Anatomy and Function of the Mandible
- The mandible is the largest and lowest bone in the facial skeleton.
- It is the only movable bone of the skull.
- It is connected to the temporal bones by the temporomandibular joints.
- The jawbone can articulate side to side as well as forward and back.
- The mandible consists of the body and two rami.
- The body of the mandible curves anteriorly and gives structure to the chin.
- The mental protuberance, or chin, is raised on both sides to form the mental tubercle.
- The mandible has a mental spine, mylohyoid line, and various depressions and attachments for muscles.
- The superior or alveolar border is hollowed into cavities for the teeth.
- The buccinator muscle attaches to the outer lip of the superior border.
- The inferior border is rounded and longer than the superior border.
- The posterior border is thick, smooth, rounded, and covered by the parotid gland.
- The ramus is flat on the outside and gives attachment to the masseter muscle.
- The mandibular foramen is located on the inside of the ramus.
- The lingula of the mandible gives attachment to the sphenomandibular ligament.
- The mandibular canal runs obliquely downward and forward in the ramus, containing the inferior alveolar vessels and nerve.
- The coronoid process is a thin, triangular eminence.
- The condyloid process consists of the mandibular condyle and the neck.
- The mandible has the mandibular foramen above the mandibular angle.
- The mandible also has other foramina, such as the mental foramen.
- The mandible forms the lower jaw and holds the lower teeth in place.
- It articulates with the left and right temporal bones at the temporomandibular joints.
- The condyloid process makes the temporomandibular joint with the temporal bone.
- The coronoid process provides attachment to the temporal muscle.
- The mandible plays a role in mastication, speech, yawning, kissing, and breathing.
Nerves
- The inferior alveolar nerve is a branch of the mandibular nerve.
- It enters the mandibular foramen and runs forward in the mandibular canal.
- The nerve supplies sensation to the gums and teeth.
- The nerve divides into two terminal branches: incisive and mental nerves.
- The incisive nerve supplies the anterior teeth, while the mental nerve supplies sensation to the chin and lower lip.
Variation and Development
- Males generally have squarer, stronger, and larger mandibles than females.
- The mental protuberance is more pronounced in males.
- Rarely, a bifid inferior alveolar nerve may be present, resulting in a doubled mandibular canal on a radiograph.
- There is variation in the shape and size of the mandible among individuals.
- The mandible can be visualised and palpated in both males and females.
- The mandible of vertebrates evolved from Meckel's cartilage.
- In recent human evolution, the oral cavity and jaws have shrunk due to the shift towards agriculture and settlement.
- This has led to orthodontic malocclusions.
- The mandible has undergone changes throughout evolution to adapt to different dietary habits.
- The shape and size of the mandible can vary among different species.
- The mandible forms as a bone from Meckel's cartilage.
- The two sides of the jawbone fuse at the mandibular symphysis during the first year of life.
- The cartilage of the ramus is replaced by fibrous tissue, forming the sphenomandibular ligament.
- Ossification takes place in the membrane covering the outer surface of Meckel's cartilage.
- Accessory nuclei of cartilage appear in different parts of the mandible during development.
- At birth, the mandible is a mere shell with sockets for teeth.
- The two segments of the bone become joined at the symphysis in the first year of life.
- The body of the mandible elongates and deepens to accommodate additional teeth.
- In adults, the alveolar and subdental portions of the body are usually of equal depth.
- In old age, the bone can become greatly reduced in volume due to tooth loss and resorption of the alveolar process.
Dislocation, Displacement, and Resorption
- Mandible can be dislocated anteriorly and inferiorly, but rarely posteriorly.
- The articular disk of the temporomandibular joint prevents posterior movement.
- Fractures in the condylar neck are common due to vulnerability.
- Temporomandibular joint dysfunction can occur due to jawbone damage.
- Symptoms include pain and inflammation.
- Mandibular alveolar process can undergo resorption when completely edentulous.
- Mental foramen may shift from the anterior surface to the superior border.
- Alveolar process absorption can bring the mandibular canal closer to the superior border.
- Excessive absorption may lead to the disappearance of the mandibular canal.
- Inferior alveolar nerve remains protected by soft tissue.
Mandibulectomy, Regeneration, and Forensic Medicine
- Surgical removal of all or part of the jawbone is known as mandibulectomy.
- Partial mandibulectomy involves the removal of a small portion.
- Segmental mandibulectomy involves the removal of a larger portion.
- Mandibulectomy is performed to remove tumors, combat cancer, and treat infections, osteonecrosis, or injuries.
- Replaced portions can be made of metal plating or bone from other parts of the body.
- Bone grafting can mitigate bone loss in the jawbone, such as in osteoporosis.
- Bone grafting is sometimes performed to support dental implants
In jawed vertebrates, the mandible (from the Latin mandibula, 'for chewing'), lower jaw, or jawbone is a bone that makes up the lower – and typically more mobile – component of the mouth (the upper jaw being known as the maxilla).
| Mandible | |
|---|---|
 Human mandible (left side) | |
 Mandible (grey) with cranium | |
| Details | |
| Precursor | 1st pharyngeal arch |
| Identifiers | |
| Latin | mandibula |
| MeSH | D008334 |
| Anatomical terms of bone | |
The jawbone is the skull's only movable, posable bone, sharing joints with the cranium's temporal bones. The mandible hosts the lower teeth (their depth delineated by the alveolar process). Many muscles attach to the bone, which also hosts nerves (some connecting to the teeth) and blood vessels. The jawbone is essential for chewing food.
Due to the Neolithic agricultural revolution (c. 10,000 BCE), human jaws evolved to be smaller. Although it is the strongest bone of the facial skeleton, the mandible tends to deform in old age; it is also subject to fracturing. Surgery allows for both the removal of jawbone fragments and regenerative methods. Additionally, the bone is of great forensic significance.
