Bevel – The point or tip of the needle. The greater the angle of the bevel with the long axis of the needle, the greater the degree of deflection as the needle passes through the soft tissues. For most injections the bevel of the needle is oriented toward bone.
Shank or shaft – Is identified by the length of the shank and the diameter of the needle lumen (gauge). The higher the gauge the smaller the internal diameter. The most common gauges are 25, 27, and 30 gauge. It has been recommended to use the smallest gauge (largest diameter) needle available which allows for easier aspiration, less deflection of the needle as it perforates the soft tissue, and less chance of breakage at the hub.3 The needle comes in three lengths, long short and ultra-short. The decision as to the length is dependent on the type of injection (block or infiltration) size of patient and thickness of tissue. The needle should not be inserted to the hub as retrieval during breakage is difficult so a long or short needle should be used for block anesthesia. The advantage of the ultra-short needle is less deflection of the needle. It may be used for infiltrations (Figure 3).
Hub – The hub is the plastic or metal piece through which the needle attaches to the syringe. The interior surface of a plastic hub is not pre-threaded. Therefore, attachment requires that the needle be pushed onto the syringe while being screwed on. Metal hub needles are usually pre-threaded. The syringe end of the needle perforates the rubber diaphragm of the cartridge when attached to the syringe.
Figure 3. Needle sizes for delivering local anesthetics
Recommendations for needle utilization are:
Sterile needles should be used.
If multiple injections are to be administered, needles should be changed after three or four insertions in a patient.
Needles must never be used on more than one patient.
Needles should not be inserted into tissue to their hub to allow for easy retrieval if the needle breaks.
To change a needle’s direction while it is still in tissues, withdraw the needle almost completely then change direction.
Never force a needle against resistance (bone) as it can increase the chance of breakage.
Do not bend needles except for intrapulpal injections.
Needles should remain capped until used and then recapped immediately after injection.
Needles should be discarded and destroyed after use.