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In
anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things. It ...

anatomy
, the mandible, lower jaw or jawbone is the largest, strongest and lowest
bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubit ...

bone
in the human
facial skeleton The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. ...
. It forms the lower
jaw The jaw is any opposable articulated structure at the entrance of the , typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth and serving t ...

jaw
and holds the lower
teeth A tooth (plural teeth) is a hard, calcified Calcification is the accumulation of calcium salts in a Tissue (biology), body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. ...

teeth
in place. The mandible sits beneath the
maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The tw ...

maxilla
. It is the only movable bone of the skull (discounting the
ossicles The ossicles (also called auditory ossicles) are three bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a spe ...
of the middle ear). It is connected to the
temporal bone The temporal bones are situated at the sides and base of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of ...

temporal bone
s by the
temporomandibular joint In anatomy, the temporomandibular joints (TMJ) are the two joints connecting the jawbone to the skull. It is a bilateral Synovial joint, synovial articulation between the temporal bone of the skull above and the Human mandible, mandible below; ...

temporomandibular joint
s. The bone is formed
in the fetus
in the fetus
from a fusion of the left and right
mandibular prominence The mandibular prominence is an embryological structure which gives rise to the lower portion of the face. The human mandible, mandible and lower lip derive from it.mandibular symphysis In human anatomy, the facial skeleton The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of t ...
, is still visible as a faint ridge in the midline. Like other
symphyses A symphysis is a cartilage, fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing together of part ...
in the body, this is a midline articulation where the bones are joined by
fibrocartilage Fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its inflexibility and toughness to the former of these constituents, and its elasticity Elasticity often refers to: *Elastici ...
, but this articulation fuses together in early childhood.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, p. 59 The word "mandible" derives from the Latin word ''mandibula'', "jawbone" (literally "one used for chewing"), from '' mandere'' "to chew" and ''-bula'' (
instrumental An instrumental is a recording normally without any vocals, although it might include some inarticulate vocal The human voice consists of sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmissio ...
suffix).


Structure


Components

The mandible consists of: * The body, found at the front * A ramus on the left and the right, the rami rise up from the body of the mandible and meet with the body at the
angle of the mandible The angle of the mandible (gonial angle) is located at the Anatomical terms of location#Anterior and posterior, posterior border at the junction of the lower border of the ramus of the mandible, ramus of the mandible. The angle of the mandible, wh ...
or the gonial angle.


Body

The body of the mandible is curved, and the front part gives structure to the
chin The human chin (also known as the mental protuberance, mental eminence and, rarely, mental osseum, tuber symphyseos) is the forward pointed part of the anterior mandible (List_of_human_anatomical_regions#Regions, mental region) below the lower l ...

chin
. It has two surfaces and two borders. From the outside, the mandible is marked in the midline by a faint ridge, indicating the
mandibular symphysis In human anatomy, the facial skeleton The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of t ...
, the line of junction of the two halves of the mandible, which fuse at about one year of age. This ridge divides below and encloses a triangular eminence, the
mental protuberance The Symphysis menti, symphysis of the external surface of the human mandible, mandible divides below and encloses a triangular eminence, the mental protuberance, the base of which is depressed in the center but raised on either side to form the ''me ...
(the chin), the base of which is depressed in the center but raised on both sides to form the
mental tubercle The mandibular symphysis In human anatomy, the facial skeleton The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue th ...
. Just above this, on both sides, the
mentalis The mentalis muscle is a paired central Skeletal muscle, muscle of the lower lip, situated at the tip of the chin. It originates from the mentum of the mandible, and inserts into the soft tissue of the chin. It is sometimes referred to as the "pout ...

mentalis
muscles attach to a depression called the incisive fossa. Below the second premolar tooth, on both sides, midway between the upper and lower borders of the body, are the
mental foramen The mental foramen is one of two foramina (openings) located on the anterior surface of the Human mandible, mandible. It is part of the mandibular canal. It transmits the terminal branches of the inferior alveolar nerve and the mental vessels. ...
, for the passage of the mental vessels and nerve. Running backward and upward from each mental tubercle is a faint ridge, the oblique line, which is continuous with the anterior border of the ramus. Attached to this is the
masseter muscle In human anatomy, the masseter is one of the muscles of mastication There are four classical muscles of mastication. During mastication, three muscles of mastication (''musculi masticatorii'') are responsible for adduction of the jaw, and one (t ...

