This is one dental myth that every dentist has to deal with at some point. And that is the myth that if a child’s lip swells up after a dental visit where local anesthetic was used, it always means the child must be allergic to something the dentist injected.
And to make matters worse, this myth is then often propagated by the child’s pediatrician.
What would you think if you saw this the day after your 8 year old got a filling on his lower right molar:
That looks pretty nasty right? Something clearly happened here. In my own experience, and in talking to other dentists, parents generally do one of four things upon seeing this:
- Parent immediately heads to the closest ER or emergency walk-in clinic.
- Parent immediately calls the pediatrician for an emergency appointment and is seen that day.
- Parent gets on Google, becomes almost immediately convinced of an incredibly dire situation, and then does either #1 or #2.
- Parent calls the dentist office.
Wouldn’t it make sense to call the dentist office? After all, it was the dentist who did the procedure, wouldn’t he/she know what is going on?
But unfortunately, options 1, 2, and 3 are often pursued. And in many of those cases, an incorrect diagnosis is frequently made, which leads to unnecessary finger pointing, as well as wasted time, confusion, and missed school for the child.
So, what does it mean when the lip swells up after a dental appointment when local anesthetic was used?
Swollen Lip = Lip Biting While Numb (99.99% of the time)
Here are two cases I’ve seen in my office:
The above photos look unpleasant, right? In both cases, lower teeth were given local anesthesia, and that numbness extended to the lip. And in both examples, the patients admitted to repeatedly biting their lip.
The repeated biting led to swelling, bleeding, and bruising. Many times, the child has no recollection of doing it, because the child was numb and felt no pain. But the next day – whoa!
It is quite easy to see how this can come from biting. Go ahead and try to bit your lower right lip with your upper front teeth. Easy, right? Do this a couple of times very hard while you’re numb and you’ll end up looking like the one of the photos.
Why This is not an Allergy
Despite seeing this on a regular basis, many dentists (myself included) still have to deal with accusations and/or false diagnoses of allergies from the injection. Here are some key points:
- Location. The injection site is nearly always located far away from the traumatized area – in some cases nearly two inches. If it were an allergy, why then is the injection site totally normal? See the photo below.
- Appearance. In general, allergic reactions do not produce a localized ulcerated area away from the injection of the alleged allergen. The appearance of this is simply not consistent with an allergic reaction.
- Lack of Systemic Symptoms. Even less severe allergic reactions will produce other symptoms such as dry mouth, hives, and other findings. None of these are typically present in lip biting.
Of course, allergic reactions can occur from the injection. However, they are exceedingly rare, and don’t present like this. For more information, see this three part series.
What Should You Do?
So, if you or your child’s lip is swollen after receiving local anesthetic, what should you do? Call your dentist. Generally speaking, pediatricians, PAs, and NPs do not have experience seeing these types of things, and then come up with what we call “creative diagnoses” which are usually incorrect. General dentists and pediatric dentists see lip biting all the time and can guide you on how to handle it.
But to stress this point, it is a myth that a swollen lip (in the absence of other findings) after a dental visit means you are allergic to lidocaine (mistakenly called novocaine).
Until the next dental myth is busted…