he connection between a tooth and jaw bone is an example of a joint
gomphosis
1675184
tooth and the jawbone is also called a joint, and is described as a fibrous joint known as a gomphosis. Joints are classified both structurally and functionally. Joints are mainly classified structurally and functionally. Structural classification is determined by how the bones connect to each other, while functional classification is determined by the degree of movement between the articulating bones. In practice, there is significant overlap between the two types of classifications. Structural classification names and divides joints according to the type of binding tissue that connects the bones to each other. There are three structural classifications of joints: Joints
Joint
9060902
in the maxillary bone and mandible. The fibrous connection between a tooth and its socket is a periodontal ligament. Specifically, the connection is made between the maxilla or mandible to the cementum of the tooth. The motion of a gomphosis is minimal, though considerable movement can be achieved over time—the basis of using braces to realign teeth. The joint can be considered a synarthrosis. The gomphosis is the only joint-type in which a bone does not join another bone, as teeth are not technically bone. In modern, more anatomical, joint classification, the gomphosis is simply considered a fibrous joint because
Fibrous joint
5262982
Dental alveolus Dental alveoli (singular "alveolus") are sockets in the jaws in which the roots of teeth are held in the alveolar process with the periodontal ligament. The lay term for dental alveoli is tooth sockets. A joint that connects the roots of the teeth and the alveolus is called "gomphosis" (plural "gomphoses"). Alveolar bone is the bone that surrounds the roots of the teeth forming bone sockets. In mammals, tooth sockets are found in the maxilla, the premaxilla, and the mandible. Socket preservation or alveolar ridge preservation (ARP) is a procedure to reduce bone loss after tooth extraction to
Dental alveolus
5355486
appliances, an area of bone under compressive force from a tooth moving toward it has a high osteoclast level, resulting in bone resorption. An area of bone receiving tension from periodontal ligaments attached to a tooth moving away from it has a high number of osteoblasts, resulting in bone formation. Thus, the tooth or teeth are slowly moved along the jaw so as to achieve a dentition that works in harmony. In this way, the width of the space between the alveoli and the root is kept about the same. The connection between the gingiva and the tooth is called
Human tooth development
1635637
the lower jaw, the articular, makes a connection with a bone of the cranium called the quadrate bone to form the articular-quadrate jaw joint. In forms transitional to mammals, the jaw joint is composed of a large, lower jaw bone (similar to the dentary found in mammals) that does not connect to the squamosal, but connects to the quadrate with a receding articular bone. Over time, as synapsids became more mammalian and less 'reptilian', they began to develop a secondary palate, separating the mouth and nasal cavity. In early synapsids, a secondary palate began to form on the sides of
Synapsid
11798154
which supplemented the growth of the tooth and gave the tooth some sensory abilities. During the early part of the development of the teeth, the roots would have been open, and the only connection that would have been facilitated would have been the cementum between the tooth and the alveolar bone, the periodontal ligament and the cementum made anchorage trabeculae would have mediated this connection. This complex, called the tripartite periodontium, during the life of "Stereosternum", would have acted as a mechanism for keeping the teeth within the jaw, working against the lateral forces that could easily pull teeth out
Stereosternum
1635636
ear bones: while modern mammals possess the malleus, incus and stapes, basal synapsids (like all other tetrapods) possess only a stapes. The malleus is derived from the articular (a lower jaw bone), while the incus is derived from the quadrate (a cranial bone). Mammalian jaw structures are also set apart by the dentary-squamosal jaw joint. In this form of jaw joint, the dentary forms a connection with a depression in the squamosal known as the glenoid cavity. In contrast, all other jawed vertebrates, including reptiles and nonmammalian synapsids, possess a jaw joint in which one of the smaller bones of
Synapsid
6039
"Allosaurus" were modestly proportioned for a theropod of its size. Paleontologist Gregory S. Paul gives a length of for a skull belonging to an individual he estimates at long. Each premaxilla (the bones that formed the tip of the snout), held five teeth with D-shaped cross-sections, and each maxilla (the main tooth-bearing bones in the upper jaw) had between 14 and 17 teeth; the number of teeth does not exactly correspond to the size of the bone. Each dentary (the tooth-bearing bone of the lower jaw) had between 14 and 17 teeth, with an average count of 16. The teeth
Allosaurus
14306572
can be determined in the upper jaw, since their sockets are preserved. The connection between the (forehead bone) and (bone running at the upper length of the snout) bones is displaced, and part of the is missing. Most of the snout is preserved, with the of the right side being well-preserved. Only the front part of the left (tooth-bearing bone of the mandible) and some of its broken teeth are preserved. The forelimb (of which all preserved parts are articulated) consists of the middle part of the and (bones of the lower arm), the extremity of the second and third
Xixiasaurus
10912552
jaws of early synapsids, including the ancestors of mammals, were similar to those of other tetrapods of the time, with a lower jaw consisting of a tooth-bearing dentary bone and several smaller posterior bones. The jaw joint consisted of the articular bone in the lower jaw and the quadrate in the upper jaw. The early pelycosaurs (late Carboniferous and early Permian) most probably did not have tympanic membranes (external eardrums), and their massive stapes bones supported the braincase, with the lower ends resting on the quadrates. But their descendants the therapsids (including mammals' ancestors) probably did have tympanic membranes and
Evolution of mammalian auditory ossicles
7926039
the jaw is composed of four bony elements and referred to as a Quadro-articular jaw because the joint is between the articular and quadrate bones. In therapsids (advanced synapsids including mammal ancestors) the jaw is simplified into an articulation between the dentary and the squamous part of the temporal bone, and hence referred to as a dentary-squamosal jaw. In therapsids, the other two bones have moved into the ear to become the malleus and incus. Squamosal bone The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull,
Squamosal bone
775197
nerve fibers can then send the information to the central nervous system for interpretation. The alveolar bone is the bone of the jaw which forms the alveolus around teeth. Like any other bone in the human body, alveolar bone is modified throughout life. Osteoblasts create bone and osteoclasts destroy it, especially if force is placed on a tooth. As is the case when movement of teeth is attempted through orthodontics, an area of bone under compressive force from a tooth moving toward it has a high osteoclast level, resulting in bone resorption. An area of bone receiving tension from periodontal
Human tooth
10912557
that it would have had if the articular and quadrate had remained part of the jaw joint. However, several studies have cast doubt on whether "Hadrocodium" did indeed possess a definitive mammalian middle ear; "Hadrocodium" likely had an ossified connection between the middle ear and the jaw, which is not visible in the fossil evidence due to limited preservation. Researchers now hypothesize that the definitive mammalian middle ear did not emerge any earlier than the late Jurassic (~163M years ago). It has been suggested that a relatively large trough in the jaw bone of the early Cretaceous monotreme "Teinolophos" provides
