Bacterial contamination in irreversible hydrocolloid impression material and gingival retraction cord

This study tested two dental materials in factory-sealed containers for the presence of bacteria that may be a source of infection. Twenty samples of two dental materials found to have contamination in a pilot study were taken from unopened containers using a sterile technique. The samples were inoculated onto chocolate agar plates and into thioglycolate broths with appropriate controls. Plates were examined, colonies were enumerated, Gram stained, and identified. The resulting contamination frequencies were compared for statistical significance using Fisher's exact test. Organisms were isolated from 10% of the negative inoculation control agar plates, while none of the control broths showed contamination. The alginate (irreversible hydrocolloid) showed contamination in 50% of the plates and in 65% of the broths (p less than 0.05). The retraction cord had a small sample size and yielded organisms on 5% of the sample plates and in 20% of the thioglycolate broths (p greater than 0.05).