Bacteriological air sampling was conducted at 25 dental units during restorative
treatment sessions before and after disinfection of dental unit waterlines (DUWL)
with hydrogen peroxide. Air samples for determining the concentration and species composition
of aerobic and facultatively anaerobic bacteria were collected with the portable
Reuter Centrifugal Sampler (RCS Plus) in the dental operation area close to patient’s
mouth. Large concentrations of airborne bacteria in the range of 0.35–40.08 × 103 cfu/m3
(median = 1.63 × 103 cfu/m3) were recorded before DUWL disinfection. After disinfection,
the concentrations were signifi cantly lower (p<0.05), ranging from 0.51–3.82 × 103
cfu/m3 (median = 0.9 × 103 cfu/m3). Streptococci were most numerous among airborne
bacteria before DUWL disinfection, forming 79.23% of total isolates. The remaining isolates
were staphylococci/micrococci (15.7%), corynebacteria (2.3%), endospore-forming
bacilli (1.45%), Gram-negative bacteria (1.31%), and actinomycetes (0.01%). After
DUWL disinfection, a signifi cant decrease in the numbers of streptococci (p<0.05) and
Gram-negative bacteria (p<0.01) was noted, while the numbers of other types of bacteria
were unaffected. Altogether, 50 species or genera of bacteria were identifi ed in the examined
air samples before and after DUWL disinfection. Of these, 36 species or genera
are considered potentially pathogenic, as a potential cause of infection, allergic disease
or intoxication. In conclusion, the high pollution of dental operation area with bacteria
indicates a need for use of preventive measures protecting dental staff and patients, such
as DUWL disinfection that proved effi cient in decrease of exposure in the present study