Let's say you are to restore # 19 with an MO composite restoration so you have given a 2% Lidocaine 1:100k epinephrine inferior alveolar nerve block to the patient. After 10 minutes of waiting, you start the prep on the tooth and the patient reports pain. What would be the approach of choice to establish profound anesthesia?
Depending on the design of the study, the reported failure rate for inferior alveolar nerve block ranges between 5 to 30 percent.
So if you numb three to five patients with inferior alveolar nerve blocks on any given day, the statistical probability of running into this problem happens almost every other day.
(Click here to learn more about the steps to take after the inferior alveolar nerve block for soft-tissue anesthesia.)
That is a significantly frequent occurrence and it would help to improve on the success rate.
In the example above, what could we do? Let’s consider the following:
Anesthetic: While it is a common belief that articaine is more effective than lidocaine, no research has been able to demonstrate the advantage.1
Elapsed time: Onset of lip anesthesia takes about four to six minutes and pulpal anesthesia onset takes 10 to 15 minutes. Often doing nothing more than waiting an additional amount of time is all that is needed for adequate anesthesia to take effect.
Missed injection: If there is no lip numbness even after 10 minutes, it is likely that the location of injection was incorrect and another injection should be attempted.
Supplementary injection: If lip numbness is present, buccal infiltration in #19, #20 with Atricaine 4% would be the next step.2
Use buffered anesthetic: Recently there has been a new product in the market, which allows for convenient alkalization of lidocaine right before injecting.3 Buffered anesthetic hastens the onset of anesthesia. So if you have deposited the anesthetic in an incorrect location, you will be able to detect this quicker. Besides, buffered anestehtic can make the injection less painful for the patient.4
Use of a timer: The moment you pick up the syringe to inject the patient, have the assistant start a timer. Its amazing how much this objective consistent measurement of time helps with the anesthesia procedure.
- It helps to slow down the speed of injection. Injecting a 2 ml volume of solution over one minute is the ideal speed to ensure patient comfort and improve success.5
- Timer helps to objectively quantify wait times after the injection.
- If the patient is not numb in the first five minutes and one needs to wait another 10, there is an objective measurement possible.
Technique: Two most common causes of a missed injection are:6
- Positioning the tip of the needle too far medially resulting in inadequate anesthesia.
- Positioning the tip of the needle too far inferiorly resulting in anesthesia of only the lingual nerve.
Ideally, one would expect to hit bone at around 20–25 mm of needle insertion. While in both of the above types of errors, most likely, one would not have hit bone. When injecting the second time, it becomes even more crucial to feel for the bone. Often choosing the point of needle insertion, which is more lateral and higher than the first insertion point, helps. During the process if you hit bone too soon you have to just retract slightly and redirect the needle a little to the medial. In this manner as the needle is advanced you have an assurance that the needle is just lateral to the medial surface of the ramus and you avoid the needle from going too far medially.
Intraosseous injection: When this first line of management fails, an intraosseous injection would be the approach of choice. Some studies would suggest that intraligamentary injection could work just the same but intraosseous injection seems to be more effective.
1. Mikesell P, Nusstein J, Reader A, Beck M, Weaver J. A comparison of articaine and lidocaine for inferior alveolar nerve blocks. J Endod. 2005 Apr;31(4):265–70.
2. Haase A, Reader A, Nusstein J, Beck M, Drum M. Comparing anesthetic efficacy of articaine versus lidocaine as a supplemental buccal infiltration of the mandibular first molar after an inferior alveolar nerve block. J Am Dent Assoc. 2008 Sep;139(9):1228–35. Erratum in: J Am Dent Assoc. 2008 Oct; 139(10):1312.
4. Kashyap VM, Desai R, Reddy PB, Menon S. Effect of alkalinisation of lignocaine for intraoral nerve block on pain during injection, and speed of onset of anaesthesia. Br J Oral Maxillofac Surg. 2011 Dec; 49(8):e72–5. doi: 10.1016/j.bjoms.2011.04.068. Epub 2011 May 18.
5. Kanaa MD, Meechan JG, Corbett IP, Whitworth JM. Speed of injection influences efficacy of inferior alveolar nerve blocks: a double-blind randomized controlled trial in volunteers. J Endod. 2006 Oct; 32(10):919–23. Epub 2006 Jul 7.
6. Milles M. The missed inferior alveolar block: a new look at an old problem. Anesth Prog. 1984 Mar-Apr; 31(2):87–90.
Vivek Mehta DMD, FAGD, Visiting Faculty, Spear Education. Follow him on Twitter @Mehta_DMD.