12/31/2025
Why Ultrasound Matters When Assessing DAO
The depressor anguli oris (DAO) plays a major role in lower facial expression, specifically pulling the corners of the mouth downward. In aesthetic practice, the DAO is commonly targeted for neuromodulation to soften a downturned smile or “sad mouth.”
However, not all DAO anatomy is textbook, and one of the most clinically relevant variations presented in this case involves aberrant or blended attachments with the buccinator muscle.
This is where ultrasound becomes critical.
Understanding the DAO–Buccinator Relationship:
• The DAO normally originates from the mandible and inserts into the modiolus at the oral commissure.
• The buccinator, a deeper facial expression muscle, forms the muscular wall of the cheek and plays a role in mastication and oral competence.
• In some patients, DAO fibers partially blend with or abnormally attach into the buccinator, rather than following a clean, superficial course.
• This variation is not reliably predictable by surface anatomy alone.
Why This Anomaly Matters Clinically:
When a buccinator-DAO anomaly is present. blind injections based on landmarks may:
• Miss the true DAO belly
• Diffuse toxin into the buccinator
• This can result in:
• Asymmetric smile
• Oral incompetence or cheek biting
• Speech or chewing changes
• Under-treatment or over-treatment of the DAO
The DAO is not a “set it and forget it” muscle.
When a buccinator attachment anomaly exists, ultrasound is the only way to see it before you treat it.
👉 If you’re treating the lower face without ultrasound, you’re treating a guess, not anatomy.
👉With ultrasound instead of assuming anatomy, you are confirming it.
UltrasoundAesthetics
