3. Milk and permanent teeth, their structure, replacement. Dentition, formula of milk and permanent teeth. Blood supply and innervation of teeth.
Teeth, dentes, are ossified papillae of the mucous membrane, used for mechanical processing of food. Phylogenetically, teeth come from fish scales that grow along the edge of the jaws and acquire new functions here. Due to wear and tear, they are repeatedly replaced by new ones, which is reflected in the change of teeth, which in lower vertebrates occurs many times throughout life, and in person twice:
1) temporary, milk, dentes decidui
2) permanent, dentes permanentes
Sometimes there is a 3rd shift. (A case of the 3rd change of teeth in a 100-year-old man was observed). Types of teeth:
3. Premolars
The teeth are located in the cells of the alveolar processes of the upper and lower jaws, connecting using the so-called hammering, gomphosis, (gomphos, Greek - nail) (the name is incorrect, since in fact the teeth are not hammered in from the outside, but grow from the inside - an example of formalism in descriptive anatomy). The tissue covering the alveolar processes is called gums, gingivae. The mucous membrane here, through fibrous tissue, tightly fuses with the periosteum; Gum tissue is rich in blood vessels (so it bleeds relatively easily), but is poorly supplied with nerves. The grooved depression located between the tooth and the free edge of the gum is called a gum pocket.
Each tooth, dens, consists of:
1. Tooth crowns, corona dentis
2. Cervix, collum dentis
3. Roots, radix dentis
The crown protrudes above the gum, the neck (a slightly narrowed part of the tooth) is covered by the gum, and the root sits in the dental alveolus and ends at the apex, apex radicis, on which even the naked eye can see a small opening at the apex - foramen apicis. Through this hole, blood vessels and nerves enter the tooth. Inside the crown of the tooth there is a cavity, сavitas dentis, in which a distinction is made between the coronal section, the most extensive part of the cavity, and the root section, the tapering part of the cavity, called the root canal, canalis radicis.
The canal opens at the apex with the apical opening mentioned above. The tooth cavity is filled with dental pulp, pulpa dentis, rich in blood vessels and nerves. Dental roots grow tightly together with the surface of the dental cells through the alveolar periosteum, periodontium, rich in blood vessels. The tooth, periodontium, alveolar wall and gum make up the dental organ.
The hard substance of the tooth consists of:
1) dentin, dentinum
2) enamels, enamelum
3) cement, cementum
The main mass of the tooth surrounding the tooth cavity is dentin. The enamel covers the outside of the crown, and the root is covered with cement.
The teeth are enclosed in the jaws in such a way that the crowns of the teeth are on the outside and form the dentition - upper and lower. Each dentition contains 16 teeth arranged in the form of a dental arch.
Each tooth has 5 surfaces:
1) facing the vestibule of the mouth, facies vestibularis, which at the front teeth comes into contact with the mucous membrane of the lip, and at the rear teeth - with the mucous membrane of the cheek;
2) facing the oral cavity, towards the tongue, facies lingualis;
3 and 4) in contact with adjacent teeth of its own, facies contactus. The contact surfaces of the teeth directed towards the center of the dental arch are designated as facies mesialis (meso, Greek - between). In the front teeth, this surface is medial, and in the back teeth, it is the anterior surface. The contact surfaces of the teeth directed in the direction opposite to the center of the dentition are called distal, facies distalis. In the anterior teeth this surface is lateral, and in the posterior teeth it is posterior;
5) chewing surface, or the surface of contact with the teeth of the opposite row, facies occlusalis.
Eruption of baby teeth, i.e. thinning of the gums and the appearance of a tooth crown in the oral cavity, begins in the 7th month of extrauterine life (the medial lower incisors erupt first) and ends by the beginning of the 3rd year. There are only 20 baby teeth. Their dental formula is:
The numbers indicate the number of teeth on half of each jaw (upper and lower): two incisors, one canine, two large molars. After six years, the replacement of baby teeth with permanent ones begins. It consists of erupting new additional teeth in excess of 20 milk teeth and replacing each milk tooth with a permanent one. The eruption of permanent teeth begins with the first large molar (six-year-old molar), by the age of 12-13 the eruption of permanent teeth ends, with the exception of the third large molar, which erupts between 18 and 30 years. . The formula for permanent human teeth on one side of the jaw is:
in total 32. In dental practice, they use a more convenient formula with the designation of teeth in numerical order, starting from the first incisor and ending with the last (third) large molar: 1, 2 (incisors), 3 (canine), 4, 5 (small molars) , b,7,8 (major molars).
