Evaluation of efficacy of microwave oven irradiation in disinfection of patient derived dental cast

Abstract

The purpose of this study was to check the efficacy of household microwave oven irradiation in disinfection of dental gypsum casts obtained from patients. Impressions of upper arch of 10 volunteers were made using irreversible hydrocolloid. The casts were poured in type III gypsum. All casts were cut into two halves. One half of each cast was irradiated in a microwave oven , set at 650 W for a total of 3 minutes and the un-irradiated half was used as control. Suspension of casts was inoculated directly on Tryptone Soya Agar plates (TSA) by spread plate method. The inoculated plates were incubated aerobically at 32°C for 48 hours. Colonies grown on the agar plates were counted using a plate count reader. The data is presented as CFU/cast. It was concluded that three minutes microwave irradiation at 650 W is effective to reduce the microbial load of dental casts. Routine use of microwave for disinfection of cast could be recommended and used in between procedures to prevent cross contamination in the dental clinics.

Comprehensive Review and Comparison of the Disinfection Techniques Currently Available in the Literature

“…Immersion disinfection ensures that all surfaces of the dental impression are exposed to the disinfectant; however, hydrocolloids and polyether materials cannot be immersed in disinfectants due to the imbibition phenomenon. Immersion disinfectants should be discarded after every use (except for glutaraldehydes) …”

“…Immersion disinfectants should be discarded after every use (except for glutaraldehydes). 12 The spray method of disinfection reduces the chance of distortion, especially in hydrocolloids and polyether, and also uses less disinfectant solution, but it may not reach the areas of undercuts and also releases air, leading to occupational exposure. 13 Antimicrobial agents have been incorporated into impression materials by the manufacturer, increasing the risk of dermal and mucosal irritation of the patient when multiple impressions are made.…”

Effect of Different Energy Levels of Microwave on Disinfection of Dental Stone Casts

“…24 However, microwave energy levels as low as 650 W have been shown to disinfect stone casts contaminated by oral flora in three minutes. 25 Therefore, lower levels of microwave irradiation may be advisable for the safe disinfection of stone casts. …”

Efficacy of Microwave Disinfection on Moist and Dry Dental Stone Casts with Different Irradiation Times

“…Another study revealed that the cast could be disinfected after five minutes of irradiation at 850 W (18). In the latter study, the disinfection of the casts contaminated by Bacillus subtilis following 10 minutes of irradiation was considered as sterilization effect of this method (18).…”

“…Since the microwave irradiation has been suggested for gypsum casts disinfecting, there are used in this context. Disinfection was reported by different irradiation techniques from one or two dry phase (10,(16)(17)(18)(19) to irradiation of the cast immersed in water18, within different times from 319 to 1018 minutes and applying different energy levels from 650 to 900 watts (W) (10,(16)(17)(18)(19). More studies have shown that applied lower levels of energy are safer for strength and accuracy of casts, than high levels and boiling the stone cast during the irradiation (17,(19)(20)(21)(22)(23).…”