Disinfection of Bacterial Contaminated Hydrophilic PVS Impresion Materials

Objective: This study evaluated disinfection of bacterially contaminated hydrophilic polyvinyl siloxane (PVS) impressions.

Methods: Four types of PVS and a polyether impression materials were used – Examix (GC America), Genie (Schein), Take1 (Kerr), Aquasil (Dentsply) and Impregum (3M ESPE). All were of a Type III light-body consistency(ISO4823:2000). Evaluated were three types of disinfectants - EcoTru (EnviroSystems), ProSpray (Certol) and bleach (diluted 1:9). Testing include spray and immersion disinfection with 10 minute exposures. A combination of bacteria, Pseudomonas aeruginosa ATCC15442, Salmonella choleraesius ATCC10708 and Staphylococcus aureus ATCC6538 was the microbial challenge (1.0 x 108 cells/mL). Specimen preparation used sterile aluminum molds with ten tapered cones (4 mm at the base and 2 mm at the point). Each cone received a covering of mucin followed by 0.01 mL of the bacteria. Impression material was injected over the cones followed by coverage with a filled sterile custom tray. Three impression trays were spray disinfected, while three underwent immersion disinfection. One tray was not disinfected (positive control) and one tray was not bacterially contaminated nor disinfected (negative control). Trays were filled with Silky Rock Stone (Whip Mix). After separation, two cones were placed into a sterile capsule and triturated into powder. Four mL of TRIS buffer (0.05M, pH 7.0) containing Na thiosulfate (0.0055% w/v) went into each tube. After mixing, the solution was serially diluted and spread plated onto selective agar. After incubation, colony counts were converted CFU/gram of set stone.

Results: No bacteria were present on either spray or immersion disinfected impressions. Culturing negative controls produced no microbial colonies. Culturing positive controls produced on average 3.35 x 105 viable cells of each test bacteria.

Conclusion: Microbial transfer from contaminated impressions to cones approached 33.5%. The results suggest that different disinfectants and application methods can disinfect bacterially contaminated PVS impression materials.