Vessels and nerves of teeth: The arteries of the teeth of the upper jaw originate from a. maxillaris; The posterior teeth of the maxilla are vascularized from the aa. alveolares superiores posteriores, anterior - from aa. alveolares superiores anteriores (from a. infraorbitalis). All teeth of the lower jaw receive blood from a. alveolaris inferior. Each alveolar artery sends: 1) branches to the teeth themselves - rami dentales, 2) branches to the periosteum of the alveoli, rami alveolaris and 3) branches to adjacent areas of the gums - rami gingivales. The outflow of blood occurs into the veins of the same name, flowing into v. facialis. The outflow of lymph occurs in the nodi lymphatici submandibulares, submentals et cervicales profundi. Innervation of the upper teeth is carried out by nn. alveolares superiores (from the II branch of n. trigeminus). Among them there are nn. alveolares superiores anteriores, medii et posteriores, forming the plexus dental is superior. The nerves of the lower teeth begin from the plexus dentalis inferior (from the n. alveolaris inferior from the third branch of the n. trigeminus).
The tooth is formed by hard (dentin, enamel, cement) and soft (pulp) tissues (Fig. 11). The basis of the tooth is dentin, dentinum, which limits the tooth cavity. In humans, dentin is covered in the crown area with enamel, and in the root area with cement, that is, in healthy tooth dentin does not come into contact anywhere external environment and tissues surrounding the tooth. Dentin is produced continuously throughout life. The formation of secondary and then tertiary dentin leads to a decrease in the tooth cavity with age. In its structure, dentin is similar to coarse-fibered bone, differing from it in the absence of cells and greater strength. There are mantle and peripulpal dentin. Dentin consists of dentin tubules (about 75,000 per 1 cubic mm) and the ground substance. The dentinal tubules in the mantle layer are oriented radially, and in the peripulpar layer - tangentially. They contain processes of odontoblasts located in peripheral parts pulp. The main substance of dentin contains collagen fibers, between which mineral salts (phosphates and carbonates of calcium, magnesium, sodium salts, etc.) are deposited. The non-mineralized parts of dentin are called interglobular spaces.
Enamel, enamelium - covers dentin in the crown area. It consists of enamel prisms and the main interprismatic substance that glues them together. Its thickness is various departments crowns are not the same and range from 0.01 mm in the neck area to 1.0-2.5 mm at the level of the tubercles and points of the chewing surface of the molars, which should be kept in mind when opening the tooth cavity. Mature enamel is the most hard cloth of the human body, and hardness increases from the cervical part to the occlusal part. The color of the enamel varies from yellow to various shades of gray-white, depending on the transparency of the enamel. The more transparent the enamel, the more the dentin, which has yellow. The transparency of enamel is determined by its homogeneity and high degree (up to 97%) of mineralization. The enamel is covered with a thin but durable, lime-free shell - the cuticle, which protects it from the damaging effects of acids and alkalis. Cement, cementum - a substance covering the root of a tooth, has a coarse fibrous structure connective tissue. It consists of collagen fibers running in different directions and a ground substance impregnated with calcium salts (up to 70%). Contains cementocytes at the apex and interroot surfaces; nutrition is diffuse from the periodontium. Cement performs the following functions: connects tooth tissue with collagen fibers of the periodontal ligament; protects root dentin from damaging influences; carries out reparative processes after fractures or treatment. The configuration of the enamel-cementum boundary varies depending on different groups teeth.
There are three possible types of connection between enamel and cement:
1) they are connected end-to-end;
2) they overlap each other;
3) the enamel does not reach the edge of the cement and an open area of dentin remains between them.
Cavity and pulp of the tooth(Fig. 10). Tooth cavity, cavitas dentis (pulparis) - a chamber inside the tooth, limited by dentin. The tooth cavity is divided into the crown cavity, cavitas coronae and the root canal, canalis radicis dentis - sections of the cavity located in the corresponding parts of the tooth. The wall of the cavity facing the chewing surface (cutting edge) is called the vault. In the roof of the cavity there are depressions in the direction of the tubercles on the chewing surface. The part of the cavity of the tooth crown opposite the arch is called the bottom of the cavity. In single-rooted teeth, the bottom of the cavity, gradually narrowing, passes into the root canal; in multi-rooted teeth, it is flattened and has openings (mouths) leading into the root canals.
