a needleless vacuum - compression injector applies a continuous vacuum between a medicament holder and an outwardly extending member spaced therefrom . the continuous vacuum holds tissue taut and immobilizes the tissue over a nozzle without puncturing the tissue . pressurized gas then injects the medicament into the tissue to a predetermined depth determined by the pressure of the gas . the outwardly extending member can be a removable sleeve . particularly for oral applications , the tissue - engaging surface of the outwardly extending member can be oval or otherwise non - circular in shape to accommodate the shape of the tissue to be injected .