Bacterial contamination of the surgical mask and forehead in aerosol-producing conservative-preventive dental treatment

Background Microbial contamination of dental professionals’ facial protective equipment and skin from aerosols and droplets generated during dental treatment has not been studied in all aspects so far. Our aim was therefore to investigate and compare treatment-related bacterial contamination of the forehead skin and surgical mask of dental practitioners. Methods We analyzed samples from 67 consecutive aerosol-producing conservative-preventive dental treatments. Sterile nylon swabs were used to collect samples from the forehead skin before and after performing treatment. Contact samples were obtained from the used surgical face masks. Samples were cultivated on agar under aerobic and anaerobic conditions. Bacteria were classified by MALDI-TOF mass spectrometry. The frequency of detection of obligate and facultative oral bacteria, as well as an increase in bacterial abundance, were examined (bacterial scoring: 0: no growth on agar; 1: 2 colonies; 2: >102 colonies; 3: dense bacterial growth). Results Bacteria were detected in 95% of the skin swabs and 76% of mask samples. Median bacterial scores were 2 for the forehead skin samples before and after treatment, and 1 for samples obtained from masks. Obligate and facultative oral bacteria were more frequent (6% and 30%) in samples from forehead skin after treatment. Samples taken from the forehead skin after treatment showed increased scores for these bacteria (28%). Five percent of samples were positive for methicillin-sensitive Staphylococcus aureus (MSSA). Obligate anaerobes were present in 3% of samples. Conclusions Although exposed during treatment, the forehead skin was significantly less contaminated with obligate oral bacteria than expected based on the surgical face mask findings. Forehead skin samples showed an increase in bacteria in the after treatment, which can be attributed to aerosol-producing procedures. We hypothesize that the forehead’s physiological skin flora may offer some protection against contamination with other microorganisms.