So the trend in my life for the past week or so has been circling around inferior alveolar nerve blocks, both managing when I miss and answering questions for other dentists about this technique. Periodically over my twenty plus years in practice I hit a spell where I miss this block more often than usual. I have learned over the years that when this happens going back to basics, and reviewing the technique and the current thoughts always helps get me back on track, so that’s what I did this week.
If you look at the research on inferior alveolar nerve blocks, the studies show a working level of anesthesia is achieved between 44 and 81% of the time. If you think about it, these aren’t very good odds for a procedure we depend on every day. One of the most common reasons not to gain adequate numbness is the relationship of the nerve to the placement of the anesthetic. One of the most important things we can do to ensure proper location is have the patient open as wide as possible. When the mandible is extended the inferior alveolar nerve is pulled taut and into position over the ramus, as the patient closes and the tension on the nerve relaxes it moves distal to the site of this injection. I place my thumb on the inside notch of the ramus and my index finger at the posterior border of the ramus extraorally. With the patient open as wide as possible, and then hub of the needle over the opposite mandibular canine, I split the difference between my thumb and index finger and the upper and lower occlusal planes, and insert the needle until I hit the ramus. Once I have reached the ramus, I pull back 3-4 mm and begin the injection. If the hub of the needle is placed anteriorly to the opposite canine the anesthetic is placed distal to the nerve, and if you move the hub posteriorly, you place anesthetic mesial to the location of the IAN.
Research shows an average onset time for profound anesthesia with an inferior alveolar nerve block of eight minutes with the range being 5-18 minutes. One of the things that is critical is scheduling for and allowing adequate time for the block to work. I ask my patients to report a tingling sensation between the commissure and the middle of the lower lip in the first 2-3 minutes. If this is not present, I go ahead and inject again.
I make sure my patients know that “their cheek and tongue” are a buy one get one free” and do not tell me the teeth are numb, it has to be their lower lip. Often, the patient reports profound anesthesia to their lower lip, and we can even test the gingival tissue with no response, but the lower molars are not adequately numb. One thing you can try is a lingual infiltration in the attached tissue, as some patients have accessory innervation to the molar roots.
There is also research showing that 1000mg of acetaminophen an hour prior to an IANB helps increase anesthesia for patients with pulpitis. Lastly, becoming proficient with the Gow-Gates technique can eliminate many frustrations trying to obtain mandibular anesthesia.. The incidence of profound mandibular anesthesia rises to as high as 98-100% with this technique, however the risk of hematomas and facial paresthesia rise as well, so it is important to be trained before using this injection routinely.