The attachments of facial muscles of the nasolabial region may be disrupted during the maxillary vestibular approach. Therefore, these muscles should be properly repositioned during closure to prevent disturbing esthetic changes. The important muscles are the nasalis group, the levator labii superioris alaeque nasi, the levator labii superioris, The levator anguli oris, and the orbicularis oris (Fig. 7-1).
The nasali group has transverse nasal and alar parts. It originates along the midline of the nasal dorsum and spreads laterally over the external aspect of the upper lateral cartilages where it intermingles with fibers of the levator labii superioris alaeque nasi and the levator labii superioris. Part of the transverse nasali inserts into the skin at the nasolabial groove, where it intermingles with fibers from the levator labii superioris alaeque nasi and oblique fibers of the orbicularis oris, forming a lateral nasal modiolus. Another portion of the transverse nasalis inserts onto the incisal crest and anterior nasal spine and is deeply in contact with the depressor septi muscle. The alar portion is ultimately reflected inward, forming the anterior floor of the nose.
Several muscle groups elevate the upper lip. The levator labii superioris alaeque nasi arises from the frontal process of the maxilla alongside the nose and passes obliquely in two segments. One segment inserts onto the lateral crus of the alar cartilage and skin of the nasalis muscle, depressor septi, and oblique bands of the orbicularis oris. The levator labii superioris arises from the infraorbital margin of the maxilla beneath the orbicularis oculi. It extends downward and medially, superficial to and intermingling with the orbicularis oris, beneath the skin of the ipsilateral lower philtral columns and the upper lip. The levator anguli oris muscle lies deep to the levator labii superioris and the zygomaticus muscle. It arises from the canine fossa of the maxilla and courses downward and medially to the commissure, where it intermingles with the fibers of the orbicularis oris muscle.
The orbicularis oris muscle consists of three distinct strata. Horizontal fibers extend from one commissure to the other, passing beneath the philtrum. Oblique bands extend from the commissures to the anteroinferior aspect of the nasal septal cartilage, anterior nasal spine, and floor of the nose. The incisal bands extend from the commissures deeply to insert onto the incisive fossa of the maxilla. All of these muscles and their investing fascia jointly contribute significantly to the position and configuration of the lateral nasal and labial regions.
The maxillary vestibular incision and the subperiosteal dissection attendant to this approach cut some of the muscular origins and strip the origins and insertions of most muscles from the bone (see Fig. 7-1), causing superolateral retraction of the tissue by the action of the zygomaticus muscles and the natural tendency for muscles to reattach in a shortened position. Lateral displacement of the nasal modiolus causes widening of the alar base with flaring of the alae from unopposed action of the dilator naris. This displacement causes deepening of the alar groove and splaying of the alar bases, nostrils, and nasal tip (Fig. 7-2). Loss of soft tissue fullness in the nasolabial region results in changes similar to those seen in the aging face: thinning and retraction of the upper lip, reduced vermilion exposure, and a more obtuse nasolabial angle. Downturning of the corners of the mouth may occur when the levators of the upper lip are detached from their origin, because the depressor of the mouth are then unopposed.
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