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Dental Anesthesia

Facial Paralysis

12/26/2011

Question:

I had a strange reaction today after receiving injections of lidocaine. I was going to have a repair of my left back molar. After the first injection of lidocaine, I was still able to feel work on the tooth. Another injection of a different anaestheic (not sure of the name) was given. Within a few minutes, I started to feel the RIGHT side of my facial go numb. I started to feel as though I would pass out. Soon I couldn`t open my right eye without difficulty. I kept having the sensation that I would pass out. Next, I noticed that I couldn`t shut my LEFT eye. The dentist became worried and brought me to the ED. After about an hour it started to resolve. My area in my mouth on the left side never did get numb. Any thoughts on what my have happened? Sounds like Bell`s palsy on the left, but what about the right side (which was more concerning to me).

Answer:

Dear Netwellness reader, 

When more anesthetic was injected on the left side, some of it diffused into the parotid salivary gland which lies deep to the inferior alveolar nerve which the dentist was trying to numb for your lower left tooth. Inside of the parotid gland lies the facial nerve, which controls your muscles of facial expression. The local anesthetic temporarily interfered with its function. That is why you could not close your left eye, and your face probably looked like it was pushed over to the right. The right and left side muscles of facial expression tend to pull in opposite directions to keep your face looking balanced. For instance, at the corners of your mouth, if the left-sided muscles cannot contract, the right side muscles will still work, so they pull the face to the right, which makes it look like there is something wrong with the right side of your face when you try to smile, but in fact, it's the left sided non-working muscles that have the problem. 

With the left side facial muscles out of balance with the right sided muscles, it is understandable why the right eye lid and forehead muscles seemed to not be normal because they were working unopposed. The left eyelid was temporarily not working because it is enervated by the left facial nerve. When the local anesthetic facial nerve block wore off, your facial nerve started working again. So, this was not a problem with the local anesthetic drug, but rather a normal reaction when the facial nerve comes into contact with the local anesthetic. Perhaps the distance between your parotid gland and the inferior alveolar nerve is closer than normal or perhaps the angle of your jaw is such that the dentist's injection tends to go straight back where the parotid is rather than more laterally (out to the side). So you might suggest to the dentist to aim the needle near where the nerve enters the lower jaw bone (called the lingula) and to actually lightly touch the bone with the needle tip before injecting. That might give a little sting but the injection should work. 

As for the feeling that you might be passing out, it could have been from your normal fear that something was terribly wrong. Because the signs and symptoms, called facial droop, are the same as when a person is having a stroke or Bell's palsy, the dentist rightfully was concerned enough for you to go the the emergency room to make sure this was not serious. 

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Response by:

Joel M Weaver, II, DDS, PhD
Faculty Emeritus
Dentistry Administration
College of Dentistry
The Ohio State University