One of the most useful tools of last resort in endodontic therapy is the ability to quickly and effectively provide profound anesthesia through the use of intra-pulpal injection. THIS METHOD SHOULD ONLY BE USED WHEN ALL OTHER ANESTHESIA METHODS HAVE BEEN UNSUCCESSFULLY TRIED. There is NO question that patient's experience a momentary, sharp discomfort. However, in cases of a "hot tooth" (lower molars especially) this is much preferred over prolonged attempts to access canals with sensitive vital tissue. The theory behind the Intra-Pulpal injection is to rapidly raise the pulpal pressure beyond the trigger level. Once this level is reached, the nerves depolarize once and then are rendered unresponsive. Studies have shown that this can be accomplished with any liquid (such as saline). Anesthetic solution is generally used because of the convenience of applying it via needle and syringe.
There are several keys to gain profound anesthesia with this technique:
(1) Always warn the patient that they will feel 2 sharp sensations, lasting only a second or two. You MUST prepare the patient first.
With proper technique, anesthesia will be profound along the entire length of the canal. In some calcified multiple canal cases it may occasionally be necessary to supplement this technique with an individual intracanal injection. Be careful to inject ONLY in cases where vital tissue (NOT necrotic contents) is present. Only a minute amount is necessary.
(2) Remove the existing restoration. Try to avoid dentin. o Again, warn the patient when you are about to penetrate dentin or expose the pulp. Choose the highest pulp horn or the area where the dentin is the thinnest. Quickly expose the pulp with a new, sharp 2 round bur (dry) turning at maximum revolution. Use a jabbing motion with the bur. The patient will start for a moment. Reassure them.
(3) Do not enlarge the exposure site. It is important to be able to lock the needle in the exposure. Use a 30 Gauge short needle and apply a right angle bend. If necessary, apply pressure to the area of the bend with your opposite index finger or thumb (forcing the needle tip into the exposure site) ALWAYS warn the patient before you inject.
(4) The patient will feel a momentary sharp sensation as the needle is introduced and the intrapulpal pressure exceeds the limit of depolarization. Anesthesia is now complete.