The Mandible

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The Mandible

The mandible or lower jaw is the largest and strongest bone of the face, and it articulates with the skull at the temporomandibular joint.

The mandible consists of a horseshoe-shaped body and a pair of rami. The body of the mandible meets the ramus on each side at the angle of the mandible.

The body of the mandible, on its external surface in the midline, has a faint ridge indicating the line of fusion of the two halves during development at the symphysis menti. The mental foramen can be seen. On the medial surface of the body of the mandible in the median plane are seen the mental spines. The mylohyoid line can be seen as an oblique ridge that runs backward and laterally from the area of the mental spines to an area below and behind the third molar tooth. The submandibular fossa, for the superficial part of the submandibular salivary gland, lies below the posterior part of the mylohyoid line. The sublingual fossa, for the sublingual gland, lies above the anterior part of the mylohyoid line. The upper border of the body of the mandible is called the alveolar part; in the adult, it contains 16 sockets for the roots of the teeth.

The lower border of the body of the mandible is called the base. The digastric fossa is a small, roughened depression on the base, on either side of the symphysis menti. The ramus of the mandible is vertically placed and has an anterior coronoid process and a posterior condyloid process, or head; the two processes are separated by the mandibular notch. On the lateral surface of the ramus are markings for the attachment of the masseter muscle. On the medial surface is the mandibular foramen for the inferior alveolar nerve and vessels. In front of the foramen is a projection of bone, called the lingula. The foramen leads into the mandibular canal, which opens on the lateral surface of the body of the mandible at the mental foramen. The incisive canal is a continuation forward of the mandibular canal beyond the mental foramen and below the incisor teeth.Below the condyloid process, or head, is a short neck.

Temporomandibular Joint

  • Articulation: Articulation occurs between the articular tubercle and the anterior portion of the mandibular fossa of the temporal bone above and the head (condyloid process) of the mandible below. The articular surfaces are covered with fibrocartilage.

  • Type of Joint: The temporomandibular joint is synovial. The articular disc divides the joint into upper and lower cavities.

  • Synovial Membrane: This lines the capsule in the upper and lower cavities of the joint.

  • Nerve Supply: Auriculotemporal and masseteric branches of the mandibular nerve

  • Movements:

The mandible can be depressed or elevated, protruded or retracted. Rotation can also occur, as in chewing. In the position of rest, the teeth of the upper and lower jaws are slightly apart. On closure of the jaws, the teeth come into contact.

  1. Depression of the Mandible.

  2. Elevation of the Mandible.

  3. Protrusion of the Mandible.

  4. Retraction of the Mandible.

  5. Lateral Chewing Movement.

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