Can’t Get Numb

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Written by the Dental Fear Central Web Team and reviewed by Lincoln Hirst BDS
Last updated on January 17, 2021

Recently, I have been seeing a new dentist after my old dentist retired. But my tooth could not be numbed. Most of my face was numb, half of my tongue was numb, but my lip or lower jaw wouldn’t go numb. Why is this happening?? My old dentist has never had a problem numbing me.

Every time I go to the dentist, the local anaesthetic hardly does a thing for me, if at all, and I experience lots of pain at every visit, even for simple things like filling a cavity!

What can I do if the local anaesthetic doesn’t work?

Unfortunately, there can be times when a tooth will just not go numb. Usually, topping up the local either in the same site or elsewhere, possibly using a different anaesthetic, will do the trick:

Don’t be afraid to ask for more – it’s not that expensive!!! Also if things are too sore at the time you can always abort and reappoint – might annoy an impatient dentist, but certainly isn’t the end of the world!! It’s your mouth – you are in control! – Mike Gow, BDS

If you’re keen to find out why you don’t get numb, this page has lots and lots of information – just keep on reading.

But if you’d just like to find out what you can do about, here are some tips!

Tip:

If you’ve repeatedly had problems getting numb in the past, especially with more than one dentist, explain the situation to potential new dentists (for example by emailing them). Ask if they are familiar with alternative techniques such as intraosseous anaesthesia (e.g. using the QuickSleeper), Akinosi block and Gow-Gates block.

We also asked some dentists for their tips:

The truth is that now dentists have a selection of anaesthetic solutions available as well as a selection of techniques they can use. In my own practice, we can choose from 5 different dental anaesthetics and we have 4 ways of delivering the anaesthetic to a particular tooth.

Mix this with a good number of possible locations to apply the anaesthetic (usually 2 – 4 possibilities per tooth), and you have a huge range of options open to you. The challenge may just be about figuring out the right mix for you.

If you are someone who has regularly had painful experiences or had problems getting numb, then please tell your dentist in advance so that they can plan to take time and use a little trial and error to find out the best way to get you nice and numb so that treatment is painless. Even if you spend just one visit working this out, it will be time well invested as generally once a dentist has worked out the right approach to getting you numb, it will work every time and it becomes your personal recipe. – Fraser Hendrie, BDS

In most cases, a very experienced dentist should be able to get you fully numb by employing some special techniques. Or you could seek out a dentist who has a special interest in root canals, they are very experienced in dealing with hard-to-numb teeth. Also, those who worked in special care services will be pretty experienced at getting people profoundly numb. – Lincoln Hirst, BDS


Why can’t I get numb?

There are (without being alarmist – it’s a rare occurrence) a number of reasons why local anaesthesia may not work as well as it should do. Don’t grin and bear it! If you don’t get numb, you should reschedule. The reasons are:

  1. poor technique
  2. anatomical variation
  3. local infection (a “hot tooth”)
  4. some forms of Ehlers-Danlos syndrome
  5. your metabolism
  6. having red hair (?)
  7. hypersensitivity due to fear(?)

Before we start…

On this page, we mention some examples of more advanced dental injection techniques. They are just examples – it would be way beyond the scope of this web page to explain all the available techniques. Although the “standard” numbing techniques work most of the time for most people, numbing teeth isn’t just a case of putting local anaesthetic next to the tooth to be numbed. It’s a bit more complex:

  • there are a variety of numbing techniques which work by numbing a single tooth
  • other numbing techniques involve numbing the nerve or nerves which supplies sensation to a group of teeth. Again, there are a variety of these techniques
  • it may also be necessary to numb so-called “accessory nerves” which may supply sensation to certain teeth
  • the anatomy and nerves are different for the lower and the upper jaw
  • some injection techniques are suitable for some teeth but not others – it depends on which tooth it is (e. g. a front tooth, a back tooth, upper jaw, lower jaw, etc.).

