Development of baby teeth. Development of teeth. Hereditary disorders of dental development

Dental development- a complex and lengthy process that begins during embryogenesis and ends at the age of 18-25 years.

In a twelve-day embryo, an anatomically defined recess (primary mouth) is separated from the head intestine by a pharyngeal membrane.

In the second month of embryo development, a thickening of the epithelium forms along the edge of the jaw processes bordering the primary mouth, which is then divided into two plates: the outer one, from which the cheeks and lips are formed, and the inner one, from which the teeth are subsequently formed.

The development of teeth begins at a time that coincides with the separation of the oral cavity from the nasal cavity (5-7 weeks of embryonic life). There are several stages (periods) in the development of teeth:

anlage and formation of primordia. In the seventh to eighth week, 10 flask-shaped outgrowths-caps are formed on the cervicolabial surface of the dental plate along its lower edge, which are the rudiments of the enamel organs of future milk teeth. At the tenth week, a dental papilla from the mesenchyme grows into each enamel organ. Along the periphery of the enamel organ is the dental sac (follicle). Thus, the tooth germ consists of three parts: the epithelial enamel organ and the mesenchymal dental papilla and dental sac;

differentiation of tooth germ cells. The cells of the enamel organ, which are adjacent to the surface of the dental papilla, form a layer of internal enamel cells, which then become anameloblasts. The outer layer of epithelial cells of the enamel organ forms the enamel cuticle;

histogenesis of dental tissues. This period begins with the germination of nerves and blood vessels into the dental papilla (4 months) and lasts longer. By the 14-15th week of intrauterine life, dentin begins to form by preodontoblasts and odontoblasts. With further development, the central part of the dental papilla turns into dental pulp.

The formation of enamel occurs as a result of the activity of enameloblasts. The process of enamel formation takes place in two stages:

formation of the organic basis of enamel prisms with their primary mineralization;

calcification of enamel prisms, leading to enamel maturation.

Mineralization begins from the surface of the enamel prisms. Each enameloblast turns into an enamel prism, so the enamel of formed teeth does not have the ability to regenerate. Permanent teeth develop similarly to the development of temporary teeth from the same dental plate. This development begins from the fifth month of embryonic life. By the time of birth, each alveolar process contains 18 dental follicles: 10 temporary and 8 permanent (incisors, canines and first molars). The formation of premolars, second and third molars occurs after the birth of a child. The end of the follicular period of tooth development coincides with the moment of its eruption.

The process of mineralization is of great importance in the formation of teeth. Mineralization of the primordial teeth begins at the seventeenth week of embryonic development of the fetus. By the time of birth, the crowns of the temporary incisors are almost completely mineralized, 3/4 of the canines, and 1/3-1/2 of the molars.

From permanent teeth During the prenatal period, mineralization of only the first molar begins. The processes of formation, formation and mineralization of teeth are the most significant moments in the development of the dentofacial system.

Teeth eruption is carried out according to certain standards: in certain average periods, paired (symmetry) eruption, eruption in a certain order.

The timing of teething is quite variable; average values can be determined. Temporary teeth erupt in the following average periods: central incisors - 6-8 months, lateral incisors - 8-12 months, first molars - 12-16 months, canines - 16-20 months, second molars - 20-30 months. By the age of 2.5-3 years, all temporary teeth have erupted. Their mineralization is completed by 3.5-4 years.

The average time for the eruption of permanent teeth is as follows: first molars - 6-7 years, first incisors - 7-8 years, second incisors - 8-9 years, first premolars - 9-11 years, canines - 10-12 years, second premolars - 11 -13 years, second molars - 12-13 years.

The main sources of dental development are the epithelium of the oral mucosa (ectoderm) and mesenchyme. In humans, there are two generations of teeth: milk and permanent. Their development proceeds in the same way from the same sources, but at different times. The formation of primary teeth occurs at the end of the second month of embryogenesis. In this case, the process of tooth development occurs in stages. It contains three periods:

· Period of formation of tooth germs;

· The period of formation and differentiation of tooth germs;

· The period of histogenesis of dental tissues.

I period- the period of formation of tooth germs includes 2 stages:

Stage 1- stage of formation of the dental plate. It begins in the 6th week of embryogenesis. At this time, the epithelium of the gingival mucosa begins to grow into the underlying mesenchyme along each of the developing jaws. This is how epithelial dental plates are formed.

