Microbial contamination of pumice used in dental laboratories

Dental appliances as well as sending and receiving prosthesis from laboratories are potential sources of cross-contamination for technicians, dentists, patients and can transmit different infectious agents as well. This study was conducted to determine the types of the microorganisms in pumice powder and pumice slurry used in dental laboratory in order to evaluate necessary disinfection control procedure in the dental settings. Twenty-four active dental laboratories of Khorram Abad participated in our study. Samples were randomly collected from prosthesis polishing containers in sterilized condition and were immediately sent to microbiology laboratory. Specimens were cultured on selective bacterial and fungal media in order to determine the microorganisms. Both oral and non-oral bacteria were recovered from pumice samples as follows: Staphylococcus aureus (15.4%), Streptococcus viridance (10.8%), Bacillus cereus (18.7%), Pseudomonas aeruginosa (12.8%), Diphtheriods (7.3%), Enterobacter cloace (4.3%), Escherichia coli (13.1%), Klebsiella pneumonia (5.4%), and Acinetobacter spp. (12.2%). The isolated fungi included Candida albicans (36.7%), other yeasts (17.3%), Fusarium spp. (13.8%), Aspergilus spp. (22.4%) and Penicillium spp. (9.8%). This study showed that polishing pumices in the form of powder or slurry were contaminated with different oral and non-oral bacteria and also fungi. Therefore, the chance of cross-contamination still severely exists, and measures should be conducted to prevent the contamination of predisposed people such as technicians, dentists and patients.