The mandible (or lower jaw bone, latin: mandibula) is the only movable cranial bone. The mandible is a single bone connected to the skull by the temporomandibular joint.
The mandible has three parts:
- body of mandible,
- ramus of mandible (2).
Body of mandible
The body of the mandible is located in the anterior part of the lower jawbone, has a curved shape, and can be divided in two parts: the base of the mandible, and the alveolar part of the mandible. The body of the mandible has two surfaces (external, internal) and two borders (superior or alveolar, and inferior).
Base of mandible
The base of the mandible is the lower part of the body of the mandible, excluding the alveolar part of the mandible, and it has an external and an internal surface.
The features on the external surface of the mandibular base are:
- mental protuberance,
- mental tubercle (2),
- mental foramen (2).
The mental protuberance is a prominence found on the outer surface of the base of the mandible forming the chin.
The mental tubercle is a prominence on either side of the mental protuberance on the external surface of the base of the mandible.
The mental foramen is an opening in the mandible located below the second premolar. It is the passage for the mental nerve, as well as a pressure point for the mandibular branch of the trigeminal nerve.
The features found on the internal surface of the mandibular base are:
- mental spine,
- digastric fossa (2),
- mylohyoid line (2),
- sublingual fovea (2),
- submandibular fovea (2).
The mental spine is a bony elevation on the internal surface of the mandible projecting toward the tongue. The mental spine is the origin site of the genioglossus and geniohyoid muscles.
The digastric fossa is an oval depression on the lower internal surface of the body of the mandible on either side of the middle line, for attachment of the anterior belly of the digastric muscle.
The mylohyoid line is a paired line on the inside of the mandible, an oblique ridge extending from the posterosuperior to anteroinferior aspect of the body of the mandible. The mylohyoid line is the origin site of the mylohyoid muscle, and its posterior part is the origin of the mylopharyngeal part of the superior constrictor muscle of the pharynx.
The sublingual fovea is a depression on the inside of the mandible for the sublingual gland. It is a paired structure on the anterior half of the body of the mandible below the mylohyoid line.
The submandibular fovea is a depression on the inside of the mandible for the submandibular gland. It is a paired structure on the posterior half of the body of the mandible below the mylohyoid line.
Alveolar part of mandible
The alveolar part of the mandible (also called the alveolar process of the mandible) is the portion of the body of the mandible that surrounds and supports the lower teeth. An alveolar process is a crested process of upper or lower jaw which 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,
- interalveolar septa,
- interradicular septa,
- alveolar yokes.
The dental alveoli are sockets in the alveolar process where the roots of the teeth lie. The dental alveoli of the mandible house the roots of the lower teeth, while the dental alveoli of the maxilla - the upper teeth.
The interalveolar septa are bony ridges between adjacent dental alveoli in the alveolar arches of the upper and lower jaw bones.
The interradicular septa are bony ridges forming compartments in dental alveoli for the roots of the teeth in both the upper and lower jaw bones.
The alveolar yokes (juga alveolaria) are eminences on the outer surface of the jaw produced by the projections of the dental alveoli. They can be seen on both the maxilla and the mandible.
Ramus of mandible
The rami of the mandible are situated on the right and left side of the lower jawbone. Each of the ramus of the mandible features several landmarks:
- angle of mandible,
- condylar process with
- head of the mandible,
- neck of the mandible,
- pterygoid fovea,
- coronoid process,
- mandibular notch.
The angle of mandible is the angle forming between the body and ramus of the mandible.
The condylar process is an articular process, a part of the ramus of the mandible. It has three landmarks: the head of the mandible, which is the articular part of the condylar process of the mandible; the neck of mandible, which is a narrow segment of the condylar process below the head of the mandible; and the pterygoid fovea - an anteromedial pit below the head of the mandible, where the lateral pterygoid muscle attaches.
The coronoid process of the mandible is a muscular process located anteriorly to the condylar process of the mandible, both are separated by the mandibular notch. The temporalis muscle attaches to the coronoid process.
The mandibular notch is a depression located on the ramus of the mandible separating the condylar and coronoid processes.
The ramus of the mandible also has an internal and an external surface.
The internal surface of the ramus of the mandible features:
- mandibular foramen (leads into the mandibular canal),
- mylohyoid groove,
- pterygoid tuberosity.
The mandibular foramen is an opening on the inner surface of each ramus of the mandible leading into the mandibular canal.
The mandibular canal is a bony passage in the mandible that transmits the inferior alveolar artery and nerve.
The mylohyoid groove or sulcus is a groove on the internal surface of the mandible extending forward and downward from the mandibular foramen. This groove is the passage for the mylohyoid nerve and the mylohyoid branch of the inferior alveolar artery.
The pterygoid tuberosity is a roughened area occasionally present on the internal surface of the ramus of the mandible near the angle of the mandible. The medial pterygoid muscle attaches to the pterygoid tuberosity.
The external surface of the ramus of the mandible presents the masseteric tuberosity.
The masseteric tuberosity is a roughened area occasionally present on the external surface of the ramus of the mandible near the angle of the mandible. The masseter muscle attaches to the masseteric tuberosity.