For a standard local anaesthetic with a vasoconstrictor, the tooth itself is numb for roughly one to two hours and the lip, tongue or cheek stays numb for about three to five hours.
Soft tissue always outlasts the tooth. The numbness you can feel — the dead lip, the tongue that will not behave — hangs around long after the working anaesthesia has gone. Nothing has failed. They are two different measurements.
Lower jaw injections last longer than upper jaw ones, sometimes considerably, and longer-acting agents used for surgery can hold soft tissue numb for eight hours or more. Most freezing in general practice is for routine fillings, where one small injection is enough and you are back to normal by lunchtime.
Pulpal Numbness Versus Soft-Tissue Numbness
Two things get frozen and they wear off at different rates.
Pulpal anaesthesia is the tooth nerve. It is the only part that has to work while the dentist is drilling, and it is the shorter of the two — around 60 minutes for an upper infiltration, up to about 90 minutes or two hours for a lower block.
Soft-tissue anaesthesia is the lip, tongue, cheek and gum supplied by the same nerve, and it typically runs two to three times longer. Appointments are planned around the pulpal window, not the numb-lip window, which is why a long procedure sometimes needs a top-up while your lip is still dead. Numb lip does not mean numb tooth.
Upper Jaw Versus Lower Jaw
| Upper jaw (infiltration) | Lower back teeth (nerve block) | |
|---|---|---|
| What is anaesthetised | The area around one or two teeth | The whole inferior alveolar nerve trunk |
| Typical pulpal numbness | About 60 minutes | About 90 minutes to 2 hours |
| Typical soft-tissue numbness | 2-4 hours, lip and cheek | 3-5 hours, half the lip, chin and tongue |
| How it feels | Localised | Half your lower face, including the tongue |
Upper jaw bone is porous, so solution placed beside the tooth diffuses through to the root. Lower back teeth sit in dense bone it cannot cross, so the dentist blocks the whole nerve trunk before it enters the jaw. That single injection switches off everything downstream, which is why a lower filling leaves half your tongue numb and an upper one does not. Lower front teeth are usually infiltrated and behave like upper teeth, so not every bottom injection lasts until dinner.
What Makes Freezing Last Longer or Shorter
- The agent. Lidocaine is the everyday workhorse. Articaine diffuses through bone well. Bupivacaine and other long-acting agents are chosen deliberately for surgery, where hours of post-operative comfort is the point rather than a side effect.
- Whether a vasoconstrictor was included. Most cartridges contain a small amount of epinephrine, which narrows local blood vessels so the anaesthetic is carried away more slowly. It roughly doubles the working time. Plain solutions without it wear off much faster and are used where a vasoconstrictor is best avoided.
- The dose, the number of injections and the technique. More solution and more sites means longer. A nerve block outlasts an infiltration; an intraligamentary injection around a single tooth wears off quickly.
- Your own metabolism. Blood flow and liver metabolism vary. Some people reliably come out of freezing early and should say so, because it is useful next time.
- Inflammation and infection. A hot, abscessed tooth is genuinely harder to numb. Infected tissue is acidic, which reduces how much of the anaesthetic can cross into the nerve, and inflamed nerves fire more readily. This is why an infected tooth needing root canal treatment sometimes takes extra injections or a different technique.
There is also a reversal agent — phentolamine mesylate — that can be injected after treatment to speed the return of soft-tissue sensation, often roughly halving the numb time. It is not standard for every filling. It comes into its own for children, who are the ones most likely to chew a numb lip on the walk home, and for adults who have to speak in public that afternoon. Ask if it is available rather than assuming it is not.
Staying Safe While You Are Numb
The freezing itself is not the risk. What people do while numb is.
- Do not chew on that side until sensation is fully back. You cannot feel your cheek or tongue getting between your teeth.
- No hot drinks. A numb palate will not warn you before a scald.
- Skip alcohol until you can feel your lip.
- Watch children closely. A young child will bite, suck or scratch at a numb lip out of pure curiosity, and a chewed lower lip swells into something alarming a few hours later. It is one of the most common preventable injuries in dentistry and it is entirely avoidable with an adult paying attention for a couple of hours.
- If you have had a tooth taken out, follow the aftercare instructions on timing food, not the moment your lip wakes up.
A bitten numb lip is not an emergency in itself, but it hurts for days once sensation returns. Prevention costs nothing.
Surgery, Sedation and Longer-Acting Freezing
For wisdom tooth removal and other surgical work — including cases referred to an oral surgeon — a longer-acting anaesthetic is a deliberate choice. Numbness through the first several hours lets you get pain relief in before the discomfort starts rather than chasing it. Expect soft tissue numb well into the evening.
Sedation is a separate thing and does not replace freezing. Nitrous oxide or oral sedation changes how you feel about the appointment; local anaesthetic is what stops you feeling the tooth. You still get frozen either way.
When Numbness Lasting Too Long Is Worth a Call
Almost all prolonged numbness is nothing. Long-acting agents, a generous dose or a block placed close to the nerve can all stretch things out.
Ring the office if:
- Numbness or tingling is still there after about eight hours with no obvious explanation.
- Any numbness persists into the next day.
- You have altered sensation rather than absent sensation — burning, electric shocks, or an area that feels wrong to touch.
- There is swelling, spreading pain or fever, which is a different problem and may need urgent attention.
Persistent nerve disturbance after a routine injection is rare, and most cases resolve over weeks to months on their own. It still needs recording and reviewing rather than waiting it out silently. Get in touch and describe exactly what you feel and where.
If You Can Feel It, Say So
The single most useful thing you can do during a filling is tell the dentist the freezing is not holding. Not by tolerating it. Not by gripping the chair. Say it.
Adding more anaesthetic mid-procedure is normal and not a sign anything went wrong. Some teeth need it, some people metabolise fast, inflamed teeth are stubborn. Nobody is impressed by a patient who suffered quietly, and pushing through pain makes the next appointment worse because your nervous system remembers. Agree a hand signal before treatment starts, and use it.
Frequently Asked Questions
How long does freezing last after a filling?
Usually one to two hours of numbness in the tooth and three to five hours in the lip, cheek or tongue. Lower jaw blocks sit at the longer end of both, upper jaw infiltrations at the shorter end.
How can I make dental freezing wear off faster?
Gentle activity and light massage of the area may help marginally, because both increase blood flow. There is no reliable home trick. The one thing that genuinely shortens it is the reversal injection, which has to be given by the dentist before you leave.
Why is my tongue numb after a filling on my bottom teeth?
The lingual nerve runs alongside the nerve being blocked and is anaesthetised at the same time. It is expected, not an error, and it is why lower fillings feel far more disruptive than upper ones.
Is it normal to need a second injection?
Yes. Anatomy varies, infected teeth resist anaesthetic, and long procedures outlast the first dose. Needing a top-up is routine.
Does freezing hurt going in?
The sting is mostly from the solution entering the tissue, not the needle. Topical gel first, slow delivery and warming the cartridge all reduce it. Tell us if injections are the part you dread — it changes how we do it.
Book a Visit
If you have a tooth that needs work, or a history of freezing that never seems to hold, bring it up before we start — it changes the plan. Anything needing an examination first gets one, costs are set out on our fees and payment page, and you get a written estimate before treatment. New here? See new patient information. A broken tooth is worth reading about before it happens, and if you are due a clean, here is how long that takes.
Book online or contact the office. More answers to the questions patients actually ask are on the blog.
Leave a Reply