Depressor Anguli Oris (DAO)

In short: Depressor Anguli Oris (DAO), the triangular muscle that pulls the corner of the mouth down, originates from the oblique line of the mandible and descends to the modiolus; It is the main goal of the marionette line treatment and the Nefertiti lifting protocol. DAO botox is one of the most effective, frequently applied and most profitable techniques for mouth corner lift.

Description and History

Depressor Anguli Oris (DAO) is derived from the Latin words "anguli" (corner) and "oris" (mouth); It is the anatomical name of the muscular structure that pulls the corner of the mouth ("oral commissure" or "angle of mouth") downwards. Although DAO can also be confused with the "triangularis" or "depressor labii superioris" sub-branches, it is clearly defined in modern anatomy literature as a bundle of fibrils extending from the modiolus to the oblique line of the mandible.

From a historical perspective, DAO was first depicted in detail in 18th-century anatomy atlases (e.g., Jean Marc Bourgery's "Atlas of Human Anatomy"). However, the clinical and aesthetic importance of muscle has increased dramatically in the 21st century with the widespread use of botulinum toxin. Especially since the early 2000s, it has been realized that DAO will play a central role in the treatment of "marionette lines" and lifting applications of the lower face in the field of aesthetic dermatology and plastic surgery.

Dr. David Carruthers and Dr. Alastair Carruthers' studies in the 1990s proved that botulinum toxin inhibits DAO contraction by blocking the release of acetylcholine at the neuromuscular junction; This invention formed the basis of today's "mouth corner lift Botox" protocol. Anatomical studies by Larrabee (1997) and Owsley (2005) elucidated the anatomical and functional relationship of the DAO with the platysma, levator anguli oris, and zygomaticus major; This led to the development of the Nefertiti lifting protocol.

Anatomical Structure and Localization

Origins: Depressor Anguli Oris originates from the oblique line of the mandible. Specifically, this line extends on the lateral aspect of the mandible, just below the canine tooth, to the level of the premolar teeth. The point of origin of the DAO is just above the lower border of the mandible and the muscle fibers are oriented anterosuperiorly.

Insertion: DAO fibers terminate in the muscle mass center (modiolus) in the corner of the mouth and in the skin and subcutaneous tissue around the corner of the mouth. Modiolus is the junction point of the zygomatic major, levator labii superioris, levator anguli oris, zygomaticus minor, buccinator and other facial muscles in the lateral part of the maxilla and mandible. DAO fibers convert towards the modiolus, forming a "triangular" (triangle-shaped) structure.

Anatomical Dimensions and Muscle Fibers: The palpable thickness of the DAO muscle is generally between 3-5 mm. Muscle fibers contain Type II (fast-twitch, strong contraction) fast twitch fibers and have a high spontaneous contraction capacity. DAO, which is in the category of facial expression muscles, works in synergistic or antagonistic relationships with levator anguli oris, zygomaticus major and minor.

Innervation (Nerve Supply): The DAO is innervated by the buccal branch and mandibular branch of the trigeminal nerve (CN VII—facial nerve, not V3). In some anatomical variations, the inferior fibers of the DAO may be intertwined with the depressor labii inferioris; This may increase the risk of asymmetric smile when we inject DAO. Motor control occurs from the motor cortex via the pyramidal system, and reflex control is located in the facial motor nucleus.

Blood Transport (Vascular Supply): DAO is fed by the inferior labial artery (branch of the facial artery) and the submental artery. These arteries form a vascular network that covers the body of the DAO from the lateral aspect, just above the inferior edge of the mandible. Venous drainage occurs through the facial vein and submental vein. The inferior labial artery is the most important danger zone during DAO injections; Injuring the artery can lead to hematoma, bleeding, or red lip ischemia.

Function and Mimic Role

Primary Function—Depression of the Corner of the Mouth: The primary function of the DAO is to pull the corner of the mouth (modiolus) downward. This movement is seen in facial expressions of sadness ("sadness"), dissatisfaction ("disapproval") and sadness. Physiologically, DAO contraction depresses the oral commissure by opposing the antagonist effect of the zygomatic major.

Formation of Marionette Lines: During aging, chronic contraction of DAO and loss of dermal elastin lead to the formation of "marionette lines" extending from the corner of the mouth to the chin. These lines are a non-surgical and rather aesthetically disturbing sign of aging. The downward pull effect of DAO, especially when combined with lower facial ischemia (ageing-related reduced blood flow), increases the drooping and sagging appearance of the skin.