Evolution of mammalian auditory ossicles
20105388
the group as a whole. The only skull bones which can be confidently referred to this group consist of a few pterygoid and postorbital fragments belonging to "Yarasuchus" as well as some fragmentary material considered to belong to "Teleocrater". These bones include a maxilla (tooth-bearing bone of the middle of the snout), frontal (part of the skull roof above the eyes), and a quadrate (part of the cranium's jaw joint). Although these fragments make it difficult to reconstruct the skull of aphanosaurs, they do show several notable features. For example, the shape of the maxilla shows that aphanosaurs had an
Aphanosauria
5813134
(1903) counted four teeth in the premaxilla, of which the front tooth was the largest in the upper jaw. In contrast, Gregory S. Paul (1988) depicted the skull with only three premaxillary teeth remaining, much smaller than those illustrated by Osborn. Each maxilla (main tooth-bearing bone in the upper jaw) contained ten teeth, and each dentary (tooth-bearing bone in the lower jaw) contained twelve teeth. The tooth rows of "Ornitholestes" were short, with the dentary (lower) row being even shorter than the maxillary (upper) row, even though the dentary bone itself was exceptionally long at the back, reaching a point
Ornitholestes
18280686
the site is otherwise known as the Proctor Lake dinosaur locality. "Wannchampsus" was described in 2014 by Thomas Adams. The type species is W. kirpachi, in honor of Wesley Kirpach, "who was instrumental in the discovery and excavations of the type specimen". The skulls are described as "low and broad", and are small; SMU 76604 is estimated at long, and SMU 76605 is estimated at long. The lower jaw lacks external mandibular fenestrae, and the third tooth of the maxilla (main tooth-bearing bone of the upper jaw) and the fourth tooth of the dentary (tooth-bearing bone of the lower jaw)
Wannchampsus
15984990
whose bone loss in the jaw area prevents them from getting conventionally oriented (vertical) dental implants. Often, tooth loss is accompanied by loss of the jaw bone which poses the problem of reconstruction of the jaw bone requiring bone grafting. The All-on-Four technique takes advantage of the dense bone that remains in the front part of the jaws and by placing the two posterior implants on an angle to avoid the sinus cavities in the upper jaw and the nerve canal in the lower jaw. For the implementation to be successful a careful analysis of the bone structure needs to
All-on-4
7845186
oviraptorids, it had a pair of tooth-like projections on the palate that were directed downwards (a feature that has been called "pseudo-teeth"). "Nemegtomaia" had small foramina (openings) on the sides of the suture (joint) between the premaxillae at the front of the snout, which may have been nutrient openings (and which indicate the presence of a keratinous bill). The lower jaw was short and deep, with a convex lower surface, and reached 153 mm (6 in) in length. The dentary bone of the lower jaw reached 50 mm (2 in) at its highest point. The mandibular symphysis (where the two-halves
Nemegtomaia
13944058
Socket preservation Socket preservation or alveolar ridge preservation (ARP) is a procedure to reduce bone loss after tooth extraction to preserve the dental alveolus (tooth socket) in the alveolar bone. A platelet rich fibrin (PRF) membrane containing bone growth enhancing elements is placed in the wound or a bone grafting material or scaffold is placed in the socket of an extracted tooth at the time of extraction. The socket is then directly closed with stitches or covered with a non-resorbable or resorbable membrane and sutured. After extraction, jaw bone has to be preserved to keep the socket in its original
Socket preservation
6773054
second row of openings runs parallel to the lower jaw edge and ends at the thirteenth tooth position, which is exceptionally far. At the inside of the dentary, the Meckelian groove at the level of the third tooth extends to the front into two superimposed narrow slits. The rear of the lower jaw shows a unique combination of a kinked suture between the angular and the surangular, and the basal trait of the surangular reaching the rear jaw edge. The rather small "foramen surangulare posterior" is not overhung by a thick bone shelf, which is rare among large theropods. The
Monolophosaurus
17379028
between the premaxilla bone at the tip of the upper jaw and the maxilla behind it. Living crocodiles have this notch, which provides room for the enlarged fourth tooth of the lower jaw when the mouth is closed. In pristichampsids and other basal crocodyloids, the fourth tooth is small and does not fit into the notch. Below is a cladogram illustrating the phylogeny of the Pristichampsidae from Brochu "et al." (2012): Pristichampsidae Pristichampsidae is an extinct family of crocodilians known from Europe during the Paleogene. Only one genus of pristichampsid are currently recognized, "Pristichampsus". Pristichampsids were highly specialized crocodilians that
Pristichampsidae
15477431
jaw. Like other therocephalians, bauriids have moderately enlarged canines. The postcanine teeth behind the canines are broad. The postcanines of the upper and lower jaw fit tightly together as an adaptation to processing plant material. An autapomorphy or unique feature of Bauriidae is the expansion of the dentary bone of the lower jaw inward toward the jaw midline, forming a wide shelf of bone to either side of the tooth row. A similar expansion of the maxilla in the upper jaw is also seen in bauriids, although it is not unique to the group as the feature has also evolved
Bauriidae
1601239
on an object, force was transmitted up through the maxilla, the primary tooth-bearing bone of the upper jaw, into surrounding skull bones. In North American tyrannosaurids, this force went from the maxilla into the fused nasal bones on top of the snout, which were firmly connected in the rear to the lacrimal bones by bony struts. These struts locked the two bones together, suggesting that force was then transmitted from the nasals to the lacrimals. "Tarbosaurus" lacked these bony struts, and the connection between the nasals and lacrimals was weak. Instead, a backwards projection of the maxilla was massively developed
Tarbosaurus
13401079
at the tip and curved upward. The teeth were nearly conical, but had distinct unserrated anterior and posterior edges. Each side of the tip of the upper jaw had four teeth, while the maxillae (main tooth-bearing bone of the upper jaw) and dentaries (tooth-bearing bone of the lower jaw) had twelve or thirteen each. The thigh bones were slender, and there were bony scutes on both the back and belly. The scutes on the upper surface were arranged in two rows running the length of the animal. Clark and Sues performed a phylogenetic analysis and found "Kayentasuchus" to have an
Kayentasuchus
6314611
Alveolar process The alveolar process () (also called the alveolar bone) is the thickened ridge of bone that contains the tooth sockets (dental alveoli) on the jaw bones that hold teeth. In humans, the tooth-bearing bones are the maxilla and the mandible. The curved part of each alveolar process on the jaw is called the alveolar arch. On the maxilla, the alveolar process is a ridge on the inferior surface, and on the mandible it is a ridge on the superior surface. It makes up the thickest part of the maxillae. The alveolar process contains a region of compact bone
Alveolar process
6314619
the periodontium (periodontitis), localized bone tissue is also lost. Alveolar process The alveolar process () (also called the alveolar bone) is the thickened ridge of bone that contains the tooth sockets (dental alveoli) on the jaw bones that hold teeth. In humans, the tooth-bearing bones are the maxilla and the mandible. The curved part of each alveolar process on the jaw is called the alveolar arch. On the maxilla, the alveolar process is a ridge on the inferior surface, and on the mandible it is a ridge on the superior surface. It makes up the thickest part of the maxillae.
