The facial artery and vein are usually not encountered during the mandibular vestibular approach unless dissection through the periosteum occurs in the region of the mandibular anterogonial notch.
The facial artery arises from the external carotid artery in the carotid triangle of the neck. At or close to its origin, it is crossed by the posterior belly of the digastric muscle, the stylohyoid muscles, and the hypoglossal nerve. In the submandibular triangle, the facial artery ascends deep to the submandibular gland, grooving its deep and superior aspect, and passes superficially to reach the inferior border of the mandible. As it crosses the mandible at the anterior border of the masseter muscle, the artery is covered on its superficial surface by skin and platysma muscle, and its pulsation can be felt at this location.
The facial vein is the drainage vein of the angular and ultimately the labial vessels. It is usually located more posterior and superficial to the artery. Of surgical significance, however, is the fact that the facial artery and vein are close to the mandible in the region of the inferior border. The only structure separating them from the bone is the periosteum (Fig. 8-2).
The only muscle of facial expression that is important from a surgical standpoint when using the mandibular vestibular approach is the mentalis muscle. All of the other muscles of facial expression are stripped from the mandible by subperiosteal dissection and are readily reattached with soft tissue closure. The mentalis muscle is unique, however, in that it is the only elevator of the lower lip and chin. If this muscle is not properly repositioned during closure, the chin will "droop" and the lower lip will take on a lifeless, sagging appearance, exposing more lower teeth.
The mentalis muscle are paired, small, conical muscles arising from the mandible, beginning at the midroot level of the lower incisor teeth and continuing inferiorly to a point below the apices. They are separated from one another by a firm septum and adipose tissue.
At the inferior portion of its origin, the mentalis muscle attaches lateral to the pogonial trigone. The fibers of this muscle pass from their origin inferiorly, inserting into the skin of the chin at the soft tissue chin prominence (Fig. 8-3). The most superior fibers are the shortest and pass almost horizontally into the skin of the upper chin. The lower fibers are the longest and pass obliquely or vertically to the skin at the lower part of the chin. The origin of the mentalis muscle determines the depth of the labial sulcus in the anterior portion of the mouth. The mentalis muscle is innervated by the marginal mandibular branch of the facial nerve._
FIGURE 8- 3 Anatomic dissection showing cross section of soft tissues of the chin. Note the direction of the mentalis muscle fibers.
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