Don’t Shock Me Bro!

As a dentist in private practice, I administer local anesthesia routinely. Or, in layman’s terms, I give numbing shots daily. That’s just two ways of saying the same thing!

Dental local anesthesia infiltration photo where no electric shock will occur

This type of injection is highly unlikely to give you an electric shock sensation

Occasionally, when I am doing certain injections (and note that there are different types of injections that dentists administer – more on that later), the patient will experience an electric shock sensation originating from the injection area. This ends up being quite a shock to the patient (pun intended) with me then subsequently spending significant time explaining why/what happened.

In addition to seeing this happen periodically in my own office, I get tons of comments and inquires on this blog about “the electric shock they got” from the dentist’s needle. Since nearly all of my articles are either about my own experiences – or from inquires I get on this blog – I decided it was time to do a post on this phenomenon.

Infiltrations versus Nerve Blocks

To understand why the electric shock occurs, a little background information is needed.

Femoral nerve block with an ultrasound

A nerve block guided by ultrasound being done by an Anesthesiologist.

In medicine – and I do consider dentistry to fall under the medical umbrella – there are various techniques for numbing a particular anatomical region. An infiltration is when local anesthetic is deposited directly adjacent to the site to be worked upon. In these cases, the local anesthetic works by affecting tiny, microscopic nerve endings that almost resemble a spider web.

In contrast, with a nerve block, the local anesthetic is deposited adjacent to a large branch of a nerve. This ends up numbing everything that the nerve supplies downstream from the area the anesthetic was administered.

To use an analogy: picture a tree. An infiltration is where anesthetic is placed next to a single leaf. A nerve block is when the anesthetic is placed next to a large branch close to where it is coming off the trunk.

Shock and Awe

When it does occur, the electric shock phenomenon is nearly always associated with a nerve block (as opposed to an infiltration). Why does this occur?

The shock sensation is believed to occur when the needle makes contact with part of the nerve trunk (sources: here, here, and here). The needle basically enters the tissue, touches the actual nerve, and the trauma from that immediate contact provokes a signal that your nervous system perceives and interprets as an electric shock feeling.

photo of needle and skull bone where you give a dental nerve block

In a mandibular nerve block, the needle is aimed right where a large nerve trunk (the inferior alveolar nerve) is about to enter the lower jaw (the mandible)

Some key facts:

  • The incidence of this occurring is between 1.3% to 8% of the time for mandibular nerve blocks (the large difference is based on different sample sizes).
  • Studies have shown that an electric shock sensation does not place the patient in a higher risk category for permanent nerve injury.
  • The most commonly involved nerve is the lingual nerve (which will give rise to a shock sensation in the tongue on the affected side.

As you can see, since the origin of the electric shock is contact with a nerve trunk, it is nearly impossible for this to occur with an infiltration.

What to Do if You Feel the Electric Shock?

With dentists administering millions of injections per year, this occurs on a regular basis throughout the world. Keep in mind:

bullseye showing that electric shock is due to hitting the nerve

An electric shock means your dentist hit a bullseye.

  1. Although the feeling was unpleasant and unexpected, the research clearly shows that this does not place you at a higher risk for permanent nerve issues (see bullet point #2 above).
  2. In many times, you get numb extremely quickly.
  3. This happens to all dentists periodically and this phenomenon alone does not mean your dentist is unqualified or negligent.

Since this occurs when the needle makes contact with the nerve trunk, it means your dentist was dead on with his/her aim. So, if you like, you can congratulate him/her on hitting a bulls-eye! Or, just understand that the human anatomy is unpredictable, and sometimes things like this happen.

Note: the sources used for this post are listed above and are also based on my own experiences. Note that I cannot answer emails to me asking for dental advice. The title for this post is based on the “Don’t Tase me Bro” incident and I have no relationship with Mr. Meyer. This post should not be construed as me providing commentary on that incident.

