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 (normal anethesia blocks, infiltration and PDL injections) HAVE BEEN UNSUCCESSFULLY ATTEMPTED. 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, protracted and uncomfortable 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. Most patients don’t mind a moment of discomfort if they understand that after that anesthesia will be profound.
(2) Remove the existing restoration. Try to avoid dentin. 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. You will now see bleeding in the exposure site. Suction as necessary to find out exactly where the pulp has been exposed. This is the target for your syringe needle.
(3) Do not enlarge the exposure site. Examine where you think the exposure may be ( mesial /distal /buccal or lingual?). This will give you some idea of the best path of insertion for the needle. Ideally, you want to place the needle down one of the canals for greatest effectiveness.. It is important to be able to lock the needle into 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. Injecting into one canal in a situation where the needle is properly locked into the chamber will invariably raise the pressure in all canals and result in total canal system anesthesia.
4) The patient will feel a momentary sharp sensation as the needle is introduced and another when the intra pulpal pressure exceeds the limit of depolarization. Anesthesia is now complete.
With proper technique, anesthesia will be profound along the entire length of the canal system. In some calcified multiple canal (such as molars, where calcification of the chamber has isolated the canals) 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.
In very stubborn cases with small amounts of apical tissue sensitivity I will also sometimes flood the access with topical anesthetic and work it toward the apex with a small file. The sensitivity is usually only momentary and anesthesia is usually complete.