Evaluation of compressed air used in the dental operatory

The authors report the findings obtained when they quantitatively examined compressed air samples from air-water syringes located in different dental operatories at the Louisiana State University School of Dentistry fo r the presence of microbial contaminants.

Streams of air of 30 seconds' duration from air-water syringes were forced through sterile modified stainless steel membrane filter holders (Millipore, Millipore Corp., Bedford, Mass.), each containing a membrane filter (average pore diameter = 0.45 micrometers). Each filter was aseptically removed, placed onto the surface of a Petri dish containing sheep blood agar and incubated under increased carbon dioxide tension at 37 C for 48 hours. The authors performed a count of the resultant microbial colonies, after which they microscopically examined the gram-stained organisms.

Bacteria were detected in 24 percent of the samples. The number of colonies observed on the filters varied among the dental units. The air from only one of the dental units sampled repeatedly was found to be free of bacterial contaminants. This contrasted with other units for which one or more samples were found to be positive for microorganisms. The majority of colonies observed were pigmented. Microscopic examination of organisms from representative colonies revealed that most were either gram-positive cocci or gram-negative diplococci and tetrads. The results of the one-sample t test were found to be significant (t = 5.6, df = 98, P = .0001). The 95 percent confidence interval was 0.15 to 0.32.

The results suggest that, at least statistically, a percentage of air lines will have bacteria present.