Carriage of oral flora on irreversible hydrocolloid and elastomeric impression materials

This study assessed the carriage and persistence of oral flora on irreversible hydrocolloid and elastomeric impression materials. In the first part of the study, a single isolate each of Streptococcus mutans, Escherichia coli, Staphylococcus aureus, and Candida albicans were inoculated onto each of two elastomeric and two irreversible hydrocolloid impression surfaces artificially created in vitro. Then the inoculum was discarded, samples of impression material (13 mm in diameter) were removed over a 5-hour period, and the remainder of viable organisms were estimated. In the second part of the study, impressions were made from 21 dentate and eight edentulous patients, and bacterial counts were estimated as described. The results showed twofold to fivefold retention of bacteria on the irreversible hydrocolloids compared with the elastomeric impression surfaces. With all impression materials, the number of viable bacteria retained within 5 hours decreased 65% to 98% except for the "disinfectant" irreversible hydrocolloid Blueprint Asept, which totally destroyed the organisms in less than 3 minutes. It is concluded that the total bacterial "load" on impression surfaces is relatively low and decreases rapidly after impression making. However, disinfection of impression surfaces should be mandatory to prevent cross-infection.