Mandible

The mandible is the only movable bone of the skull. It is a single bone connected to the each side of the skull at the temporomandibular joint. Like the maxilla, it is also a part of the viscerocranium. It forms the lower jaw.

The main parts of the mandible are:

Body of the mandible

The body of the mandible is located in the anterior part of the lower jawbone. 

It has a curved shape and can be subdivided into two smaller parts

  • Base of the mandible

  • Alveolar part of the mandible

The body of the mandible has two surfaces (external and internal) and two borders (superior or alveolar and inferior).

Base of the mandible

The base is the lower, thickened part of the body of the mandible, and it has an external and internal surface.

The features on the external surface of the mandibular base are:

  • Mental protuberance - a prominence on the outer surface forming the chin;

  • Mental tubercle (2) - a prominence on either side of the mental protuberance;

  • Mental foramen (2) - an opening in the mandible located below the second premolar; it is a passage for the mental nerve (a branch of the inferior alveolar nerve, which arises from the mandibular nerve (CN V3)), as well as a pressure point for the mandibular nerve - a mandibular branch of the trigeminal nerve (CN V3); besides nerves, through the canal also goes the mental artery which is a branch of the inferior alveolar artery (from the maxillary artery).

The features found on the internal surface of the mandibular base are:

  • Mental spine - a bony elevation projecting toward the tongue; the origin site of the genioglossus and geniohyoid muscles;

  • Digastric fossa (2) - an oval depression on the lower part of the internal surface of the mandibular body on either side of the mental spine for attachment of the anterior belly of the digastric muscle;

  • Mylohyoid line (2) - an oblique ridge extending from the posterosuperior to the anteroinferior aspect of the inner surface of the body; the origin site of the mylohyoid muscle, its posterior part is the origin of the mylopharyngeal part of the superior constrictor muscle of the pharynx;

  • Sublingual fossa (2) - a depression on the sides of the mental spine above the medial end of the mylohyoid line; the sublingual gland lies in it;

  • Submandibular fossa (2) - a depression located on the sides of the body below the mylohyoid line; the submandibular gland lies in it.

Alveolar process of the mandible

The alveolar process of the mandible is the superior portion of the body that surrounds and supports the lower teeth. An alveolar process is a crested process of the upper or lower jaw that houses the teeth. 

The curved free margin of the alveolar process is called the alveolar arch

The alveolar arch of the mandible (as the alveolar arch formed by the maxillae) features the following structures:

  • Dental alveoli - sockets in the alveolar process where the roots of the teeth lie;

  • Interalveolar septa - bony ridges between adjacent dental alveoli;

  • Interradicular septa - bony ridges forming compartments in dental alveoli for the roots of the teeth;

  • Alveolar yokes (juga alveolaria) - eminences on the outer surface of the jaw produced by the projections of the dental alveoli.

Ramus of the mandible

The rami of the mandible are situated on the right and left side of the mandible. They go upward from the body of the mandible.

Each ramus of the mandible features several landmarks:

Both processes are separated by the mandibular notch. The temporal muscle inserts onto the coronoid process.

The ramus of the mandible also has an internal and an external surface.

The internal surface of the ramus features:

  • Mandibular foramen - an opening leading into the mandibular canal - a bony passage that transmits the inferior alveolar artery, vein, and nerve;
  • Lingula - it is also known as the Spix spine; a triangular-shaped bony ridge extending superior from the mandibular foramen;
  • Mylohyoid groove - a groove on the internal surface of the mandible extending forward and downward from the mandibular foramen; it is the passage for the mylohyoid nerve (a branch of the inferior alveolar nerve) and the mylohyoid branch of the inferior alveolar artery (from the maxillary artery);

  • Pterygoid tuberosity - a roughened area occasionally present on the internal surface of the mandibular ramus near the angle of the mandible; it serves as the attachment site for the medial pterygoid muscle.

The external surface of the ramus presents the masseteric tuberosity - a roughened area present near the angle of the mandible. This tuberosity is the attachment site for the masseter muscle.