In-Depth Anatomy Review
Depressor Anguli Oris (DAO): A triangular muscle originating from the oblique line of the mandible and inserting into the modiolus. It depresses the corners of the mouth, contributing to a sad or aged appearance. Overactivity creates a persistent downturned mouth.
Injection tip: Use a superficial injection 1 cm lateral and slightly inferior to the oral commissure. Inject 2-3 units per side, avoiding medial drift that could affect the depressor labii inferioris, which would result in lip asymmetry during smiling or speaking.
Depressor Labii Inferioris (DLI): Located medial to the DAO, this muscle lowers the bottom lip. Unintended diffusion of toxin here can cause difficulty with lip eversion and speech. Always differentiate DLI from DAO using anatomical landmarks or even EMG guidance in difficult cases.
Mentalis: A dome-shaped muscle originating from the incisive fossa of the mandible, inserting into the dermis of the chin. It protrudes the lower lip and wrinkles the chin skin.
Injection tip: Inject into the muscle belly, 2 units per side, just above the periosteum, taking care to stay midline and avoid over-treatment that can lead to “witch’s chin” or lip incompetence.
Platysma: This thin, broad, superficial muscle spans from the clavicle to the inferior face, blending into the lower lip depressors and the modiolus. In aging, its contraction causes vertical banding and downward pull of the lower face.
Injection tip: Target platysmal bands with 2-3 units per injection point (5–6 total along the band). For contouring the jawline (Nefertiti Lift), inject along the mandibular border in 4–5 points per side, avoiding spread into deeper structures such as the marginal mandibular branch of the facial nerve.
Masseter: This thick quadrangular muscle originates from the zygomatic arch and inserts into the angle and ramus of the mandible. Its hypertrophy widens the lower face and can cause bruxism.
Injection tip: Palpate during clenching. Inject deep, at the lower third of the muscle, posterior to the anterior border of the masseter. Start with 20–30 units per side depending on gender and muscle bulk. Avoid the parotid duct anteriorly and facial artery medially.
Dosing & Dilution Strategy
Use standard dilution (100U reconstituted with 2.5–4.0 mL of preserved saline) for most lower face applications.
Start conservatively—lower face muscles tend to be smaller and more functionally sensitive.
Always personalize based on clinical exam, gender, patient goals, and prior response to botulinum toxin.
Avoid over-dilution which increases diffusion risk, especially in functionally critical areas.
Avoiding Complications
Asymmetry: Always inject bilaterally and symmetrically. Even 1–2 units discrepancy can result in noticeable imbalance.
Oral incompetence: Avoid injecting too close to the modiolus or in high doses to DAO/mentalis combination, which may lead to drooling, difficulty drinking from a straw, or smiling asymmetry.
Speech disturbance: Monitor effects on articulation, especially “B” and “P” sounds. This is most relevant when treating the mentalis and orbicularis oris complex.
Chewing weakness: In masseter injections, over-treatment may affect mastication. Always assess baseline strength and counsel accordingly.
Advanced Tips
Layering Technique: In some cases, injecting both the superficial DAO and deep platysmal fibers offers better modulation of dynamic pull.
Combination Therapy: For optimal jawline contouring, combine platysma botulinum toxin with dermal fillers in the prejowl sulcus or mandibular angle.
Ultrasound-Guided Injection: Emerging practice for safer and more precise toxin placement, particularly in high-risk or post-surgical patients.
Bottom Line
Botulinum toxin in the lower face requires more than just knowledge of facial anatomy. It demands mastery of depth, plane, function, and expression. Aesthetic outcomes are optimal when dosing is minimal, technique is deliberate, and anatomical precision is non-negotiable.
Stay safe. Stay subtle. Stay ahead.
➡️ Read this week’s feature and subscribe to The Cosmoplastic Digest for weekly insights, surgical techniques, and advanced aesthetic guidance. Stay ahead in aesthetics—join the community today!
|
|
Subscribe to
Your Hub for Evidence-Based Aesthetic Learning
|
​