masseter muscle
, the
depressor labii inferioris The depressor labii inferioris (or quadratus labii inferioris) is a facial muscle The facial muscles are a group of striated skeletal muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate mus ...

depressor labii inferioris
and
depressor anguli oris The depressor anguli oris muscle (triangularis muscle) is a facial muscle The facial muscles are a group of striated skeletal muscles supplied by the facial nerve (cranial nerve VII) that, among other things, control facial expression. These mu ...

depressor anguli oris
, and the
platysma The platysma muscle is a superficial Superficial may refer to: *Superficial anatomy, is the study of the external features of the body *Superficiality, the discourses in philosophy regarding social relation *Superficial charm, the tendency to be ...

platysma
(from below). From the inside, the mandible appears concave. Near the lower part of the symphysis is a pair of laterally placed spines, termed the mental spines, which give origin to the
genioglossus The genioglossus is one of the paired extrinsic muscles of the tongue. The genioglossus is the major muscle responsible for protruding (or sticking out) the tongue. Structure Genioglossus is the fan-shaped extrinsic tongue muscle that forms the maj ...

genioglossus
. Immediately below these is a second pair of spines, or more frequently a median ridge or impression, for the origin of the
geniohyoid The geniohyoid muscle is a narrow muscle situated superior to the medial border of the mylohyoid muscle. It is named for its passage from the chin ("genio-" is a standard prefix for "chin") to the hyoid bone. Structure It arises from the inferior ...
. In some cases, the mental spines are fused to form a single eminence, in others they are absent and their position is indicated merely by an irregularity of the surface. Above the mental spines, a median foramen and furrow are sometimes seen; they mark the line of union of the halves of the bone. Below the mental spines, on either side of the middle line, is an oval depression for the attachment of the anterior belly of the
digastric The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a small muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromolecules that a ...
. Extending upward and backward on either side from the lower part of the symphysis is the mylohyoid line, which gives origin to the
mylohyoid muscle The mylohyoid muscle or diaphragma oris is a paired muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of am ...
; the posterior part of this line, near the alveolar margin, gives attachment to a small part of the , and to the pterygomandibular raphe. Above the anterior part of this line is a smooth triangular area against which the
sublingual gland The paired sublingual glands are major salivary glands in the mouth. They are the smallest, most diffuse, and the only unencapsulated major salivary glands. They provide only 3-5% of the total salivary volume. There are also two other types of sal ...
rests, and below the hinder part, an oval fossa for the
submandibular gland The paired submandibular glands (historically known as submaxillary glands) are major salivary gland The salivary glands in mammals are exocrine glands that produce saliva through a system of Duct (anatomy), ducts. Humans have three paired major ...

submandibular gland
. Borders *The superior or alveolar border, wider behind than in front, is hollowed into cavities, for the reception of the teeth; these cavities are sixteen in number and vary in depth and size according to the teeth which they contain. To the outer lip of the superior border, on either side, the
buccinator The buccinator () is a thin quadrilateral muscle occupying the interval between the maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone A bone is a Stiffness, rigid tissue (anato ...

buccinator
is attached as far forward as the first molar tooth. *The inferior border is rounded, longer than the superior, and thicker in front than behind; at the point where it joins the lower border of the ramus a shallow groove; for the
facial artery The facial artery (external maxillary artery in older texts) is a branch of the external carotid artery The external carotid artery is a major artery of the head and neck. It arises from the common carotid artery when it splits into the external ...
, may be present.