Stage 2- dental ball (bud) stage. During this stage, the cells of the dental lamina multiply in the distal part and form dental balls at the end of the dental lamina.

II period- the period of formation and differentiation of tooth germs - is characterized by the formation of an enamel organ (dental cup). It includes 2 stages: the “cap” stage and the “bell” stage. In the second period, the mesenchymal cells lying under the dental ball begin to multiply intensively and create increased pressure here, and also induce, due to soluble inducers, the movement of the dental bud cells located above them. As a result, the lower cells of the dental bud protrude inward, gradually forming a double-walled dental cup. At first it has the shape of a cap (cap stage), and as the lower cells move inside the kidney it becomes bell-shaped (bell stage). In the resulting enamel organ, three types of cells are distinguished: internal, intermediate and external. Internal cells multiply intensively and subsequently serve as a source for the formation of ameloblasts - the main cells of the enamel organ that produce enamel. Intermediate cells, as a result of the accumulation of fluid between them, acquire a structure similar to the structure of mesenchyme and form the pulp of the enamel organ, which for some time carries out the trophism of ameloblasts, and later is a source for the formation of the cuticle and tooth. The outer cells have a flattened shape. Over a larger extent of the enamel organ, they degenerate, and in its lower part they form an epithelial root sheath (Hertwig’s sheath), which induces the development of the tooth root. The dental papilla is formed from the mesenchyme lying inside the dental cup, and from the mesenchyme surrounding the enamel organ-dental sac. The second period for primary teeth is completely completed by the end of the 4th month of embryogenesis.

III period- period of histogenesis of dental tissues. Dentin forms the earliest of the hard tissues of the tooth. Adjacent to the internal cells of the enamel organ (future ameloblasts), the connective tissue cells of the dental papilla, under the inductive influence of the latter, turn into dentinoblasts, which are arranged in one row like epithelium. They begin to form the intercellular substance of dentin - collagen fibers and ground substance, and also synthesize the enzyme alkaline phosphatase. This enzyme breaks down blood glycerophosphates to form phosphoric acid. As a result of the connection of the latter with calcium ions, hydroxyapatite crystals are formed, which are released between collagen fibrils in the form of matrix vesicles surrounded by a membrane. Hydroxyapatite crystals increase in size. Dentin mineralization gradually occurs.

Internal enamel cells, under the inductive influence of dentinoblasts of the dental papilla, transform into ameloblasts. At the same time, a reversal of physiological polarity occurs in the internal cells: the nucleus and organelles move from the basal part of the cell to the apical part, which from this moment becomes the basal part of the cell. On the side of the cell facing the dental papilla, cuticle-like structures begin to form. They then undergo mineralization with the deposition of hydroxyapatite crystals and turn into enamel prisms - the main structures of the enamel. As a result of the synthesis of enamel by ameloblasts and dentin by dentinoblasts, these two types of cells move further and further away from each other.

The dental papilla differentiates into the dental pulp, which contains blood vessels, nerves and provides nutrition to the dental tissues. Cementoblasts are formed from the mesenchyme of the dental sac, which produce the intercellular substance of cement and participate in its mineralization according to the same mechanism as in the mineralization of dentin. Thus, as a result of differentiation of the rudiment of the enamel organ, the formation of the main tissues of the tooth occurs: enamel, dentin, cement, pulp. The dental ligament, the periodontium, is also formed from the dental sac.

In the further development of the tooth, a number of stages can be distinguished.

Stage of growth and eruption of baby teeth characterized by the growth of dental anlages. In this case, all tissues above them gradually undergo lysis. As a result, teeth break through these tissues and rise above the gum - they erupt.

The stage of loss of milk teeth and their replacement with permanent ones. The formation of permanent teeth is formed in the 5th month of embryogenesis as a result of the growth of epithelial cords from the dental plates. Permanent teeth develop very slowly, located next to the milk teeth, separated from them by a bony septum. By the time the baby teeth change (6-7 years), osteoclasts begin to destroy the bone septa and roots of the baby teeth. As a result, baby teeth fall out and are replaced by rapidly growing permanent teeth.

Tooth structure

Anatomically, a tooth consists of three main parts: crown, neck and roots.

