Introduction

Botulinum toxin (BoNT) chemodenervation has revolutionized cosmetic surgery. Botulinum toxin treatments complement, and in some cases preclude, traditional invasive surgical procedures. Chemodenervation with BoNT is the cornerstone of minimally invasive upper facial rejuvenation. The safety and efficacy of BoNT in the upper face have been extensively documented. However, BoNT use in the lower face is less well established in well-designed clinical trials.

In the lower face, treatment strategies are traditionally focused on volume restoration; however, controlling hypermobility is also essential. Botulinum toxin is used as monotherapy or as an adjunct to other procedures in lower face rejuvenation. Treatment options include dermal fillers, chemical peels, laser resurfacing, non-invasive tightening modalities, and facelifts (with or without chin / pre-jowl implants) (Table 18.1). Although rhytidectomy can reduce the nasolabial and labiomandibular folds, this procedure cannot enhance the lip region owing to its anatomy. The perioral tissues include supportive ligaments that must be preserved, and there is a high risk of motor innervation injury affecting the perioral area through a facelift. This is due to the buccal and marginal mandibular branches of the facial nerve, which course superficially, ramify extensively, and are challenging to identify. Motor innervation injury leads to muscle weakness. A combination treatment with BoNT and fillers in the lower face has emerged as the gold standard because it addresses a broader spectrum of facial aging changes, without the need for surgery.

This chapter aims to address the use of BoNT in the orbicularis oris, mentalis, and depressor anguli oris (DAO) muscles, as they directly affect the appearance of the perioral and chin regions.

Anatomy

The perioral region, also called the lip unit, is one of the facial cosmetic units. It extends from the base of the nose (subnasal) superiorly to the nasolabial folds laterally, and to the labiomental crease inferiorly. The free edges of the vermilion borders subdivide this region into the upper lip and lower lip. Below the labiomental crease is another facial unit, the chin.

The upper lip is subdivided into the cutaneous upper lip, the vermilion upper lip, and the philtrum. The lower lip is subdivided into the cutaneous lower lip and the vermilion lower lip.

The musculature of the perioral and chin area is complex and includes the orbicularis oris, risorius, DAO, zygomaticus major, zygomaticus minor, levator anguli oris, levator labii superioris, levator labii superioris alaeque nasi (LLSAN), depressor labii inferioris, mentalis, and the platysma (Fig. 18.1).

Figure 18.1 Musculature of the lower face: a) levator labii superioris alaeque nasi, b) levator labii superioris, c) zygomaticus minor, d)zygomaticus major, e) levator anguli oris, f) orbicularis oris, g) risorius, h) DAO, i) depressor labii inferioris, and j) mentalis.

The orbicularis oris muscle origins are in the deep surface of the perioral skin, the angle of the mouth, superiorly the median plane of the maxilla, and inferiorly the mandible. This muscle inserts into the mucous membrane of lips. It is innervated by the buccal and mandibular branches of the facial nerve. Its tonus closes the rima oris; its phasic contraction compresses and protrudes the lips, aiding mastication, expression, phonation, and the actions of whistling, sucking, and kissing. Additionally, when blowing this muscle has a role resisting distension. The orbicularis oris muscle is necessary for correct speech and allows for enunciation of the letters F, M, O, and P.

The mentalis muscle originates in the body of the mandible and inserts into the orbicularis oris muscle and the skin of the chin. It elevates and protrudes the lower lip, is important for drinking, and elevates the skin of the chin when showing doubt. The mentalis is innervated by the mandibular branch of the facial nerve.

The depressor anguli oris is shaped like a triangle with the vertex located at the angle of the mouth. DAO arises from the oblique line on the anterior mandible. Its fibers blend with the orbicularis oris and are inserted into the corner of mouth. The marginal mandibular branch of the facial nerve innervates this muscle. Its main action is pulling the angle of the mouth inferiorly and laterally.

Perioral and chin aging

Aging of the perioral and chin regions is characterized by radial perioral rhytides (so called smokers’ lines or lipstick lines), decrease in vermilion fullness, inversion of the vermilion, downward turn of the oral commissures, lengthened appearance of the cutaneous portion of the upper lip, pre-jowl notch or sulcus, and chin dimpling. Additionally prominence of the labiomandibular (marionette lines), labiomental, and nasolabial folds can occur (Fig. 18.2A,B).

Figure 18.2 Some aging perioral and chin areas characteristics: a – prominence of the nasolabial folds, b – marionette line, c – radial perioral rhytides, d – pre-jowl sulcus, e – vermilion atrophy, f – prominence of the labiomental folds. Part (A) shows a, c and d; part (B) shows a, b, c, e and f.