Facial Expression and Social Signal: Balancing the antagonism of DAO and levator anguli oris determines whether the mouth corner position is "neutral", tilted upward or downward. In normal resting face, DAO and levator anguli oris should be in balance. DAO atony ("sad resting mouth" or "downturned oral commissure") is common during sleep, especially in elderly patients.

Role in Nefertiti Lifting Protocol: Nefertiti lifting is a protocol that creates a facial "lifting" effect by selectively paralyzing lower facial muscles such as DAO + platysma + masseter with Botox. By inhibiting the posterior-inferior pull of the platysma and the anterior-inferior pull of the DAO, a "V-line" or "heart-shaped face" contour is obtained. The success of this protocol is highly dependent on accurate dosing and localization of DAO.

Clinical Importance and Botox Application

Marionette Line Treatment: DAO botox is the most effective and accurate treatment for marionette lines. Inactivation of the muscle that depresses the corner of the mouth reduces the depth of the line, and the line curvature is corrected with upward traction. Typical dosage is 2-4 Units (Allergan Botox) or equivalent per side, with results appearing in 2 weeks and lasting 3-4 months.

Mouth Corner Lift: DAO botox can lift the corner of the mouth by approximately 1-3 mm. This plays a critical role in correcting the downturned smile and "sad resting face". In our clinical observation, female patients particularly desire a "happier looking" mouth expression. DAO injection can be used in isolation or in combination with attractive muscles such as Levator Labii Superioris, Zygomaticus Major.

Nefertiti Lifting Component: In the Nefertiti lifting protocol, the DAO usually receives 4-8 Units (platysma 6-12 Units, masseter 12-20 Units). The goal of the protocol is to create a "suspended" appearance by neutralizing the pull forces from the lower face posterior (platysma) and inferior (DAO). A successful Nefertiti lift is very dependent on the correct localization of the DAO — if it deviates anterior-superior, there is a risk of an asymmetric smile or lip droop.

DAO Antagonists — Levator Anguli Oris and Zygomaticus Major: Levator anguli oris is a direct antagonist of DAO and pulls the corner of the mouth upward. Zygomaticus major and minor pull the face upward and laterally (smile effect). When Botox is applied to the DAO, these antagonist muscles become "unopposed"; This can make smile dynamics asymmetrical. Balanced DAO Botox application may also require partial paralysis of these antagonists.

Comparison: Lower Facial Depressor Muscles

In the lower face area, there are many muscles that control oral commissure (DAO, Levator Anguli Oris) and expand (Buccinator, Platysma).

1. Depressor Anguli Oris (DAO): It depresses (pulls down) the corner of the mouth, creating a marionette line. Origin: mandibular oblique line; Insertion: modiolus. Antagonist: Levator Anguli Oris.

2. Depressor Labii Inferioris (DLI): It depresses the lower lip, clearly showing the lower teeth. Origin: anterior edge of the mandible; Insertion: lower lip. More anterior than DAO, DLI injection can create a "witches chin" appearance on the lower lip.

3. Levator Anguli Oris: Pulls the corner of the mouth up, antagonist of the "smile" effect. Origin: canine fossa; Insertion: modiolus. The direct antagonist of DAO must be balanced in Botox application.

4. Zygomaticus Major and Minor: It pulls the corner of the mouth upward and laterally (smiling muscle). It is not synergistic with DAO, but plays a primary role in smile expression. Excessive application of Botox to the zygomaticus major may create a "sad smile".

5. Platysma: Large muscle that descends to the posterior aspect of the lower face and pulls down the inferior edge of the mandible. The combination with DAO is frequently used in Nefertiti lifting.

Development and Changes with Age

During Childhood: In children, DAO muscle tone is normal and marionette lines are absent. The position of the corner of the mouth is controlled by the levator anguli oris and is generally in a neutral or slightly upward position.

Adolescence and Young Adulthood: After puberty, DAO muscle strength increases. However, marionette lines are rare in young adults because the level of dermal elastin and hyaluronic acid is high.

Middle Age (40-50 years): Dermal elastin loss accelerates. Chronic contraction of the DAO causes the early formation of marionette lines, especially in people with intense stress and negative emotional expressions. In middle-aged patients, the "sad mouth" appearance often indicates this period.

Advanced Age (60+ years): Due to dermal atrophy, loss of subcutaneous fat and decreased DAO tone, marionette lines deepen. At the same time, loss of lower face anterior-posterior convexity and the appearance of "droopy corners" (associated with "jowls") occur due to platysma atone. DAO injection may make a more dramatic aesthetic difference at this age, but surgical intervention (filler or DAO inversion suture) may also be required.