Ramus

The ramus () of the human mandible has four sides, two surfaces, four borders, and two processes. On the outside, the ramus is flat and marked by oblique ridges at its lower part. It gives attachment throughout nearly the whole of its extent to the masseter muscle. On the inside at the center there is an oblique
mandibular foramen The mandibular foramen is an opening on the internal surface of the ramus of the mandible for divisions of the mandibular nerve and blood vessel The blood vessels are the components of the circulatory system that transport blood throughout th ...
, for the entrance of the inferior alveolar vessels and
nerve A nerve is an enclosed, cable-like bundle of fibers (called axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences Despite the various English dialects Dialect The term diale ...
. The margin of this opening is irregular; it presents in front a prominent ridge, surmounted by a sharp spine, the lingula of the mandible, which gives attachment to the
sphenomandibular ligament The sphenomandibular ligament (internal lateral ligament) is a flat, thin band which is attached superiorly to the spina angularis (spine) of the sphenoid bone, and, becoming broader as it descends, is fixed to the Lingula of mandible, lingula of th ...
; at its lower and back part is a notch from which the mylohyoid groove runs obliquely downward and forward, and lodges the mylohyoid vessels and nerve. Behind this groove is a rough surface, for the insertion of the
medial pterygoid muscle The medial pterygoid (or internal pterygoid muscle), is a thick, quadrilateral muscle of mastication. The mandibular branch of the fifth Cranial Nerves, cranial nerve, the trigeminal nerve, innervates the medial pterygoid muscle. Structure It cons ...

medial pterygoid muscle
. The
mandibular canal In human anatomy, the mandibular canal is a canal within the mandible In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (fro ...
runs obliquely downward and forward in the ramus, and then horizontally forward in the body, where it is placed under the
alveoli Alveolus (pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Alveolus may refer to: In anatomy and zoology in general * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ...
and communicates with them by small openings. On arriving at the
incisor teeth Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whereas ...
, it turns back to communicate with the mental foramen, giving off two small canals which run to the cavities containing the incisor teeth. In the posterior two-thirds of the bone the canal is situated nearer the internal surface of the mandible; and in the anterior third, nearer its external surface. It contains the inferior alveolar vessels and nerve, from which branches are distributed to the teeth. Borders *The lower border of the ramus is thick, straight, and continuous with the inferior border of the body of the bone. At its junction with the posterior border is the angle of the mandible, which may be either inverted or everted and is marked by rough, oblique ridges on each side, for the attachment of the masseter laterally, and the
medial pterygoid muscle The medial pterygoid (or internal pterygoid muscle), is a thick, quadrilateral muscle of mastication. The mandibular branch of the fifth Cranial Nerves, cranial nerve, the trigeminal nerve, innervates the medial pterygoid muscle. Structure It cons ...

medial pterygoid muscle
medially; the
stylomandibular ligament The stylomandibular ligament is the thickened posterior portion of the investing cervical fascia The cervical fascia is fascia found in the region of the neck. It mainly refers to the deep cervical fascia. However, there are other cervical fascia ...
is attached to the angle between these muscles. The anterior border is thin above, thicker below, and continuous with the oblique line. *The region where the lower border meets the posterior border is the angle of the mandible, often called the gonial angle. *The posterior border is thick, smooth, rounded, and covered by the
parotid gland The parotid gland is a major salivary gland The salivary glands in mammals are exocrine glands that produce saliva through a system of Duct (anatomy), ducts. Humans have three paired major salivary glands (Parotid gland, parotid, Submandibular ...
. The upper border is thin, and is surmounted by two processes, the coronoid in front and the condyloid behind, separated by a deep concavity, the
mandibular notch The upper border of the ramus of mandible is thin, and is surmounted by two processes, the coronoid process anteriorly and the condyloid process The condyloid process or condylar process is the process on the human mandible In anatomy Anato ...
. Processes *The coronoid process is a thin, triangular eminence, which is flattened from side to side and varies in shape and size. *The
condyloid process The condyloid process or condylar process is the process on the human mandible In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organi ...
is thicker than the coronoid, and consists of two portions: the mandibular condyle, and the constricted portion which supports it, the neck. The condyle is the most superior part of the mandible and is part of the
temporomandibular joint In anatomy, the temporomandibular joints (TMJ) are the two joints connecting the jawbone to the skull. It is a bilateral Synovial joint, synovial articulation between the temporal bone of the skull above and the Human mandible, mandible below; ...

temporomandibular joint
. *The mandibular notch, separating the two processes, is a deep semilunar depression and is crossed by the vessels and nerve.


