Mandible – Wikipedia

Lower jaw bone
In human body, the mandible, lower jaw or jawbone is the largest, hard and lowest bone in the human facial skeleton. [ 2 ] It forms the lower yack and holds the lower tooth in station. The lower jaw sits beneath the upper jaw. It is the only movable cram of the skull ( discounting the ossicles of the center ear ). [ 3 ] It is connected to the temporal bones by the temporomandibular joints. The bone is formed in the fetus from a fusion of the leave and right mandibular prominences, and the point where these sides join, the mandibular symphysis, is placid visible as a dim ridge in the midplane. Like other symphyses in the body, this is a midplane articulation where the bones are joined by fibrocartilage, but this articulation fuses together in early childhood. [ 4 ] The news “ lower jaw ” derives from the Latin give voice mandibula, “ lower jaw ” ( literally “ one used for chewing ” ), from mandere “ to chew ” and -bula ( instrumental suffix ).

structure [edit ]

lower jaw, lateral surface, side horizon

Components [edit ]

lower jaw, median surface, side opinion The lower jaw 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 or the gonial angle.

body [edit ]

body and ramus of the lower jaw. The mandibular foramen is labeled on the right. The lingula is just above the mandibular foramen. The body of the lower jaw is curved, and the front function gives structure to the chin. It has two surfaces and two borders. From the outside, the lower jaw is marked in the midplane by a faint ridge, indicating the mandibular symphysis, the credit line of articulation of the two halves of the lower jaw, which fuse at about one year of long time. [ 5 ] This ridge divides below and encloses a trilateral tuberosity, the genial bulge ( the kuki ), the base of which is depressed in the center but raised on both sides to form the mental tuberosity. precisely above this, on both sides, the mentalis muscles attach to a depression called the acute fossa. [ 5 ] Below the second premolar tooth, on both sides, midway between the upper and lower borders of the body, are the mental foramen, for the passage of the mental vessels and steel. [ 5 ] Running back and upward from each mental nodule is a faint ridge, the oblique wrinkle, which is continuous with the front tooth border of the ramus. [ 5 ] Attached to this is the masseter muscle, the depressor labii inferioris and depressor anguli oris, and the platysma ( from below ). [ 5 ] From the at heart, the lower jaw appears concave. Near the lower depart of the symphysis is a pair of laterally placed spines, termed the mental spines, which give origin to the genioglossus. immediately below these is a second pair of spines, or more frequently a median ridge or impression, for the beginning of the geniohyoid. In some cases, the mental spines are fused to form a single eminence, in others they are absent and their place is indicated merely by an abnormality of the surface. Above the mental spines, a medial foramen and furrow are sometimes seen ; they mark the line of union of the halves of the cram. Below the mental spines, on either side of the middle line, is an ellipse depressive disorder for the attachment of the anterior belly of the digastric. Extending up and backward on either side from the lower part of the symphysis is the mylohyoid agate line, which gives lineage to the mylohyoid muscle ; the later separate of this line, near the alveolar margin, gives attachment to a minor separate of the constrictor pharyngis superior, and to the pterygomandibular raphe. Above the anterior separate of this line is a smooth triangular area against which the sublingual gland rests, and below the handicap part, an ellipse fossa for the 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 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, may be present.

ramus [edit ]

3D model of the lower jaw The ramus ( latin : branch ) of the human lower jaw has four sides, two surfaces, four borders, and two processes. On the external, the ramus is bland and marked by devious ridges at its lower character. It gives attachment throughout about the whole of its extent to the masseter muscle. [ 6 ] On the inside at the center there is an devious mandibular foramen, for the entrance of the inferior alveolar vessels and heart. The margin of this possibility is irregular ; it presents in front a outstanding ridge, surmounted by a acuate spinal column, the lingula of the lower jaw, which gives attachment to the sphenomandibular ligament ; at its lower and bet on part is a notch from which the mylohyoid groove runs obliquely down and forward, and lodges the mylohyoid vessels and steel. Behind this furrow is a rough surface, for the interpolation of the median pterygoid muscle. The mandibular duct runs obliquely downward and forward in the ramus, and then horizontally ahead in the body, where it is placed under the tooth socket and communicates with them by minor openings. On arriving at the incisor tooth, it turns back to communicate with the mental foramen, giving off two small canals which run to the cavities containing the incisor dentition. In the later two-thirds of the bone the canal is situated nearer the inner surface of the lower jaw ; and in the anterior third, nearer its external surface. It contains the inferior alveolar consonant vessels and heart, from which branches are distributed to the tooth. 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 medially; the stylomandibular ligament 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 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.

