Abstract
Objectives: Dental practice contains the use of instruments and multiuse items that should be sterilized or disinfected properly. The aim of the current study was to investigate the effect of microwave irradiation on dental stone cast disinfection in moist and dry condition. Materials and Methods: In this in vitro study, 76 stone casts were prepared by a sterile method. The casts were contaminated by Pseudomonas aeruginosa (ATCC 9027), Staphylococcus aureus (ATCC 6538), Enterococcus faecalis (ATCC 29212) as well as Candida albicans (ATCC 10231). Half the samples were dried for two hours and the other half was studied while still moist. The samples were irradiated by a household microwave at 600 W for 3, 5 and 7 minutes. The microorganisms on the samples were extracted by immersion in tryptic soy broth and .001 ml of that was cultured in nutrient agar media, incubated overnight and counted and recorded as colony forming unit per milliliter (CFU/mL). Results: The findings showed that microorganisms reduced to 4.87 logarithm of CFU/mL value on dental cast within seven minutes in comparison with positive control. Although microbial count reduction was observed as a result of exposure time increase, comparison between moist and dried samples showed no significant difference. Conclusions: Seven-minute microwave irradiation at 600 W can effectively reduce the microbial load of dental stone casts. Wetting the casts does not seem to alter the efficacy of irradiation. Keywords: Microwave Disinfection; Dental Stone Casts; Irradiation Times
Highlights
In prosthodontics, many instruments and multiuse items are used that are not sterilized or disinfected, including prostheses, impressions and especially stone casts [1] All impressions, cast models and prostheses should be properly disinfected before being sent to the prosthetic laboratory as well as when they are sent back to the dental office
The samples were randomly divided into four groups and each group was separately immersed into a Tryptic Soy Broth (TSB) with 1.5×108 CFU/ml of Pseudomonas aeruginosa (ATCC 9027), Staphylococcus aureus (ATCC 6538), Enterococcus faecalis (ATCC 29212) or Candida albicans (ATCC 10231)
Comparing colony forming unit per milliliter (CFU/mL) values of the positive control grip[ with those of the case groups after microwave irradiation showed, 2.77 to 4.87 logarithm reduction for S. aureus in moist and C. albicans in dry samples with three- and seven-minute irradiation time respectively (Table 1)
Summary
Many instruments and multiuse items are used that are not sterilized or disinfected, including prostheses, impressions and especially stone casts [1] All impressions, cast models and prostheses should be properly disinfected before being sent to the prosthetic laboratory as well as when they are sent back to the dental office. In order to reduce microbial contamination in the clinic and dental laboratory, several methods have been recommended. The most used disinfection processes are chemical methods including immersion of the contaminated objects in sodium hypochlorite [5,6]. The efficacy of this method on microorganisms has not been able to fulfill all disinfection requirements [4,7,8] and microbial transmission requires blockage by a practical, easy and effective disinfection or sterilization procedures. Microwave irradiation whose efficacy in sterilization of some contaminated objects has been revealed [9], is recommended as a practical physical sterilization method [10]. The primarily purpose of the current study was to determine the effect of the household microwave irradiation at 600W on disinfection of dental casts. In this study the effects of the humidity on disinfection of dental stone casts were tested
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