ARticle | boTulInuM ToxIn A | depressor labii inferioris, depressor anguli oris, mentalis,
and platysma), a multilamellar, compound sphincter (i.e. the orbicularis oris), and the buccinator 2
. The orbicularis oris is not a simple sphincter like the
orbicularis oculi. It is comprised of multiple lamellae of muscle fibres traversing in different directions around the mouth. It is composed of muscle fibres from the labial levators and depressors that insert into the lips, and of fibres intrinsic to the lips. The orbicularis oris comprises four independent quadrants (right, left, upper, lower) of striated muscle, each containing a larger pars peripheralis and smaller pars marginalis (i.e. eight segments total). These right and left anatomic parts are juxtaposed and roughly correspond to the exterior anatomic delineations of the free or unattached portion of the lip. The smaller pars marginalis corresponds to the vermillion of the lip and the larger pars peripheralis corresponds to the remainder of the free unattached portion of the cutaneous lip. Most of the muscle fibres in the pars peripheralis are
thought to originate within the modiolus, as a direct continuation of the many modiolar muscles. A considerable number of these muscle fibres also originate from the buccinator, which reinforces the complex of deeper intrinsic muscle fibres of the orbicularis oris. Muscle fibres of the buccinator pass anteriorly and decussate at the angles of the mouth, crisscrossing as they continue to their insertions in the upper and lower lips. Those fibres of the buccinator that arise from the area of the maxilla pass inferiorly around the angle of the mouth and insert into the lower lip. The uppermost and lowermost muscle fibres of the buccinator traverse across the lips from side to side in a purse‑string fashion without decussating. Superficial to the deep intrinsic muscle fibres of the
zygomaticus major, and the depressor labii inferioris. There are additional slips of muscle fibres of the orbicularis oris, which attach to the alveolar process of the maxilla, the nasolabial sulcus, and the nasal ala and septum superiorly, and the alveolar process of the mandible inferiorly, anchoring the orbicularis oris in place as low as the mentolabial sulcus. The function of the orbicularis oris is to close the mouth
by approximating the lips. The superficial interdigitating muscle fibres of the orbicularis oris shape the lips in different configurations and either bring the lips together, or protrude the lips and the corners of the mouth. Direct labial tractors are levators and depressors that
the orbicularis oris is not a
simple sphincter like the orbicularis oculi. it is comprised of multiple
lamellae of muscle fibres traversing in different directions around the mouth.
enter directly into the tissue of the lips without passing and interlacing with the modiolus. When these muscles contract, they exert a vertical pull at right angles on the buccal aperture. The direct labial tractors interlace fibres into a continuous sheet of muscle superficial to the intrinsic fibres of the pars peripheralis and pars marginalis as they travel through the substance of the free lip and attach to the undersurface of the dermis and mucous membrane. The buccinator, on the other hand, is not a typical mimetic muscle of the face. It is a deep, thin, quadrilateral muscle that spans the void between the maxilla and mandible, and forms the deep muscular boundaries of the cheek. The muscle fibres of the buccinator traverse forward to the modiolus near the angle of the mouth to become continuous with the intrinsic fibres of the orbicularis oris. The upper fibres of the buccinator continue as muscle fibres of the lower lip and lower fibres
buccinator/orbicularis oris is another stratum formed on either side of the mouth by the levator anguli oris and depressor anguli oris. These fibres crisscross at the corners of the mouth and continue away from each other. The fibres of the levator anguli oris continue inferiorly into the lower lip and insert into the skin near the midline of the lower lip. The muscle fibres of the depressor anguli oris follow the same pattern in the upper lip, inserting into the skin at the midline. Reinforcing these superficial transverse fibres of the upper and lower lips are interdigitating oblique muscle fibres from the levator labii superioris, the
Figure 1 72-year-old with deep peribuccal rhytides and moderate solar elastosis of the face and lips at rest: (A) before treatment, (B) 1 month after. Note the persistence of the peribuccal rhytides 1 month after a treatment of onabotulinumtoxin A, because the bulk of her wrinkles were age-related and of the static type
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of the buccinator merge with those of the upper lip without decussating and then insert into the mucous membrane and skin of the upper and lower lips. The buccinator’s function is to keep the cheek against the gums and teeth during mastication. It also keeps food in between the teeth and prevents it from becoming lodged between the teeth and cheek. on either side of and just lateral to the oral commissures,
a number of mimetic facial muscles converge to a centralised location where they interlace muscle fibres to form a dense, compact, mobile fibromuscular mass called the modiolus. The base of the modiolus (basis moduli) is adjacent and adherent to the buccal mucosa. It is located approximately 2 cm lateral to the centre of the oral commissure and measures approximately 2 cm above
July 2011 |
prime-journal.com
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