5 Reasons You Can’t Get Numb at the Dentist

As a dentist in private practice, I hear stories ALL the time about patients who “couldn’t get numb at the dentist.” Not surprisingly, many of the comments that readers post here on this site also deal with this very issue.

In response to this, I decided to compile a Top 5 list of reasons for why this happens. So here goes:

1. You have an infection
dental abscess on gums showing infection with pus

This tooth was difficult to get numb because of the infection in the gums above the tooth!

Sometimes, a patient comes in with an active infection and it can be difficult to get them completely numb. This is obviously very frustrating for both the dentist and the patient. Why does this happen?

An active dental infection will usually result in the presence of pus. In most cases, the pus is acidic. Conversely, dental anesthetics (lidocaine, novcaine, etc.) function best in slightly basic environments. The end result is that the unique chemistry of the infection “deactivates” the local anesthetic, making it so that more anesthetic is needed. And in cases of severe infections, sometimes you simply cannot get the patient 100% numb.

2. You moved during the injection

Let’s face it – some injections – but not all – hurt! And it just so happens that the one that hurts the most is the one that requires the most patient cooperation. I speak from experience having done this well over ten thousand times.

large dental needle for nerve blocks to get numb

We have to sink this needle deep into the tissue. If you move, it is easy to miss the target. Paper clip is for scale.

For lower back teeth, we nearly always need to do a nerve block.  This is where we have to go deep through muscle and other tissue and deposit the local anesthesia near the nerve. We can’t actually see the nerve – we have to use various anatomical landmarks to guide us to the area.

If you move suddenly, the needle will also move.  Most often, it will have moved away from the nerve! So we then end up depositing the anesthetic farther away from the nerve than we would like. What happens next? You don’t get numb. Fortunately, if we have to administer a second injection, it will rarely hurt, and then we can place it spot on.

On rare occasions – and this has never happened to me nor most dentists – you can move so much that the needle can actually break!

3. I am not using epinephrine

I’ve blogged about this before. Epinephrine is added to dental local anesthetics because it enhances the numbness. How does it do this? Epinephrine acts as a vasoconstrictor and reduces blood flow in the area of the injection. The end result is that the local anesthetic stays around much longer and gives a more profound feeling of numbness.

marcaine dental anesthetic with epinephrine

Marcaine with epinephrine. The epinephrine will allow for a more profound level of local anesthesia

In certain circumstances, we use a local anesthetic that does not contain epinephrine. Why? Patients with certain cardiac conditions or who take certain medications are best served with one that does not contain it. Others have experienced a mild adverse reaction (some mistakenly think they are allergic to epinephrine) and prefer we don’t use it. A small fraction of patients are allergic to the sulfite preservative so we can’t use it in those cases either.

If we can’t use epinephrine, there is a chance you won’t feel numb enough. Or we’ll have to re-inject multiple times.

4. You’re wired differently

The human body is incredibly variable. People are double jointed. Remember the kid in grade school who could move his ears? Why is Usain Bolt faster then any other human? You get the picture.

Do you think your nerves look like the drawing below?

trigeminal nerve anatomy variation can make dental numbing challenging

Nerves going to lower teeth. Each person is different! Image courtesy wikipedia commons.

If you answered yes, then you’re probably wrong!

Most people have what I might call “standard anatomy.” This means that the nerves going to your teeth are where you might expect them to be located. But just like Usain Bolt and the kid from fifth grade who could move his ears, some patients have extreme variability with the nerves going to their teeth. We see this most frequently with lower molars.

Some people may have up to 4 nerves going to their lower molar teeth. This can mean 4 different injections to get them numb! This doesn’t mean your dentist is incompetent – it means you’re wired differently. So if that happens to you, just think about Usain Bolt and the kid from fifth grade who could move his ears.

5. You have red hair

Joan from Mad Men has red hair and can't get numb at the dentist

Joan from Mad Men would have difficulty getting numb!

I’ve blogged about this on two separate occasions – here and here.

But to summarize, people with red hair have a built in resistance to local anesthetics. This means that more local anesthetic is required to achieve profound numbness in those people with red hair. The reason behind this is complex, but the genetics for red hair also confers resistance to local anesthetic.

I can say definitively that from personal experience, redheads nearly always require more local anesthetic. All of my red haired patients are aware of this – and we joke about it each and every visit!

