How local anaesthetic works at the dentist

A dental local anaesthetic works by switching off a nerve for a few hours. It blocks the tiny channels that let electrical signals travel along the nerve, so when the dentist drills, scrapes or removes a tooth, the pain message is stopped before it reaches your brain. You still feel pressure and movement, because those travel along different fibres that are less affected, but you should not feel sharp pain.

Many of the UK patients who come to our Turkish dental clinic in Antalya are nervous about the injection more than the treatment itself. Understanding what is happening, and why it occasionally needs a top-up, tends to make the whole thing feel less mysterious. This guide covers how numbing works, how long it lasts, why it sometimes does not take, and how to look after yourself afterwards.

What happens inside the nerve

Nerves carry messages as tiny electrical pulses. Each pulse moves along the nerve because sodium, a charged particle, rushes in through gates in the nerve's outer wall called sodium channels. Local anaesthetic drugs such as lidocaine and articaine slip into those channels and block them. With the gates jammed shut, the pulse cannot travel past the numbed section, however much is happening at the tooth end.

Small nerve fibres that carry pain and temperature are blocked first and most easily. Larger fibres that carry pressure and touch are more resistant. That is why you can feel the dentist pushing on a tooth, or water running in your mouth, while the tooth itself feels nothing sharp. Patients sometimes mistake pressure for the anaesthetic failing. If you are unsure, say so: the dentist can test the area before carrying on.

Most dental anaesthetic cartridges also contain a very small amount of adrenaline, also called epinephrine. It narrows the blood vessels around the injection site, so the drug stays where it is needed for longer instead of being carried away in the bloodstream. It also reduces bleeding, which helps the dentist see.

Does the injection itself hurt?

Most people feel a sharp scratch and then a dull pressure as the liquid goes in. A few simple things make it more comfortable, and most dentists use them as a matter of routine:

• Numbing gel first. A topical gel or spray on the gum takes the edge off the needle going in.
• A slow injection. Much of the discomfort comes from the liquid stretching the tissue. Injecting slowly reduces it.
• Warm cartridges and fine needles. Dental needles are very thin, and anaesthetic at body temperature stings less than cold.
• Distraction. Some dentists gently wobble the cheek during the injection. The extra sensation crowds out the feeling of the needle.

The palate, the roof of the mouth, is the one place that tends to be more uncomfortable, because the gum there is tightly bound to bone and there is little room for the liquid. Dentists often numb the outer gum first and then work through to the palate from there, which helps.

Two ways of numbing a tooth

Dentists use two main techniques, and which one they choose depends mostly on which tooth is being treated.

A lower nerve block (the inferior alveolar nerve block) usually numbs half of the lower lip, chin and tongue as well as the teeth on that side. It feels strange and lasts longer than an upper injection, but it is normal.

How long the numbness lasts

With a standard anaesthetic containing adrenaline, the tooth itself usually stays numb for around an hour or more, enough for most fillings, crown preparations and extractions. The soft tissues, meaning lip, cheek and tongue, stay numb for longer, often two to four hours and sometimes more after a lower block. The NHS notes that the feeling comes back gradually as the drug is carried away and broken down.

Longer appointments, such as implant surgery or preparing several teeth, may need more than one injection. The dentist will top up before the first dose wears off.

Why it sometimes does not take

Every dentist sees a few patients where the numbing does not work as well as expected. There are well-understood reasons, and none of them mean something is wrong with you.

• Infection and inflammation. Infected tissue is more acidic. Local anaesthetics need a mildly alkaline environment to change into the form that crosses into the nerve, so acidity slows them down. Inflamed nerves are also more easily triggered. This is why a tooth with a painful abscess can be hard to numb, and why the dentist may first treat the infection or add extra injections.
• Lower back teeth. The nerve block needs to land close to a nerve the dentist cannot see. Normal variations in anatomy mean it does not work fully first time for a noticeable minority of people. A second injection, or a different technique close to the tooth, usually solves it.
• Extra nerve supply. Some teeth pick up a little feeling from a second, smaller nerve. A small extra injection covers it.
• Anxiety. Fear makes pain feel stronger, and very anxious people can also find it harder to tell pressure from pain. This is real, not imagined.
• Not enough time. Some injections need several minutes to reach full effect.

Articaine is often used because it spreads through bone well. Several meta-analyses comparing it with lidocaine have found articaine somewhat more likely to give full numbness, particularly with infiltration. Both drugs are widely used and safe in the right dose, and the choice depends on the tooth, the procedure and your medical history.

Is it safe for older adults?

Dental local anaesthetic is used safely every day in people with all sorts of health conditions. A few things are worth telling the dentist before any injection:

• heart problems, high blood pressure or an irregular heartbeat, as the amount of adrenaline may be adjusted or an adrenaline-free product used
• blood thinners such as warfarin, apixaban, rivaroxaban or clopidogrel; UK guidance from SDCEP says most dental treatment can go ahead, but the dentist may choose a technique with less bleeding risk
• any previous reaction to a dental injection, with as much detail as you remember
• liver or kidney disease, which can affect how the drug is cleared
• any medicines for depression, as a few interact with adrenaline

A simple printed list of your medicines, with doses, saves a lot of guesswork, especially when you are being treated in another country.

After the appointment

Until the feeling returns, your mouth is easy to injure without noticing. Sensible after-care is simple:

1. Hold off on hot drinks. You cannot judge temperature on a numb lip, and scalds are common.
2. Do not chew on the numb side. People bite their cheek, lip or tongue surprisingly hard while numb. Soft food on the other side, or wait.
3. Expect a little tenderness. The injection site can feel bruised for a day or two. This is normal.
4. Call if numbness lasts. If your lip or tongue is still numb the next day, contact the dentist. This is uncommon and usually recovers, but it should be checked.

How we approach numbing at Precious Dental

Most dental treatment, from extractions to implant placement, is usually done under local anaesthetic, in Antalya as in the UK. Bring your medicines list and tell your dentist about any health conditions before the first injection; if anything is unclear, say so and they will explain the plan before starting. If you are very anxious, our page on sedation dentistry explains when sedation may be offered alongside local anaesthetic. You can read about the people who will be treating you on our dentists page.

Sources

1. NHS: Local anaesthesia
2. Becker DE, Reed KL. Local anesthetics: review of pharmacological considerations. Anesth Prog 2012 (PubMed)
3. PubMed: meta-analyses comparing articaine and lidocaine in dentistry
4. SDCEP: Management of dental patients taking anticoagulants or antiplatelet drugs

Checked October 2026. Where we give our own view as a clinic, we say so.