title: High-level microwave disinfection of dental gypsum casts.
abstract: OBJECTIVE
  To test whether microwave oven irradiation can disinfect gypsum casts in compliance with current disinfection requirements, and to determine whether this procedure would be as effective as a validated method of chemical disinfection of impressions.
  
  
  METHODS
  In 2 in vitro experiments, samples of 5 irreversible hydrocolloid impressions of a disinfected acrylic resin model were contaminated with suspensions of recommended test organisms Staphylococcus aureus and Pseudomonas aeruginosa, respectively. In 1 in vivo experiment, 10 impressions were made of 10 subjects. All impressions were poured and the resulting casts cut in 2 halves. One half of each cast was exposed to 5 minutes of irradiation in a microwave oven at 2,450 MHz and 900 W. The other halves were left untreated as controls. In a second in vivo experiment, 10 impressions were disinfected by immersion in a 0.07% solution of NaOCl at pH of about 10 for 3 minutes, and then poured. All casts were incubated aerobically in Bacto tryptic soy broth at 37 degrees C for 6 hours and assessed for bacterial growth by counting colony-forming units per milliliter (cfu/mL) of the culture. The results were analyzed using the Wilcoxon signed-rank test.
  
  
  RESULTS
  Untreated gypsum casts showed cfu/mL counts with a median log value of 6, while microwave-irradiated ones had median cfu/mL counts of 0. Casts poured from chemically disinfected impressions demonstrated cfu/mL counts with a median log value of 4.
  
  
  CONCLUSIONS
  Under the described conditions, microwave-irradiated gypsum casts satisfy current disinfection requirements, but gypsum casts poured from chemically disinfected impressions do not.
authors.affiliation: Faculty of Dentistry, Department of Oral Sciences-Prosthodontics, University of Bergen, Norway. einar.berg@odont.uib.no
authors.forename: Einar
authors.initials: E
authors.lastname: Berg
authors.forename: Oyunn
authors.initials: O
authors.lastname: Nielsen
authors.forename: Nils
authors.initials: N
authors.lastname: Skaug
mesh_terms: D000464:Alginates; D002133:Calcium Sulfate; D015169:Colony Count, Microbial; D019551:Dental Disinfectants; D003760:Dental Impression Materials; D004203:Disinfection / Q000379:methods*; D008872:Microwaves; D003765:Models, Dental / Q000382:microbiology*; D011550:Pseudomonas aeruginosa; D012973:Sodium Hypochlorite; D013211:Staphylococcus aureus; D018709:Statistics, Nonparametric
chemical_list: D000464:Alginates; D019551:Dental Disinfectants; D003760:Dental Impression Materials; D012973:Sodium Hypochlorite; D002133:Calcium Sulfate