Rice. 10. Tooth structure.
1 – enamel, 2 – cement, 3 – enamel-cementum boundary, 4 – dentin,
5 – crown cavity, 6 – root canal, 7 – tip of the tooth apex.
Teeth are an integral part of the human body and also an indicator of health. Their loss leads to significant problems with gastrointestinal tract, and the aesthetic appearance of a person deteriorates. But often the teeth are exposed various diseases, most of all caries. In this case, the destruction affects not only the enamel, but also the bone substance, which causes intense pain.
Tooth structure
A tooth is a human organ that is located in the alveoli of the jaws and consists anatomically of a crown, root and neck, which, tapering, connects the crown to the root.
Morphologically it consists of hard and soft tissues. Let's take a closer look. Enamel, which is the hardest element in the human body, covers the coronal, that is, visible, part of the tooth, and underneath it is the bone. Otherwise it is called dentin, which in its structure is quite soft and porous. Its root under the gum is covered with cement, and inside the tooth is hollow, and this void is filled with pulp, soft cloth consisting of nerves and blood vessels. They penetrate the porous dentin structure and reach the beginning of the enamel. This is what determines increased sensitivity with sudden changes in temperature in the oral cavity, as well as under the influence of other unfavorable factors.
Dentine
The bone substance of the tooth makes up its main part; in the coronal region it is covered with enamel, and under the gum the root has a shell of cement. Dentin is a supporting element that has great importance, since it performs the function of protecting the pulp from external irritants.
The bone substance of the tooth is the second strongest in the body after the enamel, despite its loose structure. One-fifth of this tissue consists of collagen, two-thirds of Not organic matter, and 10% is water. If you look at dentin under a microscope, you can see what it is. intercellular substance, unevenly covered with lime deposits. It permeates him great amount dentinal tubules, which are filled with nerve endings of the pulp.
The bone substance of the tooth is divided into three types:
- Primary dentin, which is formed before the first tooth erupts.
- Secondary, also called physiological, is characterized by formation after the appearance of the tooth, characterized by a chaotic arrangement of dentinal tubes and fibers, as well as a smaller number of them. Thus, over time, the cavity is replaced by bone material due to its thickening.
- Tertiary or replacement - formed as a result of tissue irritation, characterized by an uneven appearance with barely perceptible mineralization. In this case, the tubes are most often absent.
Dentin formation is individual and depends on many factors, for example, tooth wear or other defects in which dentin replacement occurs with to varying degrees intensity.
Enamel
This is the hardest and strongest tissue in the human body, consisting almost entirely of minerals and performing protective functions for dentin and pulp.
Its thinnest layer is located at the neck of the tooth, and its thickest is on the masticatory cusps. The strength of enamel is not constant, changing from the beginning of the tooth growth cycle to its end. Thus, after eruption it is much weaker than after several years, since its mineralization is still imperfect. But over the years, the strength of the fabric still decreases. It depends on many factors.
Also, the strength of enamel varies in different areas of the tooth. This parameter is also individual. But one feature is the same for all: upper layer fabric is always the most durable, its structure is uniform, and porosity is negligible. The closer the enamel layer is to dentin, the looser its structure becomes, and accordingly, the strength decreases.
Dentin disease
Most of all, the bone substance of the tooth is susceptible to such ailments as caries. If the damage affects only the dentin and enamel of the tooth, the disease is classified as moderate; when the root is destroyed, its deep form is observed. It all starts with damage to the surface tissues, the appearance of carious cavities, which are filled with food debris, which contributes to the onset of decay processes and further destruction of the tooth.
The affected area causes significant discomfort, responding acute pain in response to various irritants, but it is worth stopping their contact with the sore spot, as painful sensations disappear. This is a reason to visit the dentist as soon as possible and fix the problem. Otherwise, caries is quite short time will reach the root of the tooth, after which there is a high probability of losing it.
To keep your teeth healthy for as long as possible, you need to maintain good hygiene. oral cavity, eat healthy foods rich in vitamins and minerals, and also undergo regular dental examinations to identify possible tissue damage at an early stage, preventing its destruction.
We have prepared an interactive map diagram of the structure and detailed description all 23 sections of the tooth. Click on the corresponding number and you will receive all the necessary information. Using the diagram, it will be very easy to study all the features of the tooth structure.