Foramina

The mandible has two main holes (
foramina In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of li ...
), found on both its right and left sides: *The mandibular foramen, is above the mandibular angle in the middle of each ramus. *The mental foramen sits on either side of the mental protuberance (chin) on the body of mandible, usually inferior to the of the mandibular first and second premolars. As mandibular growth proceeds in young children, the mental foramen alters in direction of its opening from anterior to posterosuperior. The mental foramen allows the entrance of the mental nerve and blood vessels into the mandibular canal.


Nerves

The
inferior alveolar nerve The inferior alveolar nerve (sometimes called the inferior dental nerve) is a branch of the mandibular nerve, which is itself the third branch of the trigeminal nerve The trigeminal nerve (the fifth cranial nerve, or simply CN V) is a nerve res ...
, a branch of the
mandibular nerve The mandibular nerve (V3) is the largest of the three divisions of the trigeminal nerve, the fifth cranial nerve (CN V). Structure The large sensory root emerges from the lateral part of the trigeminal ganglion and exits the cranial cavity through ...

mandibular nerve
, (a major division of the
trigeminal nerve The trigeminal nerve (the fifth cranial nerve, or simply CN V) is a nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves Cranial nerves are the nerve A ner ...

trigeminal nerve
), enters the mandibular foramen and runs forward in the mandibular canal, supplying sensation to the teeth. At the mental foramen, the nerve divides into two terminal branches: incisive and mental nerves. The incisive nerve runs forward in the mandible and supplies the anterior teeth. The mental nerve exits the mental foramen and supplies sensation to the lower lip.


Variation

Males generally have squarer, stronger, and larger mandibles than females. The mental protuberance is more pronounced in males but can be visualized and palpated in females. Rarely, a bifid inferior alveolar nerve may be present, in which case a second mandibular foramen, more inferiorly placed, exists and can be detected by noting a doubled mandibular canal on a radiograph.


Development

The mandible forms as a bone (
ossifies Image:Bonemetabolism.svg, 300 px, Bone is broken down by osteoclasts, and rebuilt by osteoblasts, both of which communicate through cytokine (TGF-β, Insulin-like growth factor, IGF) signalling. Ossification (or osteogenesis) in bone remodeling ...
) over time from a left and right piece of
cartilage Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue Elastic is a word often used to describe or identify certain types of elastomer An elastomer is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-m ...

cartilage
, called
Meckel's cartilage In humans, the cartilaginous bar of the mandibular arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryogenesis, embryonic development of vertebrates that are recognisable precursors for many structure ...
. These cartilages form the cartilaginous bar of the
mandibular arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryogenesis, embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, ...
. Near the head, they are connected with the ear capsules, and they meet at the lower end at the mandibular symphysis, a fusion point between the two bones, by
mesodermal In all bilaterian animals, the mesoderm is one of the three primary germ layer A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrate Vertebrates () comprise all species of ani ...
tissue. They run forward immediately below the condyles and then, bending downward, lie in a groove near the lower border of the bone; in front of the
canine tooth In mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to shar ...
they incline upward to the symphysis. From the proximal end of each cartilage the
malleus The malleus, or hammer, is a hammer-shaped small bone or ossicle The ossicles (also called auditory ossicles) are three bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. ...

