Tooth development

The ontogenetic development of the teeth is a complex process used when the teeth from embryonic cells, grow and emerge in the mouth. Many vertebrates have teeth, and their development in humans and other living things are very similar. For human teeth to have a healthy oral environment during embryogenesis enamel, dentin, cementum and periodontal ligament ( periodontal ) must develop. The primary dentition is created from the sixth to eighth week before the birth, the permanent teeth in the twentieth week. ). If the development of the teeth does not begin at about this time, she did not take place. The general opinion is a factor in the tissues of the first branchial arch is necessary to initiate the process.

• 2.1 bud stage
• 2.2 cap stage
• 2.3 bell stage
• 2.4 Crown Stadium

• 3.1 enamel
• 3.2 dentin
• 3.3 cementum

• 4.1 Periodontal ligaments
• 4.2 alveolar bone
• 4.3 gums ( gingiva)

• 5.1 formation of nerve
• 5.2 Formation of vessels

• 8.1 tooth malformations

Overview

The tooth bud is a cluster of cells from which a tooth can form. These cells are derived from the ectoderm of the first branchial arch and the ectomesenchyme the neural crest. The tooth bud is composed of three parts: the enamel organ, the dental papilla and dental follicle the.

The enamel organ (Organon enameleum ) consists of an outer and inner enamel epithelium ( epithelium enameleum externum and internum ), the Schmelzretikulum ( Recticulum enameleum ) and the intermediate layer (stratum intermedium ). The cells of the inner enamel epithelium differentiate into ameloblasts, the enamel prisms and thus produce a melt coating over the dentin. The body, unite with the participation of external and internal Schmelzpithel, called ansa cervicalis. The growth of cervical cells of the enamel epithelium into deeper tissue forms of the epithelial Hertwig'sche which caused the later form of the tooth root.

The dental papilla contains cells that develop into odontoblasts dentinbildenden. The connection between the disc and the inner epithelium determines the shape of the tooth crown. Mesenchymal cells in the papilla are responsible for formation of the dental pulp.

The dental follicle produces three major tissues: cementoblasts, osteoblasts and fibroblasts. Cementoblasts form the cementum, the alveolar osteoblasts ( alveolus ) around the tooth root and periodontal ligament fibroblasts, which connect the tooth by the root cementum with the alveoli.

Timeline

The following tables show the time evolution of human teeth. The information in the initial calcification of the deciduous dentition refers to the time before birth.

Key for Tables:

• W = Weeks
• M = months
• J = annual

Development of tooth bud

One of the first steps in the formation of a tooth is the separation of vestibular and dental lamina. The dental lamina connecting the tooth bud for a certain time with the epithelial layer in the mouth.

In the development of the teeth, a distinction the following stages: bud, cap, bell and maturity. The classification is an attempt to categorize continuous running changes; the exact assignment is often difficult in individual cases ( Cate 1998:81 ). The determination is further complicated by different histological sections.

Bud stage

This section is characterized by the appearance of the tooth bud without a clear arrangement of the cells. Technically begins the stage when epithelial cells penetrate into ectomesenchyme of the jaw ( Cate 1998:82 ). The tooth bud itself is the group of cells at the end of the dental lamina.

Cap stage

The first signs of an array of cells in the tooth bud are in the cap stage. A small group of ectomesenchymal cells stops the production of extracellular substances, resulting in the formation of the dental papilla. At this point, the tooth bud grows around the ectomesenchymal arrangement, takes the form of a cap and becomes the enamel organ. A precipitate ectomesenchymal cells, which is referred to as dental follicle surrounds the enamel organ and limits the papilla. The enamel organ finally produces the enamel, dentin and the papilla of the follicle all the supporting structures of a tooth ( Cate 1998:84 ).

Bell stage

In the bell stage further differentiation takes place. The enamel organ has at this stage the shape of a bell and most of the cells, because of their star-like appearance referred to as " star-like reticulum " ( Cate 1998:84 ). The cells on the periphery of the enamel organ divided into three important layers. The cells on the outer side are called outer Zahnschmelzepithel. The cells of the papilla form the inner epithelium. The cells between the inner epithelium and the Schmelzretikulum form a layer, which is called the intermediate layer (stratum intermedium ).