Crown protrudes above the gum and is formed by enamel and dentin. Enamel- the most hard fabric body, because it contains 96-97% mineral salts(calcium phosphate and carbonate salts and calcium fluoride). Structural elements enamels are enamel prisms, 3-5 microns thick. They consist of tubular subunits with a diameter of 25 nm and crystals of mineral substances (apatites). The enamel prisms are connected using a less calcified interprismatic matrix. The prisms have an S-shaped stroke and, as a result, in the longitudinal section of the tooth they may appear cut off longitudinally and transversely. On the outside, the enamel is covered with a thin cuticle (Nasmitian membrane), formed from the pulp cells of the enamel organ.

Beneath the enamel of the crown is dentin, the underlying tissue of the tooth, which is a type of bone tissue (dentinal bone tissue). It consists of dentinoblast cells (more precisely, their processes lying in the dentinal tubules) and intercellular mineralized substance. The composition of the latter includes collagen fibrils, the main substance and a mineral component amounting to 72%. Dentin has dentinal tubules, in which processes of dentinoblasts and unmyelinated nerve fibers pass. The boundary between enamel and dentin is uneven, which contributes to a stronger connection between the two tooth tissues.

Tooth root consists of dentin and cement. Cement- this is also a type bone tissue(coarse-fiber bone tissue), containing up to 70% minerals. There are two types of cement: cellular (lower part of the root) and acellular ( top part root). Cellular cement contains cementocyte cells and is similar in structure to coarse fibrous bone tissue, but unlike it does not contain blood vessels. Acellular cement consists only of intercellular substance, the collagen fibers of which continue into the periodontium and further into the bone of the alveoli. The nutrition of cement comes diffusely from the vessels of the pulp and periodontium.

Dental pulp located in its internal cavity. It consists of several layers - outer, intermediate and inner. Highest value has an outer layer because it contains dentinoblasts. They originate from the neural crest. These cells have an elongated shape, basophilic cytoplasm and a nucleus with a predominance of euchromatin. The cytoplasm of the cells has developed protein synthesizing and secretory apparatuses and contains ovoid-shaped secretory granules. Processes extend from the apical parts of the cells and are directed into the dentinal tubules. The processes of dentinoblasts branch multiple times and, through intercellular contacts, including desmosomes and nexuses, connect with the processes of other dentinoblasts. The processes contain numerous microfilaments, due to which they are capable of contraction. Thus, dentinoblasts ensure the circulation of tissue fluid and supply dentin and enamel with minerals. The basis of the pulp is loose fibrous connective tissue with a large number of blood vessels and nerves.

The basis of the language consists of striated muscle tissue, the fibers of which run in three mutually perpendicular directions. Thanks to this, the tongue can make quite complex movements. Between the muscle bundles there are layers of loose fibrous tissue connective tissue with vessels, nerves and accumulations of fat cells.

The mucous membrane of the upper and lateral surfaces of the tongue is firmly fused with the muscles (there is no submucosa), formed by two layers: stratified squamous non-keratinizing epithelium and a lamina propria of loose fibrous connective tissue that forms the papillae of the tongue.

Distinguish 4 main types of papillae: filamentous, mushroom-shaped, leaf-shaped and grooved. The most numerous are filiform papillae, which give the tongue its roughness. These papillae do not contain taste organs. The remaining 3 types of papillae have taste organs, taste buds or bulbs, as part of the epithelium covering them. Leaf-shaped papillae are located on the lateral surfaces of the tongue and are well expressed only in children. Fungiform papillae are scattered singly along the dorsum of the tongue. The circumvallate papillae are located on the border between the body and the root of the tongue; unlike the fungiform papillae, they do not rise above the surface of the epithelium.

Taste buds have the shape of an ellipse and occupy the entire thickness of the epithelium. Consist of 4 types of cells: supporting, gustatory (sensory), basal and cells that form synapses with sensory nerve endings. Supporting cells have a round, light-colored nucleus and developed organelles for protein synthesis. The function of these cells is supporting. They support sensory cells, carry out their trophism, and secrete some substances necessary for chemoreception. Sensory cells have a dark elongated nucleus, developed mitochondria and agranular ER. Microvilli with chemoreceptor proteins are located on the apical surface. When nutrients bind to them, an action potential is formed, which is transmitted to the central nervous system, where the taste sensation is formed. Basal cells are poorly differentiated. Due to their division, sensory and supporting cells are regenerated.

The lower surface of the tongue contains a submucosa with a large number of blood vessels. This circumstance is used in medicine for sublingual administration of drugs.

