Can’t Get Numb

“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 (and subsequently, entire lower jaw) wouldn’t go numb. Why is this happening?? Should I be going to someone else? My old dentist has never had a problem numbing me.”

“Every time I go to the dentist, my Novocaine 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!”

Unfortunately there can be times when a tooth will just not go numb. Usually additional numbing either in the same site or elsewhere, possibly of a different anaesthetic, will do the trick.

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. having red hair
  6. hypersensitivity due to fear(?)

Before we start…

On this page, some examples of more advanced dental injection techniques are mentioned. They are just examples – it would be beyond the scope of a web page to explain all the techniques for the reasons given below. 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 somewhat more complex:

  • there are a variety of numbing techniques which work by numbing a single tooth
  • other numbing techniques involve freezing the nerve or nerves which supplies sensation to a group of teeth, and 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.)

If you’ve had repeated problems with a number of dentists not being able to numb you in the past, ask any potential new dentist if they are experienced with advanced local anaesthesia techniques. There are some examples of these on this page.

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:

Placement of the local anaesthetic

The most common cause of not getting numb is when the dentist has missed the spot where s/he 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 (“inferior alveolar nerve block”). Your lips should be numb right to the midline (even though the numbing is given in the back). By putting the local into a slightly different spot, the numbing problem is usually solved. But some people have an unusual anatomy (see “anatomical variation” section below). So if this doesn’t do the trick, an alternative numbing technique should be used, such as the Gow-Gates technique or the Akinosi technique, amongst others. These are considered “advanced” techniques and not every dentist knows how to do them.

If you’ve repeatedly had problems getting numb in the past, especially with more than one dentist, explain the situation to potential new dentists. Ask if they are familiar with more advanced techniques such as the Gow-Gates block and the Akinosi block. A dentist who has gone to the trouble of learning more advanced techniques will also likely be more compassionate and concerned about your comfort.

Not waiting long enough for the local to work

The tooth has not been allowed enough time to go numb. This is unlikely with modern local anaesthetics, but in some people, the action of the numbing is delayed. The solution is to wait until you are completely numb.

Giving the local too fast

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

Choice of local anaesthetic

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

If you have certain medical problems, an adrenaline-free solution might be preferred. Lidocaine without adrenaline isn’t ideal for this because it doesn’t numb the tooth well enough and wears off too quickly. Instead, prilocaine (Citanest plain) or carbocaine can be used.

Not giving enough local anaesthetic

Sometimes it just takes a greater amount of local anaesthetic to achieve profound numbing.

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 works by blocking the nerve supply to the particular region being treated. 

However, there is huge anatomical variation between people – and some people have such an unusual anatomy that the “standard” dental block used by 99% of dentists doesn’t work.

This is very rare – more commonly, you have some unusual nerve connections which mean that extra nerves supply the feeling for the tooth. When your dentist suspects that extra nerves are present, you will need additional local in the right position. In the trade, this phenomenon is known as accessory nerve supply. 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.

Unusual anatomy can be a 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 via an opening in the jawbone called the mandibular foramen.

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.

The 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.

The methods described above under the Poor Technique heading will help overcome any problems caused by anatomical variation.

3. Infection (“Hot Tooth”)

A raging localized infection (an acute abscess) can lessen the effectiveness of local anaesthetic (as an interesting aside, this is why root canal treatment has such a bad reputation – most root canals are completely painless). 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 fibers slowly, which is why local anaesthetics take a few minutes to kick in. In an acid environment, the nerve fibers look to the anaesthesia molecules like they are coated with wax and thus diffusion into the fibers is very slow 1.

As a result, the anaesthetic may not have as powerful an effect. Extra anaesthetic usually does 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)

“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)

Again, more advanced injection techniques can be used to numb the tooth (depending on the particular tooth and what is done to fix the problem). These may include the more advanced techniques mentioned in the “Poor Technique” section, like the Gow-Gates block or the Akinosi block, and also additional techniques like intraosseous anaesthesia (giving local anaesthetic into the bone – sounds a lot worse than it actually is).

Also, most of the time, it’s possible 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 you’ll be prescribed 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 (and may indeed be a more common cause of dental infections). A different antibiotic with an activity spectrum effective against anaerobes (such as Metronidazole) should be helpful.
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 giving things a try if there’s any possibility of feeling pain), 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.

It is not widely known that 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. We’ve added some additional comments in italics.

  • Find a dentist who will actually listen!
  • Personally I find articaine (“astracaine”) the best anaesthetic.
  • 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.
  • Arrange a signal to give if the anaesthetic starts to wear off (I raise my hand).
  • Top up whenever the patient indicates it’s worn off again.
  • If it’s been a procedure which can be followed by discomfort (eg wisdom tooth removal), give another injection before sending the patient home.
  • If the dental work is very minor, consult with the patient about whether local anaesthetic is even needed.
  • The lack of effectivess 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 getting diagnosed with EDS. The anaesthetist had learned about EDS at school and the issues with freezing (Canadian term for numbing) an EDS patient.
  • 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.
  • 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. Having Red Hair

There is some evidence which suggests that people who have naturally red hair may not be as easy to numb as others. The culprit appears to 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. Unfortunately, they can also make local anaesthetics less effective (the same also appears to be true for midazolam, which is used for IV sedation, and for general anaesthetic). So if you are a natural redhead, you may require a greater amount of local anaesthetic than people with other hair colours.

6. Anxiety

It has been suggested that when someone is highly stressed or anxious, the local anaesthetic may not work as well as when you’re relaxed – the effect of the local may be delayed, not pronounced enough, 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. A more parsimonious explanation is that anatomical variation, poor technique and/or individual differences in metabolism are to blame.

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)2, it is nearly always possible to ascribe the failure to achieve profound numbing to anxiety.

Whatever the reason for not getting numb may be, sedation (either nitrous oxide or IV sedation) may 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 encounter this problem with different clinicians. You will be able to communicate with your dentist when using conscious sedation, and stop immediately if you are not numb enough using a pre-agreed stop signal (though many dentists will pick up on any signs of discomfort before you’ll get a chance to use it).

Further Reading:

How to overcome failed local anaesthesia by J.G. Meechan (PDF file) (***trigger warning*** – very explicit images / written in dental-speak)

References

  1. source: https://doctorspiller.com/understanding-pain/
  2. NHS Information Centre for Health and Social Care: Adult Dental Health Survey 2009.