Mandible – Wikipedia

Lower chew the fat bone
In anatomy, the mandible, lower jaw or jawbone is the largest, strong and lowest bone in the human facial skeleton. [ 2 ] It forms the lower yack and holds the lower dentition in put. The lower jaw sits beneath the upper jaw. It is the merely movable bone of the skull ( discounting the ossicles of the center ear ). [ 3 ] It is connected to the worldly bones by the temporomandibular joints. The cram is formed in the fetus from a fusion of the entrust and correct mandibular prominences, and the point where these sides join, the mandibular symphysis, is still visible as a faint ridge in the midplane. Like early symphyses in the soundbox, this is a midplane articulation where the bones are joined by fibrocartilage, but this articulation fuses in concert in early childhood. [ 4 ] The word “ lower jaw ” derives from the Latin news mandibula, “ lower jaw ” ( literally “ one used for chewing ” ), from mandere “ to chew ” and -bula ( implemental suffix ).

structure [edit ]

lower jaw, lateral surface, side view

Components [edit ]

lower jaw, median surface, side scene 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 proper. The lingula is just above the mandibular foramen. The body of the lower jaw is curved, and the front separate 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 age. [ 5 ] This ridge divides below and encloses a triangular eminence, the mental bulge ( the kuki ), the floor of which is depressed in the center but raised on both sides to form the mental tuberosity. just above this, on both sides, the mentalis muscles attach to a depression called the incisive fossa. [ 5 ] Below the second gear premolar tooth, on both sides, midway between the upper and lower borders of the body, are the genial foramen, for the enactment of the mental vessels and heart. [ 5 ] Running backward and up from each genial tuberosity is a faint ridge, the oblique cable, which is continuous with the front tooth surround 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 inside, the lower jaw appears concave. Near the lower separate of the symphysis is a copulate 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 origin of the geniohyoid. In some cases, the genial spines are fused to form a individual tuberosity, in others they are absent and their placement is indicated merely by an constipation 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 cram. Below the mental spines, on either side of the middle argumentation, is an ellipse low for the attachment of the anterior belly of the digastric. Extending up and backward on either side from the lower separate of the symphysis is the mylohyoid note, which gives origin to the mylohyoid muscleman ; the back tooth part of this tune, near the alveolar consonant margin, gives fastening to a small function 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 back part, an ellipse pit 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 outside, the ramus is compressed and marked by devious ridges at its lower share. It gives attachment throughout about the solid of its extent to the masseter muscleman. [ 6 ] On the inside at the center there is an devious mandibular foramen, for the entrance of the inferior alveolar consonant vessels and boldness. The margin of this opening is irregular ; it presents in front a outstanding ridge, surmounted by a shrill spinal column, the lingula of the lower jaw, which gives attachment to the sphenomandibular ligament ; at its lower and back contribution is a pass from which the mylohyoid groove runs sidelong down and ahead, and lodges the mylohyoid vessels and nerve. Behind this groove is a rough surface, for the interpolation of the medial pterygoid brawn. The mandibular canal runs sidelong down and ahead in the ramus, and then horizontally forward in the body, where it is placed under the alveolus 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 posterior two-thirds of the bone the canal is situated nearer the home come on of the lower jaw ; and in the anterior third, nearer its external open. It contains the inferior alveolar 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 independent holes ( foramen ), 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 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 boldness, a branch of the mandibular nerve, ( a major division of the trigeminal nerve ), enters the mandibular foramen and runs forward in the mandibular duct, supplying sensation to the dentition. At the mental foramen, the nerve divides into two terminal branches : incisive and genial nerves. The incisive boldness runs fore in the lower jaw and supplies the anterior tooth. The mental steel exits the genial foramen and supplies sensation to the lower lip .

mutant [edit ]

Males generally have squarer, stronger, and larger mandibles than females. The mental bulge is more pronounce in males but can be visualized and palpated in females. [ citation needed ] rarely, a bifid inferior alveolar heart may be deliver, in which shell a second mandibular foramen, more inferiorly placed, exists and can be detected by noting a double over mandibular duct on a radiogram. [ 4 ]

Development [edit ]

The lower jaw forms as a bone ( ossifies ) over time from a entrust and right piece of cartilage, called Meckel ‘s cartilage. These cartilages form the cartilaginous legal profession of the mandibular arch. Near the head, they are connected with the auricle capsules, and they meet at the lower end at the mandibular symphysis, a coalition luff between the two bones, by mesoblastic tissue. They run forward immediately below the condyles and then, bending downward, lie in a furrow near the lower margin of the bone ; in front of the canine tooth they incline upward to the symphysis. From the proximal end of each cartilage the malleus and incus, two of the bones of the middle ear, are developed ; the following future share, adenine far as the lingula, is replaced by fibrous weave, which persists to form the sphenomandibular ligament. Between the lingula and the canine tooth the cartilage disappears, while the helping of it below and behind the incisor teeth becomes ossified and incorporated with this separate of the lower jaw. About the sixth week of fetal life sentence, intramembranous ossification takes put in the membrane covering the out surface of the adaxial end of Meckel ‘s cartilage, and each half of the bone is formed from a individual center which appears, near the mental foramen. By the tenth week, the fortune of Meckel ‘s cartilage which lies below and behind the incisor tooth is surrounded and invaded by the cuticular bone ( besides known as the membrane bone ). reasonably later, accessory nucleus 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 lens nucleus posse no break ossific centers but are invaded by the surrounding dermal bone and undergo assimilation. The inner alveolar edge, normally described as arising from a classify ossific focus on ( splenial center ), is formed in the human lower jaw 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 foremost year .

