What is it?
Two sensory nerves are at risk in the lower jaw. The inferior alveolar nerve runs in a canal inside the bone and carries sensation from the lower lip and the point of the chin. The lingual nerve carries sensation from one side of the tongue and part of the sense of taste. Both are sensory nerves; when they are damaged there is no facial palsy, but the quality of sensation changes.
The words used to describe how sensation has changed decide the follow-up. If sensation is completely absent it is called anaesthesia, if it is reduced, hypoaesthesia, if there is tingling and pins and needles, paraesthesia, and if touch brings on an unpleasant or painful sensation, dysaesthesia. Making this distinction sets how often you are seen and when further assessment is asked for.
Knowing when numbness is to be expected prevents both needless worry and delay. A local anaesthetic wears off over a few hours, depending on the solution used. A temporary change in sensation caused by swelling after surgery settles over days to weeks. Loss of sensation that goes past eight weeks, or that does not improve at all, is a matter for separate assessment.
Signs
You will not necessarily have all of these at once.
Why does it happen?
- 01
Wisdom tooth surgery
The roots of a lower wisdom tooth can lie next to the nerve canal. How the root relates to the canal is assessed with imaging before the operation; if they are close, the surgical technique is planned accordingly.
- 02
Implants and bone procedures
A change in sensation can occur when the safety margin left to the nerve canal while the socket is prepared is not enough, or when bleeding and swelling after the procedure press on the nerve. This is why symptoms in the first days are taken seriously.
- 03
Injections
In lower jaw and lingual blocks, the needle touching the nerve or the chemical effect of the solution can lead to numbness. A jolt like an electric shock felt as the needle goes in is a finding that should be noted.
- 04
Root canal treatment and filling material passing beyond the root
Filling material that passes out of the root tip into the nerve canal can damage the nerve both by pressure and by its chemical effect. In this picture, noticing it early and deciding quickly is what counts.
How does it progress?
- 1
Crushing of the nerve
The nerve sheath is intact and conduction has stopped for a time. At this degree sensation is expected to come back over days to weeks; this is generally the most favourable situation.
- 2
Fibres torn, the sheath intact
The fibres try to grow back and reach their target again. The return can take months; more tingling and a shrinking numb area are the changes expected in this period.
- 3
Loss of continuity of the nerve
The nerve and its sheath have been separated. Full recovery on its own is not expected; assessment for surgical repair comes onto the agenda, and that assessment should not be delayed.
- Follow-up
Mapping and recording the area
At every check the numb area is drawn on the skin, measured and recorded with the date. The area getting smaller is the clearest sign of recovery.
How is it treated?
The first thing to be done is to put your symptoms on record. Which procedure was carried out, which nerve's area is affected, what kind of sensation there is and where the numb area ends are all established. The area is drawn out, compared with the other side using simple tests such as touch and a needle tip, and dated. If needed, a CT scan is used to assess how the implant or the root relates to the nerve canal.
The decision is made early, according to the cause. If an implant is pressing on the nerve or filling material has passed into the canal, removing it comes onto the agenda, and that decision is made in a window measured in days rather than weeks. Your dentist may add drug treatment depending on the situation. Follow-up intervals are set in advance and appointments are not missed.
If there is not enough improvement within the agreed time, an assessment by oral and maxillofacial surgery and by microsurgery is requested; if pain brought on by touch continues, neurology or a pain department joins the process. It is worth being clear about this: in most mild cases sensation is expected to return, while in some people a lasting change in sensation can remain and no definite timescale can be given.
- Swelling, fever or difficulty opening the mouth appearing alongside the numbness
- The numb area getting bigger over the days instead of smaller
- Burning pain brought on by touch that wakes you at night
- Complete loss of sensation that starts straight after an implant or root canal treatment and does not ease
How is it prevented?
- Before lower jaw surgery and implants, ask for the relationship of the area to the nerve canal to be assessed with imaging, and expect the result to be explained to you.
- If you feel a jolt like an electric shock during the procedure, say so at the time; having this written in your notes helps in the follow-up later on.
- If the numbness has gone past the expected time, do not wait for days; go back to the dentist who carried out the procedure and have the numb area recorded.
- Be careful with hot food and with chewing until sensation comes back; a numb lip or tongue can be bitten or burnt without you noticing.
Frequently asked questions
- How long does the numbness take to go?
- The time depends on how severe the injury is and cannot be said at the outset. In mild cases where the nerve has only been crushed, sensation is expected to come back over days to weeks. Where the fibres are affected, the process can take months. For this reason the numb area is measured and monitored rather than a timetable being given.
- Is there a chance it will be permanent?
- In a small number of people the change in sensation can be permanent; there is no way of knowing this at the start. Where it is noticed early, recorded properly and the cause can be removed, a better outcome is expected. This is why it matters that you do not put off reporting your symptoms and that you come to your appointments.
- Is an MRI scan needed for this?
- It is not needed routinely. In most cases a cone beam CT scan is enough to show how the implant or the root filling relates to the nerve canal, and the decision is made on that. Further imaging or an electrical nerve test is only requested if the doctor carrying out the assessment thinks it is necessary.
This content is for general information and does not replace an in-person examination. Symptoms overlap between conditions, and a diagnosis can only be made clinically.