7: The Head by Regions

Chapter 7imageThe Head by Regions

1 The Face and Scalp

The face is that part of the head visible in a frontal view, that is, all that is anterior to the external ears and all that lies between the hairline and the chin. Clustered in this region are the various facial openings and their associated sensory structures.

The scalp covers the forehead, the superior aspect of the cranial vault, and the occipital region above the superior nuchal line. Laterally, the scalp blends in with the temporal area.

REGIONS OF THE FACE

The facial region may be subdivided into a number of areas (Figure 7-1): (1) the forehead, extending from the eyebrows to the hairline; (2) the temples or temporal area anterior to the ears; (3) the orbital area containing the eye and covered by the eyelids; (4) the external nose; (5) the zygomatic (malar) area (prominence of the cheek); (6) the mouth and lips; (7) the cheeks; (8) the chin; and (9) the external ear.

SENSORY (CUTANEOUS) NERVES OF THE FACE

The facial cutaneous nerve supply is principally derived from the trigeminal nerve (cranial nerve V) (Figure 7-2). Within the skull, the trigeminal nerve divides into three parts: (1) the ophthalmic nerve (cranial nerve V-1), a sensory nerve associated mainly with the orbit and its contents; (2) the maxillary nerve (cranial nerve V-2), a sensory nerve associated with the nasomaxillary complex; and (3) the mandibular nerve (cranial nerve V-3), a sensory and motor nerve associated with the lower jaw and the muscles of mastication. Only the mandibular nerve contains motor as well as sensory fibers. Each division of the trigeminal nerve contributes sensory cutaneous branches to the face.

Facial Branches of the Mandibular Nerve

The cutaneous contribution of cranial nerve V-3 to the face is fairly widespread, ranging from the temples to the chin.

Buccal Branch of Cranial Nerve V-3

The buccal branch of cranial nerve V-3 appears on the face from under the cover of the ramus of the mandible. It spreads over the cheek and conveys sensation from the skin and mucous membrane of the cheek. In addition, it conveys sensory information from the vestibular (buccal) gingiva of the mandibular molars.

ARTERIES OF THE FACE

The face is richly supplied with blood from various arteries, and the terminal branches of these various arteries anastomose freely (Figure 7-3). The entire blood supply is derived from either the internal or the external carotid arteries. Their facial branches travel as companion arteries to the sensory facial nerves described previously and, in general, carry the same names as the facial sensory nerves.

Facial Branches of the Ophthalmic Artery

The facial branches arise directly or indirectly from the ophthalmic artery of the orbit and stream out of the orbit as five branches.

Facial Branches of the Superficial Temporal Artery

The superficial temporal artery is a terminal branch of the external carotid artery that emerges onto the face between the jaw joint and the ear to ascend on the scalp. Just below the ear, it sends a branch forward as the transverse facial artery immediately below the zygomatic arch. It accompanies the auriculotemporal nerve on the side of the head.

VEINS OF THE FACE

The veins of the face follow somewhat the same pattern of distribution as the arterial supply, except for a few small but important differences (see Figures 7-3 and 7-4). Veins generally show more variability in their distribution than do arteries.

Veins that Accompany Cutaneous Nerves and Arteries

For each of the named arteries described previously as facial branches of the ophthalmic artery or maxillary artery, there are corresponding veins of the same name that flow in the opposite direction. The veins of the forehead, scalp, and upper lid flow to the superior ophthalmic vein in the orbit; the veins of the upper lip, lateral nose, and lower lid flow via the infraorbital vein to the pterygoid plexus of veins in the infratemporal region.

MUSCLES OF THE FACE

The muscles of the face, or muscles of facial expression, are derived from the second branchial arch and are supplied by the cranial nerve of the second arch, the facial nerve (cranial nerve VII) (Figure 7-5 and Table 7-1). The muscles of the scalp and the platysma muscle of the neck belong to the same muscle group.

In general, the muscles are found within the superficial fascia around the facial orifices. They perform two functions: (1) as dilators and sphincters they control the openings of the orifices, and (2) as movers of overlying skin they reflect the various facial expressions.

Most facial muscles originate from bone or from fascia, and all insert into the skin of the face. Upon contraction, therefore, they move the facial skin into various attitudes that reflect emotions, such as smiling, grinning, frowning, and forehead wrinkling of puzzlement. The muscles are grouped by regions.

Mouth

Cheek

Buccinator

MOTOR NERVES OF THE FACE: THE FACIAL NERVE

The facial nerve exits from the skull through the stylomastoid foramen at the base of the skull (see Figure 7-2). It passes inferiorly and anteriorly for several millimeters, enters the substance of the parotid gland, and here breaks up into five main groups of branches that radiate from the anterior margin of the gland and travel to various areas of the face.

