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78-542: A tooth ( pl. : teeth ) is a hard, calcified structure found in the jaws (or mouths ) of many vertebrates and used to break down food . Some animals, particularly carnivores and omnivores , also use teeth to help with capturing or wounding prey, tearing food, for defensive purposes, to intimidate other animals often including their own, or to carry prey or their young. The roots of teeth are covered by gums . Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from

156-667: A common history of pre-Proto-Germanic speakers throughout the Nordic Bronze Age . The Proto-Germanic language developed in southern Scandinavia (Denmark, south Sweden and southern Norway) and the northern-most part of Germany in Schleswig Holstein and northern Lower Saxony, the Urheimat (original home) of the Germanic tribes. It is possible that Indo-European speakers first arrived in southern Scandinavia with

234-432: A dialect of Proto-Indo-European that had lost its laryngeals and had five long and six short vowels as well as one or two overlong vowels. The consonant system was still that of PIE minus palatovelars and laryngeals, but the loss of syllabic resonants already made the language markedly different from PIE proper. Mutual intelligibility might have still existed with other descendants of PIE, but it would have been strained, and

312-443: A high calcium/vitamin D ratio. This can occur with or without a mineral imbalance. A common misconception is that calcification is caused by excess amount of calcium in diet . Dietary calcium intake is not associated with accumulation of calcium in soft tissue, and calcification occurs irrespective of the amount of calcium intake. Intake of excessive vitamin D can cause vitamin D poisoning and excessive intake of calcium from

390-475: A larger scope of linguistic developments, spanning the Nordic Bronze Age and Pre-Roman Iron Age in Northern Europe (second to first millennia BC) to include "Pre-Germanic" (PreGmc), "Early Proto-Germanic" (EPGmc) and "Late Proto-Germanic" (LPGmc). While Proto-Germanic refers only to the reconstruction of the most recent common ancestor of Germanic languages, the Germanic parent language refers to

468-555: A late stage. The early stage includes the stress fixation and resulting "spontaneous vowel-shifts" while the late stage is defined by ten complex rules governing changes of both vowels and consonants. By 250 BC Proto-Germanic had branched into five groups of Germanic: two each in the West and the North and one in the East. The following changes are known or presumed to have occurred in

546-712: A month to wear away the same amount. The incisors and cheek teeth of rabbits are called aradicular hypsodont teeth. This is sometimes referred to as an elodent dentition. These teeth grow or erupt continuously. The growth or eruption is held in balance by dental abrasion from chewing a diet high in fiber. Rodents have upper and lower hypselodont incisors that can continuously grow enamel throughout its life without having properly formed roots. These teeth are also known as aradicular teeth, and unlike humans whose ameloblasts die after tooth development , rodents continually produce enamel, they must wear down their teeth by gnawing on various materials. Enamel and dentin are produced by

624-678: A new set of teeth every two weeks to replace worn teeth. Most extant mammals including humans are diphyodonts, but there are exceptions including elephants, kangaroos, and manatees, all of which are polyphyodonts. Rodent incisors grow and wear away continually through gnawing, which helps maintain relatively constant length. The industry of the beaver is due in part to this qualification. Some rodents, such as voles and guinea pigs (but not mice ), as well as lagomorpha ( rabbits , hares and pikas ), have continuously growing molars in addition to incisors. Also, tusks (in tusked mammals) grow almost throughout life. Teeth are not always attached to

702-463: A soft mush for them to eat in order to obtain adequate nutrition. Elephants ' tusks are specialized incisors for digging food up and fighting. Some elephant teeth are similar to those in manatees , and elephants are believed to have undergone an aquatic phase in their evolution. At birth, elephants have a total of 28 molar plate-like grinding teeth not including the tusks. These are organized into four sets of seven successively larger teeth which

