Bacterial, fungal and yeast contamination in six brands of irreversible hydrocolloid impression materials.

This study assessed the level of contamination of six commercially available irreversible hydrocolloids (two containing chlorhexidine) and identified the contamination present in the materials. Petri dishes containing selective and enriched culture media were inoculated with alginate powder (0.06 g), in triplicate. After incubation (37 degrees C/7 days), the colony-forming units (CFU) were counted and Gram stained. Biochemical identification of the different morphotypes was also performed. The contamination levels for the materials were: Jeltrate--389 CFU/g; Jeltrate Plus--516 CFU/g; Jeltrate Chromatic--135 CFU/g; Hydrogum--1,455 CFU/g; Kromopan--840 CFU/g; and Greengel--59 CFU/g. Gram staining revealed the presence of Gram-positive bacillus and Gram-positive cocci. The bacteria Staphylococcus epidermidis, Bacillus subtilis, Bacillus sp., Bacillus coagulans, Bacillus licheniformis, Bacillus cereus, Micrococcus luteus, and Nocardia sp.; the filamentous fungi Aspergillus niger, Aspergillus flavus, Rhizopus sp., Neurospora sp.; and the yeast Candida sp. were isolated. The contamination detected in the impression materials points out the need for adopting measures to improve the microbiological quality of these materials. The use of contaminated materials in the oral cavity goes against the basic principles for controlling cross-contamination and may represent a risk for debilitated or immunocompromised patients.