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

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!

Doc, That Short Hurt – Part II

In Part I of this series, I wrote about why some dental injections hurt while others do not. I approached this topic knowing that there were more than five factors affecting the amount of pain felt from the “shot at the dentist.” So here we go with five more reasons:

6. Size Matters?

Dental needle photo showing needles of different sizes

Wouldn’t you be more scared of the bigger one?

Many people – both dentists and patients – incorrectly assume that the larger the needle, the more painful the dental shot is going to be. While that may seem to be true, some well designed research studies contradict this.

What is true – and this is based on years of my own observations – is that when a patient sees a large needle coming at them – they are WAY more likely to complain that it hurt.

So, the last time you received a painful shot at the dentist, did you look at the needle? If yes, the sheer size may have “psyched you” in to thinking it was going to hurt! Perhaps the time it didn’t hurt was when the dentist and/or assistant distracted you so you didn’t see the needle.

7. Good Good Good Vibrations

It is unlikely that the Beach Boys were thinking of their trips to the dentist when they composed this famous song. However, when it comes to dental injections, vibrations are good.

Many dentists, myself included, will rapidly jiggle and wiggle the area we’re about to inject. Why? According to the Gate Control Theory of Pain, the intense stimulation of the wiggling will essentially prevent the pain of the needle. Stated another way, by wiggling the area so much, that wiggling “closes the gate” that the pain signals need to travel through. See the wikipedia article if you want more info.

Dentalvibe works by creating vibrations to prevent injection pain

The DentalVibe

I can promise you that if I give you an injection without doing any wiggling, you will feel it. However, if I apply techniques from Part I of this post and wiggle a lot, you will barely feel it!

Vibrating can make such a profound impact on whether you feel pain or not that there is even a product you can buy! It is called the DentalVibe and it is basically a professional wiggler. I have not used it but have seen it demonstrated at various dental conventions.

So, if you received a dental injection that hurt, it could be in part because your dentist did not wiggle the area (please note that in some circumstances it is not possible to wiggle).

8. Speed Kills

Many patients think that the most painful part of the injection is the initial pinch as the needle penetrates. In reality, there is another part that can also hurt: the forceful pushing of the fluid (the local anesthetic) into a confined area (the cheek or gums).

photo of teaspoon and tablespoon to depict amounts of dental local anesthetic

Imagine over 1/3rd of a teaspoon injected into you over 4 seconds. Ouch! (Image courtesy wiki commons)

So, what do you think happens when you receive an entire dental shot – 1.8 cc – approx 1/3rd of a teaspoon – into your mouth in under 5 seconds? It will hurt! That entry creates tremendous pressure on the tissue at the injection site, and that leads to pain. This study confirms this fact.

One of the key elements of a pain free injection is to go slowly. I try to do it very slowly – at least 30 seconds – sometimes as long as a minute. In nearly all cases, patients say “Doc, that took a long time, but I didn’t feel a thing!”

9. Local Anesthetic Buffering

This is distantly related to Point #5 –  Choice of Local Anesthetic. But it is different enough – and its impact large enough – to warrant its own entry. And this the buffering of the local anesthetic injection. But what the heck is a buffer?

lidocaine with epinephrine has a pH below 4

This comes at a pH of less than 4.

The pH, which is a measure of the acidity of your bloodstream and tissues, is approximately 7.4. In general, the closer the local anesthetic pH is to 7.4, the less it will sting during administration. One of the most common dental anesthetic formulations in the United States – 2% lidocaine with 1:100,000 epinephrine – has a pH of 3.85! Don’t you think that will sting?

Anutra Medical buffered local anesthetic

The Anutra Local Anesthetic Buffering System I use in my office.

One way to get around this is to buffer the local anesthetic. I won’t bore you with the chemistry but ask any high schooler who took AP Chemistry and he/she can explain it in more detail. But in essence, buffering will raise the pH close to your body’s normal pH. Do you think that an injection at a pH equal to that of your body will sting? No. And many research studies support this.

So why don’t all dentists use buffered local anesthetics? Well, it is not that easy. Local anesthetics cannot be manufactured this way because they would break down with 24-48 hours. However, a new product on the market called Anutra Medical allows dentists to do just this. It has not been widely adopted yet because it is new, requires special supplies be kept in stock, and is also slightly more expensive compared to traditional injections.

Having used the product, I can say with 100% certainty that it works. Patients feel less of the shot. It’s that simple.

10. Your attitude

This is the perhaps the most important factor but also the most difficult one to describe.

If you come in feeling nervous and anxious, act somewhat hostile to the dentist and/or assistant, complain that the topical anesthetic tastes bad, don’t want to open your mouth, stare at the needle as it comes towards you, move and jerk around as the needle goes in, then the injection will hurt. I’ve had patients where I’ve employed nearly every point in this post – and it still hurt because they did not let me do my job.