1. Poor technique (or choice of technique)

Some dentists are not very good at numbing but don’t think they have a problem or don’t care that they do. Most do care, but even the most experienced practitioner may not always be able to get you numb at the first attempt. Here are the reasons:

Not giving enough local anaesthetic

Sometimes it just takes some extra local anaesthetic to achieve profound numbing.

Not waiting long enough for the local to work

This is unlikely with modern local anaesthetics, but some people take longer to go numb than others. The solution is simply to wait until you are completely numb.

Placement of the local anaesthetic

The most common cause of not getting numb is when the dentist has missed the spot where they intended to put the local anaesthetic.

This problem usually arises when trying to numb lower teeth (especially lower back teeth) by blocking the nerve which supplies sensation to them. The usual technique for numbing lower back teeth is called the “inferior alveolar nerve block”. It should make your lips numb right to the midline. If it’s not working, often all it takes is trying again and putting the local into a slightly different spot.

But some people have an unusual anatomy (see “anatomical variation” section below). So if the inferior alveolar nerve block doesn’t do the trick, your dentist may be able to use an alternative numbing technique. Examples include the Akinosi or the Gow-Gates technique. These are “advanced” techniques and not all dentists are familiar with them.

Giving the local too fast

Some local anaesthesia techniques may not work as well if the local is administered too quickly.

Choice of local anaesthetic

The most common anaesthetic solution used nowadays (lidocaine with adrenaline – also known as lignocaine or xylocaine) works best for most situations. But if for some reason it doesn’t work for you, your dentist can use a different LA solution (for example articaine).

If you have certain medical problems, it may be better to use an adrenaline-free solution (prilocaine aka Citanest plain or carbocaine).


2. Anatomical Variation

It was once explained to me that there are a small number of people who either don’t respond to anaesthesia or have a wacky nerve structure that makes it hard to place the novocain etc. where it will work 100%. I have to think this is my case. The dentist who told me this is now deceased and I’m running out of new ones to go to. If you were in my position, what would you do?

Local anaesthetic is always effective if it is given in the right spot and has enough time to take effect. It blocks the nerve supply to the region to be treated, so you can’t feel pain. However, there is huge anatomical variation between people. And some people have such an unusual anatomy that the “standard” dental block for lower bottom teeth used by 99% of dentists doesn’t work (the inferior alveolar block mentioned above). 1

Innervation of the teeth

Unusual anatomy can be a particular problem with the lower jaw, because the dental nerve in the lower jaw is buried within dense bone. So giving local next to the tooth is usually not enough on its own to make that tooth completely numb. Instead, the main nerve which supplies sensation to that half of the jaw is numbed. This is done via an opening in the jawbone called the mandibular foramen.

The main reason why some people don’t go numb easily in the lower jaw is because the opening in their jawbone isn’t in the usual place. Everyone CAN be successfully numbed, but it may be necessary to use a different technique for numbing than the “standard” inferior dental block.

In contrast, the upper jaw is more porous (sponge like), so when anaesthetic is injected next to a tooth, it can get through to the root and make the tooth go numb.

Additional Nerves

It’s quite common to have some slightly unusual nerve connections. So in addition to the “usual” nerves, there may be additional or accessory nerves that supply the feeling for the tooth. When your dentist suspects that this is happening, you will need additional local in the right position.

For example, if you have trouble with upper back teeth not getting numb, a nerve called the greater palatine nerve can be the culprit. The solution is to give extra local in a different area to numb the accessory nerve.

Similarly, some people have accessory nerves in unusual places in the lower jaw. For example, there may be an accessory innervation of the lower teeth by the mylohyoid nerve. If you’re looking for detailed technical information, this article explains more: Four Common Mandibular Nerve Anomalies That Lead To Local Anesthesia Failures.

Again, there are always workarounds to these problems, but you may need a dentist with a special interest in advanced local anaesthesia techniques.


