Session 3: Osteology of the Skull and Jaws

Oral Anatomy and Physiology — CDT NTA Level 4

Kolandoto College of Health Sciences Mwanza

The skull is the skeleton of the head. It protects the brain and the organs of special sense, and provides the framework for the face.

For the dental therapist, the two most important bones are the maxilla and the mandible, because they carry the teeth.

A sound knowledge of their landmarks is essential for extraction, local anaesthesia, radiography and the management of fractures.

Neurocranium (8 bones)

Frontal bone — forms the forehead and roof of the orbits.

Two parietal bones — form the sides and roof of the cranium.

Two temporal bones — house the ear; bear the mandibular fossa.

Occipital bone — forms the back and base; contains foramen magnum.

Sphenoid bone — the keystone of the base of the skull.

Ethmoid bone — between the orbits; forms part of the nasal cavity.

Viscerocranium (14 bones)

Two maxillae — the upper jaw.

Mandible — the lower jaw; the only mobile bone of the skull.

Two zygomatic bones — the cheek prominences.

Two nasal bones — the bridge of the nose.

Two lacrimal bones — the medial wall of the orbit.

Two palatine bones, two inferior nasal conchae and the vomer.

A paired bone forming the upper jaw. The two maxillae unite at the intermaxillary suture to form the whole upper jaw, the floor and lateral wall of the nasal cavity, the floor of the orbit, and the greater part of the hard palate.

Body — pyramidal, containing the maxillary sinus. It has four surfaces

Anterior (facial) surface — bears the canine fossa and the infraorbital foramen.

Infratemporal (posterior) surface — bears the maxillary tuberosity and the posterior superior alveolar foramina.

Orbital surface — forms the floor of the orbit; grooved by the infraorbital canal.

Nasal surface — forms the lateral wall of the nasal cavity.

Four processes

Frontal process, zygomatic process, palatine process and alveolar process.

Infraorbital foramen

About 1 cm below the orbital margin. Transmits the infraorbital nerve and vessels; the site of the infraorbital nerve block.

Alveolar process

Carries the sixteen sockets of the upper teeth. The buccal plate is thin, which favours buccal approach in extraction.

Maxillary tuberosity

The rounded posterior end. Landmark for the posterior superior alveolar nerve block; may fracture during upper molar extraction.

Incisive foramen

In the midline behind the central incisors. Transmits the nasopalatine nerve; the site of the incisive nerve block.

Greater palatine foramen

Opposite the third molar. Transmits the greater palatine nerve; the site of the greater palatine block.

Zygomatic process

Buttress transmitting masticatory forces to the cranium; overlies the roots of the upper first molar.

The largest of the paranasal sinuses, occupying the body of the maxilla.

It is pyramidal, with its base at the lateral wall of the nose and its apex in the zygomatic process.

The floor lies close to the roots of the premolars and molars, especially the first molar; in some persons the roots project into the sinus.

Clinical importance

Infection of an upper molar may spread to cause maxillary sinusitis.

Sinusitis may present as toothache in the upper posterior teeth.

A root may be displaced into the sinus during extraction, creating an oro-antral fistula.

It drains into the middle meatus of the nose, above the level of its own floor — so drainage is poor when the patient is upright.

The largest and strongest bone of the face, and the only mobile bone of the skull. It carries the lower teeth and articulates with the temporal bone at the temporomandibular joint.

Body — horseshoe-shaped, horizontal. It has

External surface — mental protuberance, mental foramen, oblique line.

Internal surface — mental spines (genial tubercles), mylohyoid line, submandibular and sublingual fossae.

Alveolar part — carries the sixteen sockets of the lower teeth.

Ramus — quadrilateral, vertical. It bears

Coronoid process — for insertion of temporalis.

Condylar process — the head articulates at the temporomandibular joint.

Mandibular notch — between the two processes.

Lingula, mandibular foramen and mylohyoid groove on the medial surface.

Angle — where the body meets the ramus.

Mandibular foramen

On the medial surface of the ramus. Transmits the inferior alveolar nerve and vessels; the target of the inferior alveolar nerve block.

Lingula

The bony spine guarding the mandibular foramen; the key landmark when giving an inferior alveolar block.

Mental foramen

Below the second premolar. Transmits the mental nerve; the site of the mental nerve block.

Mylohyoid line

Gives origin to mylohyoid, separating sublingual from submandibular space — determines the spread of dental abscess.

External oblique ridge

Guides the incision and the point of needle insertion in the inferior alveolar block.

Retromolar fossa

Behind the third molar; the site of pericoronitis around an impacted lower third molar.

The mandible commonly fractures at points of relative weakness

Condylar neck — the commonest site, often from an indirect blow to the chin.

Angle — especially where an unerupted third molar is present.

Region of the mental foramen.

The midline of the body (symphysis).

Fractures are often bilateral — a blow on one side may fracture the opposite condyle.

In the maxilla, fractures follow the classical Le Fort lines I, II and III.

At birth — both jaws consist mainly of alveolar bone containing developing tooth germs; the mandible is in two halves united by fibrous tissue at the symphysis.

In the child — the mandibular angle is obtuse, about 140 degrees; the mental foramen lies near the lower border.

In the adult — the angle is about 110 to 120 degrees; the mental foramen lies midway between the upper and lower borders.

In the edentulous elderly — the alveolar process is resorbed, the angle becomes obtuse again, and the mental foramen may come to lie at or near the upper border, exposing the mental nerve to pressure from a denture.

The skull consists of the neurocranium (8 bones) and the viscerocranium (14 bones).

The maxilla carries the upper teeth and contains the maxillary sinus, which lies close to the roots of the upper molars.

The mandible is the only mobile bone of the skull and carries the lower teeth.

The mandibular foramen, lingula, mental foramen and external oblique ridge are the key landmarks for local anaesthesia.

Resorption of the alveolar process after tooth loss changes the shape of both jaws and the position of the mental foramen.

List the bones of the neurocranium and of the viscerocranium.

Describe the four surfaces and four processes of the maxilla.

Explain the relationship of the maxillary sinus to the upper posterior teeth and give two (2) clinical consequences.

Describe the parts of the mandible.

Name the landmarks used in giving an inferior alveolar nerve block.

Describe the age changes that occur in the mandible after loss of the teeth.