Alveolar process
4326952
"Deinosuchus" was not considerably different from that of modern crocodilians. "Deinosuchus" had an alligator-like, broad snout, with a slightly bulbous tip. Each premaxilla contained four teeth, with the pair nearest to the tip of the snout being significantly smaller than the other two. Each maxilla (the main tooth-bearing bone in the upper jaw) contained 21 or 22 teeth. The tooth count for each dentary (tooth-bearing bone in the lower jaw) was at least 22. All the teeth were very thick and robust; those close to the rear of the jaws were short, rounded, and blunt. They appear to have been
Deinosuchus
3975537
tooth count for the lower jaw has not been published. "Acrocanthosaurus" teeth were wider than those of "Carcharodontosaurus" and did not have the wrinkled texture that characterized the carcharodontosaurids. The dentary (tooth-bearing lower jaw bone) was squared off at the front edge, as in "Giganotosaurus", and shallow, while the rest of the jaw behind it became very deep. "Acrocanthosaurus" and "Giganotosaurus" shared a thick horizontal ridge on the outside surface of the surangular bone of the lower jaw, underneath the articulation with the skull. The most notable feature of "Acrocanthosaurus" was its row of tall neural spines, located on the
Acrocanthosaurus
7758429
Sinus lift Maxillary sinus floor augmentation (also termed sinus lift, sinus graft, sinus augmentation or sinus procedure) is a surgical procedure which aims to increase the amount of bone in the posterior maxilla (upper jaw bone), in the area of the premolar and molar teeth, by lifting the lower Schneiderian membrane (sinus membrane) and placing a bone graft. When a tooth is lost the alveolar process begins to remodel. The vacant tooth socket collapses as it heals leaving an edentulous (toothless) area, termed a "ridge". This collapse causes a loss in both height and width of the surrounding bone. In
Sinus lift
14055486
of an antorbital fenestra, a hole in front of the eyes which is typical for archosauriforms. The lacrimal bone, which usually forms the rear edge of the antorbital fenestra, has also disappeared. Grooves cover the skull roof while foramina (tiny pores) coat the skull bones near the mouth. The maxilla (the main tooth-bearing bone of the snout) is simple and triangular due to the loss of the antorbital fenestra. The front tip of the bone possesses a toothless notch, known as a diastema, which accepts a large, caniniform (fang-like) tooth of the dentary (main toothed bone of the lower jaw).
Vancleavea
11430030
the roof of the skull was closed, and there were only nine teeth in the premaxillary bones that form the tip of the snout instead of ten, although this could be individual variation. The right jaw is better preserved than the left; at least 13 teeth were present in the right maxilla (the main tooth-bearing bone of the upper jaw), and 17 to 18 teeth were present in the right dentary, which held teeth in lower jaw. There was an unusually tall bony process on the coronoid, a bone of the lower jaw. Impressions of part of the brain and
Terminonatator
17138205
back of the jaw, and the teeth in the upper jaw completely overly the teeth in the lower jaw when the mouth is closed. Features in "Culebrasuchus "that are not found in other caimanines include the lack of ridges above the eye sockets and the large size of a hole in the lower jaw called the external mandibular fenestra. These features may be plesiomorphic ("primitive") for alligatorids. "Culebrasuchus" also has a straighter lower jaw than most other alligatorids, it lacks the ridges on the frontal bone between the eye sockets that are common among crocodylians, and the fourth tooth of
Culebrasuchus
8225910
jaw bone) in many ornithischians, but this diastema was characteristically arched in heterodontosaurids. The mandible (lower jaw) was tipped by the predentary, a bone unique to ornithischians. This bone also supported a beak similar to the one found on the premaxilla. All the teeth in the lower jaw were found on the dentary bone. Heterodontosaurids are named for their strongly heterodont dentition. There were three premaxillary teeth. In the Early Jurassic "Abrictosaurus", "Heterodontosaurus", and "Lycorhinus", the first two premaxillary teeth were small and conical, while the much larger third tooth resembled the canines of carnivoran mammals and is often called
Heterodontosauridae
13944061
extraction thus keeping the contour and integrity of the socket with successful and natural looking appearance for tooth restorative procedures. All dental prosthesis requires good jaw bone support for it to be successful in the long run. Without socket preservation, residual bones could lose volume resulting in loss of facial vertical and horizontal dimension and changes in facial soft tissues aesthetics. Socket preservation Socket preservation or alveolar ridge preservation (ARP) is a procedure to reduce bone loss after tooth extraction to preserve the dental alveolus (tooth socket) in the alveolar bone. A platelet rich fibrin (PRF) membrane containing bone growth
Socket preservation
13944059
shape. Without socket preservation, the bone quickly resorbs resulting in 30–60% loss in bone volume in the six months after dental extraction. The jaw bone will never revert to its original shape once bone is lost and tissue contour has changed. The human body reduces the amount of bone that is not sufficiently used with a daily stress; without the strain stimulus, the jaw bone behaves (with or without socket preservation) as if the space occupied by the tooth and periodontal ligament was empty. A platelet rich fibrin membrane is a membrane to prevent epithelial cell migration into the grafted
Socket preservation
13159277
an early age This can lead to bone development of an asymmetrical mandibular ramus resulting in asymmetry in the whole of the lower face. Treatment of laterognathism is either possible with orthodontic tooth movement or a surgical relocation of the lower jaw. One of the ways in which a jaw can develop abnormally is in the vertical dimension. Abnormal growth can occur in the maxilla and the mandible. The jaw is usually loosely used to refer to the mandible (considered the lower jaw). However, the maxilla is also a jaw and should thus be referred to in this respect as
Jaw abnormality
17986367
the degree of mobility is inversely related to the amount of bone and periodontal ligament support left. Grace & Smales Mobility Index Miller Classification Loss of attachment: Increased forces on the tooth: Dental Splinting A dental splint works by evening out pressure across a patients jaw. A splint can be used to protect teeth from further damage as it creates a physical barrier between lower and upper teeth. In order to treat mobility, teeth can be joined or splinted together in order to distribute biting forces between several teeth rather than the individual mobile tooth. A dental splint may also
