divided into three groups, according to the processing method: sprinkle-on with polyclave, sprinkle-on without polyclave and dough technique. After polymerization, the specimens of each group were immersed in distilled water for 24 h, 48 h, 72 h and 1 week. High-performances liquid chromatography (HPLC) was utilized to measure residual monomer content.
Results: Maximum observed RM was 1284·91±129·07 ppm measured for sprinkle-on technique without polyclave after 24 h of water immersion. At this time, the level of RM was significantly different among the three applied techniques (P<0·05). In all soaking time groups, sprinkle-on technique with polyclave released the least amount of RM. Within each group, the maximum monomer releasing was observed after the first 24 h and decreases were observed in subsequent time groups. The reduction over the time was not significant in the polyclave groups (P>0·05).
Conclusion: The sprinkle-on technique with polyclave and longer water immersion reduced residual monomer released from acrylic orthodontic appliances.