The mandibular fossa is the depression in the temporal bone that articulates with the mandible. In the temporal bone, the mandibular fossa is bounded anteriorly by the articular tubercle and posteriorly by the tympanic portion of the temporal bone, which separates it from the external acoustic meatus; the fossa is divided into two parts by the petrotympanic fissure. It is referred to as the glenoid fossa in dental literature. Temporomandibular joint This article incorporates text in the public domain from page 140 of the 20th edition of Gray's Anatomy Anatomy figure: 22:4b-07 at Human Anatomy Online, SUNY Downstate Medical Center Anatomy photo:27:st-0311 at the SUNY Downstate Medical Center
The mandible, lower jaw or jawbone is the largest and lowest bone in the human face. It holds the lower teeth in place; the mandible sits beneath the maxilla. It is the only movable bone of the skull; the bone is formed in the fetus from a fusion of the left and right mandibular prominences, the point where these sides join, the mandibular symphysis, is still visible as a faint ridge in the midline. Like other symphyses in the body, this is a midline articulation where the bones are joined by fibrocartilage, but this articulation fuses together in early childhood; the word "mandible" derives from the Latin word mandibula, "jawbone", from mandere "to chew" and -bula. 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 or the gonial angle; the body of the mandible is curved, the front part gives structure to the chin. It has two borders. From the outside, the mandible is marked in the midline by a faint ridge, indicating the mandibular symphysis, the line of junction of the two pieces of which the bone is composed at an early period of life.
This ridge divides below and encloses a triangular eminence, the mental protuberance, the base of, depressed in the center but raised on either side to form the mental tubercle. On either side of the symphysis, just below the incisor teeth, is a depression, the incisive fossa, which gives origin to the mentalis and a small portion of the orbicularis oris. Below the second premolar tooth, on either side, midway between the upper and lower borders of the body, is the mental foramen, for the passage of the mental vessels and nerve. Running backward and upward from each mental tubercle is a faint ridge, the oblique line, continuous with the anterior border of the ramus. 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. Below these is a second pair of spines, or more a median ridge or impression, for the origin of the geniohyoid. In some cases, the mental spines are fused to form a single eminence, in others they are absent and their position is indicated by an irregularity of the surface.
Above the mental spines, a median foramen and furrow are sometimes seen. 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. 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. Above the anterior part of this line is a smooth triangular area against which the sublingual gland rests, below the hinder part, an oval 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. 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, thicker in front than behind. The ramus of the human mandible has four sides, two surfaces, four borders, two processes. On the outside, the ramus marked by oblique ridges at its lower part.
On the inside at the center there is an oblique mandibular foramen, for the entrance of the inferior alveolar vessels and nerve. The margin of this opening is irregular. Behind this groove is a rough surface, for the insertion of the medial pterygoid muscle; the mandibular canal runs obliquely downward and forward in the ramus, horizontally forward in the body, where it is placed under the alveoli and communicates with them by small openings. On arriving at the incisor teeth, 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, 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 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, the medial pterygoid muscle medially.
The anterior border is thin above, thicker below, continuous with the oblique l
The jaw is any opposable articulated structure at the entrance of the mouth used for grasping and manipulating food. The term jaws is broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of most animals. In arthropods, the jaws are chitinous and oppose laterally, may consist of mandibles or chelicerae; these jaws are composed of numerous mouthparts. Their function is fundamentally for food acquisition, conveyance to the mouth, and/or initial processing. Many mouthparts and associate structures are modified legs. In most vertebrates, the jaws are bony or cartilaginous and oppose vertically, comprising an upper jaw and a lower jaw; the vertebrate jaw is derived from the most anterior two pharyngeal arches supporting the gills, bears numerous teeth. The vertebrate jaw originally evolved in the Silurian period and appeared in the Placoderm fish which further diversified in the Devonian; the two most anterior pharyngeal arches are thought to have become the jaw itself and the hyoid arch, respectively.
