Depressor anguli oris muscle: anatomy and DAO
- Muscle
- Highlighted area
Quick facts
- Origin
- Oblique line of the mandible, with a broad base, lateral to the chin.
- Insertion
- Modiolus, at the mouth corner, where it blends with other muscles of expression.
- Action
- Pulls the mouth corner down and outward (expression of sadness or displeasure).
- Innervation
- Marginal mandibular branch of the facial nerve.
- Relevance in facial harmonization
- Contributes to a downturned mouth corner and marionette lines; a target for botulinum toxin.
- In Harmy
- Sits under the Mouth Corner point of the marking.
The depressor anguli oris is a triangular muscle of facial expression that arises from the mandible and inserts at the mouth corner. When it contracts, it pulls the corner down and outward, forming the expression of sadness or displeasure. In the international literature it is called the depressor anguli oris, and the abbreviation DAO appears often in HOF courses and articles.
Where is it and how is it built?
The muscle has a broad base below and a narrow tip above:
| Feature | Description |
|---|---|
| Origin | Oblique line of the mandible, lateral to the chin |
| Course | Rises, converging toward the mouth corner |
| Insertion | Modiolus, the fibromuscular node lateral to the corner |
| Relations | Covers part of the depressor labii inferioris; at its lateral edge, it blends with fibers of the platysma |
| Innervation | Marginal mandibular branch of the facial nerve |
At the modiolus, the depressor meets the orbicularis oris, the zygomaticus major, the risorius and other muscles that move the corner. Just medial to it is the depressor labii inferioris, which lowers the lip and shows the lower teeth, and closer to the center is the mentalis muscle. The facial artery crosses the border of the mandible in front of the masseter and rises near the lateral edge of the depressor.
Why does the depressor matter in facial harmonization?
With aging, volume loss in the lower third and the strength of the depressor add up: the mouth corner drops, and the fold running from it toward the jaw forms marionette lines. In some people the downturned corner is present early, because of anatomy or expression habits, and shows even at rest.
Treatment depends on the predominant cause:
- Muscular component (the corner drops more when speaking or in expressions): botulinum toxin in the depressor can reduce the downward pull.
- Volume and support component: mouth corner filler and chin filler can give the corner support.
- Combination: common, and a staged plan usually works better.
How does it show up in the assessment?
- At rest: observe the height of the corners relative to the line between the lips.
- Expression of sadness or displeasure: the contracted depressor forms a crease running down from the mouth corner.
- Speech and smile: see whether the corner drops during speech and whether the smile is symmetrical.
- Palpation with the patient contracting: helps feel the muscle mass over the jaw.
- Chin and platysma: assess them together, because they usually work together in pulling the lower third.
Record the smile on video or photo before treatment: any pre-existing asymmetry must be documented.
Also called: DAO, depressor anguli oris, triangularis muscle of the lips.
Frequently asked questions
What is the DAO muscle?
DAO is the abbreviation for depressor anguli oris, the muscle that depresses the angle of the mouth. It arises from the mandible and pulls the mouth corner down.
Does botulinum toxin lift a downturned mouth corner?
By reducing the depressor's strength, toxin can soften the droop of the mouth corner, especially when it is caused by contraction of the muscle. When the cause is volume loss or laxity, it is usually combined with filler, at the professional's discretion.
What are the risks of toxin in the depressor anguli oris?
The most cited are an asymmetric smile and difficulty moving the lower lip, when the toxin reaches neighboring muscles. They are usually temporary, but the professional's assessment and technique reduce the risk.