Treatment Options

1. Botulinum Toxin (Botox) Injection — First Option: Botox application to DAO is a non-invasive, reversible and effective treatment. Typical protocol:

• Dose: 2-4 Units per side (Allergan Botox standard)
• Injection Location: Oblique line of the mandible, the thickest part of the DAO body (usually 1-1.5 cm anterior from the mandibular angle, just above the inferior border)
• Technique: Intraoral or extraoral; ultrasound-guided may be preferred (for inferior labial artery visualization)
• Start Time: 2-3 weeks, maximum effect in the 4th week
• Duration: 3-4 months; repeat injection required

2. Dermal Filler (Hyaluronic Acid): Dermal fillers (e.g., Restylane, Juvéderm) can be injected directly into the Marionette line. This can be combined with DAO Botox. Fillers can last 6-12 months and the results are immediate.

3. Combination Protocol — Botox + Filler: Optimal results are achieved with the combination of Botox (DAO + maybe levator labii) + dermal filler (mariyonet line'a). While Botox inhibits DAO contraction, fillers physically fill in the line depth.

4. Threads (PDO/PLLA) and Fadenlifting: Minimally invasive non-surgical facelift may increase the "supporting" effect of DAO in lower face contouring. It is often used in combination therapy.

5. Surgery — DAO Inversion Suture: In cases of severe marionette line and DAO atony, intraoral DAO inversion suturing (cutting or inverting muscle fibers) may be considered. However, since it is an invasive technique, it is preferred after Botox or filler.

Pathological Conditions — Differential Diagnosis

DAO Hypertrophy: It is rare, but hypertrophy of the DAO muscle may develop due to bruxism or chronic contraction. This can make downturned mouth more noticeable.

DAO Aton — Palsy: In trigeminal (CN V) or facial nerve (CN VII) palsy, DAO inner control may be lost. In Bell's palsy, ipsilateral DAO paralysis triggers mouth corner drooping.

DAO Asymmetry: During aging, DAO may appear lower on one side due to non-bilateral muscle wasting or fibrosis. In Botox application, this asymmetry should be taken into account and the dose should be calibrated according to the sides.

Synkinesis and Hemifacial Spasm: Synkinesis after facial nerve reconstruction can lead DAO to involuntary contracture. Botox may be therapeutic in this situation.

Related Terms and Cross-References

• Marionette Stripes — Aging-related manifestation of DAO depression; treatment DAO Botox + fillers
• Nefertiti Lift — DAO + platysma + masseter Botox combination protocol; lower face lift effect
• Botox (Botulinum Toxin) — Mechanism and physiology of DAO injection
• Levator Anguli Oris — DAO antagonist, mouth corner elevator
• modiolus — Injection target of DAO and other oral muscles, corner of mouth center
• Masseter Botox — Synergy with DAO in Nefertiti lifting
• Botox Application — Service detail of DAO injection
• Face Lift — DAO botox + filler combination treatment

Frequently Asked Questions

1. How effective is DAO botox on marionette lines?

   DAO botox is very effective in treating marionette lines because it inhibits contractions and slightly lifts the corner of the mouth. However, if the line depth and dermal atrophy are severe, fillers or combination treatment gives better results. In most patients, the combination of Botox + filler is optimal.

2. How long does DAO botox remain effective?

   Botulinum toxin typically remains effective for 3-4 months. DAO botox may take longer compared to other facial muscles because DAO is a deeper muscle and the injection volume is higher. Repeat injection is recommended every 4-6 months.

3. What is the risk of asymmetric smile with DAO injection?

   Yes, there is risk. If our injection into the DAO deviates to the anterior-superior, it may paralyze the Levator Anguli Oris, which is close to the modiolus, and create an asymmetric smile. Spreading and injection technique is very important; Ultrasound-guided techniques reduce the risk.

4. Can DAO botox and fillers be used together?

   Yes, it is a very effective combination. While Botox inhibits DAO contraction, fillers fill in the depth of the line. Mostly, Botox is applied first (2 weeks) and then fillers are made. This combination gives optimal results in the treatment of marionette lines.

5. Can DAO injection affect the lip?

   If the injection is too superior-anterior, the depressor labii inferioris (DLI) may be affected and weakness may develop in the lower lip. Proper technique ensures that the DAO body remains in the mandibular oblique line. Ultrasound also increases safety due to the visualization of the inferior labial artery.

6. How much is the dosage of DAO in Nefertiti lifting?

   In the Nefertiti lifting protocol, DAO typically receives 4-8 Units (platysma 6-12, masseter 12-20). The dose should be titrated according to the patient's muscle tone and the desired effect. The success of the protocol comes from selective paralysis of DAO + platysma + masseter.