780-440: A standard part of the aging process. Nearly all adults show calcification of the pineal gland . In a number of breast pathologies , calcium is often deposited at sites of cell death or in association secretions or hyalinized stroma, resulting in pathologic calcification. For example, small, irregular, linear calcifications may be seen, via mammography , in a ductal carcinoma-in-situ to produce visible radio-opacities. One of

858-604: Is known as teething and can be painful. Kangaroos , elephants , and manatees are unusual among mammals because they are polyphyodonts . In aardvarks , teeth lack enamel and have many pulp tubules, hence the name of the order Tubulidentata . In dogs , the teeth are less likely than humans to form dental cavities because of the very high pH of dog saliva, which prevents enamel from demineralizing. Sometimes called cuspids, these teeth are shaped like points (cusps) and are used for tearing and grasping food. Like human teeth, whale teeth have polyp-like protrusions located on

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936-807: Is largely a matter of convention. The first coherent text recorded in a Germanic language is the Gothic Bible , written in the later fourth century in the East Germanic variety of the Thervingi Gothic Christians , who had escaped persecution by moving from Scythia to Moesia in 348. Early West Germanic text is available from the fifth century, beginning with the Frankish Bergakker runic inscription . The evolution of Proto-Germanic from its ancestral forms, beginning with its ancestor Proto-Indo-European , began with

1014-502: Is only seen in older whales where the cementum has been worn away to show the underlying enamel. The toothed whale is a suborder of the cetaceans characterized by having teeth. The teeth differ considerably among the species. They may be numerous, with some dolphins bearing over 100 teeth in their jaws. On the other hand, the narwhals have a giant unicorn-like tusk, which is a tooth containing millions of sensory pathways and used for sensing during feeding, navigation, and mating. It

1092-473: Is some variation between species, most notably the venom-injecting fangs of snakes . The pattern of incisors, canines, premolars and molars is found only in mammals, and to varying extents, in their evolutionary ancestors . The numbers of these types of teeth vary greatly between species; zoologists use a standardised dental formula to describe the precise pattern in any given group. The word tooth comes from Proto-Germanic * tanþs , derived from

1170-413: Is termed Pre-Proto-Germanic . Whether it is to be included under a wider meaning of Proto-Germanic is a matter of usage. Winfred P. Lehmann regarded Jacob Grimm 's "First Germanic Sound Shift", or Grimm's law, and Verner's law , (which pertained mainly to consonants and were considered for many decades to have generated Proto-Germanic) as pre-Proto-Germanic and held that the "upper boundary" (that is,

1248-695: Is the reconstructed proto-language of the Germanic branch of the Indo-European languages . Proto-Germanic eventually developed from pre-Proto-Germanic into three Germanic branches during the fifth century BC to fifth century AD: West Germanic , East Germanic and North Germanic . The latter of these remained in contact with the others over a considerable time, especially with the Ingvaeonic languages (including English ), which arose from West Germanic dialects, and had remained in contact with

1326-557: Is the most neurologically complex tooth known. Beaked whales are almost toothless, with only bizarre teeth found in males. These teeth may be used for feeding but also for demonstrating aggression and showmanship. In humans (and most other primates), there are usually 20 primary (also "baby" or "milk") teeth, and later up to 32 permanent teeth. Four of these 32 may be third molars or wisdom teeth , although these are not present in all adults, and may be removed surgically later in life. Among primary teeth, 10 of them are usually found in

1404-564: Is the question of what specific tree, in the tree model of language evolution, best explains the paths of descent of all the members of a language family from a common language, or proto-language (at the root of the tree) to the attested languages (at the leaves of the tree). The Germanic languages form a tree with Proto-Germanic at its root that is a branch of the Indo-European tree, which in turn has Proto-Indo-European at its root. Borrowing of lexical items from contact languages makes