Tooth mobility
13484257
Angulomastacator Angulomastacator (meaning "bend chewer", in reference to both the shape of its upper jaw and to the Big Bend area of the Rio Grande, where the type specimen was found) is a genus of duck-billed dinosaur from the Campanian-age (Late Cretaceous) Aguja Formation of Big Bend National Park, Texas. It is known from a single specimen, TMM 43681–1, a partial left maxilla (the main tooth-bearing bone of the upper jaw). This bone is curved down approximately 45° at its anterior end, with the tooth row bent to fit, unlike any other hadrosaur. The unusual characteristics of the maxilla, which
Angulomastacator
20231270
short and deep backward-projecting process, where it is overlapped by the quadratojugal bone. The subtriangular and curved backward branch of the quadrate bone, which articulates with the pterygoid bone, is closer to the bottom of the bone than in most other non-bird theropods. Compared to "Sinovenator", the long jugal branch of the postorbital bone is not as long. Overall, the lower jaw is roughly triangular when viewed from the side, with a straight top margin and a curved bottom margin, and is not downturned unlike in "Sinovenator". The dentary, the tooth-bearing front lower jaw bone, is long (occupying half of
Jianianhualong
15674147
because the replacement resorption (also termed ankylosis) attaches the tooth firmly to the jaw bone and stops normal tooth eruption and impedes normal jaw growth. Research has shown that the critical factor for reduction of the death of the tooth root cells and the subsequent root replacement resorption following reimplantation of knocked-out teeth is maintenance of normal cell physiology and metabolism of the cells left on the tooth root while the tooth is out of the socket. In order to maintain this normalcy, the environment in which the teeth are stored must supply the optimum internal cell pressure, cell nutrients
Dental avulsion
11761661
lower jaw had to be put together from the pieces of the different SAM fossils as there is not one that had a complete lower jaw. When looking at the different parts however, there are indications of at least six elements present in the lower jaw of the "Mesosuchus": dentary, splenial, surangular, angular, prearticular, and articular. Evident on SAM 5882, 6046, and 6536 was a clear line of separation between the tooth and surrounding bone indicating that the teeth are implanted in the jaw, which went against the previous idea that the marginal teeth of "Mesosuchus" were ankylosed to the
Mesosuchus
1978715
and to have a sharp corner at the back. The chin can be reduced in length either by bone shaving or with a procedure called a "sliding genioplasty", where a section of bone is removed. The jaw can be reshaped through jaw reduction surgery; sometimes this is done through the mouth. The (chewing muscles) can also be reduced to make the jaw appear narrower. The biggest risk in these procedures is damage to the mental nerve that runs through the chin and jaw; other risks include damage to tooth roots, infection, nonunion, and damage to the mentalis muscle that controls
Facial feminization surgery
16820178
Pegomastax Pegomastax ("strong jaw") is a genus of heterodontosaurid dinosaur discovered in Lower Jurassic rocks in South Africa. It is based on SAM-PK-K10488, a partial skull including a postorbital bone, both dentaries (the tooth-bearing bone of the lower jaw), and a predentary (a toothless beak-like bone found at the tip of the lower jaw). From head to tail the parrot-like herbivore measured no more than 60 cm. This specimen was found in Voyizane, Joe Gqabi District, Cape Province, in rocks of the upper Elliot Formation, a rock formation that dates to the early part of the Early Jurassic (Hettangian–Sinemurian, approximately
Pegomastax
10079487
the right), namely: mammals use two bones for hearing that all other amniotes use for eating. The earliest amniotes had a jaw joint composed of the articular (a small bone at the back of the lower jaw) and the quadrate (a small bone at the back of the upper jaw). All non-mammalian tetrapods use this system including amphibians, turtles, lizards, snakes, crocodilians, dinosaurs (and their descendants the birds), ichthyosaurs, pterosaurs and therapsids. But mammals have a different jaw joint, composed only of the dentary (the lower jaw bone, which carries the teeth) and the squamosal (another small skull bone). In
Evolution of mammals
663245
to sounds of higher frequency, because these are better taken up by the inner ear (which also responds to higher frequencies than those of non-mammals). The malleus, or "hammer", evolved from the articular bone of the lower jaw, and the incus, or "anvil", from the quadrate. In other vertebrates, these bones form the primary jaw joint, but the expansion of the dentary bone in mammals led to the evolution of an entirely new jaw joint, freeing up the old joint to become part of the ear. For a period of time, both jaw joints existed together, one medially and one
Middle ear
6140250
bone wall on top of much of the snout. More to behind the nasal bones stretch out horizontally, creating a flat tongue-shaped skull crest that overgrowths and ultimately overhangs, most of the skull roof. The crest is not hollow but consists of massive bone. The crest has a low longitudinal ridge on the midline. The maxilla, the tooth-bearing upper jaw bone, is rather elongated in front. Its tooth positions increase during the lifetime of the animal, ranging from thirty-three in younger individuals to forty-eight in the holotype specimen. The teeth are stacked in a tooth battery, with up to three
Brachylophosaurus
14142318
mammals have deep roots, and this pattern is also found in some fish, and in crocodilians. In most teleost fish, however, the teeth are attached to the outer surface of the bone, while in lizards they are attached to the inner surface of the jaw by one side. In cartilaginous fish, such as sharks, the teeth are attached by tough ligaments to the hoops of cartilage that form the jaw. Some animals develop only one set of teeth (monophyodont) while others develop many sets (polyphyodont). Sharks, for example, grow a new set of teeth every two weeks to replace worn
Tooth
2154454
Teleosts dominate the seas from pole to pole and inhabit the ocean depths, estuaries, rivers, lakes and even swamps. The difference between teleosts and other bony fish lies mainly in their jaw bones; teleosts have a movable premaxilla and corresponding modifications in the jaw musculature which make it possible for them to protrude their jaws outwards from the mouth. This is of great advantage, enabling them to grab prey and draw it into the mouth. In more derived teleosts, the enlarged premaxilla is the main tooth-bearing bone, and the maxilla, which is attached to the lower jaw, acts as a
Teleost
3792710
