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!

Novocaine Allergy Part III – True Amide Allergies

This is the third installment in the Novocaine Allergy series. Part I talked about reactions to certain older style dental anesthetics which are basically not used any more in dentistry. Part II talked about allergic and sensitivity reactions to preservatives and other components found in some local anesthetics.

This now leaves us with what I call true allergies.  I use the term true to indicate it is a real allergic reaction to a dental local anesthetic – as opposed to an adverse reaction or other phenomenon. I stress this distinction because allergic reactions to modern local anesthetics are extremely rare.

Lidocaine – A Modern Dental Local Anesthetic

lidocaine local anesthetic with epinephrine used at the dentist

Lidocaine with Epinephrine is the most common formulation in the U.S.

Lidocaine was first synthesized in 1943 and became widely available in the United States in 1948. Lidocaine was based on a new chemical structure of local anesthetics called amides. This class is chemically different than the previous ones such as novocaine and cocaine.

Immediately after its introduction, lidocaine took off in popularity for many reasons. One of the reasons is because lidocaine did not cause allergic reactions the way older anesthetics did. Because of this, the older class of anesthetics – novocaine included – were phased out – and by the 1980s basically no dentists in the United States were using novocaine anymore.

Allergic to Lidocaine?

True allergies to lidocaine and other amide based anesthetics are exceedingly rare. There is conflicting evidence on the prevalence of these reactions to lidocaine and other anesthetics. A prominent 2009 article in the journal Anesthesiology says “allergic reactions to amide local anesthetics remain anecdotal.” A 2013 article published out of Saudi Arabia documents a case study of a true lidocaine allergy in a 12 year old. According to this 2002 paper, an individual with an allergy to one amide does not mean he/she will react to others. Any Google search will yield thousands of results – some from prominent medical journals with sterling reputations – and others from individuals posting their experiences and assumptions.

lidocaine and articaine both amide type local anesthetics

Most experts agree that in the cases of true allergies to lidocaine, other local anesthetics such as articaine can be used (assuming proper testing first).

The current consensus in the dental community is that true allergies to amide based local anesthetics are possible but very rare. As a patient, you have much better odds of being struck by lightning than experiencing an allergic reaction to lidocaine!

If you are injected with a local anesthetic and are allergic, what would happen? You would likely exhibit all the classic signs of an immediate type reaction: generalized swelling, itching, urticaria (hives), possible respiratory difficulty, and many other signs.

But remember, only a qualified allergist can diagnose you with an allergy.  Neither I nor any internet site can tell you definitively.

Events where you think you are allergic but are not!

I’ve witnessed firsthand hundreds of incidents where a patient thinks he or she is allergic when in reality something else is occurring. These incidents include:

photo of epinephrine which is used at the dentist in local anesthesia

A racing heart does not mean you are allergic to epinephrine!

  • A racing heartbeat (tachycardia) occurring immediately after a dental local anesthetic is administered does not mean you are allergic to either the local anesthetic or the epinephrine in it. This is a dental myth I busted here.
  • If you start to feel faint and break out in a cold sweat and nearly pass out immediately after an injection, this is most likely vasovagal syncope (and not an immediate allergic reaction).
  • If you do exhibit signs of an allergic reaction, you are far more likely to be reacting to a preservative in the local anesthetic than you are to the actual local anesthetic. The most common culprits are methlyparaben and metabisulfite.

Dental Treatment with a Documented Amide Allergy

If you are one of the rare individuals with an amide allergy confirmed by an allergist and you need dental treatment, what are your options?

  • Get the dental treatment done without any local anesthetic. I do this periodically for my own patients who don’t like the feeling of being numb. But this would only work for minor procedures, not for major ones such as extractions or root canals.
  • Have the allergist test to see your response to other amide local anesthetics. Many papers in the literature talk about individuals reacting to one amide but not another.
  • Benadryl (diphenhydramine) can be used as a local anesthetic when injected. While not as effective as amides, it can offer some degree of local anesthesia. But check with your dentist – very few dentists are prepared to do this and would need advance notice.
  • As a last resort, the dental procedures can be done under general anesthesia.

