Observation and Potential Mechanisms of Mentalis Myomodulation by Hyaluronic Acid Filler in the Treatment of Microgenia.

Abstract

Chin retrusion is commonly treated with injectables to improve proportion and attractiveness.1 For example, novel hyaluronic acid fillers with high elastic modulus (G’) and enhanced cohesivity can be used for safe and effective chin enhancement,2 with reduced downtime and a lower risk of complications compared with surgery.3 Mentalis muscle hyperactivity is frequently associated with microgenia,1 with excessive contraction during lip closure. Treatment of microgenia results in reductions of Legan’s angle, the interlabial gap, lower perioral wrinkles, and chin skin dimpling and improvements in lower facial contour, chin projection, and mentolabial fold. Recently, de Maio4 reinvigorated the concept of myomodulation by fillers, proposing that the plane and depth of injection relative to the muscle can affect function. He asserted that filler injection beneath the muscle increases muscular function, whereas injection above the muscle reduces function.4 Across decades of experience, we have observed that treating microgenia with filler below the mentalis muscle consistently and substantially reduces mentalis hyperactivity without any use of neuromodulators (Figs. 1 and 2). [See Figure, Supplemental Digital Content 1, which displays profile views before and after treatment of microgenia with hyaluronic acid filler. (Right) Frontal projection of the chin is shown following filler injection, demonstrating that a relatively small volume change (1 ml) can have a significant effect on myomodulation, https://links.lww.com/PRS/E464.] This suggests that the mechanism of myomodulation is more complicated than simply the plane of placement.Fig. 1.: Pretreatment of microgenia. A 26-year-old woman with severe chin retrusion rated grade 3 on the Allergan Chin Retrusion Scale. Pouting of the lower lip demonstrates maximum mentalis contraction with signs of skin dimpling, deepening of the mentolabial fold, and shortening of the chin.Fig. 2.: Mentalis myomodulation and aesthetic improvement, 7 days after treatment of microgenia with hyaluronic acid filler without neuromodulators. A significant down-regulating myomodulation of mentalis at maximum pouting exertion was demonstrated with an injection of 1-ml bolus of VYC-25 (Allergan, Dublin, Ireland) at the supraperiosteal plane beneath the mentalis muscle via a 27-gauge, half-inch needle, between the pogonion and mentum, after 5 seconds of negative pressure without flashback.The underlying mechanisms of mentalis myomodulation with fillers remain incompletely elucidated. We propose the following synergistic mechanisms (Fig. 3):Fig. 3.: Proposed mechanisms of myomodulation for mentalis. Following filler injection, the angle of the vector of mentalis contraction is changed from cranial-ventral to cranial-dorsal, creating a more efficient angle to support the lower lip. The mentalis muscle is also stretched; based on the Frank-Starling mechanism, the resulting length of muscle sarcomeres is no longer within the optimal range. The angle of the mentalis muscle vector is altered to a more cranial-dorsal direction, thereby offering improved support to the lower orbicularis oris during mouth closure and protrusion (pouting). By changing this angle, the mentalis is no longer required to contract to the same degree to affect its structural support of the orbicularis oris. Based on the Frank-Starling law of the length-tension relationship of striated muscles,5 filler placement results in muscle stretching, thus increasing sarcomere length. In the mentalis, the new resting length may be stretched beyond the optimal range, resulting in higher tension of the muscle fiber and hence reduced function. By contrast, in the zygomatic muscles, myomodulation following hyaluronic acid filler deposition may have the opposite effect. Here, placement of filler beneath the muscle (thereby reconstructing soft-tissue support as it was in youth) returns the length-tension relationship from low back to the optimal range, resulting in increased muscular function. Other common chin techniques involve injection of filler under the dermis with a cannula,4 potentially placing hyaluronic acid intramuscularly, resulting in an intramuscular obstacle that reduces mentalis activity. Increased soft-tissue structural support results in mild myomodulation of other lower perioral muscles. There is currently no validated mentalis hyperactivity scale for quantifying myomodulation for research purposes. We propose the creation of a Surface Electromyography Mentalis Index based on maximum lower labial protrusion–to–at rest ratio, using the root mean sum values of the voltage potentials obtained through electromyography. Treatment of microgenia using a high G’ hyaluronic acid filler in the supraperiosteal plane can improve facial profile and contour.2 We observe a substantial suppressive myomodulation of mentalis activity in patients undergoing such treatment, even in the absence of neuromodulator therapy. Various distinct mechanisms could be responsible. Further studies are required to differentiate these possibilities and assess the extent of their roles. ACKNOWLEDGMENTS The authors would like to thank Timothy Ryder, D.Phil., from Biological Communications Limited, for medical writing and editorial assistance, supported by a publication grant from Allergan. All products and equipment were supplied by the senior author (C.C.), with no industry sponsorship. DISCLOSURE Dr. Cheng has been a consultant and lecturer for Allergan, Merz, Solta, and Galderma. Ms. Cheng reports no financial interest to disclose.