The structure of human teeth
Crown
Crown ( lat. corona dentis) - the part of the tooth protruding above the gum. The crown is covered with enamel - hard tissue, 95% consisting of inorganic substances and subject to the most powerful mechanical stress.
There is a cavity in the crown - dentin (hard tissue 2-6 mm thick) comes closer to the surface, then pulp, filling both part of the crown and the root part of the tooth. The pulp contains blood vessels and nerves. Cleaning and removal of dental plaque is carried out specifically from the crowns of teeth.
Tooth neck
Cervix ( lat. collum dentis) the part of the tooth between the crown and root, covered by the gum.
Roots
Root ( lat. radix dentis) part of the tooth located in the dental alveolus.
Fissure
On the chewing surface of the back teeth, between the cusps there are grooves and grooves - fissures. The fissures can be narrow and very deep. The relief of the fissures is individual for each of us, but dental plaque gets stuck in the fissures of everyone.
It is almost impossible to clean the fissures with a toothbrush. Bacteria in the oral cavity, processing plaque, form acid, which dissolves tissue, forming caries. Even good oral hygiene is sometimes not enough. In this regard, it has been successfully used all over the world for 20 years.
Enamel
Tooth enamel (or simply enamel, lat. enamelum) - the outer protective shell of the coronal part.
Enamel is the hardest tissue in the human body, which is explained by the high content of inorganic substances - up to 97%. There is less water in tooth enamel than in other organs, 2-3%.
Hardness reaches 397.6 kg/mm² (250-800 Vickers). The thickness of the enamel layer differs in different areas of the crown part and can reach 2.0 mm, and disappears at the neck of the tooth.
Proper care of tooth enamel is one of the key aspects of human personal hygiene.
Dentine
Dentin (dentinum, LNH; lat. dens, dentis- tooth) is the hard tissue of the tooth, constituting its main part. The coronal part is covered with enamel, the root part of the dentin is covered with cement. Consists of 72% inorganic substances and 28% organic substances. Consists mainly of hydroxyapatite (70% by weight), organic material (20%) and water (10%), permeated with dentinal tubules and collagen fibers.
Serves as the basis of the tooth and supports tooth enamel. The thickness of the dentin layer ranges from 2 to 6 mm. Dentin hardness reaches 58.9 kgf/mm².
There are peripulpal (internal) and mantle (external) dentin. In peripulpal dentin, collagen fibers are located predominantly condensally and are called Ebner fibers. In mantle dentin, collagen fibers are arranged radially and are called Korff fibers.
Dentin is divided into primary, secondary (replacement) and tertiary (irregular).
Primary dentin is formed during the development of the tooth, before its eruption. Secondary (replacement) dentin is formed throughout a person’s life. It differs from the primary by a slower pace of development, a less systemic arrangement of dentinal tubules, a larger number of erythroglobular spaces, a larger amount of organic substances, higher permeability and less mineralization. Tertiary dentin (irregular) is formed during tooth trauma, preparation, caries and other pathological processes, as a response to external irritation.
Dental pulp
Pulp ( lat. pulpis dentis) - loose fibrous connective tissue that fills the tooth cavity, with a large number of nerve endings, blood and lymphatic vessels.
Along the periphery of the pulp, odontoblasts are located in several layers, the processes of which are located in the dentinal tubules throughout the entire thickness of the dentin, performing a trophic function. The processes of odontoblasts include nerve formations that conduct pain sensations during mechanical, physical and chemical influences on dentin.
Blood circulation and innervation of the pulp are carried out thanks to dental arterioles and venules, the nerve branches of the corresponding arteries and nerves of the jaws. Penetrating into dental cavity Through the apical opening of the root canal, the neurovascular bundle breaks up into smaller branches of capillaries and nerves.
The pulp helps stimulate regenerative processes, which manifest themselves in the formation of replacement dentin during the carious process. In addition, the pulp is a biological barrier that prevents the penetration of microorganisms from the carious cavity through the root canal beyond the tooth into the periodontium.
The nerve formations of the pulp regulate the nutrition of the tooth, as well as the perception of various irritations, including pain. The narrow apical foramen and the abundance of vessels and nerve formations contribute to the rapid increase in inflammatory edema during acute pulpitis and compression of nerve formations by swelling, which causes severe pain.
Tooth cavity
(lat. cavitas dentis) The space inside formed by the cavity of the crown and root canals. This cavity is filled with pulp.