Sensory Nerve Communications

The motor branches of the facial nerve communicate with cutaneous branches of the trigeminal nerve on the face and cutaneous branches of spinal nerves in the neck. It is likely that these communications represent sensory proprioceptive contributions, which distribute with the facial nerve branches to the various facial muscles.

CLINICAL NOTES

Facial Paralysis

Damage to the facial nerve results in some form of facial paralysis (Figure 7-7). The type of paralysis is dependent upon where the lesion (damage) occurs.

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Figure 7-7 Facial paralysis resulting from damage to lower motor neurons of the facial nerve (cranial nerve VII).

(Redrawn from Wilson-Pauwels L, Akesson EJ, Stewart PA: Cranial Nerves: Anatomy and Clinical Comments. Toronto, 1998, BC Decker).

FEATURES OF THE FACE

Lips (Labia)

The upper and lower lips surround the mouth, or entrance to the oral cavity (Figure 7-8). The upper lip lies between the nose above and the opening of the mouth below. Laterally, the lips are separated from the cheeks by the nasolabial groove, a furrow extending from the ala of the nose to approximately 1 cm lateral to the angle of the mouth. The philtrum is a wide (6 to 7 mm), shallow trough extending from the nose to the red (vermilion) border of the upper lip. Superiorly, the philtrum ends at the columella, the fleshy external partition between the nostrils.

The lower lip lies between the mouth above and the labiomental groove below. This groove separates the lower lip from the chin below.

The upper and lower lips are continuous at the angles of the mouth and blend laterally with the cheeks.

Labial Frenula

These are folds of mucous membrane that run in the midline of the upper lip and the lower lip from the mucosa to the labial gingiva. Secondary frenula are found in the molar and premolar areas as well.

CLINICAL NOTES

Lesions of the Lips

Even before the dentist examines the oral cavity, the lips are examined because they are targets for many types of lesions and diseases.

Angular cheilosis is an inflammation and cracking of the skin and transition zone at the angles of the mouth. It is a condition that is usually associated with a B vitamin deficiency. It may also be infected with bacteria and/or fungi and is called perlèche. Treatment consists of a regimen of antibacterial and antifungal medication. This condition is common in older edentulous patients with angular wrinkling and leakage of saliva contributing to irritation and inflammation. Restoration of facial contours with dentures helps rectify this problem.

Herpes labialis, or cold sores, are painful vesicular lesions (watery blisters) at the vermilion border of the lip that are caused by the herpes simplex virus. The vesicles rupture and form yellow crusted lesions that last about 10 days. Primary infections occur in early childhood and, after remission, the virus remains dormant in the trigeminal ganglion. The virus is opportunistic and can recur with fever-producing diseases, onset of menstruation, anxiety, exposure to sun, and occasionally dental treatment.

A labial mucocele or mucous retention cyst is a labial mucous gland with a blocked secretory duct that causes the gland and the overlying epithelium to bulge and assume a bluish tinge. Mucoceles usually occur on the lower lip. Large or noticeable cysts can be surgically removed.

Squamous cell carcinoma is a type of cancer. An ulcerated (cratered) lesion on the vermilion border of usually the lower lip that does not appear to heal over a reasonable period of time should be under suspicion and investigated.

Cheeks (Buccae)

The cheeks form the lateral movable walls of the oral cavity (Figure 7-10). Externally, the cheek includes not only the movable portion but also the prominence of the cheek over the zygomatic arch. This terminology, however, is from common usage, and our definition of cheek is confined to the movable portion.

External Nose

External Ear (Auricle)

Cartilage

A single elastic cartilage provides support for the external ear (Figure 7-12). The pendulous lower portion, or earlobe, contains no cartilage but does contain fibroareolar tissue. The cartilage of the ear is continuous with the cartilage of the external auditory meatus (canal), leading within the petrous temporal bone to the middle ear.

Eyelids (Palpebrae)

The upper and lower lids form a curtain for the ocular globe, or eyeball. When closed, the lids protect the eye from light and harmful objects.

External Features (Figure 7-13)

Layers

Skin

Extremely thin skin covers the lids of the eye (Figure 7-14). At the margins of the eye, prominent hairs, or cilia, form two or three irregular rows along the lateral five sixths of the margin. Associated with the cilia are large sebaceous glands, or ciliary glands (glands of Zeis). Infected ciliary glands result in the common stye.

The Scalp

The forehead, the anterior portion of the scalp, was considered with the face. The posterior portion of the scalp was considered with the suboccipital region.

As a unit, the scalp extends from the supraorbital margins back to the superior nuchal line posteriorly. Laterally, the scalp extends down into the temporal fossae.

Jan 5, 2015 | Posted by in General Dentistry | Comments Off on 7: The Head by Regions
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