an array of plates and spikes running along both sides of the top mid-line of the animal. Only a single complete tooth was known when Hennig published his monography in 1925. Later, a part of a dentary, the tooth-bearing bone of the front lower jaw, was found, which bears a just emerging tooth, and some tooth fragments were recovered from matrix sticking to other bones. The deep dentary is almost identical in shape to that of "Stegosaurus", albeit much smaller. Similarly, the tooth is a typical stegosaurian tooth, small with a widened base and vertical grooves creating five ridges. "Kentrosaurus
Kentrosaurus
4671771
leaf-shaped, socketed teeth: 5 to 6 per premaxilla, 24 to 30 per maxilla, and 21 to 28 per dentary (lower jaw). The thick, leaf-shaped, bluntly serrated tooth crowns were suitable for crushing plant material. The low position of the jaw joint gave the chewing muscles great leverage, so that "Plateosaurus" could deliver a powerful bite. These features suggest that it fed primarily to exclusively on plants. Its eyes were directed to the sides, rather than the front, providing all-round vision to watch for predators. Some fossil skeletons have preserved sclerotic rings (rings of bone plates that protect the eye). The
Plateosaurus
13263133
of the eothyridid "Eothyris". However, "Eothyris" only has one precanine tooth on each side of the jaw, and is probably not closely related to "Baldwinonus trux". A buttress of bone runs along the inside of the jaw above the sockets of the caniniform teeth, strengthening the jaw. This buttress extends upward like a flap to form a sharp ridge, a feature that "Baldwinonus" shares with a group of early synapsids called Ophiacodontidae. A groove of bone that presumably made space for a blood vessel runs horizontally along the inner surface of the jaw but turns downward near the buttress. In
Baldwinonus
8274951
characteristics of the lower jaw are therefore the lack of a chin on the one hand and on the other it is the considerable size of the lower jaw bone, on which, behind the wisdom tooth a fourth premolar would easily have had space to develop. Since the third molar (the wisdom tooth) is present and its dentin exposed - although only in a few places - the age of death is estimated to be about 20 to 30 years. Schoetensack concluded a relationship to modern man ("Homo sapiens") from the similarity of the dentition and put the lower jaw
Mauer 1
6378750
type bone fragment has been lost. The name was derived from Greek: απατη ("trick", "deceit") and οδους (genitive οδοντος) ("tooth", in reference to its original, incorrect identification). Apatodon Apatodon is a dubious genus of dinosaur. When Marsh named it, he thought it was a jaw with a tooth from a Mesozoic pig, but it was soon shown that the specimen was an eroded vertebra, from a dinosaur possibly from the Morrison Formation of Garden Park, Colorado. Marsh had misidentified the neural spine as the tooth of a pig-like animal (Baur, 1890). The only recovered specimen is not regarded as sufficient
Apatodon
14166635
of the lower jaw are much smaller and lower than the fourth tooth. At the tip of the jaw the first dentary tooth is procumbent, or directed forward. The teeth of the upper and lower jaws form an alternate pattern to allow the jaw to close tightly. A notch is present between the maxilla and premaxilla bones of the upper jaw, accommodating the fourth dentary tooth when the jaw is closed. The procumbent first dentary teeth fit between the first and second premaxillary teeth. This close fit allows the serrated edges of the teeth shear with one another. The articulation
Sebecus
13263132
fragment of a right maxilla or upper jaw bone, part of a quadrate bone, and several vertebrae. The maxilla contains 25 tooth sockets, some with teeth. There are sockets for five precaniniform teeth at the front of the jaw, two caniniform teeth behind them, and eight postcaniniform teeth at the back of the jaw. The margin of the jaw is straight for most of its length but curves upward toward the front tip. The large caniniform teeth in "B. trux" were initially taken as evidence for its placement within Eothyrididae, since large teeth are one of the most distinctive features
Baldwinonus
6065
the species that are regarded as synonyms of "A. fragilis", or that were misassigned to the genus, are obscure and were based on scrappy remains. One exception is "Labrosaurus ferox", named in 1884 by Marsh for an oddly formed partial lower jaw, with a prominent gap in the tooth row at the tip of the jaw, and a rear section greatly expanded and turned down. Later researchers suggested that the bone was pathologic, showing an injury to the living animal, and that part of the unusual form of the rear of the bone was due to plaster reconstruction. It is
Allosaurus
16957442
Caiman venezuelensis Caiman venezuelensis is an extinct species of caiman that lived in South America during the Pleistocene. The holotype of "C. venezuelensis" — OR-1677, a partial left premaxilla bone — was discovered in the locality of El Breal of Orocual, in the Mesa Formation, in the state of Monagas, Venezuela, the country of which derives their species name. The premaxilla preserved measures long, with an estimated total length of . It has a strong premaxillary sutural surface, a hole developed in the fourth tooth of the jaw bone, and short spaces between the alveoli, indicating that despite its size,
Caiman venezuelensis
3454476
the articular process of the lower jaw. Articular bone The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as Stem-mammal. In these animals it is connected to two other lower jaw bones, the suprangular and the angular. It forms the jaw joint by articulating with the quadrate bone of the skull. In mammals, the articular bone has migrated to the middle ear to become the malleus, while the quadrate bone becomes the incus. Paleontologists regard this as a defining characteristic of mammalian fossils. It
Articular bone
1824477
The jaw articulates via a hinge joint between the quadrate and articular. The jaws of tetrapods exhibit varying degrees of mobility between jaw bones. Some species have jaw bones completely 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 mandible (lower jaw) and the maxilla (upper jaw). In the ape there is a reinforcement to the lower jaw bone called the simian shelf. In the evolution
Jaw
5843992
the surangular bone is not preserved, several other bones of the lower jaw are, including a triangular angular bone, a gently curving prearticular bone, and a damaged yet notably concave articular bone. The angular and prearticular formed the lower edge of a large and rounded in the lower jaw (known as a mandibular fenestra) while the articular bone formed the lower part of the jaw joint. A long and tapering hyoid (tongue bone) has also been preserved. The front teeth of the upper jaw are also procumbent, and the margin of the premaxilla curves slightly upward to direct them outward.