Final Thoughts and a Disclaimer

While true allergies are rare, they can and do occur. But don’t assume. An adverse or unexpected reaction does not mean you are allergic!

And as mentioned in both the sidebar and footer of this website, this article is for informational use only and is not intended for medical advice. Please consult your physician if you believe you have an allergy and always discuss this with your dentist prior to having any dental treatment performed.

Dental MythBuster #10 – I’m allergic to epinephrine!

For this 10th Dental MythBuster, I’ve decided to tackle one of the greatest ones out there: The mythical epinephrine allergy!

Epinephrine used at the dentist photo people think they are allergic

Epinephrine for injection.

I consistently hear some variation of the following at least twice a month in my office in Orange, CT:

“Doc, for the shot, don’t use the one with epinephrine. I’m allergic to it.”

Upon hearing that, I always use a dental local anesthetic that does not contain epinephrine. But in all cases, the patient is improperly using the word “allergy.” Let’s see why.

About Epinephrine

Epinephrine, also called adrenaline, is a naturally occurring hormone and neurotransmitter in the body. It plays a critical role in the “fight or flight” response. Epinephrine has a number of different functions, including increasing the heart rate, regulating lung capacity, increasing the amount of available glucose, and many others.

Picture of epinephrine used in dentistry by dentists

Structure of Epinephrine

In addition to being naturally released by the body, epinephrine can be administered by health care providers in many situations. Epinephrine is given in many situations of acute cardiac arrest (a heart attack). It is also given in the treatment of an acute allergic reaction called anaphylaxis. It is frequently sold in an injectable form called EpiPen for those people susceptible to these types of reactions. We have an EpiPen in our office in Orange, CT as part of our emergency kit.

But the critical thing to keep in mind is that every single person produces and releases epinephrine all the time.

Why Dentists Use Epinephrine

As a dentist, I inject local anesthetic containing epinephrine at least ten times per day. Epinephrine is used because it acts to constrict the blood vessels in that area. By doing so, the local anesthetic remains in that area longer, because there is less blood flow to take the local anesthetic away. Simply stated, the epinephrine helps you feel and stay number longer.

As anyone can imagine, a dentist who does not get their patients adequately numb will soon find themselves with an empty chair! And epinephrine is a key factor in keeping patients adequately numb for procedures.

An Epinephrine Allergy?

So how can you have an allergy to a substance that your own body produces and uses every second of the day? The answer is it’s impossible! If you were allergic to it, you would be developing symptoms all the time! I won’t bore people with the technical definition of an allergy, but this is a good summary.

Carpule of lidocaine and epinephrine used by dentists in our Orange CT practice

Lidocaine with epinephrine.

So where did this myth originate? Well, most people confuse an adverse reaction with an allergic reaction. Common adverse reactions to an injection of epinephrine at the dentist can include:

  • Your heart starts to beat much more rapidly.
  • Your heart starts to beat much more forcefully.
  • The skin on your cheek – near the injection site – gets very pale.
  • You become suddenly dizzy.
  • Your shirt becomes wet from sweating (called diaphoresis).
  • You become very nervous.
  • You develop a headache.
  • And many others.

In addition, many other patients are unable to receive epinephrine due to certain medical conditions and/or medications they are taking. But this is NOT because they are allergic to it!

Dental Myth Busted!

Just like the other dental myths that I have written about (dentists no longer use novocaine, the dentist put his knee on my chest to pull my tooth, etc.), let’s bust this myth! So the next time you are at the dentist and you don’t want epinephrine, you should say:

“Doc, for the shot, don’t use the one with epinephrine. I had an adverse reaction to it.”

Until the next Dental MythBuster…

Note: since publishing this post there have been literally dozens of comments and posts which attacked me personally and/or used profanity. These comments prompted me to publish a sequel to this titled More on the Fabled “Epinephrine Allergy”. Please note that any/all comments with personal attacks and/or profanity will not be published.