A respiratory face 
mask is provided suitably sized and configured to engage at least the 
nose portion and mouth portion of a patient's face. Gas from a 
gas supply and 
scavenging set normally used in 
dentistry is operatively coupled to the 
mask via a 
breathing circuit to supply fresh gas and evacuate exhaled 
waste gas. A gas flow compensator in the 
breathing circuit automatically prevents re-
breathing of exhaled gas. Because the 
mask has a sealing 
cushion, 
contamination of the clinical room where the apparatus is being used also is avoided. In an alternatively preferred embodiment, the fresh 
gas supply tube and the 
exhalation limb of the breathing circuit are replaced by a single length of co-axial flexible tubing connected between the face mask and a branched 
coupling. The branched 
coupling, in turn, includes a first 
branch for connection to the fresh 
gas supply nozzle of the “dental” set-up and a second 
branch for connection to a flexible flow-through 
reservoir bag used to store waste or exhaled gas. A one-way valve is disposed between the second 
branch output 
nozzle and the input of the flexible bag. The output of the flexible flow-through bag is connected to the vacuum module of the “dental” set-up. The second branch of the 
coupling, the one-way valve, and the flexible flow-through 
reservoir bag define the 
exhalation limb of the breathing circuit.