In short. One side of the lower lip not pulling down is the sign to watch for. How to test it, what it usually means, and when to contact the team rather than wait.
Key points
- Sit in front of a mirror and show your lower teeth as far as you can, then smile deliberately and hold it.
- Compare the two sides of the lower lip rather than the whole face.
- Ask somebody to photograph you doing it, once a week, at the same distance and in the same light.
The nerve that moves the lower lip passes near the outer surface of the mandible on its way forward. It can be bruised, stretched or, uncommonly, divided during an angle reduction. The result is a lower lip that does not pull downwards on one side, which shows when the patient shows the lower teeth or speaks. It is the finding the team watches for most closely after this operation, and it is one the patient can track as well.
What weakness actually looks like
The lower lip is pulled down by a small muscle on each side, so a weakness on one side makes the mouth look uneven when it moves. On the affected side the lip does not depress, the lower teeth on that side are harder to show, and the smile can look asymmetrical. At rest the face may look entirely normal, which is why the examination asks the patient to move rather than only to sit still.
How to test it at home
Sit in front of a mirror and show your lower teeth as far as you can, then smile deliberately and hold it. Compare the two sides of the lower lip rather than the whole face. Ask somebody to photograph you doing it, once a week, at the same distance and in the same light. A change over time is what matters, and a photograph taken today is the only reliable way to compare with a photograph taken next month.
What it usually means
Most weakness after this operation is a nerve that has been stretched or bruised rather than cut. That kind recovers on its own, usually over weeks to months, and it often improves in stages rather than steadily. A nerve that has been divided does not recover without repair. The distinction is not always clear at the beginning, which is why the finding is documented and watched and, where there is reason to suspect a division, investigated rather than simply observed.
When to contact the team
Weakness that appears in the first days and then stays the same is the expected pattern and is watched. Weakness that is new after the first week, or that is getting worse rather than better, is not. So is weakness that arrives with a swelling that is increasing, because a collection of blood can press on the nerve and needs to be dealt with rather than waited out.
Contact the team the same day
- Weakness of the lower lip that appears after the first week, or that is worsening rather than improving.
- Weakness together with swelling that is increasing rather than settling, or a feeling of pressure under the jaw.
- Difficulty swallowing, drooling you cannot control, or any difficulty breathing.
Documenting a weakness on the day it appears, with a photograph, gives the team something to compare against. That record is what makes the difference between watching a nerve recover and failing to notice that it is not.
Frequently asked questions
Does a weak lower lip after an angle reduction recover on its own?
Usually, when the nerve has been stretched or bruised rather than cut. That kind of injury recovers over weeks to months and often improves in stages rather than steadily, which is why it is recorded and reviewed rather than treated. A nerve that has been divided does not recover without repair, and the distinction is not always clear at the beginning, which is why the finding is investigated when there is reason to suspect it.
Should I wait for my next appointment to mention a weakness?
No. A weakness that is new after the first week, or that is getting worse rather than better, should be reported the same day. So should a weakness that arrives with swelling that is increasing, because a collection of blood can press on the nerve and needs to be dealt with rather than waited out. The early weeks are exactly when reporting changes what can be done.
What will the team do if a weakness does not improve?
The first step is to establish what kind of injury it is, from the examination and the record of how it has changed. Where the pattern suggests the nerve has been divided rather than bruised, exploration is considered, because a divided nerve has no route to recovery on its own. Where it suggests bruising, the plan is watching and documenting, since nothing reliably speeds that up.
Risks & Limitations
- The change is permanent and the amount removed is treated as fixed. Bone that has been taken away cannot be put back, and material added later does not behave like the mandible it replaces.
- The canal carrying the nerve to the chin runs inside the bone being cut. Numbness of the chin and lower lip is expected rather than rare, usually improves over months, and may not return fully.
- The nerve that moves the lower lip runs near the outer surface of the bone. Weakness after surgery is usually temporary and usually resolves; a lasting weakness is uncommon but possible.
- The vessels supplying the face run close to the surface of the angle. Bleeding afterwards is the complication this operation most wants to avoid, because a collection of blood in the floor of the mouth can compromise the airway.
- The masseter is detached from the bone it was attached to and reattaches. Width can partly return if the muscle thickens again, which is not the bone growing back.
- Swelling hides the result for months. The face reads wider than expected at two weeks, unevenly at three months, and the result is judged honestly at around a year.
When to Seek Care
- Difficulty breathing, a feeling of pressure or swelling in the floor of the mouth, or difficulty swallowing. Seek emergency care at once.
- Swelling that is increasing rather than settling after the first week, or that is much greater on one side. Contact the team.
- Weakness of the lower lip that appears after the first week, or that is worsening rather than improving.
- Numbness that is spreading rather than staying stable, or a wound in the mouth that is opening or discharging.
- Fever, or feeling generally unwell with a swollen and tender jaw. Calf pain or swelling in one leg, or chest pain and shortness of breath, need emergency care at once.
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.