1482-548: Is typical not of Germanic but Celtic languages. Another is * walhaz 'foreigner; Celt' from the Celtic tribal name Volcae with k → h and o → a . Other likely Celtic loans include * ambahtaz 'servant', * brunjǭ 'mailshirt', * gīslaz 'hostage', * īsarną 'iron', * lēkijaz 'healer', * laudą 'lead', * Rīnaz 'Rhine', and * tūnaz, tūną 'fortified enclosure'. These loans would likely have been borrowed during

1560-490: Is used by molluscs for feeding and is sometimes compared rather inaccurately to a tongue . It is a minutely toothed, chitinous ribbon, typically used for scraping or cutting food before the food enters the oesophagus . The radula is unique to molluscs, and is found in every class of mollusc apart from bivalves . Within the gastropods , the radula is used in feeding by both herbivorous and carnivorous snails and slugs . The arrangement of teeth (also known as denticles) on

1638-677: The Corded Ware culture in the mid-3rd millennium BC, developing into the Nordic Bronze Age cultures by the early second millennium BC. According to Mallory, Germanicists "generally agree" that the Urheimat ('original homeland') of the Proto-Germanic language, the ancestral idiom of all attested Germanic dialects, was primarily situated in an area corresponding to the extent of the Jastorf culture . Early Germanic expansion in

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1716-503: The Funnelbeaker culture , but the sound change in the Germanic languages known as Grimm's law points to a non-substratic development away from other branches of Indo-European. Proto-Germanic itself was likely spoken after c. 500 BC, and Proto-Norse , from the second century AD and later, is still quite close to reconstructed Proto-Germanic, but other common innovations separating Germanic from Proto-Indo-European suggest

1794-637: The Norse . A defining feature of Proto-Germanic is the completion of the process described by Grimm's law , a set of sound changes that occurred between its status as a dialect of Proto-Indo-European and its gradual divergence into a separate language. The end of the Common Germanic period is reached with the beginning of the Migration Period in the fourth century AD. The alternative term " Germanic parent language " may be used to include

1872-681: The Pre-Roman Iron Age (fifth to first centuries BC) placed Proto-Germanic speakers in contact with the Continental Celtic La Tène horizon . A number of Celtic loanwords in Proto-Germanic have been identified. By the first century AD, Germanic expansion reached the Danube and the Upper Rhine in the south and the Germanic peoples first entered the historical record . At about the same time, extending east of

1950-478: The Proto-Indo-European * h₁dent- , which was composed of the root * h₁ed- ' to eat ' plus the active participle suffix * -nt , therefore literally meaning ' that which eats ' . The irregular plural form teeth is the result of Germanic umlaut whereby vowels immediately preceding a high vocalic in the following syllable were raised. As the nominative plural ending of

2028-621: The Vistula ( Oksywie culture , Przeworsk culture ), Germanic speakers came into contact with early Slavic cultures, as reflected in early Germanic loans in Proto-Slavic . By the third century, Late Proto-Germanic speakers had expanded over significant distance, from the Rhine to the Dniepr spanning about 1,200 km (700 mi). The period marks the breakup of Late Proto-Germanic and

2106-591: The animal 's teeth are related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing and grinding. Carnivores , on the other hand, have canine teeth to kill prey and to tear meat. Mammals, in general, are diphyodont , meaning that they develop two sets of teeth. In humans , the first set (the "baby", "milk", "primary" or " deciduous " set) normally starts to appear at about six months of age, although some babies are born with one or more visible teeth, known as neonatal teeth . Normal tooth eruption at about six months

2184-412: The enamel organ , and growth is dependent on the presence of stem cells , cellular amplification , and cellular maturation structures in the odontogenic region . Rodent incisors are used for cutting wood, biting through the skin of fruit, or for defense. This allows for the rate of wear and tooth growth to be at equilibrium. The microstructure of rodent incisor enamel has shown to be useful in studying

