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Updated: Jan 3, 2021

You’ve had that patient come in who says “I never get numb enough” every single time they have to have a filling done, especially on the mandible they always say they can’t get numb.

We all understand that a patient with a “hot tooth” will have more challenges to anesthetize AND there are some who have the capability to metabolize the anesthetic quickly. Well my friends I am here to tell you there are several reasons for it. BUT…. the most common is anatomical variation.

Life would be grand if everyone had textbook anatomy, but that just isn’t the case. People all have different neural pathways. A nerve could travel along a different aspect of the bone or branch off in a different location. Plus, there are some nerves which create a small accessory nerve to a tooth it wasn’t “designed” to innervate. Ugh! Don’t they know they are breaking the rules of what the textbook said?!?!

This is what you need to be aware of...

The mylohyoid nerve, which branches off from the IA nerve just above the mandibular foramen can sometimes innervate the mandibular first molar. There are a few ways to combat this anesthesia quandary. If you have given the Inferior Alveolar (IA) injection and the mandibular first molar still has pulpal sensation but everywhere else is fairly numb, your first hunch should be accessory innervation of the mylohyoid nerve.

Your options are to infiltrate on the lingual side of the mandibular first molar. Targeting the small fiber of the mylohyoid nerve feeding the molar or re-anesthetize the quad by giving a different injection like the Gow-Gates (GG) or Vazirani Akinosi (VA). These injections tend to get the IA, lingual, buccal, and mylohyoid nerves…basically getting the major portion of the nerve trunk.

Another option is to use Articaine and infiltrate on the facial surface of this tooth. Articaine (septocaine) has the capabilities to move through that thick mandibular bone and provide excellent anesthesia to the region.

(Special note* if there is pulpal anesthesia and the patient is feeling discomfort on the buccal soft tissue you probably need to give the long buccal injection as well. As a reminder the IA injection is designed to take care of the pulp of all the mandibular teeth and lingual tissue of the quadrant. It will not take care of the facial soft tissue and periosteum, this is what the long buccal (buccal) injection is used for.)

Even more troublesome is if the patient has a bifid inferior alveolar nerve. While this is a rare occurrence (less than 1% of the population), it can cause quiet an issue. A bifid IA nerve can happen along any point of the nerves pathway and can result in two mandibular foramens (and canals). Which means a different target zone for us clinicians. A patient with this condition will have anesthesia failure to several mandibular teeth. Thankfully, with the rise of 3D imaging we can identify these individuals easier and provide the proper anesthesia techniques for them, such as GG or VA.

Bifid IA. Photo Credit Journal of Oral and Maxillofacial Surgery

With maxillary teeth it is not uncommon to have accessory innervation from the palatal nerves. However, because the maxillary bone is thin and porous, most anesthetic can easily penetrate and bathe the dental plexus. You may find the crossover innervation happening more often for palatal roots. Occasionally, maxillary anterior teeth will have additional innervation from the nasopalatine nerves. I're thinking great now I have to give those dreaded palatal me, most patients would rather have that, than feel what's happening with the tooth.

Another aspect to remember is due to high vascularity especially around the posterior portion of the maxilla, patients may quickly metabolize the anesthetic.

Soooo make sure you are paying attention to your site of insertion and aspirating to verify you aren’t in a vessel.

I know it can be challenging at times, but I hope these reminders will help you process why your patient is struggling with getting numb.

Pay attention to the patient’s anatomy. If the mandibular molar isn’t getting numb make sure you think about that mylohyoid nerve and double check your radiographic images for other unusual anatomical situations, like a bifid IA nerve. Understanding the anatomical flow and variations you may encounter will arm you with the information you need to give your best shot!



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