We considered data of environmental monitoring during three working days in a dentist's office who habitually employs nitrous oxide (N2O): conscious sedation is used to alleviate anxiety and to diminish or eliminate dental pain. Three different nose masks were tested to determine influence on environmental pollution by N2O. The study shows that the levels of N2O always remains low with the use of proper dental procedures, although the chose of the type of nose mask can further diminish air pollution and the exposure of dental personnel.