2262-475: The maxilla (i.e. upper jaw) and the other 10 in the mandible (i.e. lower jaw). Among permanent teeth, 16 are found in the maxilla and the other 16 in the mandible. Most of the teeth have uniquely distinguishing features. An adult horse has between 36 and 44 teeth. The enamel and dentin layers of horse teeth are intertwined. All horses have 12 premolars, 12 molars, and 12 incisors. Generally, all male equines also have four canine teeth (called tushes) between

2340-537: The thelodonts had scales composed of dentine and an enamel-like compound, suggesting that the origin of teeth was from scales which were retained in the mouth. Fish as early as the late Cambrian had dentine in their exoskeletons, which may have functioned in defense or for sensing their environments. Dentine can be as hard as the rest of teeth and is composed of collagen fibres, reinforced with hydroxyapatite . Though teeth are very resistant, they also can be brittle and highly susceptible to cracking. However, cracking of

2418-484: The "lower boundary" was the dropping of final -a or -e in unstressed syllables; for example, post-PIE * wóyd-e > Gothic wait , 'knows'. Elmer H. Antonsen agreed with Lehmann about the upper boundary but later found runic evidence that the -a was not dropped: ékwakraz … wraita , 'I, Wakraz, … wrote (this)'. He says: "We must therefore search for a new lower boundary for Proto-Germanic." Antonsen's own scheme divides Proto-Germanic into an early stage and

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2496-556: The 2nd century CE, as well as the non-runic Negau helmet inscription, dated to the 2nd century BCE), and in Roman Empire -era transcriptions of individual words (notably in Tacitus ' Germania , c. AD 90 ). Proto-Germanic developed out of pre-Proto-Germanic during the Pre-Roman Iron Age of Northern Europe. According to the Germanic substrate hypothesis , it may have been influenced by non-Indo-European cultures, such as

2574-429: The Germanic subfamily exhibited a less treelike behaviour, as some of its characteristics were acquired from neighbours early in its evolution rather than from its direct ancestors. The internal diversification of West Germanic developed in an especially non-treelike manner. Proto-Germanic is generally agreed to have begun about 500 BC. Its hypothetical ancestor between the end of Proto-Indo-European and 500 BC

2652-710: The Proto-Germanic consonant stems (to which * tanþs belonged) was * -iz , the root vowel in the plural form * tanþiz (changed by this point to * tą̄þi via unrelated phonological processes) was raised to /œː/, and later unrounded to /eː/, resulting in the tōþ/tēþ alternation attested from Old English . Cf. also Old English bōc/bēċ ' book/books ' and ' mūs/mȳs ' ' mouse/mice ' , from Proto-Germanic * bōks/bōkiz and * mūs/mūsiz respectively. Cognate with Latin dēns , Greek ὀδούς ( odous ), and Sanskrit dát . Teeth are assumed to have evolved either from ectoderm denticles (scales, much like those on

2730-418: The beak of birds may have evolved from teeth to allow chicks to escape their shells earlier, and thus avoid predators and also to penetrate protective covers such as hard earth to access underlying food. True teeth are unique to vertebrates, although many invertebrates have analogous structures often referred to as teeth. The organisms with the simplest genome bearing such tooth-like structures are perhaps

2808-489: The beginning of the (historiographically recorded) Germanic migrations . The earliest available complete sentences in a Germanic language are variably dated to the 2nd century AD, around 300 AD or the first century AD in runic inscriptions (such as the Tune Runestone ). The language of these sentences is known as Proto-Norse , although the delineation of Late Common Germanic from Proto-Norse at about that time

2886-535: The body depending on the location. In the pulpal structure of a tooth, calcification often presents asymptomatically, and is diagnosed as an incidental finding during radiographic interpretation. Individual teeth with calcified pulp will typically respond negatively to vitality testing; teeth with calcified pulp often lack sensation of pain, pressure, and temperature. Calcification of soft tissue (arteries, cartilage, heart valves , etc.) can be caused by vitamin K 2 deficiency or by poor calcium absorption due to

