Various Frequencies Of Ultrasonic Reduce Residual Monomer In Acrylic Restoration

Objective: One major problem of auto-polymerized acrylic resin are residual monomers which affect properties of material and irritate to oral tissue. Many previous studies on reducing residual monomer are not of practical use because a long chair-time required. Thus, an ultrasonic treatment was recommended to decreased chair-time in reducing the residual monomer in acrylic resin. The study aimed to compare the amount of residual methyl methacrylate (MMA) monomers in an auto-polymerized acrylic resin after immersion in an ultrasonic cleaner set at different frequencies. Method: Forty-two disc shaped specimens made of an auto-polymerized acrylic resin (Unifast Trad, GC, Japan) were randomly divided into seven groups: Control (C), immersion in 50^oC water for 1 hour (PC), and immersion in 50^oC water in ultrasonic cleaners at 28 kHz (F1), 40 kHz (F2), 60 kHz (F3) for 5 minutes, 28 kHz for 2.5 minutes followed by 60 kHz for 2.5 minutes (F4) and 28 kHz for 5 minutes followed by 60 kHz for 2.5 minutes. The amount of residual monomer was determined by HPLC. The data were analyzed with one-way ANOVA and Tukey’s HSD at a 95% confidence level. Results: The results showed that the amounts of residual monomer in all treated group were significantly lower than control group (p<0.05) and there was no significant different in group PC, F1, F2, F4 and F5 (p>0.05). The amount of residual monomer in group F3 was significantly higher than PC, F1 and F4 (p<0.05). Conclusion: The ultrasonic treatment with low frequencies (28 and 40 kHz) for 5 minutes, combination frequencies of low and high frequencies (28 followed by 60 kHz) for 5 or 7.5 minutes have an effect on reducing residual monomers in an auto-polymerized acrylic resin when immered in 50^oC waterbath for 1 hour. Also,  lesser chair-side time might required.