In short. The muscle is detached from the bone it was attached to and has to reattach. Why width can partly return months later although no bone grows back.
Key points
- Width that comes back between six and twelve months rarely has anything to do with the bone, which does not grow back.
- It is the masseter thickening again, which happens when it is worked hard.
- It feels soft rather than hard under the fingers and it becomes more prominent when the teeth are clenched.
The masseter is the muscle that gives the jaw most of its power to chew, and it inserts on the angle and the ramus of the mandible. When part of the angle is removed, part of what the muscle was attached to goes with it. The muscle is then left to reattach to the bone that remains, and how it does that is one of the reasons a result can change after the shape has apparently settled.
What happens to the attachment
The muscle is detached from the bone during the operation so the cut can be made, and it is then returned to the remaining bone and held there by the tissues around it while it heals. The attachment that forms is a scar attachment rather than the original one, and it takes weeks to become firm. For that period the muscle is not pulling on the bone in the way it did, which is part of why the early appearance is not the final one.
A width that returns is usually muscle
Width that comes back between six and twelve months rarely has anything to do with the bone, which does not grow back. It is the masseter thickening again, which happens when it is worked hard. It feels soft rather than hard under the fingers and it becomes more prominent when the teeth are clenched. That distinction decides what is offered next, because a second operation on the bone is not the answer to a muscle that has regained bulk.
Why the muscle thickens again
Muscle responds to load by getting bigger. A patient who clenches during the day, grinds at night, or chews heavily on one side is loading the masseter the way an athlete loads a limb. After the operation the muscle has less bone beneath it, and if it enlarges it changes the width of the lower face again. This is not a failure of the operation and it is not bone regrowth; it is the same muscle behaving the way muscle behaves.
What is watched, and when
This is a late finding rather than an early one, and it is judged at the same point as the rest of the result, which is around a year. Before then the width is dominated by swelling, so a jaw that looks wide at three months says little. If width does return later, the assessment looks at the muscle rather than at the bone, and what is offered acts on muscle.
Things worth reporting rather than waiting out
- A width that increases steadily after six months, rather than staying stable.
- New or worsening pain over the angle when chewing, rather than soreness that is settling.
- A return of the clenching or grinding that was present before the operation.
The muscle is not an afterthought to this operation. It is attached to the part of the bone being reduced, it is what chews, and it is the most likely explanation for a width that comes back.
Frequently asked questions
Can the masseter be left attached during an angle reduction?
Not when the corner itself is being cut. Part of the muscle attachment is on the bone being removed, so the muscle is lifted to reach the cut and returned afterwards. Where only the outer cortex is reduced, the muscle is still in the way but its attachment to the border is left more nearly intact, which is one difference between the two versions of the operation.
If the width partly returns months later, how do I tell whether it is the muscle?
Muscle feels soft under the fingers, becomes more prominent when the teeth are clenched, and changes with how hard the jaw is being worked. Bone is hard and does not change with clenching. The distinction matters because what is offered is different, and a second operation on the bone is not the answer to a muscle that has regained bulk.
Does a muscle that regains bulk mean the operation failed?
It means the operation did what it was planned to do and the muscle has since behaved like a muscle. The bone was reduced and stayed reduced. What brings width back is the masseter enlarging under load, which is a separate finding and one that is assessed on its own terms rather than counted as an error in the first operation.
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.