Masseter Muscle Morphometric Changes After Botulinum Toxin Type A Injection: A Prospective 3-Month Study

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Anatomy

Background:

• Myofascial pain of the masticatory muscles, often linked to bruxism, significantly impacts quality of life.
• Botulinum toxin type A (BoNT-A) is an adjunctive treatment for refractory cases, but its effect on masseter muscle size over time is not fully understood.

Purpose of the Study:

• To investigate the temporal pattern of masseter muscle morphometric changes after BoNT-A injection using 3D imaging.
• To establish a 3D imaging and morphometric methodology for assessing BoNT-A treatment effects.

Main Methods:

• Prospective observational pilot study involving 11 adults with myofascial pain and bruxism.
• BoNT-A (100 U total) administered to masseter and temporalis muscles.
• Structured-light 3D facial scans acquired at baseline, 1 month, and 3 months post-injection.
• Standardized masseter region of interest defined using cutaneous landmarks.

Main Results:

• 3D scanning demonstrated significant reductions in bilateral masseter surface displacement at 1 and 3 months post-injection compared to baseline.
• Measurement precision was high, with excellent repeatability and landmark reliability.
• Changes in masseter size were bilaterally symmetric and occurred within the first month.

Conclusions:

• 3D structured-light scanning is a reliable method for detecting subtle facial contour changes following BoNT-A injections.
• This imaging technique can complement clinical and patient-reported outcomes in assessing BoNT-A treatment.
• Further studies with larger sample sizes are needed to confirm these findings.