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Aerosol transmission is an important mode of COVID-19 (SARS-CoV-2) infection. Dentists and dental hygienists, who provide medical treatment and care in the oral cavity, may be exposed to expiratory aerosols of asymptomatic infected persons. To compare the effectiveness of devices in reducing the risk of transmission to dentists and dental hygienists, we conducted experiments in a dental treatment room at Nippon Dental University. The measurements were carried out in five cases: a) the basic case (conventional air conditioning), b) a case with the circulator placed in the center of the room and operated in high air flow mode, c) a case with a circulator placed behind the patient and operated in low air flow mode, d) a case with the circulator blowing from inside to outside, e) a case using an extraoral vacuum, and f) a case with a portable neck fan hanging on the dentist manikin. The results indicated that all measures were effective in reducing the risk of infection, and case e showed the highest reduction in aerosol concentration. However, because extraoral vacuums are expensive, it is important to reduce the risk as much as possible by selecting circulators or portable neck fans according to the budget of each hospital.