The hyoid system suspends the jaw from the braincase of the skull, permitting great mobility of the jaws. While there is no fossil evidence directly to support this theory, it makes sense in light of the numbers of pharyngeal arches that are visible in extant jawed vertebrates, which have seven arches, primitive jawless vertebrates, which have nine; the original selective advantage offered by the jaw may not be related to feeding, but rather to increased respiration efficiency. The jaws were used in the buccal pump that pumps water across the gills of fish or air into the lungs in the case of amphibians. Over evolutionary time the more familiar use of jaws, in feeding, was selected for and became a important function in vertebrates. Many teleost fish have modified jaws for suction feeding and jaw protrusion, resulting in complex jaws with dozens of bones involved; the jaw in tetrapods is simplified compared to fish. Most of the upper jaw bones have been fused to the braincase, while the lower jaw bones have been fused together into a unit called the mandible.
The jaw articulates via a hinge joint between the articular. The jaws of tetrapods exhibit varying degrees of mobility between jaw bones; some species have jaw bones fused, while others may have joints allowing for mobility of the dentary, quadrate, or maxilla. The snake skull shows the greatest degree of cranial kinesis, which allows the snake to swallow large prey items. In mammals the jaws are made up of the maxilla. In the ape there is a reinforcement to the lower jaw bone called the simian shelf. In the evolution of the mammalian jaw, two of the bones of the jaw structure were reduced in size and incorporated into the ear, while many others have been fused together; as a result, mammals show little or no cranial kinesis, the mandible is attached to the temporal bone by the temporomandibular joints. Temporomandibular joint dysfunction is a common disorder of these joints, characterized by pain and limitation of mandibular movement. Sea urchins possess unique jaws which display five-part symmetry, termed the Aristotle's lantern.
Each unit of the jaw holds a single, perpetually growing tooth composed of crystalline calcium carbonate. Muscles of mastication Otofacial syndrome Predentary Prognathism Rostral bone Jaw at the US National Library of Medicine Medical Subject Headings
In human anatomy, the mandibular canal is a canal within the mandible that contains the inferior alveolar nerve, inferior alveolar artery, inferior alveolar vein. It runs obliquely downward and forward in the ramus, horizontally forward in the body, where it is placed under the alveoli and communicates with them by small openings. On arriving at the incisor teeth, it turns back to communicate with the mental foramen, giving off a small canal known as the mandibular incisive canal, which run to the cavities containing the incisor teeth, it carries branches of artery. It is continuous with the mental mandibular foramen; the mandibular canal is close to the apices of the second molar in 50% of the radiographs. In 40%, canal is away from the root apices, in only 10% of the radiographs the root apices appeared to penetrate the canal. In root canal therapy of the second molar one should be cautious of over extending the reamer or the root canal filling materials because there is a possible risk of inferior alveolar nerve injury.
Human mandible Inferior alveolar artery This article incorporates text in the public domain from page 173 of the 20th edition of Gray's Anatomy Anatomy photo:27:09-0104 at the SUNY Downstate Medical Center
Torus mandibularis is a bony growth in the mandible along the surface nearest to the tongue. Mandibular tori are present near the premolars and above the location of the mylohyoid muscle's attachment to the mandible. In 90% of cases, there is a torus on both the left and right sides, making this finding a predominantly bilateral condition; the prevalence of mandibular tori ranges from 5% - 40%. It is less common than bony growths occurring on the palate, known as torus palatinus. Mandibular tori are more common in Asian and Inuit populations, more common in males. In the United States, the prevalence is 7% - 10% of the population, it is believed. They are associated with bruxism; the size of the tori may fluctuate throughout life, in some cases the tori can be large enough to touch each other in the midline of mouth. It is believed that mandibular tori are the result of local stresses and not due to genetic influences. Mandibular tori are a clinical finding with no treatment necessary, it is possible for ulcers to form in the area of the tori due to trauma.
The tori may complicate the fabrication of dentures. If removal of the tori is needed, surgery can be done to reduce the amount of bone, but the tori may reform in cases where nearby teeth still receive local stresses. Marquette University School of Dentistry - Oral & Maxiollofacial Pathology, What Could This Be? What are mandibular tori