Microwave Disinfection of Complete Dentures Contaminated In Vitro with Selected Bacteria

Purpose: This study evaluated the effectiveness of microwave irradiation for disinfection of simulated complete dentures. Materials and Methods: Seventy dentures were fabricated in a standardized procedure, subjected to ethylene oxide sterilization, individually inoculated (10(7) cfu/mL) with Staphylococcus aureus (n = 20), Pseudomona aeruginosa (n = 20), and Bacillus subtilis (n = 30) and incubated for 24 hours at 37 degrees C. After that, 40 dentures were selected for microwaving. For each microorganism, 10 dentures were submitted to microwave irradiation at 650 W for 3 minutes. In addition, 10 dentures contaminated with B. subtilis were irradiated for 5 minutes. Thirty non-microwaved dentures (n = 10 for each bacteria) were used as positive controls. Replicate aliquots (25 mu L) of suspensions were plated at dilutions of 10(-3) to 10(-6) on plates of selective media appropriate for each organism. After incubation (37 degrees C for 48 hours), colonies were counted (cfu/mL). TSB beakers with the microwaved dentures were incubated at 37 degrees C for a further 7 days to verify long-term disinfection. The data were statistically analyzed by the Kruskal-Wallis test (alpha = 0.05). Results: No evidence of growth was observed at 48 hours for S. aureus and P. aeruginosa on plates, and no turbidity was visible in the TSB beakers of these specimens after 7 days of incubation. Dentures contaminated with B. subtilis and irradiated for 3 minutes produced microbial growth on six plates and turbidity on all TSB beakers. Microwaving for 5 minutes resulted in survival of B. subtilis in two plates and two beakers. Conclusion: Microwave irradiation for 3 minutes at 650 W produced sterilization of complete dentures contaminated with S. aureus and P. aeruginosa. Dentures contaminated with B. subtilis were disinfected by microwave irradiation after 3 and 5 minutes at 650 W.