If you come in nervous but allow yourself to be relaxed, keep an open mind about things, and allow us to use our techniques (super topical anesthetic, wiggling, buffering, etc.), then you will feel little to no pain on injection.

Now I realize that not all dentists are the same – and not all dentists actively seek out new products/techniques to reduce injection pain. But most do. And most will be happy to talk to you about how to reduce the pain of the injection.

Might there be a Part 3 of this series? Maybe. If you have ideas, techniques, or products, email me at and maybe I’ll come up with reasons 11 through 15!

Doc, That Shot Hurt – Part I

As a dentist in private practice, I probably administer local anesthetic about ten times a day. Or to state this in terms that patients like to use, I probably give about ten shots each day. Sometimes more, sometimes less.

Very often, my patient will say something like “Wow, I barely felt that! You’re good.” But other times, I’ll hear “Wow, that hurt! My last dentist didn’t hurt me like this!”

The degree to which you will feel the shot while in the dental chair is dependent upon a number of factors. In fact, there are so many factors that they will be spread across two blog posts. Here’s part 1:

1. Location, Location, Location!

roof of the mouth or palate shot photograph

Any injection on the palate will hurt!

Just as the real estate saying goes, location is probably the number one factor in determining how much, if at all, a dental injection will hurt.

It is universally agreed upon by both dentists and patients that the shot on the roof of the mouth (more formally known as a palatal injection) hurts the most. Why? First off, the type of gum tissue present does not allow for topical anesthetic to work effectively. Secondly, the tissue is so tight and firm that the local anesthetic fluid has literally nowhere to go – making it very painful as the fluid is pushed in.

Conversely, other areas, such as on the outside of an upper tooth, we can make almost painless. You would literally not even know the injection occurred. This, however, assumes other factors are taken into account (those factors are outlined here and in the next post).

2. Topical Anesthetic

topical anesthetic used for dental injections photo

Topical Anesthetic

Topical anesthetic, more frequently referred to as “numbing jelly,” will reduce the initial “pinch” of the injection.

How does it do it?

The jelly is actually an anesthetic – just a viscous form similar to what is injected. When applied to the inside of the mouth, it will numb the area in approximately 1 minute. By making the superficial layers numb, the initial sensation of the pinch of the needle is either eliminated or reduced.

Most dentists use standard topical anesthesia these days. Some dentists, myself included, will use a high powered version that is compounded at a local pharmacy. When used properly, this type can almost completely eliminate the sensation of the needle.

If your dentist does not use topical anestheisa, you should request it. It makes a BIG difference.

3. Temperature

thermometer photo showing temperature affects pain from dental shots

Temperature of the local anesthetic affects how much you feel it.

This should be very obvious. Dental anesthetic is typically at room temperature – approximately 68 degrees Fahrenheit – and your body temperature is approximately 98 degrees Fahrenheit. Don’t you think that the 30 degree difference in temperature will make the shot be more painful?

If you answered yes, you are correct. And many research studies have confirmed this. It can make such a difference that there are actually local anesthetic warmers that dentists can buy.

Having used warmers before, I can attest that they appear to make a difference in how much you feel. But again, this assumes all other techniques are being used.

4. Presence of an Infection

Occasionally, a patient will have a significant dental infection that requires treatment. In many of those cases, an injection needs to made directly into the infected site.

pericoronitis photo where the dental shot will hurt

An injection into this infected tooth – with pericoronitis – will hurt.

Infected tissue is already hypersensitive. And the patient is already extremely distressed. And in many cases, there is a buildup of pus which is causing an increase in pressure. So what happens when you inject 1.8 cc of a local anesthetic into the infected area? You feel pain. This is because of the hypersensitivity, the likely buildup of pus underneath, and the stress.

So, injections into infected areas will always hurt, no matter what I or any other dentist try to do.

5. Choice of Local Anesthetic

First off, we dentists no longer use novocaine. In the United States, there are many different type of local anesthetics available. These include lidocaine, articaine, mepivicaine, bupivicaine, and many others. Some come with epinephrine and some come without.

According to some research studies, the choice of local anesthetic can affect how much pain you feel. This is because of differences in pH (the acidity). In humans, the pH at the injection site is typically 7.4. Doesn’t it make sense that the closer the local anesthetic is to 7.4 the less pain you will feel?

Lidocaine local anesthetic used for dentist shots

Some research says lidocaine hurts more than other local anesthetics!

One local anesthetic, prilocaine (brand name Citanest), has a pH of between 6.0 and 7.0. Many other common local anesthetics have pHs of approximately 5.0. So it stands to reason that prilocaine will hurt less because its pH is much closer to our body’s normal pH.

Well, one study confirms this finding, while another study finds no difference in type of anesthetic.

You might be asking then, why don’t all dentists use prilocaine? Prilocaine does not last as long as other local anesthetics. And many dentists (myself included) feel it is not as effective in getting patients properly numb. So many dentists elect not to use it.

Believe it or not, there are 5 more reasons why some shots hurt more than others. Part II can be found here.