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 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.[5]
  • The mandibular notch, separating the two processes, is a deep semilunar depression and is crossed by the masseteric vessels and nerve.

Foramina [edit ]

The lower jaw has two main holes ( foramen ), found on both its good 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 apices 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.[4]

Nerves [edit ]

The inferior alveolar consonant heart, a branch of the mandibular boldness, ( a major division of the trigeminal boldness ), enters the mandibular foramen and runs forward in the mandibular canal, supplying sensation to the tooth. At the mental foramen, the steel divides into two terminal branches : acute and genial nerves. The acute boldness runs ahead in the lower jaw and supplies the front tooth tooth. The mental steel exits the mental foramen and supplies sensation to the lower sass .

variation [edit ]

Males by and large have squarer, stronger, and larger mandibles than females. The mental bulge is more marked in males but can be visualized and palpated in females. [ citation needed ] rarely, a bifid inferior alveolar nerve may be present, in which case a moment mandibular foramen, more inferiorly placed, exists and can be detected by noting a duplicate mandibular duct on a radiogram. [ 4 ]

Development [edit ]

The lower jaw forms as a bone ( ossifies ) over time from a leave and right firearm of cartilage, called Meckel ‘s cartilage. These cartilages form the cartilaginous bar of the mandibular arch. Near the head, they are connected with the ear capsules, and they meet at the lower goal at the mandibular symphysis, a fusion compass point between the two bones, by mesoblastic tissue. They run forward immediately below the condyles and then, bending down, lie in a rut near the lower margin of the cram ; in front of the canine tooth they incline up to the symphysis. From the proximal end of each cartilage the malleus and incus, two of the bones of the in-between ear, are developed ; the adjacent succeed part, american samoa far as the lingula, is replaced by hempen tissue, which persists to form the sphenomandibular ligament. Between the lingula and the canine tooth the cartilage disappears, while the parcel of it below and behind the incisor teeth becomes ossified and incorporated with this part of the lower jaw. About the one-sixth workweek of fetal liveliness, intramembranous ossification takes place in the membrane covering the out airfoil of the adaxial 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 workweek, the parcel of Meckel ‘s cartilage which lies below and behind the incisor tooth is surrounded and invaded by the cutaneous bone ( besides known as the membrane bone ). slightly former, accessory core 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 nucleus possess no separate ossific centers but are invaded by the surrounding cutaneous bone and undergo absorption. The inner alveolar frame, normally described as arising from a classify ossific center ( splenial center ), is formed in the human lower jaw by an ingrowth from the independent multitude of the cram. At birth the bone consists of two parts, united by a fibrous symphysis, in which ossification takes place during the first class .

Aging [edit ]

At parturition, the body of the bone is a mere plate, containing the sockets of the two incisor, the canine, and the two deciduous molar teeth, imperfectly partitioned off from one another. The mandibular duct is of big 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 dense ( 175° ), and the condyloid fortune is about in channel with the torso. The coronoid process is of relatively boastfully size, and projects above the level of the condyle. After birth, the two segments of the bone become joined at the symphysis, from below up, in the first class ; but a trace of separation may be visible in the begin of the second year, near the alveolar gross profit. The torso becomes elongated in its hale length, but more specially behind the mental foramen, to provide distance for the three extra teeth developed in this share. The astuteness of the body increases owing to increased growth of the alveolar consonant part, to afford room for the roots of the tooth, and by thickening of the subdental parcel which enables the jaw to withstand the mighty action of the masticatory muscles ; but, the alveolar fortune is the thick of the two, and, consequently, the head contribution of the body lies above the external oblique muscle line. The mandibular canal, after the moment teething, is situated precisely above the grade of the mylohyoid line ; and the mental foramen occupies the position usual to it in the pornographic. The angle becomes less obtuse, owing to the separation of the chew by the teeth ; about the fourth year it is 140°. In the adult, the alveolar and subdental portions of the soundbox are normally of equal depth. The mental foramen opens halfway between the amphetamine and lower borders of the bone, and the mandibular canal runs about twin with the mylohyoid line. The ramus is about erect in commission, the slant measuring from 110° to 120°, besides the adult condyle is higher than the coronoid process and the sigmoid notch becomes deeper. In old long time, the bone can become greatly reduced in bulk where there is a loss of teeth, and attendant resorption of the alveolar consonant action and interalveolar septum. consequently, the head separate of the cram is below the external oblique muscle tune. The mandibular canal, with the genial foramen opening from it, is closer to the alveolar consonant border. The ramus is external oblique muscle in direction, the lean measures about 140°, and the neck of the condyle is more or less bent backward .

function [edit ]

The median and lateral pterygoid muscles ; the cheekbone arch and a fortune of the ramus of the lower jaw have been removed
The lower jaw forms the lower call on the carpet and holds the lower tooth in set. It articulates with the left and veracious temporal bones 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.