Cavity of the tooth crown
(lat. cavitas coronae) Part of the tooth cavity located under the crown and repeating its internal contours.
Tooth root canals
Root canal ( lat. canalis radicis dentis) - represents the anatomical space inside the tooth root. This natural space within the coronal part of the tooth consists of a pulp chamber, which is connected by one or more main canals, as well as more complex anatomical branches that can connect the root canals to each other or to the surface of the tooth root.
Nerves
(lat. nervae) Neuronal processes passing through the apex of the tooth and filling its pulp. The nerves regulate the nutrition of the tooth and conduct pain impulses.
Arteries
(lat. arteriae) Blood vessels through which blood from the heart flows to all other organs, in in this case- into the pulp. Arteries nourish dental tissues.
Vienna
(lat. venae) Blood vessels that carry blood from organs back to the heart. The veins enter the canals and penetrate the pulp.
Cement
Cement ( lat. - cementum) - specific bone tissue covering the root and neck of the tooth. Serves to firmly secure the tooth in the bone alveolus. Cement consists of 68-70% inorganic components and 30-32% organic substances.
Cementum is divided into acellular (primary) and cellular (secondary).
Primary cement is adjacent to the dentin and covers the lateral surfaces of the root.
Secondary cement covers the apical third of the root and the bifurcation area of multi-rooted teeth.
Root tips
(lat. apex radicis dentis) The lowest points of the teeth, located on their roots. At the tops there are openings through which nerve and vascular fibers pass.
Apical foramina
(lat. foramen apices dentis) Places of entry of vascular and nerve plexuses into the dental canals. The apical foramina are located at the apex of the tooth roots.
Alveolus (alveolar socket)
(alveolar socket) ( lat. alveolus dentalis) A notch in the jawbone into which the roots enter. The walls of the alveoli form strong bone plates impregnated with mineral salts and organic substances.
Alveolar neurovascular bundle
(lat. aa., vv. et nn alveolares) A plexus of blood vessels and nerve processes passing under the alveolus of the tooth. The alveolar neurovascular bundle is enclosed in an elastic tube.
Periodontium
Periodontium ( lat. Periodontium) - a complex of tissues located in the slit-like space between the cement of the tooth root and the alveolar plate. His average width is 0.20-0.25 mm. The narrowest section of the periodontium is located in the middle part of the tooth root, and in the apical and marginal sections its width is slightly greater.
The development of periodontal tissue is closely related to embryogenesis and teething. The process begins in parallel with the formation of the root. The growth of periodontal fibers occurs both from the side of the root cement and from the side of the alveolar bone, towards each other. From the very beginning of their development, the fibers have an oblique course and are located at an angle to the tissues of the alveoli and cementum. The final development of the periodontal complex occurs after tooth eruption. At the same time, the periodontal tissues themselves are involved in this process.
It should be noted that, despite the mesodermal origin of the constituent components of the periodontium, the ectodermal epithelial root sheath takes part in its normal formation.
Gingival grooves
(lat. sulcus gingivalis) Gaps that form where the tooth crown meets the gums. The gingival grooves run along the line between the free and attached parts of the gum.
Gum
Gums ( lat. Gingiva) is a mucous membrane covering the alveolar process of the upper jaw and the alveolar part of the lower jaw and covering the teeth in the cervical area. From clinical and physiological points In terms of vision, the gums are divided into interdental (gingival) papilla, marginal gum or gingival margin (free part), alveolar gum (attached part), mobile gum.
Histologically, the gum consists of stratified squamous epithelium and the lamina propria. There are oral epithelium, junctional epithelium, and sulcal epithelium. The epithelium of the interdental papillae and attached gingiva is thicker and can become keratinized. In this layer there are distinguished spinous, granular and horny layers. The basal layer consists of cylindrical cells, the spinous layer consists of polygonal cells, the granular layer consists of flattened cells, and the stratum corneum is represented by several rows of completely keratinized and nucleated cells that are constantly exfoliated.
Mucous papillae
(lat. papilla gingivalis) Fragments of gums located at their elevation in the area between adjacent teeth. Gingival papillae come into contact with the surface of dental crowns.
Jaws
(lat. maxilla - upper jaw, mandibula - lower jaw ) Bony structures that form the basis of the face and the largest bones of the skull. The jaws form the mouth opening and determine the shape of the face.