The dental lamina disintegrates, which causes the generated tooth is completely separated from the epithelium of the mouth; the two combine again when the tooth in the mouth emerges ( Cate 1998:87 ). The crown of the tooth, which is influenced by the shape of the inner epithelium increases during this stage of their shape. All teeth through this process; why they make different shaped crowns (eg incisors against canines ), is still unclear. Two hypotheses dominate. One theory is that there is in ectomesenchyme during the development of components for each form. The components for a particular type (eg incisors ) are localized in one area and dissipated rapidly in other parts of the mouth. The other model, indicating that the epithelium is a group of ectomesenchymal cells programmed to produce teeth having a predetermined shape. This group of cells (clone ) excites the dental lamina, to form a tooth bud. The growth of the lamina is made in a " progress zone " section. Once this zone is far enough away from the first tooth bud, a second bud develops. The two hypotheses are not mutually exclusive necessarily mutually exclusive. The dentistry assumes that both models the development at certain times affect ( Cate 1998:89 ).

In this phase also enamel knots, ropes and niches can occur ( Cate 1998:86 ).

Crown Stadium

Fixed tissues, including enamel and dentin, develop in the next stage, as the crown stage (or maturity ) is called. At this time important cellular changes take place. The rapid division of the epithelial cells (mitosis ), which led to increase in the earlier phases of the tooth bud now terminates at the point where the tips of the teeth are formed. This is where the first solid mineralized tissue. At the same time the cells of the inner epithelium change their shape from columnar to cubic. The nuclei move closer to the stratum intermedium ( Cate 1998:95 ) of the papilla.

The adjacent cell layers of the papilla suddenly grow and differentiate into odontoblasts, which form the dentin ( Ross 2003:444 ). The odontoblasts would not exist without the change in the inner epithelium. They secrete a secretion, an organic matrix, into their immediate environment. The matrix containing the material necessary for the formation of dentine. The odontoblasts migrate it to the center of the optic disc. In contrast to the formation of the enamel dentin thus extends from outside to inside. On the road inwards cytoplasmic boom left behind. The unique, tubular appearance of dentin under the microscope is a consequence of its formation around these boom ( Cate 1998:95 ).

The cells of the inner epithelium but an organic matrix against the dentin, which is immediately mineralized and the tooth enamel. Outside of the dentine are ameloblasts which continue the formation of the enamel to the outside, so that on the outer side of the tooth formed of new material is added.

Formation of solid tissue

Enamel

The formation of enamel, also called amelogenesis, occurs during the crown stage. The formation of dentin and enamel is characterized by a reciprocal induction; Dentin is always formed before the tooth enamel. The latter is formed in two phases. In the secretory phase proteins and an organic matrix form a partially mineralized enamel in the maturation phase of mineralization is completed. ( Cate 1998:197 )

Mineralization in the first phase is carried out by the enzyme alkaline phosphatase. ( Ross 2003:445 ) This usually occurs in the third or fourth month of pregnancy mineralized tissue represents the first appearance of enamel in the body, which then spreads outward.

In the ripening phase of the ameloblasts transport some used in the production of enamel substances to the outside. These are mainly proteins, which are used to complete mineralization at the end of this stage. The most important proteins are amelogenin, ameloblastin, enamelin and tuftelin. ( Ross 2003:447 )

Dentin

Known as dentinogenesis formation of dentin is the first identifiable feature in the crown stage. The various stages lead to different types of dentin: Manteldentin ( Korff - dentin) as well as primary, secondary and tertiary dentin.

The dentinbildenden odontoblasts differentiate from the cells of the dental papilla. You begin to secrete an organic matrix around the future tip of the tooth near the inner epithelium. This matrix contains collagen fibers with a large diameter from 0.1 to 0.2 microns. ( Cate 1998:136 ) The odontoblasts move to the center of the tooth and form an offshoot, which is referred to as the odontoblast process. ( Cate 1998:95 ) This leads to the secreting of hydroxyapatite crystals and the mineralization of the matrix. The approximately 150 microns thick layer is the Manteldentin. ( Cate 1998:138 )

While the Manteldentin arises from a preexisting ground substance of the dental papilla, primary dentin, the developed in other ways. Odontoblasts are so large that no extracellular resources can contribute to an organic matrix. The larger odontoblasts but the collagen in smaller quantities from, which clearly structured, heterogeneous cores arise. In addition, other substances such as lipids, phosphoproteins and phospholipids are secreted. ( Cate 1998:139 )

The secondary dentin is - much slower - formed after the completion of root formation. The development proceeds in the vicinity of the crown faster than at other points of the tooth. (Summit 2001:13 ) She continues throughout life and is responsible for the smaller pulp in the elderly. ( Cate 1998:128 ) The tertiary dentin (also known as a repairing dentin) is produced in response to stimuli such as Abkauung or dental caries. (Summit 2001:183 )

Cementum

Known as Cementogenesis formation of root cementum occurs at a late stage in the development of the teeth. Cementoblasts are the responsible cells. There are two types of root cementum: cellular and acellular.

