Microbial contamination of removable prosthodontic appliances from laboratories and impact of clinical storage

Decontamination of dental instruments has recently been the subject of considerable debate. However, little information is available on the potential bacterial colonisation of dental appliances returning from dental laboratories and their need for decontamination. This study investigated the extent and nature of microbial contamination of removable prosthodontic appliances produced at different dental laboratories and stored in two clinical teaching units (CTU 1 and CTU 2) of a dental hospital and school. Forty consecutive dental prosthodontic appliances that were being stored under varying conditions in the two clinical teaching units were selected for study; the appliances having been produced 'in-house' (hospital laboratory) or 'out-of-house' (external commercial laboratory). Two appliances, that were known to have undergone decontamination before storage, were used as controls. Swabs were taken according to a standard protocol and transferred to the microbiological laboratory with bacterial growth expressed as colony forming units (cfu) per cm(2). Microbial sampling yielded growth from 23 (58%) of the 40 appliances studied (CTU 1, n = 22; CTU 2, n = 18), with 38% of these having a high level of contamination (>42,000 cfu/cm(2)). The predominant bacteria isolated were Bacillus spp. (57%), pseudomonads (22%) and staphylococci (13%). Fungi of the genus Candida were detected in 38% of the samples. There was no significant difference in contamination of the appliances in relation to either their place of production or the CTU (p >0.05). However, the level of contamination was significantly higher (p = 0.035) for those appliances stored in plastic bag with fluid (n = 16) compared to those stored on models (n = 19). No growth was recovered from the two appliances that had undergone decontamination before storage. The research showed that appliances received from laboratories are often contaminated and therefore there is a need for routine disinfection of such items before use and a review of storage conditions required