malleus
and
incus The ''incus'' or anvil is a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear. The ''incus'' receives vibrations from the ''malleus'', to which it is connected laterally, and transmits these to the ''s ...
, two of the bones of the middle ear, are developed; the next succeeding portion, as far as the lingula, is replaced by fibrous tissue, which persists to form the
sphenomandibular ligament The sphenomandibular ligament (internal lateral ligament) is a flat, thin band which is attached superiorly to the spina angularis (spine) of the sphenoid bone, and, becoming broader as it descends, is fixed to the Lingula of mandible, lingula of th ...
. Between the lingula and the canine tooth the cartilage disappears, while the portion of it below and behind the incisor teeth becomes ossified and incorporated with this part of the mandible. About the sixth week of fetal life,
intramembranous ossification Intramembranous ossification is one of the two essential processes during fetal A fetus American and British English spelling differences#ae and oe, or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops fr ...
takes place in the membrane covering the outer surface of the ventral end of Meckel's cartilage, and each half of the bone is formed from a single center which appears, near the mental foramen. By the tenth week, the portion of Meckel's cartilage which lies below and behind the incisor teeth is surrounded and invaded by the
dermal bone A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification Intramembranous ossification is one of the two essential processes during fetal A fetus American and British English spelling diffe ...
(also known as the membrane bone). Somewhat later, accessory nuclei of cartilage make their appearance: *a wedge-shaped nucleus in the condyloid process and extending downward through the ramus; *a small strip along the anterior border of the coronoid process; *smaller nuclei in the front part of both alveolar walls and along the front of the lower border of the bone. These accessory nuclei possess no separate ossific centers but are invaded by the surrounding dermal bone and undergo absorption. The inner alveolar border, usually described as arising from a separate ossific center (''
splenialThe splenial is a small bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of the body, produce red blood cell, red and white blood cells, sto ...
center''), is formed in the human mandible by an ingrowth from the main mass of the bone. At birth the bone consists of two parts, united by a fibrous symphysis, in which ossification takes place during the first year. File:Gray178.png, Figure 3: Mandible of human embryo 24 mm. long. Outer aspect. File:Gray179.png, Figure 4: Mandible of human embryo 24 mm. long. Inner aspect. File:Gray180.png, Figure 5: Mandible of human embryo 95 mm. long. Outer aspect. Nuclei of cartilage stippled. File:Gray181.png, Figure 5: Mandible of human embryo 95 mm. long. Inner aspect. Nuclei of cartilage stippled.


Aging

At birth, the body of the bone is a mere shell, containing the sockets of the two incisor, the canine, and the two deciduous
molar teeth The molars or molar teeth are large, flat teeth A tooth (plural teeth) is a hard, calcification, calcified structure found in the jaws (or mouths) of many vertebrates and used to Mastication, break down food. Some animals, particularly carniv ...
, imperfectly partitioned off from one another. The mandibular canal is of large size and runs near the lower border of the bone; the mental foramen opens beneath the socket of the first deciduous molar tooth. The angle is obtuse (175°), and the condyloid portion is nearly in line with the body. The coronoid process is of comparatively large size, and projects above the level of the condyle. After birth, the two segments of the bone become joined at the symphysis, from below upward, in the first year; but a trace of separation may be visible in the beginning of the second year, near the alveolar margin. The body becomes elongated in its whole length, but more especially behind the mental foramen, to provide space for the three additional teeth developed in this part. The depth of the body increases owing to increased growth of the alveolar part, to afford room for the roots of the teeth, and by thickening of the subdental portion which enables the jaw to withstand the powerful action of the masticatory muscles; but, the alveolar portion is the deeper of the two, and, consequently, the chief part of the body lies above the oblique line. The mandibular canal, after the second dentition, is situated just above the level of the mylohyoid line; and the mental foramen occupies the position usual to it in the adult. The angle becomes less obtuse, owing to the separation of the jaws by the teeth; about the fourth year it is 140°. In the adult, the alveolar and subdental portions of the body are usually of equal depth. The mental foramen opens midway between the upper and lower borders of the bone, and the mandibular canal runs nearly parallel with the mylohyoid line. The ramus is almost vertical in direction, the angle measuring from 110° to 120°, also the adult condyle is higher than the coronoid process and the sigmoid notch becomes deeper. In old age, the bone can become greatly reduced in volume where there is a loss of teeth, and consequent resorption of the
alveolar process The alveolar process () (also called the alveolar bone) is the thickened ridge of bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Tr ...