The acellular variant forms first. The cementoblasts differentiate from follicular cells, which can reach the surface of the tooth root only when the Hertwig'sche epithelial ( " Hertwig 's epithelial root sheath " - HERS ) begins to decay. The cementoblasts but fine collagen fibrils perpendicular to the root surface from before they move away from the tooth. Move more collagen is deposited to lengthen and thicken the bundles of fibers. Other proteins such as bone sialoprotein and osteocalcin are also secreted. ( Cate 1998:236 ) The acellular cementum contains a secretion matrix of proteins and fibers. If the mineralization begins, the cementoblasts from the cementum and the remaining fibers on the surface remove combine with the periodontal ligaments.

The cellular cementum occurs when the tooth formation is almost completed and the closing tooth (in contact ) with an opposing tooth. ( Cate 1998:241 ) It is formed around the fiber bundles of the periodontal ligament. The cementoblasts become trapped in the cementum they produce.

The origin of cementoblasts is different in the two types of cementum. The most common hypothesis is that the cells of the cellular cementum of the adjacent bones come from, while the cells of the acellular variety from the dental follicle stem ( Cate 1998:241 and 243 ). Cellular cementum is not found, however, in teeth with a root ( Cate 1998:241 ). In premolars and molars, it is found only in the vicinity of the root tip and between the individual roots.

Formation of the periodontium

The periodontium, the supporting structure of a tooth, comprised of the cementum, the periodontal ligaments, the gums and the alveolar bones. Of these, only the root cement is a part of the tooth. The bone surrounding the roots to support them and to form a kind of pedestal. The periodontal ligaments connect the bones with the cementum and the gingiva is visible in the mouth surrounding tissue.

Periodontal ligaments

The periodontal ligament arise from cells of the dental follicle. With the emergence there are differences between milk teeth and permanent teeth, as well as in various animal species. ( Cate 1998:245 ) In any case, the process with fibroblasts from the dental follicle that secrete collagen, which interacts with the fibers on the surface of the adjacent bone and cementum begins. ( Ross 2003:453 ) This creates an attachment that develops in the mouth at the emergence of the tooth. The occlusion constantly influenced the formation of the periodontal ligament, resulting in different alignment results ( horizontal or straight) to the formation of fiber bundles. ( Cate 1998:245 )

Alveolar bone

If root and cementum arise formed in the bone environment. Bone-forming cells in the whole body is referred to as osteoblasts. When alveolar bone, these cells originate from the dental follicle. ( Cate 1998:244 ) Similarly to the formation of the primary root cementum, collagen fibers arise on the surface in the vicinity of the tooth and stay there until they connect to the periodontal ligaments.

Like any other bone in the human body, and the alveolar bone changes during life. Osteoblasts and osteoclasts, bone created destroy, especially when pressure is applied to a tooth. ( Ross 2003:452 ) If as when you try to move through orthodontics teeth, a tooth, a compression force to the bone exercises below, you can reach a high level osteoklastisches, leading to bone resorption. A bone, which is set by periodontal ligaments in tension, has a lot of osteoblasts which form new bone.

Gums ( gingiva)

The connection between the gum and tooth is called dentogingival connection. A distinction is made gingival, sulkulare and connection epithelium. They are formed from the cells of the epithelial cuff between the tooth and mouth. ( Cate 1998:247 f )

Regarding the formation of the gums are still many open questions, but you know that hemidesmosomes are responsible between the gingival epithelium and the tooth for the primary epithelial links. ( Cate 1998:248 ) anchor the cells by small fibrous structures that represent the remnants of ameloblasts. Once that happens, the junctional from the reduced enamel epithelium, a product of the enamel organ forms, and divides rapidly. That leaves this layer grow rapidly. The ameloblasts are no longer supplied with nutrients and stunted, resulting in the formation of a gingival sulcus.

Formation of nerves and vessels

Nerves and blood vessels often parallel to each other in the body and they are formed at the same time and in a similar manner. This is not true in the area of the tooth, where the trend is different. ( Cate 1998:93 )

Formation of nerve

Axons approach the tooth during the cap stage and grow on the dental follicle to. Once they arrived there, the nerves develop around the tooth bud and penetrate into the papilla, once the formation has been used by dentin. They do not grow in the enamel organ. ( Cate 1998:93 )

Formation of vessels

Blood vessels grow in the dental follicle and penetrate during the cap stage in the papilla. ( Cate 1998:93 ) At the entrance of the optic disc that groups of blood vessels. Their number is reached to the beginning of the crown stage is a maximum and the papilla to the pulp of the tooth. Throughout life, the pulp tissue decreases in the tooth, so the blood supply to the tooth decreases with age. ( Ross 2003:452 ) The gingival organ is by its epithelial origin free of blood vessels and the mineralized tissues of the tooth enamel and dentin do not need a supply of nutrients through the blood.

