After a numbing injection

An injection of local anaesthetic blocked the nerve supplying the tooth, so that you could not feel what was being done. It works on the nerve rather than on the tooth, which is why the lip, the cheek, the tongue or half the chin go numb along with it.

The numbness often wears off within two to four hours, although it can last up to six hours, and occasionally longer, depending on the anaesthetic used and on what was done. Measure from when the injection was given rather than from when you got home.

Several things move it within that range:

• Which anaesthetic was used. Some are chosen deliberately to outlast the appointment, where the dentist wanted you comfortable afterwards. Those take longer to wear off.
• Where it was given. An injection for a lower back tooth blocks a larger nerve further back in the jaw, and commonly numbs the lip, chin and tongue on that side for longer than the tooth itself needed.
• How much was needed, and how you personally respond — which varies more between people than most expect.

Pins and needles mean it is wearing off. An odd, fizzing, slightly uncomfortable return of sensation is the normal end of it, not a problem.

Ring your dentist if it is lasting longer than you were led to expect — and certainly if you are still numb the following day, or if the altered feeling is spreading, worsening, or turning uncomfortable rather than simply fading. It is usually temporary even then, but it should be looked at and written down.

This is the whole of the advice, and it matters most for children.

• Do not eat. Not because it harms anything, but because you cannot feel your cheek or lip and will chew them without knowing.
• Nothing hot to drink. You will not feel a scald until the feeling comes back, and then you will have two problems.
• Try not to test it. Biting, sucking or chewing at a numb lip to see whether it has worn off is how most of the damage happens.
• Cool drinks are fine. Once normal sensation has returned, so is soft food.

If you have a numb child with you

A bitten lip or cheek is the thing paediatric leaflets warn about first, and the way to prevent it is to keep watching until the feeling has properly come back — two to three hours at least, sometimes longer, not one.

• Tell them the lip is asleep, not swollen. Children often look in the mirror, decide their lip has gone wrong, and get upset.
• Keep them off food until the feeling is properly back.
• Keep an eye on them. The chewing is usually idle and unconscious.

If they do bite it, expect a sore red or white patch, or a small ulcer, which is uncomfortable for a few days and then heals on its own. Soft food, cool drinks, and paracetamol if they need it. Ring if it is large, or if it is not settling.

• The tooth may be tender once the numbness goes, particularly if something was done to it. That is from the treatment rather than from the injection.
• The injection site can ache for a day or two, rather like a bruise. Common, and it settles.
• Your jaw may be stiff, especially after a long appointment with your mouth open.

The instructions you were given by the dentist who treated you take precedence over anything on this page. They know which anaesthetic they used, where they put it and how long it was meant to last; this page does not. Where the two differ, follow theirs.