The Efficacy Study of Facial Biomechanical A-Type Botox Injection in Reshaping the Jawline

Aging-related changes of the mandibular margin are common, and with increasing aesthetic awareness, the demand for non-surgical jawline rejuvenation is growing.

To compare the efficacy and safety of a facial biomechanical injection technique versus a microdroplet injection technique for botulinum toxin type A jawline rejuvenation, using ultrasound and three-dimensional (3D) imaging for anatomical assessment rather than real-time injection guidance.

From September 2023 to February 2024, 36 individuals (4 males, 32 females) seeking improvement in jawline laxity were enrolled at the First Affiliated Hospital of Bengbu Medical University. In a split-face, self-controlled design, the left hemiface received the facial biomechanical injection technique (observation group) and the right hemiface received the microdroplet injection technique (control group), yielding 72 treated hemifaces (36 per group). Each hemiface received a total of 20 U of botulinum toxin type A: four 5-U boluses in the facial biomechanical group and twenty 1-U microdroplets in the control group. Ultrasound imaging and 3D deviation color maps were used to evaluate soft-tissue changes at baseline and 30 days, 60 days, and 90 days after treatment. Outcome measures included Cervicomental Angle Severity (CAS, primary endpoint), Global Aesthetic Improvement Scale (GAIS), Visual Analogue Scale (VAS) scores for pain, ultrasound-based soft-tissue thickness at a standardized mandibular point, and qualitative 3D color-map changes.

Both techniques improved CAS grades over time; however, the facial biomechanical injection technique produced greater improvement in CAS at 60 and 90 days compared with the microdroplet technique (P < 0.001). GAIS scores favored the facial biomechanical group at 30 days (P < 0.05). VAS scores during injection were significantly lower with the facial biomechanical technique (P < 0.001), reflecting better procedural comfort. Qualitative 3D deviation color maps and ultrasound measurements suggested a relative reduction in subcutaneous soft-tissue thickness along the mandibular margin in the facial biomechanical group, consistent with enhanced jawline definition. No serious adverse events occurred, and all treatment-related effects were transient and self-limited.

In this pilot split-face study, the facial biomechanical botulinum toxin type A injection technique provided greater medium-term improvement in jawline contour and patient-reported comfort than the microdroplet technique, with a similar short-term safety profile.

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