Modiolus (mouth)

Last revised by Daniel J Bell on 28 Jul 2022

The modiolus (plural: modioli), also known as the modiolus anguli oris or commissural modiolus, is a small fibromuscular structure at the corner of the mouth where fibers from multiple facial muscles converge, and helps coordinate the action of these muscles.

The convergence of the fibers of nine facial muscles at the oral commissure in combination with fascial components forms a small firm mobile fibromuscular mass on each side of the mouth called the modiolus. The modiolus approximates to a truncated conical shape up to 1 cm in depth, which reaches up to 2 cm superior, lateral and inferior to the oral commissures. Its rounded base abuts and is inseparable from the buccal mucosa and its superficial aspect is closely adherent to the dermis ~1 cm lateral to the point at which the upper and lower lips join (commissure), close to the second upper premolar tooth 1,3-5,8.

The facial muscles forming the modiolus are zygomaticus major, orbicularis oris, buccinator, levator anguli oris, mentalis, depressor labii inferioris, depressor anguli oris, platysma and risorius muscles. The fascial components encompass the superficial musculoaponeurotic system, junction between superficial and deep facial fascias, deep facial fascia and parotid fascia 1,3-5.

The modiolus acts as a common insertion point for multiple facial muscles so that the simultaneous action of these muscles and their effects on the cheeks, chin, lips, commissures, vestibule of the mouth and both jaws may be consolidated. This results in finely controlled actions so that phonation, shouting, sobbing, deglutition, drinking, mastication, etc., may all be coordinated in their execution 3,5,7.

The modiolus has been described on CT and MRI as a small relatively poorly circumscribed structure lying at its expected anatomical location just lateral to the angle of the mouth 4,8.

The Latin word, "modiolus" means hub of a wheel, and is well-named, as in both the cochlea and at the angle of the mouth, the two modioli act as central foci around which other structures converge. Modiolus is a diminutive form of "modius" meaning a measure of grain (one sixth of a bushel) 6,9,10.

The modiolus is an important structure for the practitioners of cosmetic dentistry. The facial muscles that insert into the modiolus are key to the aesthetics of the lips coming together as the commissures at the corners of the mouth. The levator (predominantly zygomaticus major and levator anguli oris muscles) and depressor muscles (predominantly depressor anguli oris and platysma muscles) oppose one another across the modiolus 3,7.

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