3. Infection (“Hot Tooth”)

A raging localized infection (an acute abscess) can lessen the effectiveness of local anaesthetic. You can read more about abscesses on our root canal treatment page.

The signs of acute infection are heat, redness and severe pain. If you have an abscess and you don’t have these symptoms, you have a chronic abscess, which doesn’t need antibiotics first. Also, the local anaesthetic will work as normal.

Numbing depends on the pH of the tissue. When there is an abscess (an acute area of infection), the pH drops and the environment becomes acidic. Local anaesthetic is very pH sensitive. Even in a normal environment, it seeps into nerve fibres slowly, which is why local anaesthetics take a few minutes to kick in. In an acidic environment, the nerve fibres look to the anaesthesia molecules like they are coated with wax and thus diffusion into the fibres is very slow.

As a result, the anaesthetic may not have as powerful an effect. Using more local anaesthetic (or using a different technique) usually does the trick:

It’s very very rare for a tooth to be so acutely infected that local won’t work properly. Usually, you can get around it by either putting more local in or else using a block injection to freeze the entire quarter of the mouth rather than just around the tooth. – Gordon Laurie, BDS

Another option is to bring the acute infection under control using antibiotics first. In that case, the pH in the tissue rises again, and the local anaesthetic will work normally.

What do I do if the antibiotics don’t work?

Often your dentist will prescribe penicillins of some sort (e. g. amoxicillin), or an equivalent antibiotic if you’re allergic to penicillins. Usually, they’re very effective, but not always. These antibiotics kill off some bacteria, typically the aerobic (oxygen-breathing) bugs. But sometimes it can be necessary to kill off anaerobic bugs which contribute to the infection as well. A different antibiotic with an activity spectrum effective against anaerobes (such as Metronidazole) may help.

It may not always be possible to get rid of the infection completely, but it may have reduced enough to allow for comfortable treatment. If things don’t get any better (and you’re scared of trying again), you may want to look into sedation options, such as laughing gas or IV sedation.

With a painful abscess, the rule is to establish drainage. Opening up into the abscess through the tooth will produce almost immediate rapid relief of pain and can be better than waiting for 12-24 hrs for antibiotics to kick in. It’s not a painless method, but if you’re in unbearable pain anyway…


4. Ehlers-Danlos Syndrome

Ehlers-Danlos syndrome (EDS) is a group of rare genetic disorders which affect the connective tissues. Connective tissues include tissue such as skin, bone, organs and muscles. Symptoms may include joint hypermobility, easy bruising and stretchy skin. The symptoms can vary in severity and type, making each affected person’s case unique.

Ehlers-Danlos Syndrome may also be a cause of not getting numb (enough) during dental treatment. What follows is some general advice from a person with EDS. Hopefully, her advice will help others with EDS who “can’t get numb” and the dentists who treat them.

1. Find a dentist who will actually listen!

2. Personally, I find articaine the best anaesthetic.

3. If anaesthetic typically wears off fast in the patient (like me), the dentist should wait around after injecting and monitor for its effectiveness. If it has had some effect but then seems to stop or wear off then inject more. Don’t wander off and wait for it to take effect like in a normal patient – by the time the dentist returns the anaesthetic has often worn off.

4. Arrange a signal to give if the anaesthetic starts to wear off (I raise my hand).

5. Top up whenever the patient indicates it’s worn off again.

6. If there may be discomfort after a procedure (e.g. wisdom tooth removal), give another injection before sending the patient home.

7. If the dental work is very minor, consult with the patient about whether local anaesthetic is even necessary.

8. The lack of effectiveness of local anaesthetic doesn’t just apply to dental work, but also to pain relief during labour (epidurals, spinals) and to accident repair (stitches etc.). In fact, the epidural wearing off repeatedly was what led me to get diagnosed with EDS. The anaesthetist had learned about EDS at school and the issues with freezing (Canadian term for numbing) an EDS patient.