alveolar process
and interalveolar septa. Consequently, the chief part of the bone is below the oblique line. The mandibular canal, with the mental foramen opening from it, is closer to the alveolar border. The ramus is oblique in direction, the angle measures about 140°, and the neck of the condyle is more or less bent backward. File:Gray182.png, Newborn File:Gray183.png, Childhood File:Gray184.png, Adult File:Gray185.png, Old age


Function

The mandible forms the lower jaw and holds the lower teeth in place. It articulates with the left and right
temporal bone The temporal bones are situated at the sides and base of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of ...

temporal bone
s at the temporomandibular joints. *Condyloid process, superior (upper) and posterior projection from the ramus, which makes the temporomandibular joint with the temporal bone *Coronoid process, superior and anterior projection from the ramus. This provides attachment to the
temporal muscle In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of concerned with the study of the structure of s and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things. It i ...

temporal muscle
. Teeth sit in the upper part of the body of the mandible. *The frontmost part of teeth is more narrow and holds front teeth. *The back part holds wider and flatter teeth primarily for chewing food. These teeth also often have wide and sometimes deep grooves on the surfaces.


Clinical significance


Fracture

One fifth of facial injuries involve a mandibular fracture. Mandibular fractures are often accompanied by a 'twin fracture' on the opposite side. There is no universally accepted treatment protocol, as there is no consensus on the choice of techniques in a particular anatomical shape of mandibular fracture clinic. A common treatment involves attachment of metal plates to the fracture to assist in healing. The mandible may be dislocated anteriorly (to the front) and inferiorly (downwards) but very rarely posteriorly (backwards). The
articular disk of the temporomandibular joint The articular disk is a thin, oval plate, which is made from fibrous connective tissue, non vascular, placed between the condyle of the mandible and the mandibular fossa. Its ''upper surface'' is concavo-convex from before backward, to accommodate ...
prevents the mandible from moving posteriorly, making the condylar neck particularly vulnerable to fractures. The mandibular alveolar process can become resorbed when completely edentulous in the mandibular arch (occasionally noted also in partially edentulous cases). This resorption can occur to such an extent that the mental foramen is virtually on the superior border of the mandible, instead of opening on the anterior surface, changing its relative position. However, the more inferior body of the mandible is not affected and remains thick and rounded. With age and tooth loss, the alveolar process is absorbed so that the mandibular canal becomes nearer the superior border. Sometimes with excessive alveolar process absorption, the mandibular canal disappears entirely and leaves the inferior alveolar nerve without its bony protection, although it is still covered by soft tissue.


Forensic medicine

When remains of humans are found, the mandible is one of the common findings, sometimes the only bone found. Skilled experts can estimate the age of the human upon death because the mandible changes over a person's life.


Other vertebrates

In
lobe-finned fish Sarcopterygii (; from Greek language, Greek: , flesh, and , fin)—sometimes considered synonymous with Crossopterygii ("fringe-finned fish", from Greek , fringe)—is a clade (traditionally a class (biology), class or subclass) of the Osteicht ...
es and the early fossil
tetrapod Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a sp ...
s, the bone homologous to the mandible of mammals is merely the largest of several bones in the lower jaw. In such animals, it is referred to as the dentary bone or ''os dentale'', and forms the body of the outer surface of the jaw. It is bordered below by a number of splenial bones, while the angle of the jaw is formed by a lower
angular boneThe angular is a large bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of the body, produce red blood cell, red and white blood cells, store ...
and a suprangular bone just above it. The inner surface of the jaw is lined by a ''prearticular'' bone, while the
articular bone The articular bone is part of the lower jaw of most vertebrates Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animal ...
forms the articulation with the skull proper. Finally a set of three narrow ''coronoid bones'' lie above the prearticular bone. As the name implies, the majority of the teeth are attached to the dentary, but there are commonly also teeth on the coronoid bones, and sometimes on the prearticular as well. This complex primitive pattern has, however, been simplified to various degrees in the great majority of vertebrates, as bones have either fused or vanished entirely. In
teleost Teleostei (Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximat ...
s, only the dentary, articular, and angular bones remain, while in living
amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial animal, ter ...
s, the dentary is accompanied only by the prearticular, and, in
salamander Salamanders are a group of amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most spe ...