Neural composition of the taste analyzer:

bipolar neuron of the petrosal or geniculate ganglion. Its dendrite forms a synapse with the taste cells of the taste buds, and the axon goes to the taste nucleus neuron medulla oblongata;

Neuron of the taste nucleus of the medulla oblongata. Its axon goes to the neurons of the optic thalamus;

· neuron of the optic thalamus, sends its axon to the hippocampal cortex and Ammon's horn;

· neurons of the hippocampal cortex and Ammon's horn.

Two layers of dentin, differing in the course of collagen fibers in it:

Peripulpal dentin . Inner layer , making up the majority of dentin, characterized by a predominance of fibers running tangentially to the dentino-enamel border and perpendicular to the dentinal tubules ( tangential fibers , or Ebner fibers ).

Raincoat dentin . Outer layer , 150 µm thick, covering peripulpar dentin. It is formed first and is characterized by a predominance of collagen fibers running in the radial direction, parallel to the dentinal tubules - radial fibers , or Corfu fibers . The mantle dentin smoothly transitions into the peripulpal dentin. The matrix of mantle dentin is less mineralized than the matrix of peripulpal dentin and contains relatively fewer collagen fibers.

Rice. Contents of the dentinal tubule. OOBL - odontoblast process; CF - collagen (intratubular) fibrils; NV - nerve fiber; POP - periodontoblastic space filled with dentinal fluid; PP - boundary plate (Neumann membrane).

No. 63 Features of dentin calcification, types of dentin: interglobular dentin, mantle and peripulpar dentin. Predentin. Secondary dentin. Transparent dentin. Reactions of dentin to damage.

As already noted, dentin is a hard tissue and its salt content resembles bone. However, dentin calcification differs from that in bone tissue. Hydroxyapatite crystals can be of different shapes: needle-shaped in the interfibrillar substance, lamellar - along collagen fibrils, granular - around dentinal tubules. Hydroxyapatite crystals are deposited in dentin in the form of spherical complexes - globules, visible under an optical microscope. Globules come in different sizes: large in the crown, small in the root. In bone tissue, calcium salts are deposited evenly in the form of tiny crystals. Calcification of dentin goes unevenly.

Between the balls there are areas of non-calcified dentin base substance, representing interglobular dentin. Interglobular dentin differs from globular dentin only in the absence of calcium salts in its composition. Dentinal tubules pass through ipterglobular dentin without interruption or change in their course. They do not have peritubular dentin. An increase in the amount of ipterglobular dentin is considered a sign of insufficient dentin calcification. This is usually due to metabolic disorders during tooth development due to malnutrition and/or insufficient nutrition (hypo-vitaminosis, endocrine diseases, fluorosis). For example, in the teeth of children with rickets, the amount of interglobular dentin sharply increases simultaneously with a violation of enamel calcification.

Very large areas of interglobular dentin in the form of dark semi-arcs or irregular rhombuses in accordance with the size of the balls are located in the tooth crown at the border of peripulpar and mantle dentin. With age, partial calcification of interglobular dentin may occur.

In the area of the tooth root (in the area of the dentino-cemental boundary), areas of interglobular dentin are very small and closely spaced. In the form of a dark stripe, they form the so-called granular Toms spot. Dentinal tubules, entering the granular layer of Toms, sometimes merge with individual grains of this layer. The zone of hypomineralized dentin also includes predentin.

In the dentin of a formed tooth, there is always a normally non-calcifying internal part of the peripulpal dentin facing the pulp, directly adjacent to the odontoblast layer. On preparations (tooth sections) stained with hematoxylin and eosin, it looks like a thin, oxyphilic-stained strip 10-50 microns wide.

The structural components of dentin are dentinal tubules and ground substance.

Dentinal tubules are tubes with a diameter of 1 to 4 microns, radially penetrating the dentin in the direction from the pulp to the enamel (in the crown area) or cement (in the root area). In the outward direction, the dentinal tubules narrow cone-shaped. Closer to the enamel, they give off lateral V-shaped branches; in the area of the root apex there are no branches. In addition, the canaliculi of the crown are S-shaped curved, and almost straight at the root. Due to the radial orientation of the tubules, their density is greater on the pulp side than in the outer layers of dentin. The density of their arrangement is higher in the crown than in the root. The inner surface of the dentinal tubules is covered with a thin organic film of glycosaminoglycans (Neumann membrane).

interglobular dentin - areas with uncalcified or slightly calcified ground substance, preserved between the globules. Dentin, in which only the first phase of mineralization has passed, dentinal tubules pass through it.