Dental Local Anesthesia and Ehlers Danlos Syndrome

Ehlers Danlos Syndrome is a group of similar inherited disorders that adversely affect the connective tissue. Patients with this disease experience problems in the skin, joints, blood vessels, and other areas. In addition, some disorders within the syndrome also make the individual resistant to local anesthesia.

Unfortunately very few dentists are aware of this phenomenon. And in addition, there are patients out there with undiagnosed Ehlers Danlos, as well as patients with EDS who are not aware of the issues with local anesthesia. What happens? The patient ends up having a very unpleasant time at the dentist with both the dentist and patient trying to figure out what is going on!

About Ehlers Danlos Syndrome

Ehlers Danlos and dental local anestheticIt is not the point of this blog post to talk about the Syndrome in great detail. There are plenty of other sites out there that accomplish this. However, to understand how this affects dentistry and the dreaded “novocaine shot,” you need to know a bit about the disease.

Ehlers Danlos affects connective tissue. Connective tissue is basically the “glue” that holds other tissue and organs together. Specifially, there are defects with the production of collagen, which is the major protein in connective tissue. While there are six major types of EDS, they are all generally characterized by hypermobile joints (joints that can move way beyond what would be considered normal), joint pain, fragile and easily bruised skin, and other findings.

Not all of the genes responsible for Ehlers Danlos are known and there is active research into all parts of this syndrome.

Why Does Local Anesthesia Not Always Work?

First, it needs to be mentioned that not all of the six types of EDS make the patient resistant to dental local anesthetic. Based on research (here and here), it appears that Type III – Hypermobility is the one in which this phenomenon is seen.

dental injections don't always work in Ehlers Danlos

For those with some types of Ehlers Danlos, you will need MANY injections of very specific anesthetics for effective local anesthesia.

Unfortunately, the mechanism behind why the local anesthesia is less effective is not well understood. The current theory focuses on the “looseness” of the connective tissue. Since the connective tissue is defective, it is very easy for the local anesthetic to quickly move away from the site that is being anesthetized. Stated another way, the connective tissue barriers that hold the local anesthesia in place for the duration of the dental procedure are weak and easily broken.

The end result is that the patient is not sufficiently numb for the dental procedure, leading to pain. Patients get confused, discouraged, angry, and ultimately avoid the dentist, which then makes things even worse down the road.

What Should Dental Patients Do?

Ehler Danlos hypermobility which can affect dental local anesthesia

If you can do this with your thumb, you may have Ehlers Danlos.

As a dentist who treats patients in private practice, I am disappointed that this issue is not well known in the dental community. Ask most dentists and unfortunately, most will not be aware of this. In fact, in what is considered the bible of dental local anesthesia (A Handbook of Local Anesthesia by Stanley Malamed), there is no mention of phenomenon (I searched the 6th edition).

Here are some tips:

  1. Find a dentist who has experience with Ehlers Danlos. There is nothing wrong with calling an office and asking if the dentist is familiar with EDS and this local anesthetic phenomenon.
  2. Identify yourself early on as having Ehlers Danlos to the hygienist and dentist.
  3. Find an opportunity to meet with the dentist in advance of any procedure requiring local anesthetic to review the plan (remember that the office may have to order a special type of local anesthetic).
  4. Consider taking a medication beforehand to relax you.
  5. Be ready for a longer than normal appointment.
  6. At the completion of the appointment, especially if it was successful, ask the dentist for detailed records on the local anesthesia (what local anesthetic, how much administered, where administered, etc.)

In some cases, nitrous oxide and/or IV sedation may be necessary to complement the local anesthesia.

My own experience treating patients with Ehlers Danlos has shown that most of the time, we can achieve local anesthesia. I attribute my success to knowing the pharmacology of local anesthetics as well as other injection techniques. To use a pun based on EDS, with a little “flexibility” in selecting local anesthetics and injection sites, we can nearly always succeed!

How Long Does Novocaine Last?

One of the most common questions I see both in private practice and on this site relates to how long you will be numb after a dental procedure. In dentistry, there are a lot of factors that affect the duration, ranging from the type of the anesthetic to the location given, so there is no one correct answer.

