In short. The mental nerve carries feeling from the lower lip, the chin and the gum in front of them, and a genioplasty disturbs it by handling and stretching rather than dividing it. Numbness, tingling and a lip that feels unfamiliar are expected, usually improve over a year or more, and can leave part of the area reduced for good.
Key points
- The nerve leaves the jaw below the first premolar on each side.
- The cut runs beside and below that opening, and the nerve is stretched, not divided.
- Numbness feels like a dentist's anaesthetic wearing off unevenly.
- Feeling returns in patches over a year or more; the chin point is usually last.
- A numb area that grows larger after the first weeks should be reported.
What the mental nerve supplies
The mental nerve carries feeling from the lower lip, the chin and the gum in front of them back to the brain. It leaves the jaw through a small opening on each side, on the outer surface of the bone, below the first premolar tooth. In a genioplasty the cut is made in the bone beside and below that opening. The nerve is not usually divided. It is handled and stretched, and that is enough to disturb it.
What the numbness actually feels like
What a patient feels is not pain. It is a change in sensation. The lip and chin feel thick, or as though they have been numbed at the dentist and the numbness is wearing off unevenly. Some people describe tingling, a coldness, or a sense that the lip does not belong to them. Eating and drinking take attention, because the lip does not report what is on it. None of this means something has gone wrong.
How does feeling return?
Recovery of feeling is slow and uneven. The first change is usually noticed once the swelling has gone down, and it continues for months. It often returns in patches rather than all at once, and the last area to recover is commonly the skin right over the chin point. Most people recover most of their sensation. Part of the lip or chin can stay reduced indefinitely, and that possibility belongs in the decision rather than in the follow-up.
There is no treatment that reliably speeds it up, and the honest answer is that time does most of the work. What helps is protection while feeling is reduced: checking the temperature of food and drink, and being careful when shaving or applying anything hot near the chin, because the skin cannot warn you.
What is expected in the first weeks
A lower lip that feels swollen, asleep or unfamiliar is expected after this operation. So are a slight dribble when drinking, difficulty sensing small crumbs on the lip, and an odd sensation when the chin is touched. These are not signs that the nerve has been injured beyond the usual.
| Sensation or sign | What it feels like | What it suggests | What to do |
|---|---|---|---|
| Reduced feeling in the lip and chin | Thick, asleep, as after dental anaesthesia wearing off | Disturbance from handling and stretching | Wait; it usually improves |
| Tingling or coldness | A lip that does not feel like your own | Disturbance | Wait; it usually improves |
| A slight dribble when drinking | The lip does not report what is on it | Disturbance | Take care with eating and drinking |
| Crumbs not sensed on the lip | Reduced touch information | Disturbance | Take care with eating and drinking |
| An odd sensation when the chin is touched | Changed sensation over the chin | Disturbance | Wait; it usually improves |
| A numb area that is getting larger after the first weeks | Not the usual pattern of recovery | Needs review | Report it rather than waiting |
| Loss of movement in the lower lip | Different from loss of feeling | Needs review | Report it |
| Pain in the jaw with fever or discharge from the mouth | Infection rather than nerve disturbance | Needs review | Report it |
How is sensation monitored?
Monitoring is by asking rather than by measuring. At follow-up visits the surgeon will ask where feeling is normal and where it is not, and will test light touch on both sides. The useful record is where the change is and whether the area is getting larger or smaller. An area that is shrinking is recovering.
Is feeling the same as function?
Feeling is not the same as function. The lip still moves, the mouth still closes and the chin still works; what changes is the information the lip sends back. A patient who understands that before the operation is not alarmed by it afterwards.
What makes lasting numbness more likely
Two things make lasting numbness more likely. One is a second operation in the same bone, because the nerve has already been disturbed and the scar around it makes it less forgiving. The other is a movement large enough to bring the segment close to the nerve canal. Both are known before the operation rather than discovered after it.
Which signs need review rather than waiting?
- A numb area that is getting larger rather than smaller after the first weeks.
- Loss of movement in the lower lip, as opposed to loss of feeling in it.
- Pain in the jaw with fever or discharge from the mouth, which suggests infection rather than nerve disturbance.
Sources
- American Society of Plastic Surgeons: guidance on genioplasty and nerve injury
- NICE: interventional procedures guidance relevant to facial bone surgery
- Cochrane Library: systematic reviews relevant to nerve disturbance after orthognathic surgery
Source links open each organisation's search results for the topic. Document-level confirmation is pending the reviewer's sign-off.
Internal links
Frequently asked questions
How long does numbness of the lip usually last?
It is present from the day of operation, begins to improve once the swelling has gone down, and continues slowly for a year or more. It frequently returns in patches, and the skin over the chin point is usually the last to recover. In some patients a part of the lip or chin stays reduced for good rather than recovering fully.
Is there anything that helps sensation return?
There is no treatment that reliably speeds it up, and the honest answer is that time does most of the work. What helps is protection while feeling is reduced: checking the temperature of food and drink, and being careful when shaving or applying anything hot near the chin, because the skin cannot warn you.
How would I know if the nerve had been injured rather than just disturbed?
The distinction is made partly by time and partly by examination. Disturbance improves, at least in part, over the first year. An injury that does not recover becomes clearer as the months pass, and the examination at follow-up records where feeling is present and where it is not, on each side separately.
Risks & Limitations
- Numbness of the lower lip and chin is expected after a cut in the jaw; it usually improves over months and may not return completely.
- A second operation in the same bone carries a higher chance of numbness that does not recover fully.
- The change is fixed once the bone heals, and reversing it means cutting again rather than removing something.
- Final results are judged at three months or later, and more fairly at a year, not in the first weeks.
When to Seek Care
- Difficulty breathing or chest pain — seek emergency care immediately.
- Fever with swelling, redness or discharge over the jaw, which may mean infection around the plates.
- A numb area of the lip or chin that is getting larger rather than smaller after the first weeks.
- Loss of movement in the lower lip, or an incision inside the mouth that opens.
References & Further Reading
- American Society of Plastic Surgeons (ASPS) — procedure and safety guidance
- National Institute for Health and Care Excellence (NICE, UK) — relevant guidance
- Cochrane Library — systematic reviews
- Chinese Medical Association Plastic Surgery Branch — clinical guidance
This page is patient education, not medical advice, and it does not cite individual studies. Discuss your own case with a qualified clinician. To arrange an assessment at Chongqing West District Hospital, see Contact & Consultation.