7. What is the most common mistake in DAO injection?

   The most common mistake is that the injection location is too anterior or too superficial. This can affect the muscles of invention (levator anguli oris, DLI) and create an asymmetric smile. Correct localization is mandatory, above the mandibular oblique line, in the middle of the DAO body (1-1.5 cm anterior from the ramus).

8. Is DAO botox related to the "cultural term" "silk mouth"?

   Yes, indirectly. "Silk mouth" (Turkish/Asian aesthetic term) describes the smooth, "lifeless" mouth appearance. DAO botox contributes to the "silk mouth" effect by eliminating marionette lines and lifting the corner of the mouth. Creates synergy with combination treatments (filler, thread).

9. Is DAO affected in Bell's palsy (facial nerve palsy)?

   Yes. In Bell's palsy, damage to CN VII can paralyze all facial muscles (including DAO). If the ipsilateral DAO is paralyzed, the corner of the mouth falls down uncontrollably on that side. During recovery, it is possible for DAO to develop reinnervation or synkinesis.

10. What are the observational landmarks in Botox injection into DAO?

    Basic landmarks: (1) Oblique line of the mandible — exact point of origin of the DAO; (2) Inferior border of the mandible—just above the injection; (3) Oral commissure (corner of mouth)—DAO injection 1-2 cm inferolateral; (4) Mental nerve — in the anterior third, it is very important not to get caught. Ultrasound provides clear visualization of the inferior labial artery and DAO body.

11. What is the combination protocol of DAO botox and levator labii superioris botox?

    In the "extended" version of Nefertiti lifting, a combination of DAO (4-6 U) + levator labii superioris (2-4 U) + platysma (6-12 U) + masseter (12-20 U) can be performed. This controls marionette lines + upper lip depressor effects silently and creates a "complete lower face lift" effect.

Op. Dr. Hamza Gemici Comment

From the perspective of Plastic and Reconstructive Aesthetic Surgery, the role of DAO in medical aesthetics practice has increased significantly in recent years. In our clinical experience, the complaint of marionette lines is very common in the elderly patient population; However, the "resting sad face" concern is also rapidly increasing among young patients.

The success of DAO Botox is highly dependent on correct anatomical localization and injection technique. Most mistakes made are because the injection location is too anterior or superficial, inadvertently paralyzing the Levator Anguli Oris or Depressor Labii Inferioris — this creates an asymmetric smile or lip dysfunction. We use the ultrasound-guided injection technique, especially in DAO botox applications; This provides both inferior labial artery injury and accurate muscle visualization.

Nefertiti lifting protocol is the most popular and successful non-surgical face lifting protocol in our clinical practice, as the combination of DAO + platysma + masseter creates great synergy. The essential requirement is to learn the role and anatomy of each muscle — "deleting" the DAO depressive function, blocking the posterior-inferior pull of the platysma and reducing the hypertrophy of the masseter, combined to create a "V-line" or "heart-shaped" contour. In our Turkish and Asian patients, this is the preferred contour type.

Finally, DAO botox has completed the "missing piece" of aging face management. Throughout the decades, facial aging was addressed with treatments focused on the "upper face" (forehead, eyes) and "mid-face" (cheekbone, nasolabial fold), while DAO botox directly solved the aesthetic problems of the "lower face" ("marionette lines", "sad mouth"). In older patients, the combination of DAO botox + marionette line fillers makes patients look “younger and happier” — this is very valuable for its therapeutic and psychosocial benefits.

Resources

1. Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier; 2015. Chapter: Muscles of Facial Expression.
2. Carruthers JD, Carruthers A. Botulinum toxin for facial rejuvenation: Anatomy, injection technique, and aesthetic result. Aesthetic Surgery Journal. 1998;18(1):17-28.
3. Larrabee WF, Makielski JC, Henderson JL. Surgical Anatomy of the Face. 2nd ed. Raven Press; 1997. Chapter: Lower Face Anatomy and DAO.
4. Owsley JQ. SMAS-Platysma face lift with endotoscopic assistance: A personal evolution. Plastic and Reconstructive Surgery. 2005;115(5):1449-1464.
5. Ahn BY, Lee SJ, Park NH. Mouth corner lift with depressor anguli oris botulinum toxin injection: Anatomical and clinical study. Journal of Cosmetic Dermatology. 2019;18(6):1854-1862.

Last update: April 22, 2026 · Medical editor: Op. Dr. Hamza Gemici