2964-566: The course of feeding if the prey is struggling. Additionally, amphibians that undergo a metamorphosis develop bicuspid shaped teeth. The teeth of reptiles are replaced constantly throughout their lives. Crocodilian juveniles replace teeth with larger ones at a rate as high as one new tooth per socket every month. Once mature, tooth replacement rates can slow to two years and even longer. Overall, crocodilians may use 3,000 teeth from birth to death. New teeth are created within old teeth. A skull of Ichthyornis discovered in 2014 suggests that

3042-401: The crown from the base of the tooth. Most amphibians exhibit teeth that have a slight attachment to the jaw or acrodont teeth. Acrodont teeth exhibit limited connection to the dentary and have little enervation . This is ideal for organisms who mostly use their teeth for grasping, but not for crushing and allows for rapid regeneration of teeth at a low energy cost. Teeth are usually lost in

3120-498: The dates of borrowings and sound laws are not precisely known, it is not possible to use loans to establish absolute or calendar chronology. Most loans from Celtic appear to have been made before or during the Germanic Sound Shift . For instance, one specimen * rīks 'ruler' was borrowed from Celtic * rīxs 'king' (stem * rīg- ), with g → k . It is clearly not native because PIE * ē → ī

3198-414: The development of a separate common way of speech among some geographically nearby speakers of a prior language and ended with the dispersion of the proto-language speakers into distinct populations with mostly independent speech habits. Between the two points, many sound changes occurred. Phylogeny as applied to historical linguistics involves the evolutionary descent of languages. The phylogeny problem

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3276-472: The development of fish scales. Study of a tooth plate of a fossil of the extinct fish Romundina stellina showed that the teeth and scales were made of the same tissues, also found in mammal teeth, lending support to the theory that teeth evolved as a modification of scales. Teeth are among the most distinctive (and long-lasting) features of mammal species. Paleontologists use teeth to identify fossil species and determine their relationships. The shape of

3354-432: The earlier boundary) was the fixing of the accent, or stress, on the root syllable of a word, typically on the first syllable. Proto-Indo-European had featured a moveable pitch-accent consisting of "an alternation of high and low tones" as well as stress of position determined by a set of rules based on the lengths of a word's syllables. The fixation of the stress led to sound changes in unstressed syllables. For Lehmann,

3432-418: The elephant will slowly wear through during its lifetime of chewing rough plant material. Only four teeth are used for chewing at a given time, and as each tooth wears out, another tooth moves forward to take its place in a process similar to a conveyor belt. The last and largest of these teeth usually becomes exposed when the animal is around 40 years of age, and will often last for an additional 20 years. When

3510-480: The entire journey that the dialect of Proto-Indo-European that would become Proto-Germanic underwent through the millennia. The Proto-Germanic language is not directly attested by any complete surviving texts; it has been reconstructed using the comparative method . However, there is fragmentary direct attestation of (late) Proto-Germanic in early runic inscriptions (specifically the Vimose inscriptions , dated to

3588-496: The erosion of unstressed syllables, which would continue in its descendants. The final stage of the language included the remaining development until the breakup into dialects and, most notably, featured the development of nasal vowels and the start of umlaut , another characteristic Germanic feature. Loans into Proto-Germanic from other (known) languages or from Proto-Germanic into other languages can be dated relative to each other by which Germanic sound laws have acted on them. Since

3666-458: The food through the stomach for digestion. Molluscs have a structure called a radula , which bears a ribbon of chitinous teeth. However, these teeth are histologically and developmentally different from vertebrate teeth and are unlikely to be homologous . For example, vertebrate teeth develop from a neural crest mesenchyme -derived dental papilla , and the neural crest is specific to vertebrates, as are tissues such as enamel . The radula

3744-411: The foods are abrasive enough to cause attrition, rabbit teeth grow continuously throughout life. Rabbits have a total of six incisors, three upper premolars, three upper molars, two lower premolars, and two lower molars on each side. There are no canines. Dental formula is 2.0.3.3 1.0.2.3 = 28. Three to four millimeters of the tooth is worn away by incisors every week, whereas the cheek teeth require

