A single-blind randomized prospective cohort study was conducted with an assessment of efficacy and safety according to the clinical parameters, ultrasound control and electromyographic (EMG) assessment of changes in the function of the mentalis muscles during structural and anatomical treatment of chin retrusion with hyaluronic acid filler.

MATERIAL AND METHODS

10 healthy volunteers (9 females and 1 male, average age 44.6 years) with moderate and severe chin retrusion (Grade 2-5 on the Five-point photonumeric Croma Chin Projection Assessment Scale — FCPAS) were treated with the dermal filler in the right and left chin area (supraperiostally/submuscularly (n=5) or subcutaneously/supramuscularly (n=5) relative to the mentalis muscles). Clinical, ultrasound and EMG assessments were performed before and 30 days after injections.

RESULTS

After the filler injection, full regression of chin retrusion (Grade 1) was achieved in 70% of the participants, significant decrease in retrusion (Grade 2) was reached in 30% of subjects. Improvement in the appearance of the chin area was noted by 100% of the participants (+2 grades and +1 grade on the Global Aesthetic Improvement Scale (GAIS) in 80% and 20% of the participants, respectively). The responder rates according to clinical assessment scales were 90% based on the Face Appearance Self-Assessment Scale (FACE-Q), 100% on FCPAS and 100% on GAIS. After the filler injection, an assessment of the mentalis muscles status at rest and with voluntary maximum contraction (cutaneous EMG), as well as with electrical stimulation (stimulation EMG) showed no significant changes in the amplitude, duration and area of the M responses of both mentalis muscles and the amplitude of the bioelectric activity of the mentalis muscles with voluntary contraction. In 3 (30%) participants with initial constant low-amplitude tonic activity of the right and left mentalis muscles in a state of mimic rest (an indirect sign of the mentalis muscles hypertonicity), a significant decrease in this indicator (n=1) and a complete regression of this type of muscle activity (n=2) were recorded, which indirectly indicated normalization of the mentalis muscles tone. The data suggested the presence of a probable effect of mechanical myomodulation after the chin treatment with dermal filler. The effects of superficial (above the muscle) and deep (under the muscle) injection of the dermal filler did not significantly differ in terms of clinical scales and dynamics of EMG parameters of the mentalis muscles. A favorable safety profile was noted.

CONCLUSION

The injection of a dermal filler according to the proposed protocol to restore/create volume of the chin is clinically highly effective and does not disrupt the voluntary activity of the mentalis muscles. The effect of selective myomodulation was established in 30% of patients. The feature of this effect is the action on tone, but not on the function of facial muscles, and the presence of the necessary condition in the form of initial muscle hypertonicity in a muscle resting state. Further studies with objective methods of imaging diagnostics of the structure and function of facial muscles are needed to continue studying the effect of myomodulation after injection of dermal fillers.

Keywords. myomodulation, dermal filler, hyaluronic acid, electromyography, mentalis muscles, facial muscles hypertonicity