Bacterial species and factors influencing the contamination of the inner and outer layers of face masks used in dentistry.

Background: Many patients are clinically consulted in dental clinics, where aerosol-generating procedures are widely used. In our previous study, we evaluated the temperature, humidity and contamination rates on the inner layer of masks according to the mask-wearing time. However, it is important to assess the contamination rates on the outer layer of masks used in dentistry as well. Previously, while examining the contamination rates, we only identified the associated bacteria; no detailed analysis of bacterial species depending on the mask-wearing time was conducted. Furthermore, we did not evaluate factors that could contribute to the contamination of masks.

Objectives: The present study was intended to supplement the limitations of our previous study.

Material And Methods: The used masks were collected. Thereafter, colony forming unit (CFU) quantification and 16S rDNA sequencing were performed to calculate the contamination rates and identify bacterial species. Data on the participants' medical and dental history was collected. The participants filled out a questionnaire and underwent saliva tests.

Results: On the inner and outer layers of the masks, 3.3 × 108 and 8.5 × 108 CFUs were found, respectively. The contamination rates of the masks increased with the increasing mask-wearing time. There was no correlation between the contamination rate on the inner layer and other factors, such as the probing depth (PD) ≥4 mm, the bleeding rate, the calculus rate, and saliva characteristics. The inner layer contamination rate increased as the number of treated teeth increased, and as the saliva buffering capacity decreased. The outer layer contamination rate increased with the number of times the mask was touched.

Conclusions: The contamination rates were higher on the outer layer than on the inner one, and the CFU count increased with the mask-wearing time. The following bacterial species were found on the masks: Staphylococcus epidermidis (S. epidermidis); Staphylococcus aureus (S. aureus); Staphylococcus capitis (S. capitis); Streptococcus oralis (S. oralis); and Streptococcus koreensis (S. koreensis). Oral health conditions may have affected the contamination of the inner layer. In addition, the number of times the mask was touched may have affected the contamination of the outer layer.