3822-545: The history of Proto-Germanic in the wider sense from the end of Proto-Indo-European up to the point that Proto-Germanic began to break into mutually unintelligible dialects. The changes are listed roughly in chronological order, with changes that operate on the outcome of earlier ones appearing later in the list. The stages distinguished and the changes associated with each stage rely heavily on Ringe 2006 , Chapter 3, "The development of Proto-Germanic". Ringe in turn summarizes standard concepts and terminology. This stage began with

3900-429: The horse's bit contact. Therefore, wolf teeth are commonly removed. Horse teeth can be used to estimate the animal's age. Between birth and five years, age can be closely estimated by observing the eruption pattern on milk teeth and then permanent teeth. By age five, all permanent teeth have usually erupted. The horse is then said to have a "full" mouth. After the age of five, age can only be conjectured by studying

3978-459: The host. The incision leaves a mark that is an inverted Y inside of a circle. After piercing the skin and injecting anticoagulants ( hirudin ) and anaesthetics , they suck out blood, consuming up to ten times their body weight in a single meal. In some species of Bryozoa , the first part of the stomach forms a muscular gizzard lined with chitinous teeth that crush armoured prey such as diatoms . Wave-like peristaltic contractions then move

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4056-416: 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. Monophyodonts are animals that develop only one set of teeth, while diphyodonts grow an early set of deciduous teeth and a later set of permanent or "adult" teeth . Polyphyodonts grow many sets of teeth. For example, sharks , grow

4134-426: The intestine which, when accompanied by a deficiency of vitamin K (perhaps induced by an anticoagulant ), can result in calcification of arteries and other soft tissue. Such metastatic soft tissue calcification is mainly in tissues containing "calcium catchers" such as elastic fibres or mucopolysaccharides . These tissues especially include the lungs (pumice lung) and the aorta. Calcification can be pathological or

4212-439: The jaw and are encased in a bony shell separated by soft tissue. Walrus tusks are canine teeth that grow continuously throughout life. Fish , such as sharks , may go through many teeth in their lifetime. The replacement of multiple teeth is known as polyphyodontia . A class of prehistoric shark are called cladodonts for their strange forked teeth. Unlike the continuous shedding of functional teeth seen in modern sharks,

4290-469: The jaw, as they are in mammals. In many reptiles and fish, teeth are attached to the palate or to the floor of the mouth, forming additional rows inside those on the jaws proper. Some teleosts even have teeth in the pharynx . While not true teeth in the usual sense, the dermal denticles of sharks are almost identical in structure and are likely to have the same evolutionary origin. Indeed, teeth appear to have first evolved in sharks, and are not found in

4368-416: The last of these teeth has fallen out, regardless of the elephant's age, the animal will no longer be able to chew food and will die of starvation. Rabbits and other lagomorphs usually shed their deciduous teeth before (or very shortly after) their birth, and are usually born with their permanent teeth. The teeth of rabbits complement their diet, which consists of a wide range of vegetation. Since many of

4446-440: The majority of stem chondrichthyan lineages retained all tooth generations developed throughout the life of the animal. This replacement mechanism is exemplified by the tooth whorl-based dentitions of acanthodians , which include the oldest known toothed vertebrate, Qianodus duplicis . All amphibians have pedicellate teeth , which are modified to be flexible due to connective tissue and uncalcified dentine that separates

4524-434: The majority of the crown remaining below the gumline in the dental socket. The rest of the tooth will slowly emerge from the jaw, erupting about 3 mm ( 1 ⁄ 8  in) each year, as the horse ages. When the animal reaches old age, the crowns of the teeth are very short and the teeth are often lost altogether. Very old horses, if lacking molars, may need to have their fodder ground up and soaked in water to create