Masiakasaurus
5594936
the nasal cavity, and possibly connected to the Jacobson's organ (an olfactory sense organ). The maxilla was short and deep, and probably contained a sinus. The maxilla had a series of foramina that corresponded with each tooth position there, and these functioned as passages for erupting replacement teeth. The mandible articulated with the skull below the back of the orbit. The tooth-bearing part of the lower jaw was long, with the part behind being rather short. Though not preserved, the presence of a predentary bone is indicated by facets at the front of the lower jaw. Like other pachycephalosaurs, it
Stegoceras
6100299
The sponge-like bone formations lead to early tooth loss and permanent tooth eruption problems. The condition also affects the orbital area, creating an upturned eye appearance. The cause of cherubism is believed to be traced to a genetic defect resulting from a mutation of the SH3BP2 gene from chromosome 4p16.3. While the condition is rare and painless, the afflicted suffer the emotional trauma of disfigurement. The effects of Cherubism may also interfere with normal jaw motion and speech. Currently, removal of the tissue and bone by surgery is the only treatment available. This condition is also one of the few
Cherubism
20761826
This type of overdenture overlies natural tooth structures. Frequently, elective root canal treatment and coronal modification are carried out on the teeth that are used as abutments. This means that the pulpal tissues and crowns of the natural teeth are removed, followed by contouring of the tooth structure above the gum. This allows even distribution of occlusal stress onto the abutment teeth and soft tissues. Other than that, retention of natural teeth in the jaw helps preserve bone by delaying the process of bone resorption in the jaw. Selection of abutment teeth depends on a few factors including: To provide
Overdenture
3785909
facilitate the complex action by which the snake draws prey into its mouth. Green A: the joint between the frontal bone and nasal bone. It allows the nose to upturn slightly, increasing gape and assisting in swallowing. Green B: allows the lower jaws to bow outwards, further increasing the gape. Blue: the joint between the supratemporal and parietal. Immobile, except for Dasypeltis. In most snakes, teeth are located on the dentary of the lower jaw, the maxilla, the palatine bone and the lateral pterygoid plate. The latter form an "inner row" of teeth that can move separately from the rest
Snake skeleton
20805284
the jaw, the dentary tooth row also twists slightly outwards. The front of the jaw also possesses an enlarged tooth known as a parasymphyseal tusk, although this tooth is less than twice as wide as the rest of the marginal teeth. A deep longitudinal groove known as an oral sulcus is visible below the marginal tooth row. The inner row of conical teeth form out of the three coronoid bones which lie inwards from the dentary. This feature is practically unique to lapillopsids among early Triassic temnospondyls, as most other groups have much more reduced coronoid teeth. Lydekkerinids, for example,
Manubrantlia
14529098
patients that were seen for a dislocated jaw. Dislocation of jaw Dislocations occur when two bones that originally met at the joint detach. Dislocations should not be confused with Subluxation. Subluxation is when the joint is still partially attached to the bone. When a person has a dislocated jaw it is difficult to open and close the mouth. Dislocation can occur following a series of events if the jaw locks while open or unable to close. If the jaw is dislocated, it may cause an extreme headache or inability to concentrate. When the muscle's alignment is out of sync, a
Dislocation of jaw
3967256
equal to the minimum height of the lower jaw. In the holotype, they are in length, which even surpasses the minimum height of the lower jaw. In other theropods, a comparable tooth length is only known from the possibly closely related "Genyodectes". In contrast, several members of the Abelisauridae feature very short tooth crowns. In the holotype, each half of the dentary, the tooth-bearing bone of the mandible, was equipped with fifteen teeth, which are however poorly preserved. Both specimens MWC 1 and UMNH VP 5278 show only eleven teeth in each dentary, which were, as shown by the latter
Ceratosaurus
20006018
eventually becoming short, peg-like structures at the back of the tooth row; the back of the tooth row corresponding to the front 1/3 of the nasoantorbital fenestra, which is unusual among ctenochasmatids (where the teeth usually stop entirely before the fenestra). The first tooth at the front of each jaw is also somewhat shortened, being only half the length of the second. Collectively, the teeth, which would have interlocked when the jaw was closed, form a comb-like complex that would have been used for filter-feeding. Among ctenochasmatids, the jugal bone of "Liaodactylus" is quite narrow, especially below the large eye
Liaodactylus
9567418
is the long established idea that bone changes shape in accordance with the forces applied. Significantly, a recent finite element analysis study, analysing the distribution of force through the jaw of an 8 year old child, observed overall compression in the soft tissues above, and tension in the soft tissues below, unerupted teeth. Because bone resorbs when compressed, and forms under tension, this finite element analysis strongly supports the new theory. Further work is required, however, to confirm this new theory experimentally. Although tooth eruption occurs at different times for different people, a general eruption timeline exists. Typically, humans have
Tooth eruption
7844950
an almost global distribution, including Antarctica. The tritylodont's skull has a high sagittal crest. They retained the reptilian joint between the quadrate bone of the skull and the articular bone of the lower jaw—the retention of the vestigial reptilian jawbones is one of the reasons they are technically regarded to not be mammals, but are instead mammaliamorphs. The back of the skull had huge zygomatic arches for the attachment of its large jaw muscles. They also had a very well-developed secondary palate. The tritylodont dentition was very different from that of other cynodonts: they did not have canines, and the
Tritylodontidae
12628746
The lower jaw has a pair of holes only visible from the inside edge of the jaw. The larger hole at the rear part of the bone complex, known as a posterior Meckelian foramen, was thin and elongated in rhinesuchids. An additional hole on the underside of the jaw joint is only visible from below. This hole, the chorda tympanic foramen, was large in this family. On the upper side of the jaw joint, a thin groove known as an arcadian groove stretches towards the lingual (tongue) side of the jaw and separates other bony bumps located among the jaw
Rhinesuchidae
11824224
the species and low in one of them ("E. mahalanobsi"). There is also a boss situated on the ventral margin of the jugal. The anteroventral process is an anteroposteriorly short triangular bone, while in most other dicynodonts it is long and pointed. The teeth in the upper and lower jaw differ both in morphology as well as in tooth replacement. The teeth of the upper jaw tend to be larger (5-9mm) than those of the lower jaw (<5mm) and are serrated on the anterior edge while the lower jaw has serrations on the posterior edge. Although it was originally thought
Endothiodon
1642191
and the temporal bone is involved in translational movement—this is the secondary gliding motion of the jaw as it is opened widely. The part of the mandible which mates to the under-surface of the disc is the condyle and the part of the temporal bone which mates to the upper surface of the disk is the articular fossa or glenoid fossa or mandibular fossa. The articular disc is a fibrous extension of the capsule in between the two bones of the joint. The disc functions as articular surfaces against both the temporal bone and the condyles and divides the joint
Temporomandibular joint
3454475
Articular bone The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as Stem-mammal. In these animals it is connected to two other lower jaw bones, the suprangular and the angular. It forms the jaw joint by articulating with the quadrate bone of the skull. In mammals, the articular bone has migrated to the middle ear to become the malleus, while the quadrate bone becomes the incus. Paleontologists regard this as a defining characteristic of mammalian fossils. It is analogous to, but not homologous to
Articular bone
16054176
diastema in the premaxillary tooth row, and a diastema in between the premaxillary and maxillary teeth. The dentary bone of the lower jaw has ten teeth on either side, with two diastemata separating them. The forward-most teeth are suited for capturing food, while the back teeth are adapted for food processing. The palatine bone in the roof of the mouth connects to the maxilla bone of the snout by a region of bone called the cuneiform process. "Caipirasuchus" also has large pterygoid and ectopterygoid bones and a well-developed hole in front of the eye sockets called the antorbital fenestra. Caipirasuchus
Caipirasuchus
14529086
Dislocation of jaw Dislocations occur when two bones that originally met at the joint detach. Dislocations should not be confused with Subluxation. Subluxation is when the joint is still partially attached to the bone. When a person has a dislocated jaw it is difficult to open and close the mouth. Dislocation can occur following a series of events if the jaw locks while open or unable to close. If the jaw is dislocated, it may cause an extreme headache or inability to concentrate. When the muscle's alignment is out of sync, a pain will occur due to unwanted rotation of
Dislocation of jaw
5594935
orbit. The relatively large jugal bone formed the lower margin of the orbit, extending far forwards and down towards the jaw joint. It was ornamented with ridges and nodes in a radiating arrangement. The nasal openings were large and faced frontwards. The nasal bone was thick, heavily sculpted, and had a convex profile. It formed a boss (shield) on the middle top of the skull together with the frontal bone. The lower front of the premaxilla (front bone of the upper jaw) was rugose and thickened. A small foramen (hole) was present in the suture between the premaxillae, leading into
Stegoceras
2764821
the rest of the cartilage to enter the middle ear where it becomes the incus. Quadrate bone The quadrate bone is part of a skull in most tetrapods, including amphibians, sauropsids (reptiles, birds), and early synapsids. In these animals it connects to the quadratojugal and squamosal in the skull, and forms part of the jaw joint (the other part is the articular bone at the rear end of the lower jaw). It is formed by endochondral ossification and is formed from the hindmost part of the primitive cartilaginous upper jaw. In snakes, the quadrate bone has become elongated and very
Quadrate bone
2764819
Quadrate bone The quadrate bone is part of a skull in most tetrapods, including amphibians, sauropsids (reptiles, birds), and early synapsids. In these animals it connects to the quadratojugal and squamosal in the skull, and forms part of the jaw joint (the other part is the articular bone at the rear end of the lower jaw). It is formed by endochondral ossification and is formed from the hindmost part of the primitive cartilaginous upper jaw. In snakes, the quadrate bone has become elongated and very mobile, and contributes greatly to their ability to swallow very large prey items. In some
Quadrate bone
12768173
long and deep maxilla (the main bone of the upper jaw), which was thick along the margin where the alveoli (tooth sockets) were placed, thinning upward. The interdental plates of the maxilla were thin, fused, porous, and triangular. There were triangular nutrient foramina between the plates, each containing the tip of an erupting tooth. The narial fossa (depression) in front of the bony nostril was long and contained a subnarial fenestra, which was much larger than those of "Giraffatitan" and "Camarasaurus". The dentaries (the bones of the lower jaws that contained the teeth) were robust, though less than in "Camarasaurus".
