Ultrasonic treatment reduced residual monomer in methyl methacrylate-based orthodontic base-plate materials

Abstract

Objective: To evaluate the effect of ultrasonic treatment time on the level of residual monomer (LRM) in methyl methacrylate (MMA)-based orthodontic base-plate materials. Methods: Forty-eight-disc specimens with a 50-mm diameter and 3-mm thickness fabricated from Orthocryl (OC, Dentaurum) and Orthoplast (OP, Vertex) self-cure acrylic were prepared according to their manufacturers' instructions and ISO 20795-2 (2013). They were randomly divided into eight groups (n=6): Group I, untreated controls; Groups II and III, immersed in room temperature water for 24 and 72 h respectively; Groups IV-VIII immersed in 50°C water in an ultrasonic bath for 3, 5, 10, 15 and 20 min respectively. The LRM was determined using a high-performance liquid chromatography. Data were analyzed by a one-way ANOVA, followed by Tukey's HSD post hoc test (P < 0.05). Results: The LRM in OC II-VIII groups were significantly lower than those in the OP II-VIII, and were lower than that in the OC I. The LRM in OP III group was lower than that in the OP I. The LRM in OP VI-VIII groups were not significantly different from that in the OP III. Conclusion: Water immersion at 50°C in an ultrasonic bath for 10-20 min reduced the LRM in MMA-based orthodontic base-plate materials. The results revealed a convenient reduction of the residual monomer within a short period of time in clinical practice.