Botulinum Toxin Type A Injection Sites for Oral Commissure Ptosis

Oral commissure ptosis is a common aesthetic concern that presents as abnormal downward displacement of the mouth corners at rest, leading to a sad, angry or aged appearance. Botulinum toxin type A (BTX-A) injection is the first-line treatment, but there is no consensus on the optimal injection site in the depressor anguli oris (DAO) muscle.

This multicenter randomized controlled trial will enroll 266 subjects with oral commissure ptosis from 5 top Chinese stomatological hospitals. Subjects will be randomly assigned 1:1 to receive either upper DAO or lower DAO BTX-A injection. The primary endpoint is the improvement of oral commissure ptosis angle at 1 month post-treatment. Secondary endpoints include objective efficacy measures, subjective aesthetic evaluations, and safety profiles during a 6-month follow-up.

This study aims to determine the optimal injection site for Chinese population, establish standardized operation specifications, and provide level I evidence for clinical practice.

Inclusion criteria

• Aged 18 to 60 years, any gender
• Meet the diagnostic criteria for oral commissure ptosis: bilateral oral commissure ptosis angle (angle between the oral commissure point and the horizontal line of the ipsilateral vermilion border) > 1° at rest
• Have clear aesthetic demand for oral commissure ptosis improvement and can complete full-cycle follow-up
• No redness, swelling, ulcer, scar, deformity or active infection in the perioral and mental regions
• Have not participated in other interventional clinical trials within 3 months before enrollment

Exclusion criteria

• Hypersensitivity to botulinum toxin type A, lidocaine or excipients of injection preparations; or contraindications to botulinum toxin injection (myasthenia gravis, Lambert-Eaton syndrome, motor neuron disease, severe liver and kidney dysfunction, coagulation disorders, uncontrolled autoimmune diseases, malignant tumors)
• History of mid-lower facial botulinum toxin type A injection, soft tissue filling, laser/radiofrequency rejuvenation, perioral surgery or orthognathic treatment within 6 months before enrollment
• Planned perioral treatment within 6 months after enrollment that may affect efficacy evaluation
• Pregnant or lactating women, or those planning to become pregnant within 6 months
• Acquired oral commissure ptosis caused by facial nerve palsy/sequelae, perioral scar traction, severe jaw deformity or severe alveolar bone resorption
• Severe facial asymmetry (difference in bilateral oral commissure ptosis angle > 2°)
• History of botulinum toxin allergy or severe adverse reactions after previous botulinum toxin injection
• Currently using aminoglycoside antibiotics, quinine, calcium channel blockers, anticoagulants or other drugs that may affect botulinum toxin efficacy or increase bleeding risk and cannot discontinue
• History of mental illness, drug/alcohol abuse, or poor compliance unable to complete follow-up
• Other conditions deemed unsuitable for enrollment by the investigator