Treatment of the midface with botulinum toxin

Introduction

The midface is the area of the face between the glabella and the subnasal region. It has a complex muscular anatomy, demanding full anatomic knowledge and a precise injection technique. The small muscles in this area are important for social interaction as they are involved in critical functions that express emotions. These include the orbital portion of the orbicularis oculi, zygomaticus major (ZM) and minor, levator of the upper lip (LLS) and ala of the nose (LLSAN), LLS, nasalis, depressor septi nasi (DSN), risorius, and buccinator, which are functionally integrated through the superficial muscular aponeurotic system (SMAS) ( Fig. 20.1 ).

Although the combination of botulinum toxin and fillers provides the best results and greater patient satisfaction, neuromodulators alone can prove to be a useful tool in this area. Attention should be paid to the correspondence of the units of onabotulinumtoxinA, incobotulinumtoxinA, abobotulinumtoxinA, and prabotulinumtoxin A (see Chapter 11 and Table 20.1 ).

“Bunny” lines

“Bunny” lines are wrinkles produced at the lateral nasal walls that radiate from the medial canthal region and run inferomedially on each side of the nose. They result primarily from contraction of the superior nasalis (pars transversalis) fibers but may have accessory action from the LLSAN, inferomedial orbicularis oculi, and superficial lateral fibers of the procerus.

Bunny lines appear when patients smile, speak, or frown, but they can also become prominent after the glabellar lines or crow’s feet have been treated with neuromodulators without concomitant blockage of the nasalis muscle.

Injection sites and dosage

When the nasalis is the only muscle responsible for the wrinkles, intradermal injections placed high on the lateral nasal sidewall and well medial to the nasolabial sulcus (to avoid inadvertent LLSAN weakness) show good results. If the procerus or the orbicularis oculi plays a role in the formation of bunny lines, these muscles should be treated. Dose ranges have been reported as 2 to 8 U for onabotulinumtoxinA on each side or 10 to 20 U for abobotulinumtoxinA. Fig. 20.2 shows the site of injection and a patient before and after the bunny lines treatment. See Video 20.1 .

Gummy smile

A “gummy smile” is characterized by excessive exposure of the gums. LLSAN originates from the medial maxilla before bifurcation and insertion into the medial orbicularis oris and nasal ala. Its contraction works with the LLS and DSN to elevate the upper central lip. Hyperactivity of these muscles may lead to excessive elevation of the upper lip on smiling, revealing the upper gums.

Treatment of this muscle can also be used to attenuate the medial nasolabial fold (NLF) in patients with primary muscular etiology (young patients with mild-to-moderate NLF). With the latter indication, it is important to remember that lip lengthening will occur concomitantly; therefore, it is prudent not to use neuromodulators for this purpose in patients without a gummy smile.

The visibility of the posterior gum is caused by hypercontraction of the ZM. In this case, treatment of the gummy smile should address the point where LLSAN, LLS, and ZM converge laterally to the lateral alar base. This lengthens the upper lip to reduce the full incisor and upper gum show.