Emergence of the tooth

Although researchers agree that it is the emergence of the tooth ( tooth eruption ) is a complex process, they still argue about the mechanisms that control the process. ( Riolo 2003:142 ) Some common theories that have been disproved. The tooth is moved neither by the growing root nor by the growing bone in the mouth. It is pressed not by the pressure vessels or " padded hammock " upwards. (Harris 2002:1-3 ) The latter theory, presented Harry Sure, taught by the 30s up to the 50s. Thus was a band under the tooth, watched the safety on a histological section under the microscope, is responsible for the emergence. Later the "tape", however, identified as artifact formed during the preparation of the cut. (Harris 2002:3 )

After today the most widespread theory of the periodontal ligament for the main impetus ensure in this process. Let the tooth come forth by their collagen fibers shrink and connect across while contracting the fibroblasts. (Harris 2002:5 )

When the time for the emergence of the teeth is individual, there is a general timeline. People usually have 20 primary teeth and 32 permanent teeth. (PDF, 79 kB ) The dentition of deciduous teeth only primary teeth are visible. When the first permanent teeth appear, the mixed dentition takes place. When the last baby teeth fall out ( exfoliation ), one speaks of the permanent dentition.

The primary dentition begins with the appearance of the central incisors in the lower jaw ( at the age of eight months ) and lasts to appear the first permanent molars at the age of six years. ( Ash & Nelson 2003:38,41 ) The milk teeth usually appear in the following order shown:

( Ash & Nelson 2003:38 )

In general, four teeth appear in six months that the teeth emerge in the mandible than in the maxilla before and that the process in females takes place earlier than in male. During the primary dentition, the tooth buds of permanent teeth develop below the primary teeth, close to the palate or tongue.

The mixed dentition begins with the appearance of the first permanent molar (aged six years ) and lasts until the last primary tooth fails with eleven or twelve years. ( Ash & Nelson 2003:41 ) The permanent teeth in the upper jaw appear in a different order than the teeth in the lower jaw.

Since there are no pre-molars in the primary dentition, the posterior teeth milk teeth are replaced by permanent premolars. If milk teeth fall out before permanent teeth are ready as a replacement, permanent teeth can slip forward, thereby losing space for other teeth in the mouth. This can lead to misaligned ( malocclusion ), which may require orthodontic treatment to prepare a eugnathes bite.

The permanent dentition begins with the loss of the last milk tooth aged 11 to 12 years. As a result, the third molars (wisdom teeth) are often removed due to lack of space carious destruction or breakdown due to disturbances. The most common reasons for the loss of teeth are carious destruction or periodontitis.

( Ash & Nelson 2003:53 ) M = months; J = annual

Nutrition

As with other aspects of human growth, the diet has an effect on the development of teeth. Essential nutrients for a healthy tooth include calcium, phosphorus, fluoride, and vitamins A, C and D. Calcium and phosphorus are required for the formation of hydroxyapatite crystals and their proportion in the blood is regulated by the vitamin D. Vitamin A is responsible for the formation of keratin and vitamin C for collagen. Fluoride can be a part of the crystal in the tooth and makes it more resistant to demineralization and caries. ( Ross 2003:453 )

Nutrient deficiency can have numerous consequences for the development of the teeth. In the absence of calcium, phosphorus, vitamin D and the solid constituents of the tooth may be less mineralized. Deficiency of vitamin A leads to a reduction of the enamel. Missing fluoride accelerated demineralization when the tooth is exposed to an acidic environment, and delayed re- mineralization. Fluoride overdoses lead to fluorosis, in which form white to brown discoloration in the form of spots or stripes on the enamel surface.

Abnormalities

In the development of the teeth can lead to various abnormalities.

In a anodontia tooth development is not at a hypodontia only partially successful. The anodontia rarely occurs, usually at a ectodermal dysplasia, while hypodontia is one of the most common abnormalities that affects 3.5-8.0 % of the population ( not counting the wisdom teeth). The lack of wisdom teeth can be at 20-23 % of the population notice followed by the second molar tooth ( molar) and lateral incisor. The hypodontia is often associated with the absence of the dental lamina, which against external influences such as infections or chemotherapeutic medications makes vulnerable and is associated with some syndromes such as Down syndrome or Crouzon 's disease. ( Neville 2002:70 )

In a Hyperdontie to supernumerary teeth develop. It occurs in one to three percent of Caucasians and more common in Asians. ( Neville 2002:70 ) In 86 % of cases the Hyperdontie usually affects a single extra incisors in the upper jaw. ( Kahn 2001:49 ), an excess of dental lamina is assumed as the cause of Hyperdontie.