Transparent (sclerosed) dentin - occurs as a result of a gradual narrowing of the dentinal tubules, with excessive deposition of peritubular dentin, which leads to the closure of the lumen of a group of tubules.

Secondary dentin is physiological, regular. It is formed after teething and is characterized by a slow growth rate and narrow dentinal tubules.

mantle dentin - dentin located directly under the enamel and surrounding the peripulpal D.; characterized by a radial arrangement of collagen fibers.

Peripulpal dentin forms after the deposition of the mantle dentin layer and constitutes the majority of primary dentin.

Predentin- tooth tissue, which is the non-calcified basic substance of dentin, is located in the form of a strip between the dentin layer and the odontoblast layer.

No. 64 Sources of dentin development. Primary and secondary dentin. Replacement dentin. Zones of hypomineralized dentin. Dentin of the crown and dentin of the root of the tooth.

Source of development dentin are odontoblasts (dentinoblasts) - superficial cells of the pulp, derivatives of mesenchyme. The apex of dentinoblasts has processes that secrete organic substances of a fibrillar structure - the dentin matrix - predentin. From the end of 5 months, calcium and phosphorus salts are deposited in the predentin, and the final dentin is formed.

Histogenesis of dental tissues: 1 - dentin, 2 - odontoblasts, 3 - dental pulp, 4 - anameloblasts, 5 - enamel.

Primary dentin. It is formed during the period of tooth formation and eruption, making up the main part of this tissue. It is deposited by odontoblasts at an average speed of 4-8 µm/day, periods of their activity alternate with periods of rest. This periodicity is reflected by the presence of growth lines in dentin. Types of growth lines:

Owen's contour lines– directed perpendicular to the dentinal tubules.

Abner's growth lines– are located with a periodicity of 20 microns. Between the Ebner lines, with a periodicity of 4 microns, there are lines corresponding to the daily rhythm of dentin deposition. Ebner lines correspond to a 5-day cycle.

Secondary dentin (physiological) . It is formed after tooth eruption and is a continuation of primary dentin. The rate of deposition of secondary dentin is less than that of primary dentin. As a result of its deposition, the contours of the tooth chamber are smoothed.

Tertiary dentin (replacement). It is formed in response to irritating factors only by those odontoblasts that respond to irritation.

Primary, secondary and tertiary dentin. PD - primary dentin; VD - secondary dentin; TD - tertiary dentin; PRD - predentin; E - enamel; P - pulp.

Hypomineralized dentin . Dentin is separated from the pulp by a layer hypomineralized dentin .Zones of hypomineralized dentin include: 1) Interglobular dentin, 2) Toms granular layer.

1). Interglobular dentin. It is located in layers in the outer third of the crown parallel to the dentin-enamel border. It is represented by irregularly shaped areas containing non-calcified collagen fibrils, between which there are single dentine globules.

2). Toms granular layer. It is located on the periphery of root dentin and consists of small, slightly calcified areas (grains)

Dentine crown area it is covered with enamel, at the root - with cement. Root dentin forms the wall of the root canal, opening at its apex with one or more apical openings that connect the pulp with the periodontium. This connection in the root is often also provided by accessory canals that penetrate the dentin of the root.

№ 65 Structure of cellular and acellular cement. Nutrition of cement.

Cement is referred to as the supporting apparatus of the tooth. Included in the periodontium.

Cementum is one of the mineralized tissues of the tooth. The main function is participation in the formation of the supporting apparatus of the tooth. The thickness is minimal in the area of the tooth neck and maximum in the root area.

There are acellular and cellular cementum.

Acellular (primary) does not contain cells and consists of calcified intercellular substance, which includes collagen fibers and ground substance. Cementoblasts, which synthesize the components of the intercellular substance during the formation of this type of cement, move outward, towards the periodontium, where the vessels are located. Primary cementum is slowly deposited as teeth erupt and covers the 2/3 of the root surface closest to the neck.

Cellular cement (secondary) is formed after tooth eruption in the apical third of the root and in the area of bifurcation of the roots of multi-rooted teeth. Cellular cement is located on top of acellular cement or is directly adjacent to dentin. In secondary cementum, cementocytes are immured in calcified intercellular substance.

