Objectives: To assess, qualitatively and quantitatively, the contamination of silicone impressions arriving at dental laboratories. To identify potential pathogenic microorganisms transmitted
via dental impressions. Methods: Thirty two randomly selected partial and full, maxilla and mandible, silicone impressions were swabbed using sterile swabs. Swabs were transferred directly into 2ml sterile Reduced Transport Fluid (RTF) (Syed & Loesche 1972) and vortexed for 30 seconds. One ml was removed and serially diluted in 9 ml sterile physiological saline (0.85%). Dilutions were plated out onto selective media; Mannitol salt agar (MSA), Sabouraud dextrose agar (SAB), and non-selective media; Columbia agar supplemented with 5% horse blood (CBA), Nutrient agar (NA) and R2A agar. Inoculated plates were incubated at 37±1°C for 24-48 hours (MSA, CBA, SAB and NA); 37±1°C plus 10% CO2 for 24-48 hours (CBA) and 23±1°C for 5-7 days (R2A). Preliminary identification of bacterial isolates was based on colony morphology, haemolytic reaction, Gram-staining and biochemical reactions. Further identification, where appropriate, was performed using API 20 NE and API STAPH (BioMérieux, France) identification kits. The germ-tube test was performed on yeast isolates. Results: Twenty nine of the thirty two impressions were contaminated, only one uncontaminated impression was labelled as having been disinfected. Three hundred and forty four different colony morphologies were selected for preliminary identification. Gram-positive cocci were the predominant isolates cultured from the impressions. The proportions of positive cocci, negative rods, positive rods and yeasts were 68.02%, 12.5%, 10.17% and 9.30% respectively. All Gram-negative rods were catalase and oxidase positive, all yeasts were germ-tube positive. Conclusion: It appears that not all impressions arriving at dental laboratories are disinfected. To date, the study has identified potential pathogens such as
Candida albicans and
Pseudomonas aeruginosa.
Syed, S.A. Loesche, W.J. (1972) Survival of human dental plaque flora in various transport media. Applied Microbiology 24 (4), 638-644