Marginal Mandibular Branch: Anatomy and Jawline
- Artery
- Nerve
Quick facts
- Origin
- Branch of the facial nerve that leaves the anterior and inferior border of the parotid gland.
- Course
- Runs near the lower border of the mandible, beneath the platysma, and crosses the facial vessels superficially.
- Muscles
- Depressor anguli oris, depressor labii inferioris and mentalis.
- Sign of injury
- The lower lip does not move down on one side in a broad smile or when showing the lower teeth.
- Relevance in orofacial harmonization (HOF)
- A structure to watch around the jawline, the pre-jowl sulcus and lower-third procedures.
The marginal mandibular branch is one of the terminal branches of the facial nerve. It leaves the parotid gland, runs near the lower border of the mandible and controls the muscles that lower the lower lip and the corner of the mouth: the depressor anguli oris, the depressor labii inferioris and the mentalis. It is motor: injury to it changes the movement of the lower lip, not sensation.
What is the course of the marginal branch?
| Segment | What to look for |
|---|---|
| Exit | Anterior and inferior border of the parotid, near the angle of the jaw |
| Behind the facial artery | May run slightly below the border of the mandible, especially with the head turned and with age |
| Crossing the mandible | Passes over the facial artery and vein, near the anterior border of the masseter |
| In front of the facial artery | Usually sits above the border of the mandible, on its way to the depressors |
| Plane | Deep to the platysma, covered by it along almost its whole course |
The point where the nerve crosses the facial vessels, at the mandibular border in front of the masseter, is the segment most often cited as needing attention in the region. The position varies between people and between sides, and there are double branches or connections with the buccal branch.
Why does it matter in orofacial harmonization (HOF)?
- Jawline and pre-jowl: filling the jawline and the pre-jowl sulcus happens close to its course. The procedure is covered in jawline filler.
- Other lower-third procedures: threads, submental liposuction and heat-based technologies in the region describe the nerve as a structure to protect.
- Toxin: injections into the depressor anguli oris and the platysma can diffuse to the depressor labii inferioris and mimic paresis of the marginal branch, temporarily. See drooping lip after toxin.
How does it show up in the assessment?
- Functional test: ask the person to show the lower teeth or make a forced "ee" grimace. The side with the intact branch lowers and turns out the lip.
- Telling it apart from the cervical branch: weakness of the platysma alone also changes the smile, but the person can still turn out the lower lip.
- Documentation before the procedure: prior lip asymmetry is common and must be in the initial photo and video.
The area is covered in jawline.
Also called: marginal mandibular branch, marginal mandibular nerve, ramus marginalis mandibulae.
Frequently asked questions
What happens when the marginal mandibular branch is injured?
The lower lip on the affected side stops moving down and turning outward when smiling broadly or showing the lower teeth, which makes the smile asymmetric. Lip sensation does not change, because the nerve is motor.
Can botulinum toxin mimic an injury to the marginal branch?
Yes. Toxin in the depressor anguli oris or in platysmal bands that diffuses to the depressor labii inferioris produces a similar picture, but a temporary one. The injection history helps tell them apart.