Aging [edit ]

At birth, the body of the bone is a bare plate, containing the sockets of the two incisor, the canine, and the two deciduous molar teeth, imperfectly partitioned off from one another. The mandibular canal is of large size and runs near the lower bound of the bone ; the mental foramen opens beneath the socket of the beginning deciduous molar tooth. The slant is obtuse ( 175° ), and the condyloid fortune is about in argumentation with the soundbox. The coronoid process is of relatively 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 up, in the first base year ; but a trace of separation may be visible in the begin of the second year, near the alveolar margin. The body becomes elongated in its unharmed length, but more specially behind the mental foramen, to provide quad for the three extra teeth developed in this part. The depth of the body increases owing to increased emergence of the alveolar consonant separate, to afford room for the roots of the tooth, and by thickening of the subdental part which enables the chew to withstand the mighty action of the masticatory muscles ; but, the alveolar consonant share is the deep of the two, and, consequently, the chief part of the body lies above the oblique occupation. The mandibular canal, after the second dentition, is situated good above the degree of the mylohyoid line ; and the mental foramen occupies the position usual to it in the adult. The angle becomes less dense, owing to the separation of the yack by the teeth ; about the fourthly year it is 140°. In the adult, the alveolar and subdental portions of the body are normally of peer depth. The genial foramen opens midway between the upper berth and lower borders of the bone, and the mandibular canal runs closely parallel with the mylohyoid credit line. The ramus is about upright in direction, the fish measuring from 110° to 120°, besides the adult condyle is higher than the coronoid summons and the sigmoid notch becomes deeper. In honest-to-god age, the bone can become greatly reduced in volume where there is a loss of teeth, and attendant resorption of the alveolar process and interalveolar septum. consequently, the foreman separate of the bone is below the devious line. The mandibular canal, with the mental foramen opening from it, is closer to the alveolar surround. The ramus is devious 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 zygomatic arch and a part of the ramus of the lower jaw have been removed
The lower jaw forms the lower jaw and holds the lower tooth in space. It articulates with the bequeath and right temporal role 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 berth region 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 often accompanied by a ‘twin fracture ‘ on the opposite side. There is no universally accepted discussion protocol, as there is no consensus on the option of techniques in a particular anatomic form of mandibular fault clinic. A common discussion involves attachment of metal 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 front ) and inferiorly ( downwards ) but very rarely posteriorly ( backwards ). The articular phonograph record of the temporomandibular joint prevents the lower jaw from moving posteriorly, making the condylar neck particularly vulnerable to fractures. [ 5 ] The mandibular alveolar 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 about on the superior bound of the lower jaw, rather of opening on the anterior open, changing its proportional stead. however, the more deficient consistency of the lower jaw is not involve and remains slurred and rounded. With senesce and tooth loss, the alveolar consonant process is absorbed so that the mandibular canal becomes nearer the superior boundary line. sometimes with excessive alveolar summons assimilation, the mandibular canal disappears entirely and leaves the inferior alveolar boldness without its bony protection, although it is still covered by soft weave. [ 4 ]

forensic medicine [edit ]

When remains of humans are found, the lower jaw is one of the common findings, sometimes the only bone found. skilled experts can estimate the old 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 fossil tetrapods, the bone homologous to the lower jaw of mammals is merely the largest of respective 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 issue of splenial bones, while the fish of the call on the carpet is formed by a lower angular bone and a suprangular bone barely above it. The inner surface of the yack is lined by a prearticular bone, while the articular bone forms the articulation with the skull proper. finally a specify 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 normally besides teeth on the coronoid bones, and sometimes on the prearticular arsenic well. [ 10 ] This building complex primitive model has, however, been simplified to versatile degrees in the capital majority of vertebrates, as bones have either fused or vanished wholly. In teleosts, entirely the dentary, articular, and angular bones remain, while in life amphibians, the dentary is accompanied only by the prearticular, and, in salamanders, one of the coronoids. The lower chew the fat of reptiles has entirely a individual coronoid and splenial, but retains all the early crude bones except the prearticular and the periosteum. [ 10 ] While, in birds, these respective bones have fused into a individual structure, in mammals most of them have disappeared, leaving an exaggerated dentary as the only remaining bone in the lower chew the fat – the lower jaw. As a result of this, the primitive yack articulation, between the articular and quadrate bones, has been lost, and replaced with an entirely modern articulation between the lower jaw and the temporal role bone. An intermediate stage can be seen in some therapsids, in which both points of articulation are award. aside from the dentary, only few other bones of the primitive lower jaw remain in mammals ; the early articular and quadrate bones survive as the malleus and the incus of the middle ear. [ 10 ] last, the cartilaginous fish, such as sharks, do not have any of the bones found in the lower yack of other vertebrates. rather, their lower jaw is composed of a cartilagenous structure homologous with the Meckel ‘s cartilage of other groups. This besides remains a significant element of the jaw in some primitive bony fish, such as sturgeons. [ 10 ]

club 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
reference : https://thaitrungkien.com
Category : Tutorial

Related Posts

Trả lời

Email của bạn sẽ không được hiển thị công khai.