Want to see reasons 6 through 10? Here they are!

Redhead Dread

Do redheads dread a trip to the dentist?

Redheads dread the dentist due to resistance to local anesthesia

Redheads. Image courtesy The New York Times

When I stumbled across this article in the New York Times back in 2009, the conclusions seemed eerily familiar.  In my own personal experiences as a dentist in Orange, CT and elsewhere, patients with red hair seemed to be more apprehensive regarding dental care, and also seemed to have the dreaded “well, it looks like you’re not quite numb enough with the first shot, let me give you a bit more” phenomenon occur to them with much greater frequency than patients with darker hair and complexions.

As much as I would like to delve into the true scientific details, those facts go beyond the scope of this post.  But to summarize, redheads have a mutation (basically a change in their genetic makeup) that produces red hair and fair skin.  But that same mutation also affects receptors in the brain that govern pain perception.  Although the exact mechanism is not quite fully understood, studies show that redheads have resistance to lidocaine.  Lidocaine is the most commonly used dental local anesthetic used in the United States. Chances are, when you visit the dentist, and get “The Shot”, you are receiving lidocaine.

So if redheads have resistance to lidocaine, then they are more likely to feel pain during a dental procedure.  But does that translate into more dental anxiety?  Of course.  You don’t need published research to reach that conclusion!   However, in medicine and dentistry, we do like to have our conclusions backed up by sold research.  A 2009 article by the Journal of the American Dental Association did confirm that redheads have “increased dental-care anxiety” and exhibit “avoidance of dental care.”

As a practicing dentist, I always look at research and then ask myself how the findings apply to my patients, either past, present, or future.  This is true not just with this specific research finding but with all the developments that are continuously occurring in dentistry.  A lot of research doesn’t immediately apply. However, this is one case in which the findings have immediately impacted how I approach my patients – specifically patients with red hair.

Lidocaine also known as xylocaine is a dental local anesthetic used in the United States

Dental Carpule of Lidocaine with epinephrine. Redheads have a documented resistance to Lidiocaine.

No dentist is perfect and can get 100% of the patients 100% numb with the first injection.  Any dentist that claims that is lying. There are too many factors that come into play.  As a dentist, it is tempting to find something or someone to blame when your patient does not get numb with the first injection.  Blame the assistant!  The anesthetic must be expired!  The patient moved!  The sun was in my eyes!  The sun was in the patient’s eyes!  It was a full moon last night!  This happens to all dentists and to all patients – independent of hair color.

However, upon thinking back on my own patients who were “tough” to get numb, a disproportionately large percentage had red hair and fair skin.  These patients seemed to require 2 to 3 injections to get numb.  Another observation is that these patients always knew they would need more.  They were the first ones to say “Hey doc, I always seem to need 2 or 3 shots every time I get a cavity filled.”  But they never knew why they needed more local anesthetic.

In my experience, if you know a patient is going to be a challenge to effectively anesthetize, administering extra local anesthetic right off the bat is the best solution. The patient appreciates it.  The second injection, if done properly, will rarely hurt, and will almost guarantee that the patient does not feel any part of the procedure. Since this article was published in the New York Times in 2009, I’ve told numerous redheads about it.  Upon telling them, they nearly universally have an expression of “Wow!! Now I finally understand why I’ve always felt pain and dreaded coming to the dentist.”  And from then on, their fears are reduced, permanently.

So how do we approach redheads who avoid care because of past negative experiences?  This is a lot more challenging! Most redheads are unaware that their genetics are pre-determining them to have more pain in the dental chair (unless more local anesthesia is administered).  So they must be informed of this. Simply informing anxious patients of this genetic phenomenon and how we address it is enough for many patients.  More severe cases of dental anxiety require different approaches.  I have training in sedation dentistry which has allowed me to treat patients who have moderate to severe dental phobias. This has allowed me to personally treat hundreds of patients too scared for “regular dentistry.”  But unfortunately, very few dentists have the training, equipment, and staff to do sedation dentistry safely. I will try to describe other techniques in a future blog post.

Many redheads still do dread the dentist, but now they don’t need to anymore.  There are many dentists out there equipped with this knowledge helping redheads overcome their anxieties, one patient at a time.