Structure
The mandible is made up of a body and two rami that articulate with the temporal bone (the temporomandibular joint), and forms the lower jaw.
Body
The body is U-shaped, with internal and external surfaces separated by upper and lower borders.
The external surface is relatively smooth and characterised by the mental protruberance (which forms the chin) and the mental foramina which convey like-named vessels and nerves. The internal surface demonstrates the mylohyoid line for attachment of the mylohyoid muscle of the tongue. The posterior part of this line forms the attachment for the pterygomandibular raphe (and therefore some of the superior constrictor and buccinator muscles). The anterior part of this line may extend a bifid for attachment of geniohyoid below and genioglossus above.
The base extends posteriorly and becomes thicker as it does so. At about the midline lies the digastric fossa for attachment of the digastric muscle. The upper border contains the alveolar projection and 16 alveoli for the mandibular teeth.
Rami
The rami are quadrilateral projections which ascend from the posterior part of the body. Their external (lateral) surface is relatively smooth, and the internal (medial) surface contains the mandibular foramen for the inferior alveolar neurovascular bundle.
The inferior border is continuous with the base of the mandible, meeting it at the angle of the mandible. This is usually prominent in males and may be inverted in females. The superior aspect of the mandible is noted for two processes, the coronoid process (sharp and anterior) and the condylar process (thicker and blunter).
The muscles of mastication all attach to the mandible. Masster inserts on to the external surface of the ramus, the medial pterygoid to the internal surface, the lateral pterygoid to the coronoid process and the temporalis muscle to the condylar process.
Variations
A birth, the mandible is joined anteriorly by a fibrous ‘symphysis menti’. This unites over the coming years.
When teeth are lost from the mandible, the bony structure of the alveoli is resorbed. In an edentulous older person, the height of the body of the mandible may be greatly reduced, with the mental foramen lying at the top of the mandible instead of midway.
