Mandible

Key Features & Anatomical Relations

The mandible (or lower jaw bone) is a single, large, U-shaped bone found along the anteroinferior aspect of the cranium. It is classified as an irregular bone, lodges the mandibular (lower) teeth and contributes to the formation of the viscerocranium. The mandible includes the following bony features:

- parts: body, rami, and alveolar, condylar, and coronoid processes;

- surfaces: internal and external surfaces of body, medial and lateral surfaces of rami, anterior and posterior borders of rami, and base of mandible;

- landmarks: mandibular symphysis, mylohyoid and oblique lines, sublingual and submandibular fossae, and superior and inferior mental spines.

More information regarding these bony features can be found in the Parts, Surfaces and Landmarks tabs for this bone.

The mandible is located:

- superior to the hyoid bone;

- inferior to the temporal and zygomatic bones and maxillae.

It articulates with the right and left temporal bones at the temporomandibular joints.

Ossification

Ossification of the mandible occurs at multiple ossification centers, these are found in the:

- right and left halves of the mandible, which appear in utero during the second month;

- right and left condylar processes, which appear in utero later;

- right and left coronoid processes, which appear in utero later;

- mental protuberance, which appears in utero during the seventh month.

The ossification center for the right and left halves of mandible form the right and left halves of its body and rami on its corresponding sides. Each half fuses with the condylar and coronoid processes on their same sides before birth. At birth, the right and left halves of the mandible remains unfused, with a mandibular symphysis located between them. They fuse with each other during the first to third years after birth. The mental protuberances fuse with the rest of the mandible during the first year after birth (Standring, 2020).

Variations

In each individual, the shape and size of the mandible changes with age.

In some individuals:

- accessory mental foramina may be present;

- the coronoid processes may be present in an elongated form;

- a bony outgrowth may be present along the internal surface of the body of the mandible, known as a torus mandibularis (Tubbs, Shoja and Loukas, 2016).

The mandible also displays sexual dimorphism. In males, the mandible tends to be larger and more robust than in females. The chin is squarer, the mandibular condyles are larger, and the sites of muscle attachment tend to be more pronounced than in females (Standring, 2020; White and Folkens, 2005).

Surface Anatomy

Regarding surface anatomy, the body, rami, mental protuberances, and the alveolar, condylar, and condyloid processes can all be palpated.

List of Clinical Correlates

- Fracture of mandible

- Dislocation of mandible

- Temporomandibular joint dysfunction

- Micrognathism

- Macrognathism

- Hyperplasia of coronoid process

- Hyperplasia of condylar process

References

Standring, S. (2020) Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd edn.: Elsevier Health Sciences.

Tubbs, R. S., Shoja, M. M. and Loukas, M. (2016) Bergman's Comprehensive Encyclopedia of Human Anatomic Variation. Wiley.

White, T. D. and Folkens, P. A. (2005) The Human Bone Manual. Elsevier Science.