The numbness after the injection will not go: how long should it last?

A local anaesthetic works by stopping the signal the nerve carries for a while. In the tooth, what that comes to is your not feeling pain during the treatment. In soft tissue, it comes to the lip, the tongue and the cheek losing their feeling. The two effects come from the same drug but do not end at the same time: the numbness in soft tissue carries on for hours after the effect in the tooth has finished. The work being over does not mean the numbness is over.

With local anaesthetics that contain a vasoconstrictor, the usual duration reported for numbness in the lip and tongue is three to five hours. Several things change that: the type of anaesthetic used, whether it contains a vasoconstrictor, the dose given and the technique applied. A block given in the lower jaw covers a wider area than an infiltration in the upper jaw and usually lasts longer. That is why numbness lasting until the evening after treatment on a lower molar is more to be expected than numbness after work on an upper front tooth.

Which tissue is numb tells you which nerve is involved, and that is useful information when numbness drags on. The lower lip and the point of the chin take their sensation from the inferior alveolar nerve. One half of the tongue is supplied by the lingual nerve, for both touch and taste. The upper lip, the cheek and the side of the nose come from branches of the maxillary nerve. When you ring the clinic, saying exactly which area is numb speeds up the assessment directly.

A little-known detail: there is a drug that reverses numbness in soft tissue. Phentolamine mesylate blocks the effect of the vasoconstrictor in the anaesthetic solution and speeds up the removal of the drug from the area. In one study in children, the time for feeling in the lip to return to normal was about two hours in the group given no drug and around half an hour in the group that was given it. No product containing this active ingredient is authorised in Turkey; not a single entry containing phentolamine comes up in the summary of product characteristics database held by the Turkish Medicines and Medical Devices Agency (TITCK). So an option used outside Turkey is not routinely offered here.

While the numbness lasts, the real risk is not the pain but the tissue itself being left unprotected. Biting a lip or tongue you cannot feel, without noticing, can turn into a sore that lasts for days after the numbness has gone. In one study in children, about one in five of the patients who were not given the reversal drug injured their lip by biting it a few hours after treatment; in the group given the drug, that figure stayed at 2%. The mechanism is the same in adults: chewing before the numbness has gone, having a hot drink and chewing gum are the known routes to this injury.

Numbness that goes markedly beyond the expected duration is usually caused by the needle touching the nerve directly, or by an injection given very close to it. This is rare. The figures reported for how rare vary over a very wide range, because a good part of the mild cases are never recorded at all. Being rare does not make it unimportant for the person living through it; it is something that should be reported.

Which nerve is most often involved in needle-related cases can come as a surprise. In about 70% of the cases reported the lingual nerve is involved, and in 30% the inferior alveolar nerve. In other words, the complaint "half my tongue is still numb and I cannot taste anything" is more common in this picture than numbness in the lip, and it should not be taken lightly.

The sharp, electric-shock-like or burning sensation felt during the injection is something people often ask about. Slightly more than half of the patients who go on to have prolonged numbness describe that sensation. It cuts both ways: having felt it does not mean the nerve has been damaged, and not having felt it does not mean it has not been. What decides the matter is not the sensation at the time but the duration afterwards. Even so, if you did feel something like that, tell your dentist and ask for it to be recorded.

The good news about the course is this: between 85% and 94% of needle-related sensory disturbances settle on their own. Recovery usually comes within weeks, sometimes months, and it comes gradually. But the picture changes as time goes on; in a loss of sensation that has gone past nine months with no improvement at all, the chance of it being permanent rises. That is why the timeline matters: waiting should not be a plan but a process that is followed.

The distinction below is not a diagnosis; it is a framework showing when you can relax and when you need to ring the clinic.

The sequence below sets out the steps to follow from the moment the numbness starts to go beyond the expected duration. The place to go is the dentist who carried out the procedure.

1. 1

   Write down the times

   Note the time the procedure finished, the time the numbness began to lessen and how it was the next morning. This is the most useful information there is at the assessment; times estimated from memory make it harder.

2. 2

   Compare it with the other side

   With the tip of a clean cotton bud, touch the numb side lightly first and then the other side. Is there a difference, and if so how much? Do this once a day at the same time. Do not test with anything pointed; you will injure tissue that cannot feel.

3. 3

   Ring the clinic and tell them four things

   Which procedure was done, which side, which area is numb (the lower lip, the point of the chin, half the tongue) and when it started. Those four speed up the assessment directly.

4. 4

   Ask your dentist these questions

   Which anaesthetic was used, which technique was applied, how many cartridges were given, and whether you mentioned feeling something like an electric shock during the injection. Having all of this written into your file is the basis for the follow-up that comes after.

5. 5

   A follow-up timetable is set

   A sensory examination establishes a starting point and is repeated at set intervals. If three months pass with no improvement at all, a referral to an oral and maxillofacial surgeon, or to a centre experienced in nerve problems, comes onto the agenda.

These do not take each other's place; which one is right is decided by how long the numbness has lasted, where it is and how severe it is.

The real danger in this period is not the numbness itself but the tissue being left unprotected and the report being delayed.

The course below is a general framework; it varies with the anaesthetic used, with the technique and with the person.

1. The first hours

   The tooth feels no pain, the lip and tongue have no feeling, and speaking and drinking become difficult. What to do in this period is to wait and protect the tissue.

2. Three to five hours

   This is the usual duration reported for numbness in the lip and tongue. When the tingling starts, the feeling is coming back.

3. The same evening

   The numbness is expected to have eased markedly. If there is still no change at all, note the time so that you can check it the next morning.

4. The next day and after

   Numbness that is still there the next day should be reported. The great majority of cases in this picture improve gradually over weeks, sometimes months; where the picture does not improve, the timetable is planned according to the specialist assessment.

The numbness itself usually calls for no extra procedure; what determines the scope is how far the assessment and the follow-up go. These are the items that determine it:

Whether the numbness stays within the usual duration

Numbness that wears off in the expected time needs no extra appointment; in a prolonged picture, a sensory examination and follow-up appointments come into it.

Which area the numbness covers

A loss of feeling that takes in half the tongue and a picture confined to the lower lip can call for follow-up of different intensity.

Whether imaging is needed

If the procedure was carried out in an area close to the nerve, the existing images may need rereading, or a further image may be asked for.

Referral to a specialist

In a picture that has gone past three months without improving, a specialist assessment is a separate process and a separate item.