Anatomy of the head, neck and skull
At the end of this chapter you should have an understanding and knowledge of:
- 1. The anatomy of the head, neck and skull.
- 2. The nerve supply to the teeth and their surrounding structures.
- 3. The major blood vessels of the head and neck.
- 4. The salivary glands.
- 5. The muscles of the head and neck.
As part of multi-disciplinary team, knowledge of the structures of the head, neck and skull is needed. Along with a basic understanding of conditions and lesions that patients may present within the maxillofacial outpatients department, such knowledge forms an important base for the dental care professional.
It is important to understand the presentation of a healthy mouth in order to recognise abnormalities. When the maxillofacial surgeon looks in a patient’s mouth they examine the teeth for signs of caries, the gingiva for any indications of periodontal disease and the oral mucosa and tongue to ensure its presentation is normal. In a healthy mouth the teeth should sit firmly in the alveolar bone, being attached to it by the periodontal ligaments. The bone and periodontal ligaments are covered by the gingiva lining the alveolar ridge. The gingiva is attached to the neck of the tooth at the junctional epithelium with the gingival crevice being no more than 2 mm. The gingivae is pink in colour, having an orange peel effect with a tight gingival cuff around the tooth. There should be no bleeding on probing and, sub-gingivally, the periodontal ligaments and alveolar bone should be intact. Any examination that highlights disease will be investigated and treated accordingly.
In order to describe the position of a structure relative to another, the following terms are often used in dentistry:
- • Anterior – In front of.
- • Posterior – Behind.
- • Superior – Above.
- • Inferior – Below.
- • Medial – Towards the mid-line.
- • Lateral – Away from the mid-line or to one side of.
The skull (Figures 2.1 and 2.2) has two defined areas: the cranium and facial. There are eight bones that make up the cranium. The single bones are the frontal, occipital, sphenoid and ethmoid and the paired bones are the parietal and temporal.
Bones of the neurocranium
Part of the cranium, this single bone forms the forehead, known as the frontal eminences. Within the frontal bone lie the frontal sinuses. The frontal bone consists of many landmark areas such as the supericiliary arches, supraorbital margins, glabella and nasion.
The area of thickened bone which lies beneath the eyebrows.
The area below the supericiliary arches round to the superior area of the orbits.
The area of frontal bone which joins the supericiliary arches. The frontal suture can sometimes be traced on and above the glabella.
This is the midpoint of the frontonasal suture, and is the connection between the frontal and nasal bones. The frontonasal suture is found below the frontal suture.
This single bone forms the lower posterior area of the cranium. Areas of the occipital bone include the squama, foramen magnum, hypoglossal canal, occipital condyles, external occipital protuberance and external occipital crest. The following explains where they sit anatomically:
- • Squama: The occipital squama has a curved surface and is the area above and behind the foramen magnum.
- • Forman magnum: Oval in shape, this opening is in the lower part of the occipital bone.
- • Hypoglossal canal: A tunnelled canal found in the base of each occipital condyle.
- • Occipital condyles: Two bony protrusions at the base of the occipital, which articulate with the first cervical vertebrae.
- • External occipital protuberance: This prominent, curved area of bone is found halfway between the magnum foramen and the top of the occipital bone.
- • External occipital crest: An external crest which extends downwards from the occipital protuberance to the foramen magnum.
- • Sphenoid: A winged-shaped bone which forms part of the external and internal neurocranium. The outer edge of the wing is located anterior to the temporal bone.
This bone comprises a vertical and horizontal plate, a lateral mass (orbital plate and ethmoid sinuses) and a mid-nasal concha and crista galli. It is a complex, deeply seated bone between the nasal cavity and orbits. It forms part of the nasal septum along with the vomer; it also forms the medial aspect of the walls of the orbit and nasal cavity.
These paired bones form a simple curved shape. The parietal bones form the superior, lateral and posterior area of the cranium.
The temporal bones are paired, one found on each side. They form the side and base of the skull. Each single temporal bone comprises the squama, tympanic and petrous regions. The temporal bone forms part of the temporal mandibular joint. The following explains where they are positioned anatomically:
- • Squama: A broad, flat area of the temporal bone which is found in the anterior and superior region.
- • Tympanic: A curved plate of bone which surrounds the external auditory meatus and also forms the bony regions of this structure.
- • Petrous: A pyramid-shaped bone at the base of the skull between the sphenoid and occipital bones.
The facial area of the skull consists of 14 bones. The majority of these bones are paired, with the exception of the single mandible and vomer. The paired bones are the maxilla, zygomatic, nasal, lacrimal, palatine and inferior nasal conchae.
This bone forms the lower third of the face, and is the only movable bone within the skull as it can swing from side to side. It is made up of the following anatomical features:
- • Angle of the mandible: This is where the ascending ramus meets the body of the mandible to form an angle.
- • Body of the mandible: This is the main part of the mandible that extends anteriorly from the angle to the corner of the mental protuberance.
- • Ramus: This area is the vertical section of the mandible that extends above the angle to join with the condyle and coronoid process.
- • Condyle: This forms part of the temporomandibular joint and is the rounded bone that sits posteriorly at the top of the ramus.
- • Coronoid process: This forms part of the temporomandibular joint and is the bony projection that sits anteriorly at the top of the ramus.
- • Sigmoid notch: This is the depression in the bone that is situated between the condyle and coronoid process.
- • Mental foramen: A foramen is a natural opening in bone which permits vessels to enter and exit. The mental foramens are found marginally below and in the region of the first and second pre-molar teeth.
- • Mental protuberance: This bone is the prominent anterior projection of the mandible and forms the chin. The size and shape of this bone depicts the size and shape of the chin.
- • External oblique line (ridge): An external oblique ridge extends across the external surface of the body of the mandible.
- • Mylohyoid ridge: This bone is an attachment for the mylohyoid muscle and is an internal ridge that runs on the internal surface of the mandible.
- • Lingula: This is a bony projection that is situated on the anterior border of the mandibular foramen to protect the mandibular nerve as it enters the mandibular foramen.
- • Genial tubercles: These are slight prominent bones which sit just above the lower border of the mandible in the midline.
This bone, along with the ethmoid and palatine bones, forms part of the nasal septum.
This bone forms the upper jaw and comprises of the following anatomical features:
- • Incisive foramen: This is located in the anterior aspect of the palate in the region of the incisor teeth. It permits the nasopalatine nerve, also known as the long sphenopalatine, to enter into the mouth.
- • Alveolar process: This is a ridge-like bone which is made up of sockets for the mandibular and maxillary teeth to sit in. The roots of a tooth are embedded in this process. It may be referred to as the maxillary and mandibular ridge.
- • Canine fossa: