Residual monomer reduction in the mma-based orthodontic base-plate materials by water immersion in ultrasonic bath

Abstract

Objective: To compare the levels of residual monomer between Orthocryl and Orthoplast; and to compare the levels of residual monomer in self-cured orthodontic base-plate materials among the different reduction methods.

Materials and methods: A total of 96 disc specimens (3x50 mm) were prepared from Orthocryl® (Dentaurum, Germany) and Orthoplast® (Vertex, The Netherlands), according to the instructions of the manufacturers and ISO 20795-2 (2013). The specimens from each brand were divided into eight groups (6 specimens per group). Group I were left untreated as controls. Groups II and III were immersed in the-room-temperature (25°C) water for 24 and 72 hours, respectively. Groups IV-VIII were immersed in 50°C water of an ultrasonic bath for 3, 5, 10, 15 and 20 minutes, respectively. The level of residual monomer was determined by using high performance liquid chromatography. Data were analyzed by a two-way ANOVA, followed by a one-way ANOVA Tukey’s HSD post hoc test at 0.05 significant level.

Results: In group II-VIII, the Orthocryl groups showed a statistically significantly lower residual monomer level than the Orthoplast groups. In the Orthocryl groups, the levels in group II-VIII were significantly lower than group I, while the level in group VIII was significantly lower than those in groups II, III. In the Orthoplast groups, no significant differences existed between group I and II, but the level in group III was significantly lower than that in groups I. The levels in group VI, VII and VIII were not significantly differences with those in groups III, but the level in group VIII was significantly lower than that in groups VI.

Conclusion: In the same monomer reduction method, the levels of residual monomer in Orthocryl were lower than those in Orthoplast. Water immersion at 50°C in an ultrasonic bath for 10-20 minutes reduced the amount of residual monomer in an orthodontic acrylic base-plate material, which was similar to or better than water immersion for 24 and 72 hours at room temperature. However, less time was required.​