• Pajima Thaitammayanon D.D.S.
• Chintana Sirichompun D.D.S., M.D.Sc., Diplomate, Thai Board of Orthodontics
• Chairat Wiwatwarrapan B.Sc, M.S.

Objective To compare the residual monomer in two brands of MMA-based orthodontic base-plate
materials before and after water immersion (for 24 and 72 hours).

Materials and Methods A total of 36 disc specimens (3 x 50 mm) were prepared from MMA-based
orthodontic base-plate materials; Orthocryl (Dentaurum) and Orthoplast (Vertex) according to the
manufacturersû instructions and ISO 20795-2 (2013). The specimens from each brand were divided
into three groups (six specimens per group). Group I was those before water immersion and served as
controls. Groups II and III were those after water immersion for 24 and 72 hours, respectively.
The level of residual monomer was determined by using high performance liquid chromatography.
Numerical data were analyzed by a one-way ANOVA, followed by Tukeyûs post hoc test (p<0.05).

Results Means (wt%) of residual monomer concentration in controls, 24-and 72-hour-water
immersion groups were 3.37, 2.42, 2.34 in Orthocryl groups, and 3.35, 3.15, 2.80 in Orthoplast groups.
The greatest amount of residual monomer was detected in the controls. Some statistically significant
differences were found between those with water immersion and their controls (p<0.05). In Orthocryl
groups, no significant differences existed between the 24-and 72-hour-water immersion groups.

Conclusion Residual monomers in Orthocryl and Orthoplast with water immersion for 24 and 72
hours are less than that before water immersion.

(CU Dent J. 2015;38(Suppl):67-74)