Brachiosaurus
20963779
least 1.5 times taller than the vertical thickness of the front tooth-bearing lower jaw bone, the dentary, at its tallest point. The right lower jaw has a preserved length of fourteen centimetres. To the front, it gradually curves to below. A piece at the front has broken off. The original length of the jaw including this piece was estimated at about eighteen centimetres. The missing piece was assumed by the authors to have borne one additional tooth. The fossil shows four teeth, which then would have been the second to fifth. The second and third teeth are elongated, recurved and
Klobiodon
7758443
the lateral technique will also be an important decision criterion. However, the transalveolar approach is unlikely to be effective in cases of advanced levels of bone reduction at the implant site. Educational Resources Sinus lift Maxillary sinus floor augmentation (also termed sinus lift, sinus graft, sinus augmentation or sinus procedure) is a surgical procedure which aims to increase the amount of bone in the posterior maxilla (upper jaw bone), in the area of the premolar and molar teeth, by lifting the lower Schneiderian membrane (sinus membrane) and placing a bone graft. When a tooth is lost the alveolar process begins
Sinus lift
14529090
of the jaw. The joint involved with jaw dislocation is the temporomandibular joint (TMJ). This joint is located where the mandibular condyles and the temporal bone meet. Membranes that surround the bones help during the hinging and gliding of jaw movement. For the mouth to close it requires the following muscles: the masseter, temporalis, and medial pterygoid muscle. For the jaw to open it requires the lateral pterygoid muscle. There are four different positions of jaw dislocation: posterior, anterior, superior and lateral. The most common position is anterior, while the other types are rare. Anterior dislocation shifts the lower jaw
Dislocation of jaw
8866019
localized or generalized deep ache or pain, often of multiple jawbone sites. The teeth often appeared sound and suppuration was not present. Even so, the dentist often began extracting one tooth after another in the region of pain, often with temporary relief but usually to no real effect. Today a growing body of scientific evidence indicate that this disease process, in the cancellous bone and bone marrow, is caused by bone infarcts mediated by a range of local and systemic factors. Bone infarcts as well as damage to the deeper portion of the cancellous bone is an insidious process. It
Osteonecrosis of the jaw
6377056
elevated above the jaw bone. The first two tooth pairs were pointed somewhat to the front; the teeth more to the back pointed more sideways; the most posterior preserved stood perpendicular to the jaw. The teeth increased in size until the third pair which was the largest. The fourth pair was equal to the first but the fifth, sixth and seventh pairs were markedly smaller, less than half in size; it is this feature which is recalled by the specific name. Pairs eight, nine and ten again equalled the first. After a narrow hiatus between the second and third snout
Caulkicephalus
8912691
after birth, between the petrous portion of the temporal and the jugular process of the occipital bone. Synchondrosis Where the connecting medium is hyaline cartilage, a cartilaginous joint is termed a synchondrosis. An example of a synchondrosis joint is the first sternocostal joint (where the first rib meets the manubrium). In this example, the rib articulates with the manubrium via the costal cartilage. (The rest of the sternocostal joints are synovial plane joints.) Sometimes, this is a temporary form of joint called epiphyseal growth plate, where the cartilage is converted into bone before adult life. Such joints are found between
Synchondrosis
5814104
while some later ornithischian groups possessed teeth capable of grinding plant material, "Scelidosaurus" had smaller, less complex leaf-shaped teeth suitable for cropping vegetation and jaws capable of only vertical movement, due to a short jaw joint. Paul Barrett concluded that "Scelidosaurus" fed with a puncture-crush system of tooth-on-tooth action, with a precise but simple up-and-down jaw movement, in which the food was mashed between the inner side of the upper teeth and the outer side of the lower teeth, without the teeth actually touching each other as shown by very long vertical wear facets on the lower teeth alone. In
Scelidosaurus
20035693
the splenial anteroventrally in a vertical joint. The splenial is preserved only at the joint, forming a bulge on the ventral margin. It is inferred then that the intramandibular joint is situated far anteriorly. This resembles that of "Pachyrhachis". The tooth row extends the same length as exhibited in the upper jaw for equal alignment. In contrast to the jaw, "Pachyophis" teeth clearly resemble that of snakes. Their dentition show thecodont nature, their teeth fitted into bowl like alveoli lined on the jaw bones. The enamel layer of the teeth is well developed with large, hollow pulp cavities possessing small
Pachyophis
20096772
is hollow and was likely air-filled (pneumatic). "Caelestiventus" is heterodont, with three different tooth shapes - long fang-like spikes, large "leaf-shaped" blades, and tiny blades. There are two long, spike teeth near the front of each side of the lower jaws that were likely opposed by similar teeth at the tip of the skull snout (premaxilla). In the lower jaws, behind the fangs, is a tooth gap (diastema) which is followed by 38 tiny teeth on each side of the lower jaw (mandibular ramus). Each upper jaw bone (maxilla) is armed with twelve large, blade-like, triangular teeth. Both sides of
Caelestiventus
1635635
jaw transition is a good classification tool, as most other fossilized features that make a chronological progression from a reptile-like to a mammalian condition follow the progression of the jaw transition. The mandible, or lower jaw, consists of a single, tooth-bearing bone in mammals (the dentary), whereas the lower jaw of modern and prehistoric reptiles consists of a conglomeration of smaller bones (including the dentary, articular, and others). As they evolved in synapsids, these jaw bones were reduced in size and either lost or, in the case of the articular, gradually moved into the ear, forming one of the middle
Synapsid
20437851
continues as the "handle of malleus", which connects to the tympanic membrane. Between the neck and handle of the malleus, "lateral" and "anterior processes" emerge from the bone. The malleus is unique to mammals, and evolved from a lower jaw bone in basal amniotes called the articular, which still forms part of the jaw joint in reptiles and birds. Embryologically it is derived from the first pharyngeal arch along with the incus. The malleus is one of three ossicles in the middle ear which transmit sound from the tympanic membrane (ear drum) to the inner ear. The malleus receives vibrations
