THE IA: MAKE IT YOUR BEST SHOT!
Updated: Feb 4, 2021
This injection seems to cause several clinicians difficulties. Things such as trouble getting profound anesthesia or missing the target all together and injecting into the parotid gland (YIKES!). Many have anxiety over the depth of insertion…which makes sense, there is so much anatomy in that small area. The blood vessels, muscles and the zings that constantly happen when administering can make anyone feel like they are traveling through the forest chanting LIONS and TIGERS and BEARS…OH MY!
WHAT IS IT?
The Inferior Alveolar Nerve Block (IA) is a mandibular block which will cover all teeth in the quadrant injected. This Includes the periodontium and gingival tissue of the premolars to midline as well as all the lingual tissue and half of the tongue (because the lingual nerve is a travel buddy for the IA nerve). It is important to note that the buccal tissue and periodontium around the molars will not be impacted. Which means the clinician will need to administer the buccal injection as well.
HOW DO YOU ADMINISTER?
Syringe set-up is the first step with this shot. The needle selection should be a 25 or 27 gage long needle. The reason we want to select a long needle is because the depth of insertion is deeper than what a short needle can handle.
Palpate the ramus of the mandible confirming its width and locating the coronoid notch (the indentation where the ramus meets the body of the mandible). The notch acts as a nice place holder for your thumb or finger of the retraction hand. While this may not seem crucial it really does help with getting your base line of needle orientation established.
You also need to identify the pterygomandibular raphe. If it’s been a few years since you took an anatomy course, and you are thinking to yourself the WHAT?!? Here is a little reminder, this is the thick band of tissue which basically runs from the maxilla towards the mandible. I often tell my students that it feels like a rubber band going from both arches. This is a crucial landmark because it creates the most medial reference point for needle insertion. With some of our patients identifying that awesome landmark can be hard. When you feel for the coronoid notch just move your finger/thumb posteriorly towards the raphe and manipulate the mucosa until you can feel it. Another way is to move your cotton swab in the region until you bump up against it. Once you have located it, place your cotton swab with topical near that space.
One of my favorite identifiers for this injection is the patients bite line. When your patient is open this line acts like the level indicator for the height of insertion. On most people it is so EASY to see. As a bonus, sometimes the most posterior portion of the bite line will end with a triangular shape of raised tissue, which almost acts like an arrow, pointing to the exact spot to insert. The goal is to be about 10 mm above the mandibular occlusal plane, which is a little superior to the opening of the mandibular canal (our target point). Using the bite line as a reference, along with assuring your needle is not below the level of the coronoid notch, will help make sure you aren’t too low.
One tip I try to keep in mind, is if I am not sure if I am at the correct height of insertion, just move a couple of millimeters up toward the maxilla. It almost turns into a hybrid of a Gow-Gates (you can check that out on an earlier post) and the IA.
Align the barrel on the opposite side of the mouth, just over the premolars. For example, if you are getting the lower right quadrant numb the barrel should be at the corner of the left side of the mouth. Making sure to stay distal to the canine and keep the barrel level with the mandibular occlusal plane.
Insert the needle along the pathway just described until bone has been contacted. This is about 22-26 mm (which is why a long needle must be used). Care must be taken to contact bone, to make sure you are in the proper location and avoid the potential to miss and inject into the parotid gland.
If you contact bone early there could be a couple of issues to look at. First, make sure you are close to the raphe. If you are too far away from it, you could contact prematurely. Also, if you are too low (closer to the mandible than the maxilla) you may contact bone early as well. If you are confident those two aspects are appropriate and you have inserted about 10 mm, then re-aligning the barrel over the anterior teeth to move past the boney roadblock should do the trick. The key is to make sure to move the barrel back over the premolars after you have moved past the obstacle. If you haven’t even gotten to about 10 mm of depth penetration, I advise withdrawing and inserting again a little higher staying closer to that raphe. I strongly suggest having the needle hug that raphe, just make sure you DO NOT go on the medial side of it.
If you have inserted and there are only a couple of millimeters left of the needle showing and you haven’t contacted bone, move the barrel towards the molars. Make sure you withdraw the needle a few millimeters before you re-align your syringe, so you don’t end up causing a large deflection of the needle.
Once you have reached the proper depth, aspirate, and deposit solution. The time for numbing to take effect could be a little longer than the maxillary injections. To combat this, you can sit the patient up and let gravity help you out.
If you happen to be a clinician that is having difficulties with this injection, please know you aren’t alone. Even the best “injection givers” will go through periods of time when they are in a slump. Sometimes, you just have to pause and really evaluate what you are currently doing so you know what you need to fix.
With a little review I know you will give your best shot!
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