In general, and this is a very broad generalization with many exceptions, you can expect to be numb for approximately 2 to 3 hours after you leave the office. Want to learn what factors affect how long you will be numb?

To use or not to use Epinephrine

lidocaine with epinephrine dental local anesthetic

Lidocaine with Epinephrine

Perhaps the most important factor that affects how long you will be numb is the presence (or absence) of epinephrine.

Epinephrine acts to constrict the blood vessels where the anesthetic is injected. By constricting the blood vessels, you have less blood flow in and out of the numbed-up area, and the local anesthetic does not get carried away from the teeth and nerves as quickly. As a result, you remain numb longer and the numbing sensation is much more profound.

Occasionally, some of the epinephrine can end up in the bloodstream, leading your heart to beat more rapidly and some other symptoms. Some people then mistakenly assume they are allergic to epinephrine which is impossible. See this MythBuster post and a follow-up article on why this is not possible.

If you receive an injection with an anesthetic without epinephrine, on average, you will be numb for about 1 hour or slightly less after you leave. This assumes your dentist uses one of the two most common: 3% carbocaine/mepivicaine or Citanest Plain/4% Prilocaine.

Type of Anesthetic

Besides the presence of epinephrine, the type of local anesthetic also plays a role. First off, novocaine is not used anymore, so I personally have no idea how long novocaine would last.

marcaine dental anesthetic will last a long time

This brand of dental local anesthetic can often last 8 hours.

Bupivacaine, which goes under the brand name Marcaine (at least in dentistry), can last a long time. In formulations without epinephrine, it can last 4 – 8 hours. When used in dentistry with epinephrine, it can last for 8 hours or more. In my experience, when I give bupivacaine with epinephrine for removing wisdom teeth, I tell patients that they can be numb until the next morning. Many of them report going to bed and still being numb.

Amount of Local Anesthetic Administered

Root canal procedure you need to be extremely numb

For a root canal, you typically need extra local anesthetic

This seems pretty obvious right? In general, the more you receive, the longer you’ll be numb. But remember that twice as much does not mean you will be numb twice as long. But you will be numb much longer.

For a straightforward filling, one shot (1.7 mL or cc) is typically sufficient, unless you are a patient who is difficult to get numb (see here and here on this phenomenon). For procedures that are a bit more involved, such as an extraction or root canal, dentists typically give more than one injection. The end result is you can often be numb for four or five hours afterwards.

Location, Location, Location!

Real estate is not the only area where this saying is relevant. The location – the area in the mouth where the local anesthetic is injected – plays a role in how long you will be numb.

a nerve block will last longer than other types of dental injections

A nerve block for a lower molar.

For a lower back tooth to be worked upon, you nearly always needs a nerve block. Nerve blocks last longer than infiltrations – which is when the anesthetic is placed directly next to the tooth.  In generalizing data from this paper, if you receive a nerve block, you will be numb approximately 25 to 30% longer than if you received an infiltration.

So what does all this mean? If you had a lower molar worked on, you were likely given a nerve block, and therefore you will likely be numb longer than if you received an injection for an upper front tooth.

Final Thoughts

This list is not exclusive. There are a lot of other factors – metabolism, genetics, hair color – but these four are the most common. I may do a follow-up post where I talk about the other factors. Comments are welcome.

 

More on the Fabled “Epinephrine Allergy”

Ever since I posted Dental MythBuster #10 – I’m Allergic to Epinephrine back in November 2013, I have observed its growing popularity. But much to my surprise, the “epinephrine allergy” post generated a tremendous number of comments and emails which attempted to refute my assertions and/or attack me personally. In fact, one email even threatened physical harm!

photo of epinephrine where people believe they are allergic

Many believe they are allergic to this.

I had no idea that I would strike such a nerve. Apparently, there are many individuals out there who are convinced they are allergic to a substance that has been running through their bloodstream since before they left their mother’s uterus. And they will stop at nothing to attack, ridicule, or even threaten anyone who might suggest otherwise.

