An instrument is described for minimizing pain during administration by injection of a liquid, such as, an anesthetic. The instrument includes a main body having a rod mounted freely for vibration and a single use tip removably mounted on the forward end of the main body by a first type of motion and removable by a second and different type of motion. The tip is held on the instrument by an elastic overmold. A vibration unit imparts vibrations to the tip. Demounting of the single use tip will rupture the overmold and render the single use unfit for further use. A method of operating the instrument is described and a single use tip is described.
