two functions 1 it determines the single dose volume of the powder agent to be delivered and 2 it defines the receptacle wherein the powder is conveyed from the hopper orifice 15 to the air stream conduit elements 27 28 the shuttle bar return spring 19 reciprocates the shuttle bar 16 when inactivated in order to realign the shuttle bar receiving cavity 24 with the hopper orifice 15 so that the next powder charge may enter the cavity 24 the recess 17 maintains the shuttle bar 16 in proper position in the housing 12 and restrains the shuttle bar from undesired movement relative to the hopper 13 and the air stream conduit elements 27 28 also the recess 17 has a sufficiently close fit with the shuttle bar 16 to prevent the powder from spilling during the transport from the hopper to the air stream as seen in fig1 and 2 the housing 12 can be the support member for the delivery nozzle 26 and accessory components as above mentioned when the device 11 is actuated the powder is introduced into the air stream and is conveyed to the delivery nozzle 26 said nozzle 26 performs the following functions a it is the instrument for aiming the powder at a specific dental area in need of therapy.