Effect of microwave disinfection on compressive and tensile strengths of dental stones

Efficacy of Disinfection of Dental Stone Casts: Virkon versus Sodium Hypochlorite

OBJECTIVES

The purpose of this experimental study was to compare the disinfection efficacy of sodium hypochlorite and peroxygenic acid (Virkon) solutions for dental stone casts contaminated with microbial strains.

MATERIALS AND METHODS

A total of 960 spherical stone beads with a diameter of 10 mm were prepared and used as carriers of bacterial inoculums. They were individually inoculated by soaking in broth culture media containing each of the four understudy microorganisms. Different concentrations of Virkon and hypochlorite solutions were prepared using distilled water and then were sprayed on the surfaces of dental casts contaminated with Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis and Candida albicans. The pour plate technique was used to evaluate the antimicrobial efficacy of each solution. Microbicidal effect (ME) was calculated according to the log10 of control colony counts minus the log10 of the remaining colony counts after the antimicrobial procedure. Statistical difference was assessed using the Kruskal Wallis and the Man Whitney U tests with a significance of 95%.

RESULTS

We observed different bactericidal effects of Virkon at various concentrations; 1% Virkon killed S. aureus, P aeruginosa, and Candida albicans, while 3% Virkon solution was required to kill B. subtilis. For S. aureus, P. aeruginosa, and C. albicans, no significant difference was observed between 1% Virkon and 0.525% sodium hypochlorite (P >0.05). For B. subtilis, the efficacy of 3% Virkon and 0.525% sodium hypochlorite was not significantly different (P >0.999).

CONCLUSION

According to the obtained results for Virkon and based on its low toxicity and good environmental compatibility, it may be recommended as an antimicrobial disinfectant for dental stone casts as non-critical items.

Effect of different energy levels of microwave on disinfection of dental stone casts

BACKGROUND AND AIMS

Current chemical methods may not efficiently disinfect dental stone casts. The aim of this study was to investigate if microwave irradiation is effective for disinfection of stone casts.

MATERIALS AND METHODS

In this laboratory study, three groups (n = 162) of prepared spherical stone beads as carriers with a diameter of 10 mm were inoculated by separately soaking in three broth culture media, each containing a study microorganism-Pseudomonas aeruginosa, Staphylococcus aureus or Candida albicans. Six inoculated carriers were used for every test, including irradiation in a household microwave oven at 300, 450, 600 or 900 W energy level, or soaking in 0.03%, 0.06%, 0.12%, 0.25% or 0.50% concentration of sodium hypochlorite solution, at 1, 2, or 3-minute test times. Positive and negative control groups were considered for each test. All treated carriers were then individually transferred to nutrient broth culture medium and one milliliter from each tube was cultured in nutrient agar media over night. Colony forming unit per milliliter (CFU/mL) was counted, and multi-factor ANOVA was used to analyze data (α = 0.05).

RESULTS

Microwave irradiation at 600 W resulted in high-level disinfection in 3 minutes. Immersion of the stone casts in hypochlorite solution at 0.06% concentration resulted in disinfection after 2 minutes.

CONCLUSION

According to the results, high level disinfection of the stone casts can be achieved by microwave irradiation at 600 W in 3 minutes, similar to a validated chemical method.