Malleus
5453050
of an artificial material that was found to chemically bond with bone. One of its main medical advantages is its biocompatibility, seen in its ability to avoid an immune reaction and fibrous encapsulation. Its primary application is the repair of bone injuries or defects too large to be regenerated by the natural process. The first successful surgical use of Bioglass 45S5 was in replacement of ossicles in the middle ear, as a treatment of conductive hearing loss. Other uses include cones for implantation into the jaw following a tooth extraction. Composite materials made of Bioglass 45S5 and patient's own bone
Bioglass
10014748
the snout tip while the tooth row would extend almost as far back as the tooth row of the maxilla, both features unlike "Prolacerta" and "Proterosuchus". Only 5 teeth are preserved in the left dentary, but more than 22 were likely present in life. A thick left splenial (a bone of the inside and lower edge of the lower jaw), similar to that of "Proterosuchus", is also preserved. The teeth of "Tasmaniosaurus" are ankylothecodont, meaning that they are both fused to the skull and jaw bones by thin ridges (ankylodont) as well as placed in deep sockets (thecodont). They are
Tasmaniosaurus
11623502
pair of tooth spirals (parasymphysial tooth whorls) bearing tusk-like teeth. The most well-preserved specimen of "Onychodus" has been found at the Gogo Formation of Western Australia giving palaeontologists more information about the structure of the fish. Other species of "Onychodus" are known only from poor material based on isolated tusks, teeth and scales. The most characteristic feature is a pair of retractable, laterally compressed tusk whorls at the front of the lower jaw. These were not attached to any other bone, but fit into a pair of deep cavities on the palate and were free to move. The lower jaw
Onychodus
18894951
the rear frill. The Chinese "Sinoceratops" has similar epiparietals, but in addition a central midline epiparietal and bumps below the epiparietals, which are lacking in "Wendiceratops". The maxilla, the upper jaw bone, of "Wendiceratops" had at least twenty-six tooth positions, in each of which several teeth were stacked to form a tooth battery. No orbital horns have been found. The nasal bone bore a vertical nasal horn. The exact size and profile of this horn are unknown but one broken specimen has a height of 115 millimetres and a base length of nine centimetres. Contact facets with the prefrontal bone
Wendiceratops
5152342
lepospondyls, namely "microsaurs" and a few "nectrideans" such as "Scincosaurus" and diplocaulids. Adelospondyls take this one step further. They possess only a single bone between the jaw joint and the skull roof. This bone is often believed to be a fusion between the tabular and the squamosal (termed a "tabular-squamosal" or "squamosotabular"), although it is also conceivable that the tabular disappeared completely leaving only the enlarged squamosal in its place. Adelospondyls can also be characterized by their vertebrae compared to other lepospondyls. They were spool-shaped and high in number, with "Acherontiscus" having an estimate of 64 vertebrae and an indeterminate
Adelospondyli
13281032
Pachygenelus Pachygenelus is an extinct genus of tritheledontid cynodonts. Fossils have been found from the Karoo basin in South Africa and date back to the Early Jurassic. "Pachygenelus" had both an articular-quadrate and dentary-squamosal jaw joint characteristic of ictidosaurs. Only mammals possess the dentary-squamosal articulation, while all other tetrapods possess the typical arcticular-quadrate articulation. Thus the jaw of "Pachygenelus" can be seen as transitional between non-mammalian synapsids and true mammals. Another feature of "Pachygenelus" that is shared with mammals is plesiomorphic prismatic enamel, or enamel arranged into strengthened prisms. The upper and lower tooth rows occluded with one another, although
Pachygenelus
6145417
upper beak are missing. The length of the skull is estimated at 87 centimeters (34 in) from the tip of the upper beak to the base of the quadrate that articulates with the lower jaw at the back of the skull. Potential diagnostic characteristics of "Kritosaurus" include a predentary (lower beak) without tooth-like crenulations, a sharp downward bend to the lower jaws near the beak, and a heavy, somewhat rectangular maxilla (upper tooth-bearing bone). Based on the skull originally referred to "Anasazisaurus", the form of the complete crest is that of a tab or flange of bone, from the nasals,
Kritosaurus
62036
arrangement that further emphasizes shearing (as in a pair of scissors). In herbivores, the crushing force of the masseters is relatively more important than is shearing. The jaw joint is generally well above the plane of tooth occlusion, allowing extra room for masseteric attachment on the dentary and causing the rotation of the lower jaw to be translated into straight-ahead crushing force between the teeth of the upper and lower jaws. Dentition relates to the arrangement of teeth in the mouth, with the dental notation for the upper-jaw teeth using the upper-case letters I to denote incisors, C for canines,
Carnivora
10849829
description, his rival Othniel Charles Marsh published on a sizable lower jaw recovered by John Bell Hatcher in 1889 from Lance Formation rocks in Niobrara County, Wyoming. Marsh named this partial jaw "Trachodon longiceps". It is cataloged as YPM 616. As noted by Lull and Wright, this long slender partial jaw shares with Cope's specimen a prominent ridge running on its side. However, it is much larger: Cope's specimen had a dentary, or tooth-bearing bone of the lower jaw, that is long, whereas Marsh's dentary is estimated at long. A second mostly complete skeleton (AMNH 5886) was found in 1904
Edmontosaurus annectens
1852879
straighter posterior margin, and a more concave occiput in "Probainognathus". The jaw of "Probainognathus" is of particular phylogenetic importance. Morphologically, the dentary makes up most the lower jaw, and it curves and extends down posteriorly to the area of the articular and jaw articulation. Correspondingly, in the upper jaw, the squamosal bone becomes situated next to the quadrate. The posterior end of this enlarged dentary fits into a small nook in the squamosal of the upper jaw, and displays the beginning of the evolution of the squamosal-dentary jaw joint. This squamosal-dentary jaw articulation is the same joint exhibited by mammals,
Probainognathus