The cells have a flattened shape and lie in cavities (lacunae). The structure of cementocytes is similar to osteocytes of bone tissue. But, unlike bone, cement does not contain blood vessels, and its nutrition is diffuse from the periodontal vessels.

No. 66 Development and morphofunctional characteristics of dental pulp. Features of the structure of coronal and root pulp. The role of pulp in the formation and trophism of dentin. Morphological basis of the sensory and protective function of the tooth.

Pulp, or pulp of the tooth (pulpa dentis) is a complex connective tissue organ with various cellular structures, blood vessels, rich in nerve fibers and receptor apparatus, completely fills the tooth cavity, gradually turning into periodontal tissue in the area of the apical foramen

The pulp develops from the dental papilla, formed by mesenchyme. Mesenchymal cells transform into fibroblasts and begin the production of collagen fibers and ground pulp substance.

PULP STRUCTURE:

Odontoblasts

Fibroblasts

Macrophages

Dendritic cells

Lymphocytes

Mast cells

Poorly differentiated cells

Coronal pulp

Root pulp-

In the coronal pulp, secondary dentin is provided with tubules, without a radial direction. In the root pulp, ODB produces amorphous dentin, weakly canalized.

The pulp performs a number of important functions: 1) plastic - participates in the formation of dentin (due to the activity of the odontoblasts located in them); 2) trophic - ensures the trophism of dentin (due to the vessels located in it); 3) sensory(due to the presence of a large number of nerve endings); 4) protective and reparative (through the production of tertiary dentin, the development of humoral and cellular reactions, inflammation).

No. 67 Sources of development and significance of the dental pulp. Layers of the pulp, their cellular composition. Blood supply and innervation of the pulp.

Pulp formation.

Functions of the pulp:

plastic (formation of secondary dentin and primary odontoblasts)

trophic (the main substance of the pulp is the medium through which nutrients from the blood enter the cells)

protective (formation of tertiary dentin)

regulatory

The blood supply to the pulp is provided by blood vessels that penetrate into it both through the apical foramen of the tooth root and through a system of numerous additional canals of the tooth - its lateral walls. Arterial trunks accompany veins. Pulp vessels are characterized by the presence of numerous anastomoses. Innervation is carried out by the nerve branches of the corresponding arteries and nerves of the jaw.

The cellular composition of the pulp is polymorphic.

The specific cells for pulp are odontoblasts or dentinoblasts. The bodies of odontoblasts are localized only at the periphery of the pulp, and the processes are directed into the dentin.

Odontoblasts form dentin during tooth development and after tooth eruption.

The most numerous cells in the pulp are fibroblasts. They take part in the formation of the fibrous capsule surrounding the source of inflammation during pulpitis.

Pulp macrophages are able to capture and digest dead cells, components of the intercellular matrix, microorganisms and participate in immune reactions as antigen-presenting cells.

In the peripheral layers of the coronal pulp near the vessels there are dendritic cells with a large number of branching processes; they absorb the antigen, process it and present it to lymphocytes during immune reactions. There are B lymphocytes and T lymphocytes.

The intercellular substance consists of collagen fibers immersed in the ground substance. Pulp collagen belongs to types 1 and 3. There are no elastic fibers in the pulp.

The main substance contains hyaluronic acid, chondroitin sulfates, proteoglycans, fibronectin, and water.

Coronal pulp has 3 layers

dentinoblastic or odontoblastic (peripheral)

subdentinoblastic (intermediate). There are 2 zones: outer, cell-poor and inner, cell-rich.

pulp core (central) root pulp contains connective tissue with a large number of collagen fibers and is more dense. In it, the layering of structures is not traced, and zones are not distinguished.

No. 68 Coronal and root pulp of the tooth. Cellular elements and intercellular substance. Reactive properties. The denticles are true and false.

Coronal pulp– loose connective tissue rich in vessels and nerves. Contains different cells, odontoblasts have a prismatic or pear-shaped shape, arranged in several rows.

Root pulp- contains connective tissue with a large number of collagen fibers and has a higher density than in the crown.

PULP STRUCTURE:

Odontoblasts (ODB) cells, specific to the pulp, form dentin and provide its trophism.

Fibroblasts (PB) are the most numerous pulp cells in young people. The function of FB is the production and maintenance of the necessary composition of the intercellular substance of connective tissue, the absorption and digestion of the components of the intercellular substance.

