• Wadjakorn Thummawanich, D.D.S
• Chairat Wiwatwarrapan, B.Sc., M.S.*
• Chintana Sirichompun, D.D.S. (Hons), M.D.Sc. (Orthodontics), Dip.Th.B.O.

Background/objectives: To evaluate the mechanical and physical properties of a self-cured methyl
methacrylate (MMA)-based orthodontic base-plate material after 50°C water immersion in ultrasonic
bath and conventional monomer reduction methods.

Materials and methods: Twenty-four rectangular and twenty-four disc shaped specimens of an MMAbased
orthodontic base-plate material were prepared, and randomly divided into four groups (n=6):
Group I, untreated controls; Groups II and III, immersed in room temperature water for 24 and 72
hours respectively; and Groups IV immersed in 50°C water in an ultrasonic bath (100 Watts, 40 kHz)
for 10 minutes. Their flexural strength, flexural modulus, microhardness, water sorption, and water
solubility were measured. The data was analyzed by a one-way analysis of variance, followed by a
post hoc Tukeyûs test at a 95% confidence interval.

Results: The flexural strength and flexural modulus of Group IV were significantly higher than those
of Group I; however, microhardness, water sorption, and water solubility were not significantly different.
Compared to Group I, Groups II and III showed no significant difference in flexural strength,
microhardness, water sorption, or water solubility. However, the flexural modulus of Groups II and III
were significantly higher than Group I.

Conclusions: After post-polymerization treatment by water immersion at 50°C in an ultrasonic bath
for 10 minutes, the mechanical and physical properties of MMA-based orthodontic base-plate material
were improved or unchanged.

(CU Dent J. 2018;41:33-40)