Dental anatomy is considered one of the most complex components of the human body; many studies are devoted to the structure of the oral cavity. scientific works, but some aspects have not yet been thoroughly studied. For example, why do some people grow wisdom teeth while others don’t? Or why some of us suffer from toothache more often than others. More detailed information about the individual features of the structure, possible pathologies and anomalies in the development of teeth, look on the pages of our website.
A tooth consists of hard and soft parts. The hard part of the tooth is divided into enamel, dentin and cement; the soft part of the tooth is represented by the so-called pulp.
Enamel (enamelum) covers the crown of the tooth. It reaches its greatest development at the top of the crown (up to 3.5 mm). The enamel contains a small amount of organic substances (about 3...4%) and mainly inorganic salts (96...97%). Among inorganic substances, the overwhelming majority are calcium phosphates and carbonates and about 4% are calcium fluoride. The enamel is constructed from enamel prisms (prisma enameli) thickness 3-5 microns. Each prism consists of a thin fibrillar network containing crystals hydroxyapatites, having the form of elongated prisms. The prisms are arranged in bundles, have a tortuous course and lie almost perpendicular to the surface of the dentin. In cross section, enamel prisms usually have a multifaceted or concave-convex shape. Between the prisms there is a less calcified adhesive substance. Thanks to the S-shaped curved course of the prisms on the longitudinal sections of the tooth, some of them are cut more longitudinally, and others more transversely, which causes alternating light and dark enamel stripes (the so-called Schröger lines). On longitudinal sections you can see even thinner parallel lines (Retzius lines). Their appearance is associated with the periodicity of growth and different zonal calcification of the prisms, as well as with the reflection in the structure of the enamel of force lines that arise as a result of the action of the force factor during chewing.
The outside enamel is covered with a thin cuticle (cuticula enameli), which quickly wears off on the chewing surface of the tooth and remains noticeable only on its lateral surfaces. The chemical composition of enamel changes depending on the metabolism in the body, the intensity of dissolution of hydroxyapatite crystals and remineralization of the organic matrix. Within certain limits, enamel is permeable to water, ions, vitamins, glucose, amino acids and other substances coming directly from the oral cavity. In this case, saliva plays an important role not only as a source of various substances, but also as a factor that actively influences the process of their penetration into tooth tissue. Permeability increases under the influence of acids, calcitonin, alcohol, dietary deficiency of calcium salts, phosphorus, fluorine, etc. Enamel and dentin are connected through mutual interdigitation.
Dentine (dentinum) forms most of the crown, neck and root of the tooth. It consists of organic and inorganic substances: organic matter 28% (mainly collagen), inorganic matter 72% (mainly calcium and magnesium phosphate with an admixture of calcium fluoride).
Dentin is built from a basic substance that is penetrated by tubes, or tubules ( tubuli dentinalis). The ground substance of dentin contains collagen fibrils and mucoproteins located between them. Collagen fibrils in dentin are collected in bundles and have predominantly two directions: radial and almost longitudinal, or tangential. Radial fibers predominate in the outer layer of dentin - the so-called mantle dentin, tangential- in the inner, peripulpar dentin. In the peripheral areas of dentin, so-called interglobular spaces, which are its non-calcified areas, looking like cavities, with uneven, spherical surfaces. The largest interglobular spaces are found in the crown of the tooth, and small but numerous ones are found in the root, where they form granular layer. Interglobular spaces take part in the metabolism of dentin.
The main substance of dentin is penetrated by dentinal tubules, in which processes of dentinoblasts located in the dental pulp pass, and tissue fluid. The tubules originate in the pulp, near the inner surface of the dentin, and, fan-shaped, end on it outer surface. Acetylcholinesterase, which plays an important role in the transmission of nerve impulses, was found in the processes of dentinoblasts. The number of tubules in dentin, their shape and size are not the same in different areas. They are located more densely near the pulp. In the dentin of the tooth root, the tubules branch throughout, and in the crown they give almost no lateral branches and break up into small branches near the enamel. At the border with cement, dentinal tubules also branch, forming arcades that anastomose with each other.
Some tubules penetrate the cementum and enamel, especially in the area of the masticatory tubercles, and end in flask-shaped swellings. The tubule system provides trophism to dentin. Dentin in the area of connection with enamel usually has a scalloped edge, which contributes to a more durable connection. Inner layer The walls of the dentinal tubules contain many precollagen argyrophilic fibers, which are highly mineralized compared to the rest of the dentin substance.