While I generally attempt to stay away from the more controversial dental topics out there (like public water fluoridation or amalgam fillings containing mercury), I do feel compelled to publish additional facts and data to support the fact that an epinephrine allergy does not exist!

You Could be Reacting to Sulfites or Latex

Many individuals who claim to have an epinephrine allergy learn, either through an allergist or through my blog, that their post-injection symptoms were caused by either sensitivity or allergies to two components found in most dental injections: sulfite preservatives and/or latex.

Sulfites found in local anesthetics and red wine can give you allergic reactions.

Sulfites are found in most red wine and in local anesthetics containing epinephrine.

Sulfites are used to preserve epinephrine in dental anesthetics. Sulfites can provoke severe sensitivity reactions in certain individuals. If you receive a dental injection with sulfites and you are sensitive to it, the reaction can closely resemble an allergic type response (for in depth details on sulfites and dental local anesthetics, see this post I published).

On the tip of every dental local anesthetic carpule is a tiny piece of latex. Studies have shown that the latex allergen can enter into the local anesthetic solution when that latex is pierced for an injection. But those same studies also show no reports of an allergic reaction due to the latex. (Study info: Shojaei AR, Haas DA. Local anesthetic cartridges and latex allergy: a literature review. J Can Dent Assoc. 2002;68:622-626.)

I mention all this to demonstrate that there are at least two chemicals in the injection which could potentially cause an allergic type response. But it’s not the epinephrine!

It’s Documented in Textbooks and Articles

Many readers of my first post simply attacked me personally and stated that I was wrong. Others wanted proof. Here is a screen shot from an online article:

Article proving that an allergy to epinephrine does not exist

This screen shot is from this article in the magazine Dentistry Today. It says “allergy to epinephrine cannot occur.” It can’t get any more clear cut than with that statement!

Need more proof? In the book a Handbook of Local Anesthesia by Dr. Stanley Malamed, he writes:

Allergy to epinephrine cannot occur in a living person.

This is on page 320 from the 5th edition.

Why isn’t an Epinephrine Allergy Listed on the Drug Insert or Prescribing Information?

After tobacco companies, pharmaceutical firms are probably the biggest litigation targets out there. Haven’t we all seen ads on TV looking for plaintiffs to sue drug companies? Ever hear of the website 1800baddrug.com?

Naturally, drug companies list all the known adverse effects on the drug sheet. If they don’t list something, and then an event occurs, the attorneys will have a field day! So if an allergy to epinephrine existed, wouldn’t it be listed on the drug sheet?

penicillin lists an allergic reaction as a  risk

Unlike epinephrine, the insert for penicillin mentions the risk of allergy.

Look at the drug inserts for these common medications: Zithromax (Z-Pak), Penicillin, Bactrim

On all of these, you will see mentions of allergic reactions. This indicates that known allergies can occur after taking the medications.

Now look at the prescribing information for all these forms of epinephrine: Epinephrine Auto Injector, Epi-Pen, Epinephrine Injection.

None of them mention an allergy to epinephrine (note that some mention a reaction to the sulfite).

So I’ll pose the question again: if an allergy to epinephrine existed, wouldn’t it be listed on the drug sheet? Why would the drug companies fail to include it knowing they could potentially be sued over its exclusion?

Note that I’ve used the terms Drug Insert and Prescribing Information quite liberally here. There are many variations depending upon who it is for (consumer vs. prescriber), but it is the FDA-required document that pharmaceutical companies must publish.

Show us a Mechanism

If you’ve made it this far, and you’ve already read my first post, you’ve hopefully learned that an allergy to epinephrine is not possible. But for those determined skeptics, I’ll make this request:

Please provide a plausible mechanism for how you can be allergic to a chemical that has been in your bloodstream since before birth and is currently being synthesized and released in your body as you read this.

Should you wish to post comments on this article, I will ask politely that you refrain from profanity and/or personal attacks. And if you read this and your heart starts to race (either because you’re angry at me or you’re excited with what you learned), that’s because of the adrenaline being released into your bloodstream… to which you are not allergic!