Teeth sit in the upper share of the body of the lower jaw .

  • 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 [edit ]

fracture [edit ]

One fifth of facial injuries involve a mandibular fracture. [ 8 ] Mandibular fractures are frequently accompanied by a ‘twin fault ‘ on the antonym side. There is no universally accepted treatment protocol, as there is no consensus on the choice of techniques in a detail anatomic human body of mandibular fracture clinic. A common treatment involves attachment of metallic element plates to the fracture to assist in healing. [ 9 ]

Causes of mandibular fractures[7]
Cause Percentage
Motor vehicle accident 40%
Assault 10%
Fall 10%
Sport 5%
Other 5%

The lower jaw may be dislocated anteriorly ( to the battlefront ) and inferiorly ( downwards ) but identical rarely posteriorly ( backwards ). The articular harrow of the temporomandibular joint prevents the lower jaw from moving posteriorly, making the condylar neck particularly vulnerable to fractures. [ 5 ] The mandibular alveolar consonant process can become reabsorb when completely edentulous in the mandibular arch ( occasionally noted besides in partially edentulous cases ). This resorption can occur to such an extent that the mental foramen is virtually on the superior bound of the lower jaw, rather of opening on the anterior airfoil, changing its relative stead. however, the more deficient torso of the lower jaw is not affect and remains thick and rounded. With age and tooth loss, the alveolar process is absorbed so that the mandibular canal becomes nearer the lake superior boundary line. sometimes with excessive alveolar process preoccupation, the mandibular canal disappears entirely and leaves the inferior alveolar nerve without its bony protection, although it is still covered by soft tissue. [ 4 ]

forensic music [edit ]

When remains of humans are found, the lower jaw is one of the coarse findings, sometimes the only bone found. skilled experts can estimate the age of the human upon death because the lower jaw changes over a person ‘s life. [ 5 ]

early vertebrates [edit ]

In lobe-finned fishes and the early dodo tetrapods, the bone homologous to the lower jaw of mammals is merely the largest of several bones in the lower chew. In such animals, it is referred to as the dentary bone or os dentale, and forms the body of the out surface of the chew the fat. It is bordered below by a number of splenial bones, while the angle of the yack is formed by a lower angular bone and a suprangular bone fair above it. The inner surface of the chew the fat is lined by a prearticular bone, while the articular cram forms the articulation with the skull proper. last a set up of three narrow coronoid bones dwell above the prearticular cram. As the name implies, the majority of the teeth are attached to the dentary, but there are normally besides teeth on the coronoid bones, and sometimes on the prearticular american samoa well. [ 10 ] This complex archaic pattern has, however, been simplified to respective degrees in the great majority of vertebrates, as bones have either fused or vanished entirely. In teleosts, only the dentary, articular, and angular bones remain, while in exist amphibians, the dentary is accompanied only by the prearticular, and, in salamanders, one of the coronoids. The lower call on the carpet of reptiles has only a single coronoid and splenial, but retains all the other primitive bones except the prearticular and the periosteum. [ 10 ] While, in birds, these assorted bones have fused into a one structure, in mammals most of them have disappeared, leaving an exaggerated dentary as the only remaining bone in the lower jaw – the lower jaw. As a leave of this, the primitive jaw articulation, between the articular and quadrate bones, has been lost, and replaced with an entirely fresh joint between the lower jaw and the temporal bone. An intermediate stage can be seen in some therapsids, in which both points of articulation are portray. aside from the dentary, merely few other bones of the primitive lower jaw remain in mammals ; the erstwhile articular and quadrate bones survive as the malleus and the incus of the center auricle. [ 10 ] ultimately, the cartilaginous fish, such as sharks, do not have any of the bones found in the lower yack of other vertebrates. alternatively, their lower jaw is composed of a cartilagenous social organization homologous with the Meckel ‘s cartilage of other groups. This besides remains a significant element of the jaw in some primitive osseous fish, such as sturgeons. [ 10 ]

society and culture [edit ]

extra images [edit ]

See besides [edit ]

This article uses anatomic terminology

References [edit ]

Public domain This article incorporates text in the public domain from page 172 of the 20th edition of Gray ‘s Anatomy (1918)

  • Media related to Mandibles at Wikimedia Commons
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