The lips cover more than the area of the red part of the mouth. They also include the skin adjacent to the red part of the mouth. It must be considered as an anatomic unit with extensions superior to the nose and inferior to the chin (Salasche and Bernstein 1988). Perfect lip
Fig. 5.35 Frontal (a) and lateral view (b) on landmarks of the upper lip
structure includes a visible white or transition line between the mucosa and skin, a "V" shaped Cupid's bow, fulfilled medial tubercle and vermillion, and ascendant line in the oral commissures. The ratio between the upper and lower lips, at golden proportions, is 1:1.618.
A very important topographic landmark is the philtrum. The midpoint of the upper cutaneous lip is highlighted by the two vertically oriented ridges of the philtrum. The Cupid's bow is the concavity at the base of the philtrum (Fig. 5.35). It is also very important to take into account the surroundings of the lips, which are the labio-mental and nasolabial lines. If too deep, these lines may give an older appearance.
The skin of the upper lip is very thin and lacks subcutaneous fat. The lack of additional support at this level and excess of muscular movement may lead to the breakdown of the perioral area, producing wrinkling.
The major muscle of the lips is the orbicularis oris muscle. It has circumferential fibers that are responsible for the sphincter function of the mouth. There are circumoral muscles, which are intimately associated with the orbicularis oris. These muscles elevate, depress, and retract the lips, producing complex movements during normal function. The levators lie from medial to lateral: the labii superioris alaeque nasi levator, the labii superioris levator, the zygomatic minor and major, and the risorius muscles. The depressors include the depressor anguli oris, the depressor labii inferioris, and the mentalis muscles.
Sensory innervation of the upper lip is provided by the infraorbital nerve. The lower lip is innervated by the mental nerve. The motor innervation of the orbicularis oris is provided by the buccal branches of the facial nerve. The muscles that act around the mouth are either innervated by the buccal or the marginal mandibular branches of the facial nerve.
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