A sharp-pointed metal instrument used for penetrating tissue. A biopsy needle is hollow and is used for the removal of a tissue sample for examination. A Gilmore needle (dental standard BS 29917 & 6039) is used for measuring the working and setting time of a material such as dental cement or plaster of Paris. Hypodermic needles are hollow and used for injecting substances such as local anaesthetic into tissues or for aspirating fluid from a cavity. Local anaesthetic needles are manufactured in varying lengths from about 35mm for nerve block injections to about 6mm for intraligamentary injections; they are also made in varying gauges from 25 gauge for block injections to provide some needle rigidity to finer 27 or 30 gauge for intraligamentary analgesia. The finer gauge needles are, however, unreliable when checking for blood aspiration. A suture needle is a straight, curved, or J-shaped pointed needle used for sewing tissues; it may be round, cutting, or reverse cutting. Cutting needles have three cutting edges, one on either side and one on the inside curve. A 16–22mm curved cutting or reverse cutting needle held in a needle holder is used for most intra-oral surgery. The needle may be equipped with an eye for the suture material or may have the suture material fused into it (a so-called atraumatic needle).