A dilaceration is an abnormal bending of a tooth, which was almost always caused by trauma, by which the formed tooth bud is moved. At its creation, a force to move the tooth from the original position, causing the rest of the tooth forms in an unnatural angle. Cysts or tumors in the vicinity of the tooth bud can also cause dilaceration. It can be pushed through a trauma to the gums and milk teeth, making the tooth bud of the permanent tooth is moved. ( Neville 2002:86 )

Tooth abnormalities

The causes of regional odontodysplasia (tooth malformation ) are unknown, they are not in any case, genetic cause. It is assumed that a fault in the development of mesenchymal and ectodermal structures of the teeth, a disorder in the neural crest cells, an infection or a lack of vascular supply, the latter hypothesis is the most widespread. Also, radiation therapy can lead to odontodysplasia. ( Neville 2002:99 ) affected by this abnormality teeth may persist, so do not break, have small crowns and have unnatural shapes. The teeth are smaller, show increased pits and furrows and often have a brown to yellowish discoloration. Radiographically recognize a large Pulpenlumen with a thin hard tissue sheath, root growth is delayed, enamel and dentin can hardly be distinguished, the radio-opacity is reduced. These teeth appear on radiographs often translucent and " wispy ", giving them the nickname Ghost teeth (ghost teeth) has introduced. ( Kahn 2001:58 )

Delineate these, enamel formation disorders, such as the molar incisor hypo - mineralization, which can be caused by trauma, medications, diet, birth incidents and numerous acute or chronic childhood diseases or their treatment, the cause is still largely unknown. Also included is one of Turner's tooth, the tooth germ of the permanent tooth damage caused by diseased baby teeth. The amelogenesis imperfecta is a genetic disorder in which there is a disturbance of enamel formation. Tetracycline teeth caused by Tetracyclingabe during pregnancy or in children because tetracyclines are incorporated with calcium in an irreversible complex formation in the child's tooth enamel.

Tooth development in animals

Developmentally, the teeth of vertebrates from specialized skin scales ( placoid scales ) are derived from, some of which cover the whole body with original vertebrates and form a kind of exoskeleton.

This can for example be well at the relatively primitive sharks (see cartilaginous fish ) understand their dental education from that of the other vertebrates differs significantly. Because their teeth have no roots, sharks easily lose teeth when they eat, which must therefore be continuously replaced. Zoologists estimate that a single shark in a year can lose up to 2,400 teeth. Shark teeth form from the above placoid scales near the tongue and move on to the jaw in rows to the outside where they are used and fail later.

While in mammals, to humans belong, the teeth form one row in the maxilla and mandible ( There are differences in the morphology, number, the timeline and the types of teeth ), are found in other vertebrate groups some more rows of teeth in different localization. Certain groups of vertebrates such as Birds and turtles have also lost their teeth again in the course of evolution. Birds derived from dinosaurs (see Archaeopteryx ) since about 70 million years ago, for example, form no more teeth, have but obviously partly retain the associated genetic makeup that under special circumstances, such as in the context of mutations can induce tooth formation ( atavism ).

The formation of dental enamel is almost identical in humans and other mammals. The ameloblasts and enamel organ, including the dental papilla works similarly. ( Frandson 1992:305 ) While the ameloblasts in humans and most other animals die - making further formation of enamel impossible - the development of lagomorphs, chinchillas and guinea pigs, and some teeth of other mammals ( " rootless teeth " ) continuously use continued, forcing them to wear down their teeth by chewing on various materials. If chewing is not possible, their teeth can come through the mouth (pike bite ). The rootless teeth consist of two halves, the counterparts to crown and root. The lip is half covered with enamel and resembles a crown, while the half of the tongue is covered with dentin and resembles a root. Both occur simultaneously and grow for a lifetime.

The mineral distribution in the enamel of rodents is different from the in monkeys, dogs, pigs and humans. In teeth of horses the enamel and dentin layers are connected to each other, which increases the strength and decreases the wear of the teeth.

Even among mammals, some animal groups, such as certain whales, armadillos, anteaters and sloths the formation of enamel ( filmstrip final ) or the tooth formation generally abandoned. This was accompanied by a loss of function associated enamelin gene ENAM.