salamander
s, one of the coronoids. The lower jaw of
reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptile
s has only a single coronoid and splenial, but retains all the other primitive bones except the prearticular and the periosteum. While, in birds, these various bones have fused into a single structure, in mammals most of them have disappeared, leaving an enlarged dentary as the only remaining bone in the lower jaw – the mandible. As a result of this, the primitive jaw articulation, between the articular and
quadrate bone The quadrate bone is a skull The skull is a bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of ...
s, has been lost, and replaced with an entirely new articulation between the mandible and the temporal bone. An intermediate stage can be seen in some
therapsid Therapsida is a major group of eupelycosauria Eupelycosauria is a large clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic— ...

therapsid
s, in which both points of articulation are present. Aside from the dentary, only few other bones of the primitive lower jaw remain in mammals; the former articular and quadrate bones survive as the
malleus The malleus, or hammer, is a hammer-shaped small bone or ossicle The ossicles (also called auditory ossicles) are three bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. ...

malleus
and the
incus The ''incus'' or anvil is a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear. The ''incus'' receives vibrations from the ''malleus'', to which it is connected laterally, and transmits these to the ''s ...
of the middle ear. Finally, the
cartilaginous fish Chondrichthyes (; ) is a class (biology), class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed ...
, such as
shark Sharks are a group of elasmobranch fish characterized by a Chondrichthyes#Skeleton, cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified withi ...

shark
s, do not have any of the bones found in the lower jaw of other vertebrates. Instead, their lower jaw is composed of a cartilagenous structure homologous with the Meckel's cartilage of other groups. This also remains a significant element of the jaw in some primitive bony fish, such as
sturgeon Sturgeon is the common name Common may refer to: Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common Boston Common (also known as the Common) is a central public park in downtown Boston, Massachusetts. It is s ...

sturgeon
s.


Society and culture

* In the
Book of Judges The Book of Judges (, ') is the seventh book of the Hebrew Bible The Hebrew Bible or Tanakh (; Hebrew Hebrew (, , or ) is a Northwest Semitic languages, Northwest Semitic language of the Afroasiatic languages, Afroasiatic language ...
,
Samson In the Hebrew Bible The Hebrew Bible or Tanakh (; Hebrew: , or ), is the Biblical canon, canonical collection of Hebrew language, Hebrew scriptures, including the Torah, the Nevi'im, and the Ketuvim. These texts are almost exclusively i ...

Samson
used a donkey's jawbone to kill a thousand
Philistines The Philistines were an ancient people who lived on the south coast of Canaan A 1692 map of Canaan, by Philip Lea Canaan (; Northwest Semitic Northwest Semitic, known as Syro-Palestinian in dialect geography, is a division of th ...
. *Dental remains of
Adolf Hitler Adolf Hitler (; 20 April 188930 April 1945) was an Austrian-born German politician who was the dictator of Nazi Germany, Germany from 1933 to 1945. Adolf Hitler's rise to power, He rose to power as the leader of the Nazi Party, becoming Cha ...

Adolf Hitler
including part of a mandible with teeth were the solitary physical evidence used to confirm his death in 1945. The Soviet account published in 1968 describes and photographically depicts the jawbone as being broken off at the alveolar process.


Additional images

File:Mandible.jpg, Lateral view File:Processus_alveolaris.png, Alveolar process


See also

* *
Oral and maxillofacial surgery Oral and maxillofacial surgery is a surgical specialty focusing on reconstructive surgery of the face, facial trauma surgery, the oral cavity, head and neck, mouth, and jaws, as well as facial cosmetic surgery. Specialty An oral and maxil ...
* Simian shelf *
Terms for anatomical location Term may refer to: *Terminology Terminology is a general word for the group of specialized words or meanings relating to a particular field, and also the study of such terms and their use. This is also known as terminology science. Terms are word ...


References


External links

* {{Authority control Vertebrate anatomy Parts of a bird beak Facial bones