We’ve all been in this exact situation. You administer an Inferior Alveolar Nerve Block (IANB) perfectly, wait ample time, the patient’s lip and tongue go completely numb, and then you start working on a lower molar only for the patient to jump right out of the chair. That’s when you start with the classic excuses: “Oh, that’s just pressure, not pain,” or “You’re just a bit nervous.” But deep down, you know something is genuinely wrong.
The truth is, in most of these instances, the problem isn’t with your injection technique itself. The real issue often stems from an “uninvited guest” you simply didn’t account for: Accessory Innervation. Put simply, the Inferior Alveolar Nerve isn’t the sole player responsible for transmitting pain sensations from these teeth to the brain. Other nerves, originating from different areas, assist in this crucial task.
In this article, we’re going to reveal who these hidden adversaries are. We’ll specifically focus on the biggest one, and show you exactly how to overcome it with a simple, smart injection technique that will completely transform your approach to mandibular anesthesia.
Who Are the Usual Suspects? A List of Accessory Nerves
When an IANB doesn’t quite hit the mark, one of these “guests” is typically the culprit. Research has pinpointed 7 potential sources of accessory innervation to the mandible:
-
Mylohyoid Nerve: This one is the star of our story today and the primary suspect in the vast majority of cases.
-
Posterior Superior Alveolar Nerve
-
Middle Superior Alveolar Nerve
-
Nasopalatine Nerve
-
Greater Palatine Nerve
-
Lingual Nerve
-
Facial Nerve
While this list might seem extensive, trust us, 99% of your challenges will be related to the very first one.
The Mylohyoid Nerve: Your Number One Foe to Master
This nerve is unequivocally the most common and significant reason behind failed profound anesthesia in lower molars. Studies indicate that the incidence of accessory innervation from the Mylohyoid Nerve to these teeth can be found in over 60% of individuals! (1). It has a particular affinity for innervating the mesial root of the mandibular first molar.
The Fatal Mistake We All Make:
When a patient still reports feeling pain, what’s usually the first thing that springs to mind? Administering a buccal infiltration injection right next to the tooth. And right there? That’s the disaster.
The Reality: The Mylohyoid Nerve travels along the lingual aspect of the mandible! This means the anesthetic you’re diligently injecting buccally isn’t even reaching it. You are, quite literally, depositing the anesthetic in one place while the nerve is somewhere else entirely, and your patient remains in pain, leaving you to keep saying, “It’s just pressure, not pain, sir.”
How to Precisely Target the Mylohyoid Nerve: The Mylohyoid Nerve Block
To decisively overcome this issue, you need to deliver a specific injection designed to target this nerve right in its anatomical location. The technique itself is quite straightforward and doesn’t demand any extraordinary skills.
Needle Penetration Point:
-
Locate the apex of the tooth you’re working on. Your entry point will be slightly below and posterior to that apex, within the floor of the mouth.
Needle Movement:
-
Advance the needle gently until you feel a slight resistance, indicating the needle has contacted the lingual aspect of the mandible.
Depth:
-
The required depth is quite minimal, only about 3 to 5 mm.
Injection:
-
Perform aspiration to ensure you are not within a blood vessel.
-
Slowly inject approximately 0.6 ml of anesthetic (which is roughly one-third of a cartridge). Injection in this area targets the nerve on the lingual aspect of the bone, anesthetizing it before it enters the tooth (2).
With this simple injection, you effectively block the accessory innervation, and you’ll find your patient completely comfortable, allowing you to proceed with your work without any further hitches.
What If You’d Rather Not Give This Injection? (Plan B and C)
If you’re not keen on administering an additional injection, or if the clinical situation makes it challenging, there are alternative techniques that often yield higher success rates than the conventional IANB. This is because they anesthetize the nerves from a more superior location, thereby ensuring they block the Mylohyoid nerve before it branches off.
-
Gow-Gates Nerve Block: This technique anesthetizes the entire mandible from a much higher position, closer to the condyle. Its success rate is exceptionally high because it effectively blocks all potential accessory nerves (3).
-
Vazirani-Akinosi Block: This is a closed-mouth technique, making it incredibly useful in cases of trismus. It also achieves anesthesia from a higher anatomical point.
-
Intraosseous Injections: These are more advanced techniques, such as PDL (Periodontal Ligament) Injection or systems like Stabident. These methods deliver anesthetic directly into the bone surrounding the tooth, bypassing all issues of accessory innervation. However, they do require specific training and specialized equipment.
Are There Complications from the Mylohyoid Injection?
Frankly, complications are exceedingly rare, primarily because you’re injecting into a relatively superficial area. However, as with any injection, minor bleeding or a hematoma could occur if a small blood vessel is nicked.
The Takeaway: Don’t Let the Mylohyoid Outsmart You
The next time your IANB fails, before you question your own skills or the anesthetic itself, consider the Mylohyoid nerve. And please, resist the urge to perform a buccal infiltration, as it’s truly ineffective in this scenario.
The Bottom Line:
-
Accessory innervation, particularly from the Mylohyoid nerve, is the most common reason for failed anesthesia in lower molars.
-
The solution is a straightforward Mylohyoid block administered from the lingual aspect.
-
If you prefer not to use it, consider alternatives like the Gow-Gates or Vazirani-Akinosi blocks.
When you add this powerful tool to your skill set, you’ll undoubtedly see a significant increase in your success rate for mandibular anesthesia, and your patients’ confidence in you will grow even more.