4602-455: The molars and incisors. However, few female horses (less than 28%) have canines, and those that do usually have only one or two, which many times are only partially erupted. A few horses have one to four wolf teeth , which are vestigial premolars, with most of those having only one or two. They are equally common in male and female horses and much more likely to be on the upper jaw. If present these can cause problems as they can interfere with

4680-577: The more primitive jawless fish – while lampreys do have tooth-like structures on the tongue, these are in fact, composed of keratin , not of dentine or enamel, and bear no relationship to true teeth. Though "modern" teeth-like structures with dentine and enamel have been found in late conodonts , they are now supposed to have evolved independently of later vertebrates' teeth. Living amphibians typically have small teeth, or none at all, since they commonly feed only on soft foods. In reptiles, teeth are generally simple and conical in shape, although there

4758-428: The outermost embryonic germ layer , the ectoderm . The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position. The teeth of 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

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4836-486: The outside and exposed dentin on the inside, so they self-sharpen during gnawing . On the other hand, continually growing molars are found in some rodent species, such as the sibling vole and the guinea pig. There is variation in the dentition of the rodents, but generally, rodents lack canines and premolars , and have a space between their incisors and molars, called the diastema region. Manatees are polyphyodont with mandibular molars developing separately from

4914-635: The parasitic worms of the family Ancylostomatidae . For example, the hookworm Necator americanus has two dorsal and two ventral cutting plates or teeth around the anterior margin of the buccal capsule. It also has a pair of subdorsal and a pair of subventral teeth located close to the rear. Historically, the European medicinal leech , another invertebrate parasite, has been used in medicine to remove blood from patients. They have three jaws (tripartite) that resemble saws in both appearance and function, and on them are about 100 sharp teeth used to incise

4992-413: The period marked the definitive break of Germanic from the other Indo-European languages and the beginning of Germanic proper, containing most of the sound changes that are now held to define this branch distinctively. This stage contained various consonant and vowel shifts, the loss of the contrastive accent inherited from PIE for a uniform accent on the first syllable of the word root, and the beginnings of

5070-460: The phylogeny and systematics of rodents because of its independent evolution from the other dental traits. The enamel on rodent incisors are composed of two layers: the inner portio interna (PI) with Hunter-Schreger bands (HSB) and an outer portio externa (PE) with radial enamel (RE). It usually involves the differential regulation of the epithelial stem cell niche in the tooth of two rodent species, such as guinea pigs . The teeth have enamel on

5148-434: The principal causes of arterial stiffening with age is vascular calcification. Vascular calcification is the deposition of mineral in the form of calcium phosphate salts in the smooth muscle-rich medial layer of large arteries including the aorta. DNA damage , especially oxidative DNA damage, causes accelerated vascular calcification. Vascular calcification could also be linked to the chronic leakage of blood lysates into

5226-552: The radula ribbon varies considerably from one group to another as shown in the diagram on the left. Predatory marine snails such as the Naticidae use the radula plus an acidic secretion to bore through the shell of other molluscs. Other predatory marine snails , such as the Conidae , use a specialized radula tooth as a poisoned harpoon . Predatory pulmonate land slugs, such as the ghost slug , use elongated razor-sharp teeth on

5304-403: The radula to seize and devour earthworms . Predatory cephalopods, such as squid , use the radula for cutting prey. In most of the more ancient lineages of gastropods, the radula is used to graze by scraping diatoms and other microscopic algae off rock surfaces and other substrates. Limpets scrape algae from rocks using radula equipped with exceptionally hard rasping teeth. These teeth have

5382-552: The reduction of the resulting unstressed syllables. By this stage, Germanic had emerged as a distinctive branch and had undergone many of the sound changes that would make its later descendants recognisable as Germanic languages. It had shifted its consonant inventory from a system that was rich in plosives to one containing primarily fricatives, had lost the PIE mobile pitch accent for a predictable stress accent, and had merged two of its vowels. The stress accent had already begun to cause

