BIOANATOMY AND BIOMECHANICS
The lips and perioral region are central features of appearance. The lips also provide oral competence at rest and during mastication. They are central to facial expression and are sensory organs both for food and personal contact. The lips have rich vasculature and sensory innervation.
The perioral region is bounded by the nasolabial folds laterally and superiorly and by the mental crease of the chin inferiorly. The lips are suspended only by muscles and the fibrous tissues of the modiolus at each oral commissure. For that reason, the lips and the oral commissures are mobile free margins, and reconstruction of the perioral region requires meticulous planning to direct tension in appropriate vectors. Pull on the upper lip margin creates the appearance of a “hair lip,” distortion of the lateral oral commissure can lead either to drooling or a sneer, and depression and/or eversion of the lower lip can lead to a loss of oral competence.
The upper lip is often divided into subunits (Fig. 9.1).1 The philtral subunit lies centrally and its lateral borders are the medial borders of the lateral subunits. The lateral subunits of the upper lip are bounded by the vermillion, the philtrum, the inferior margin of the ala, and the nasolabial fold. A small triangular extension of the lip that lies lateral to the ala and medial to the superiormost nasolabial fold is known as the apical triangle. Although small in size, it provides a recognizable declination between the lip, nose, and cheek, and it should be maintained as an aesthetic marker where feasible.
Lip subunits: The upper lip is divided into a philtral subunit and two lateral subunits. The lateral subunits each contain an apical or “sacred” triangle lateral to nasal ala. Maintaining the integrity of the philtrum, apical triangle, and nasolabial folds are goals of upper lip reconstruction
The inner margin of the lip is the mucosa of the mouth. The wet mucosa becomes vermillion as it exits the oral aperture and forms the red lip. Beneath the mucosa is a submucosal layer rich in minor salivary glands. The vermillion itself lies directly on a circumoral band of orbicularis oris and the underlying musculature has a rich vascular supply. This, coupled with a lack of keratinization, leads to the red color of the lip. The bulk of the lip is created by the orbicularis oris that forms concentric rings and gives the lips their shape, definition, and function.
Motor innervation of the upper lip is from a plexus of nerves supplied by the zygomatic, buccal, marginal mandibular, and cervical branches of the facial nerve. These nerves are highly anastomosed and deeply seated. Hence neural injury affecting perioral function is rare with the one exception being damage to the marginal mandibular nerve as ...