9. Once you’ve met one EDS patient, you’ve met… one EDS patient. Don’t assume that all people with EDS react the same way. Some EDS people don’t feel an effect until after they’ve left the office. Others can react one way on one visit and another way on another visit depending on the treatment.

10. There are other EDS pointers for dentists – you need to be sure that your neck is supported during dental procedures. Your dentist should allow frequent breaks during prolonged treatment to avoid straining the ligaments of the jaw. Gums and tissues are fragile and bleed and tear easily. Sutures may not hold.

You can find additional information here:


5. Your metabolism

Your body’s biochemistry may be slightly different from that of the average person, and this may prevent the anaesthetic from working as expected. While most people are numb after 5 to 10 minutes, others take much longer to get numb. In some people, the anaesthetic wears off much faster than expected, whereas in others, it lasts much longer than expected.

The key is to find a solution together with your dentist – it just takes some extra time and a bit of trial and error.


6. Having Red Hair (?)

Some studies have suggested that people who have naturally red hair may not be as easy to numb as others. 23 The culprit might be a mutation in the melanocortin-1 receptor gene (or MC1R for short). Mutations in the MC1R gene lead to fair skin and red hair in humans. So if you are a natural redhead, you may need more local anaesthetic than people with other hair colours.

This research has been widely cited, but the evidence is actually quite flaky, involving a very small sample, and has never been replicated on a larger scale.

So this may well turn out to be a myth. It was also thought that redheads needed a greater amount of drugs for IV sedation and general anaesthesia – until more large scale research showed that this is not true: Myths in Anesthesiology: Do Redheads Have Special Needs?


7. Anxiety (?)

It’s been suggested that when someone is highly stressed or anxious, the local anaesthetic may not work as well as when you’re relaxed. The local anaesthetic may not kick in as quickly, it may not be as effective, or it may wear off too quickly.

We don’t know whether this theory is true or not. Most people with high levels of anxiety get numb without a problem. Or they usually get numb in one location, and not in another. It may be that people who have experienced inadequate numbing in the past are understandably very anxious. And when the numbing fails again, this is interpreted as their anxiety causing the anaesthetic to fail – when the real reason might be anatomical variation, poor technique, or individual differences in metabolism.

Also, since nearly all people experience at least some degree of anxiety during dental treatment (and 48% of people in the UK have moderate to severe levels of dental anxiety)4, it is nearly always possible to attribute incomplete numbing to anxiety.

Sedation and Pain Perception

Whatever the reason for not getting numb may be, sedation (either nitrous oxide or IV sedation) can help with altering the perception of pain. People seem to react to stimuli differently when sedated, and for some people, this makes all the difference.

So sedation is well worth considering if you repeatedly don’t get numb with different clinicians. You will be able to communicate with your dentist when using conscious sedation. This means that you can stop immediately if you are not numb enough using a pre-agreed stop signal (though often, dentists will pick up on any signs of discomfort before you’ll get a chance to use it).


Visit our support forum to get help with this and other fears, or to simply get things off your chest!

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Further Reading

Footnotes and Sources of Information

  1. Four Common Mandibular Nerve Anomalies That Lead To Local Anesthesia Failures. James L. Desantis, DDS, M.D., and Charles Liebow, DMD, Ph.D. (2014). Chairside Magazine Volume 9, Issue 2.[]
  2. Anesthetic requirement is increased in redheads (2004). Liem EB, Lin, C-M, Suleman, M-I, Doufas, AG, Gregg, RG, Veauthier, JM, Loyd, G, Sessler, DI. Anesthesiology. 2004 Aug;101(2):279-83.[]
  3. Increased Sensitivity to Thermal Pain and Reduced Subcutaneous Lidocaine Efficacy in Redheads (2006). Liem, EB, Joiner, TV, Tsueda, K, Sessler, DI. Anesthesiology. 2005 Mar; 102(3): 509–514.[]
  4. NHS Information Centre for Health and Social Care: Adult Dental Health Survey 2009.[]