| boTulInuM ToxIn A | ARticle
place patients at risk of developing adverse sequelae if the toxin diffuses into the adjacent depressor labii inferioris. even when the appropriate dose is precisely injected, vigorous massaging of the area after the injection can displace the toxin into adjacent muscle fibres and cause similar adverse effects.
Chin puckering and deep mental crease A hyperkinetic mentalis can produce an involuntary localised dimpling or an overall puckering of the chin, creating convolutions of deep ridges and furrows while a person speaks or conveys a particular expression. for those who consciously or involuntarily crinkle their chin during animation, or even while at rest, these changes generally go undetected (Figure 5). Chin puckering can be a frustrating annoyance
when it occurs postoperatively as a secondary synkinesis of augmentation mentoplasty19
. As
not all the bony attachments of the muscle fibres of the mentalis can be repositioned exactly as they were before instillation of a chin implant, the contracting fibres of the mentalis become anomalously reattached to the mentum, producing an irregular crimping of the skin surface, either at rest or with each movement of the mentalis.
the contralateral side is probably more centrally located. for these patients, an alternative one‑point injection technique is more appropriate. This is accomplished by injecting 4–6 u onabotulinumtoxinA deeply into the centre of the mentum at the apex of the mental protuberance. It is imperative to avoid inadvertent diffusion of the toxin into any of the muscle fibres of the orbicularis oris, which can result in sphincter and motor movement irregularities. light massage will relieve the pain of injection. Vigorous massage will displace the toxin and cause it to diffuse, producing untoward sequelae.
dynamic wrinkling and
corrugations of the surface of the chin or concavity of a (labio) mental crease is produced by a hyperkinetic mentalis.
Outcomes Relaxing the hyperkinetic muscle fibres of the mentalis can reduce or eliminate involuntary convolutions and corrugations of the chin. A weakening of the mentalis can drop the anterior projection of the skin slightly downward, attenuating an already deep transverse labiomental crease and possibly rotating the lower lip slightly upward. When the transverse labiomental crease is exceptionally deep and resistant to treatment, elevating and effacing it with soft tissue fillers is
Functional anatomy Dynamic wrinkling and corrugations of the surface of the chin or concavity of a (labio)mental crease is produced by a hyperkinetic mentalis. The mentalis is a short, stout, conical, two‑bellied muscle that originates deeply to the depressor labii inferioris on the anterior aspect of the mandible, on either side of the midline at the level of the incisive fossa and root of the lower lateral incisors. It travels downward, converging its muscle bellies toward the midline to insert with multiple fibrous attachments into the skin of the apex of the chin on either side of the frenulum of the lower lip. Some of its fibres interdigitate superiorly with fibres of the orbicularis oris and laterally with the fibres of the depressor labii inferioris. The mentalis assists other reciprocating synergistic
perioral muscles to depress, protrude and evert the lower lip during drinking, eating and speaking. With age, the loss of dermal collagen, elasticity and soft tissue support, as well as diminution in the bone structure and subcutaneous fat, can enhance the appearance of uncontrollable chin convolutions and dimpling. It is often advisable to treat both the presence of marionette lines and chin dimpling during the same session.
Dosing A hyperactive mentalis can be relaxed by injecting 3–4 u of onabotulinumtoxinA deeply into the muscle at one point on each side of the midline of the mentum at the apex of its protuberance. This two‑point injection technique is appropriate if the patient has a vertical mental cleft or a widely shaped, square chin. If the patient has a narrow, rounded or pointed chin, the insertion of the mentalis into the undersurface of the skin with its paired muscle belly of
prime-journal.com | July 2011
Figure 5 63-year-old woman at rest before (A) 4 U of onabotulinumtoxin A were injected into her mentalis. Note the crimping of the chin and deep mental crease at rest and while pronouncing words containing the letter ‘F’ (B). Same patient at rest (C) and animating 3 weeks after (D) treatment. Note the reduction of chin crimping and effacement of the mental crease
an advisable alternative. Deeply placed injections of soft tissue fillers across the anterior aspect of the mentum will recontour and rejuvenate the chin, and injections of botulinum toxin into the mentalis will actively sustain and prolong the improvement. for those who have a distorted chin as a result of a
previous augmentation mentoplasty, injections of botulinum toxin A can produce a softening and relaxing effect. The addition of a soft tissue filler will augment and prolong the corrective effects produced by the toxin.
Complications When injections are placed too high on the lower lip, the orbicularis oris and even the depressor labii inferioris can be weakened, particularly when using the two‑point injection technique. Diffusion of the toxin into the depressor labii inferioris and orbicularis oris also can
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