On transverse sections of dentin, concentric parallel lines are noticeable, the appearance of which is obviously associated with the periodicity of dentin growth.
Between dentin and dentinoblasts there is a stripe predentine, or non-calcified dentin, consisting of collagen fibers and amorphous substance. Experiments using radioactive phosphorus have shown that dentin grows gradually by layering insoluble phosphates in predentin. Dentin formation does not stop in adulthood. Thus, secondary, or replacement, dentin, characterized by the unclear direction of dentinal tubules and the presence of numerous interglobular spaces, can be found both in predentin and in the pulp (so-called denticles, islands of dentin in the pulp). Denticles are formed due to metabolic disorders and local inflammatory processes. They are usually localized near dentinoblasts, whose activity is associated with the formation of denticles. The source of their development is dentinoblasts. Small amounts of salts can penetrate into dentin through the periodontium and cementum.
Cement (cementum) covers the root of the tooth and the neck, where in the form of a thin layer it can partially extend onto the enamel. The cement thickens towards the root apex.
The chemical composition of cement is close to bone. It contains about 30% organic substances and 70% inorganic substances, among which salts of phosphate and calcium carbonate predominate.
By histological structure A distinction is made between acellular, or primary, and cellular, or secondary, cement. Acellular cementum located predominantly in the upper part of the root, and cellular- in its lower part. In multi-rooted teeth, cellular cement lies mainly at the branching of the roots. Cellular cement contains cells - cementocytes, numerous collagen fibers that do not have a specific orientation. Therefore, cellular cement in structure and composition is compared with coarse fibrous cement. bone tissue, but unlike it, it does not contain blood vessels. Cell cement may have a layered structure.
Acellular cement contains neither cells nor their processes. It consists of collagen fibers and an amorphous adhesive substance lying between them. Collagen fibers run in longitudinal and radial directions. The radial fibers directly continue into the periodontium and then, in the form of perforating (Sharpey's) fibers, enter the alveolar bone. WITH inside they merge with the collagenous radial fibers of dentin.
The cement is nourished diffusely through the blood vessels of the periodontium. The circulation of fluid in the hard parts of the tooth occurs due to a number of factors: blood pressure in the vessels of the pulp and periodontium, which changes with temperature changes in the oral cavity during breathing, eating, chewing, etc. Of particular interest are data on the presence of anastomoses of dentinal tubules with cell processes cement. This connection of the tubules serves as an additional nutritional system for dentin in case of disruption of the blood supply to the pulp (inflammation, pulp removal, filling the root canal, cavities, etc.).
Pulp (pulpa dentis), or dental pulp, is located in the coronal cavity of the tooth and in the root canals. It consists of loose fibrous connective tissue, in which three layers are distinguished: peripheral, intermediate and central.
Peripheral layer The pulp consists of several rows of multi-processed pear-shaped cells - dentinoblasts, characterized by pronounced basophilia of the cytoplasm. Their length does not exceed 30 microns, width - 6 microns. The dentinoblast nucleus lies in the basal part of the cell. A long process extends from the apical surface of the dentinoblast and penetrates the dentinal tubule. It is believed that these processes of dentinoblasts are involved in the supply of mineral salts to dentin and enamel. The lateral processes of dentinoblasts are short. In their function, dentinoblasts are similar to bone osteoblasts. Alkaline phosphatase was found in dentinoblasts, which plays an active role in the processes of calcification of dental tissues, and in their processes, in addition, mucoproteins were identified. The peripheral layer of the pulp contains immature collagen fibers. They pass between the cells and continue further into the collagen fibers of dentin.
IN intermediate layer The pulp contains immature collagen fibers and small cells, which, undergoing differentiation, replace outdated dentinoblasts.
Central layer The pulp consists of loosely lying cells, fibers and blood vessels. Among the cellular forms of this layer, adventitial cells, macrophages and fibroblasts are distinguished. Both argyrophilic and collagen fibers are found between the cells. No elastic fibers were found in the dental pulp.
The dental pulp is of decisive importance in the nutrition and metabolism of the tooth. Pulp removal slows down dramatically metabolic processes, disrupts the development, growth and regeneration of the tooth.
83. Stomach. Structure.
In the middle part of the digestive tract occurs mainly chemical treatment food under the influence of enzymes produced by the glands, the absorption of food digestion products, the formation of feces (in the large intestine).