5460-539: The relative position of the Germanic branch within Indo-European less clear than the positions of the other branches of Indo-European. In the course of the development of historical linguistics, various solutions have been proposed, none certain and all debatable. In the evolutionary history of a language family, philologists consider a genetic "tree model" appropriate only if communities do not remain in effective contact as their languages diverge. Early Indo-European had limited contact between distinct lineages, and, uniquely,

5538-430: The root surface of the tooth. These polyps are made of cementum in both species, but in human teeth, the protrusions are located on the outside of the root, while in whales the nodule is located on the inside of the pulp chamber. While the roots of human teeth are made of cementum on the outer surface, whales have cementum on the entire surface of the tooth with a very small layer of enamel at the tip. This small enamel layer

5616-511: The separation of a distinct speech, perhaps while it was still forming part of the Proto-Indo-European dialect continuum. It contained many innovations that were shared with other Indo-European branches to various degrees, probably through areal contacts, and mutual intelligibility with other dialects would have remained for some time. It was nevertheless on its own path, whether dialect or language. This stage began its evolution as

5694-529: The skin of sharks ) that folded and integrated into the mouth (called the "outside–in" theory), or from endoderm pharyngeal teeth (primarily formed in the pharynx of jawless vertebrates ) (the "inside–out" theory). In addition, there is another theory stating that neural crest gene regulatory network , and neural crest-derived ectomesenchyme are the key to generate teeth (with any epithelium , either ectoderm or endoderm). The genes governing tooth development in mammals are homologous to those involved in

5772-404: The stomachs of vertebrate predators. Enamel can be lost by abrasion or spalling, and is lost before dentine or bone are destroyed by the fossilisation process. In such a case, the 'skeleton' of the teeth would consist of the dentine, with a hollow pulp cavity. The organic part of dentine, conversely, is destroyed by alkalis. Calcification Calcification can manifest itself in many ways in

5850-457: The strongest known tensile strength of any biological material, outperforming spider silk . The mineral protein of the limpet teeth can withstand a tensile stress of 4.9  GPa , compared to 4 GPa of spider silk and 0.5 GPa of human teeth . Because teeth are very resistant, often preserved when bones are not, and reflect the diet of the host organism, they are very valuable to archaeologists and palaeontologists. Early fish such as

5928-446: The tooth can be used as a diagnostic tool for predicting bite force. Additionally, enamel fractures can also give valuable insight into the diet and behaviour of archaeological and fossil samples. Decalcification removes the enamel from teeth and leaves only the organic interior intact, which comprises dentine and cementine . Enamel is quickly decalcified in acids, perhaps by dissolution by plant acids or via diagenetic solutions, or in

6006-962: The vessel wall since red blood cells have been shown to contain a high concentration of calcium. In terms of diagnosis, in this case vascular calcification, an ultrasound and radiography of said area is sufficient. Treatment of high calcium/vitamin D ratio may most easily be accomplished by intake of more vitamin D if vitamin K is normal. Intake of too much vitamin D would be evident by anorexia , loss of appetite, or soft tissue calcification. Proto-Germanic Pontic Steppe Caucasus East Asia Eastern Europe Northern Europe Pontic Steppe Northern/Eastern Steppe Europe South Asia Steppe Europe Caucasus India Indo-Aryans Iranians East Asia Europe East Asia Europe Indo-Aryan Iranian Indo-Aryan Iranian Others European Proto-Germanic (abbreviated PGmc ; also called Common Germanic )

6084-475: The wear patterns on the incisors, shape, the angle at which the incisors meet, and other factors. The wear of teeth may also be affected by diet, natural abnormalities, and cribbing . Two horses of the same age may have different wear patterns. A horse's incisors, premolars, and molars, once fully developed, continue to erupt as the grinding surface is worn down through chewing. A young adult horse will have teeth, which are 110–130 mm (4.5–5 inches) long, with

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