Macrophages(MF) pulps ensure pulp renewal, participating in the capture and digestion of dead cells and components of the intercellular substance

Dendritic cells(Dk) – function – absorption of various antigens, their processing and presentation to lymphocytes. Induce proliferation of T lymphocytes

Lymphocytes(Lc) - in small quantities, during inflammation their content increases sharply. LCs actively synthesize immunoglobulins (mainly IgG) and provide humoral immune responses.

Mast cells(Tk) - located perivascularly, characterized by the presence in the cytoplasm of large granules containing biologically active substances (heparin, histamine)

Poorly differentiated cells concentrated in the subodontoblastic layer. They can give rise to ODB and FB. Cell content decreases with age.

Intercellular substance

True denticles

False denticles

No. 69 Development and structure of the dental pulp. Morphofunctional features of the crown pulp and tooth root pulp. Reactive properties and pulp regeneration. Denticles.

PULP STRUCTURE:

Odontoblasts (ODB) cells, specific to the pulp, form dentin and provide its trophism.

Macrophages(MF) pulps ensure pulp renewal, participating in the capture and digestion of dead cells and components of the intercellular substance

Dendritic cells(Dk) – function – absorption of various antigens, their processing and presentation to lymphocytes. Induce proliferation of T lymphocytes

Lymphocytes(Lc) - in small quantities, during inflammation their content increases sharply. LCs actively synthesize immunoglobulins (mainly IgG) and provide humoral immune responses.

Mast cells(Tk) - located perivascularly, characterized by the presence in the cytoplasm of large granules containing biologically active substances (heparin, histamine)

Poorly differentiated cells concentrated in the subodontoblastic layer. They can give rise to ODB and FB. Cell content decreases with age.

Intercellular substance The pulp has a glandular consistency. This is a matrix that contains cells, fibers and blood vessels.

True denticles-- areas of dentin deposition in the pulp -- consist of calcified dentin, surrounded at the periphery by odontoblasts, as a rule, contain dentinal tubules. The source of their formation is considered to be preodontoblasts, which transform into odontoblasts under the influence of unclear inducing factors

False denticles are found in the pulp much more often than true ones. They consist of concentric layers of calcified material, usually deposited around necrotic cells and not containing deitin tubes.

Pulp formation.

1) under the dentinoblasts, in the depths of the cerebral papilla, mesenchymal cells gradually turn into connective tissue cells of the dental crown pulp. Fibroblasts synthesize the usual components of the intercellular substance

One of the key moments in tooth development is associated with this synthesis. At a certain time, fibroblasts begin to produce the amorphous substance of the crown pulp at an increased rate. Therefore, pressure will increase in the pulp, which stimulates tooth eruption.

Pulp is a specialized loose connective tissue that fills the tooth cavity in the crown area.

With age, the frequency of formation of decalcified structures (calcifications) in the pulp increases. Diffuse deposition of hydroxyapatite crystals in the pulp is called petrification. Petrifications are usually found in the root of the tooth along the periphery of blood vessels, nerves or in the vascular wall.

Areas of local decalcification - denticles, are localized in the pulp and are classified as abnormal dentin-like formations.

№ 70 The structure of the dental pulp. Blood supply and innervation. Features of the structure of the coronal and root pulp.

Histologically, the pulp can be divided into 3 zones:

The peripheral layer is formed by a compact layer of odontoblasts 1-8 cells thick, adjacent to the predentin.

The intermediate (subodontoblastic) layer is developed only in the coronal pulp; its organization is characterized by significant variability. The composition of the intermediate layer includes the outer and inner zones:

a) the outer zone is nuclear-free (Weil’s layer) b) the inner (cellular, or more correctly cell-rich) zone contains numerous and diverse cells: fibroblasts, lymphocytes, poorly differentiated cells, preodontoblasts, as well as capillaries, myelinated and non-myelinated fibers;

The central layer is represented by loose fibrous tissue containing fibroblasts, macrophages, larger blood and lymphatic vessels, and bundles of nerve fibers.

The pulp is characterized by a very developed vascular network and rich innervation. The vessels and nerves of the pulp penetrate into it through the apical and accessory foramina of the root, forming a neurovascular bundle in the root canal.

In the root canal, arterioles give off lateral branches to the layer of odontoblasts, and their diameter decreases towards the crown. In the wall of small arterioles, smooth myocytes are arranged circularly and do not form a continuous layer.

The blood supply to the pulp has a number of features. In the pulp chamber the pressure is 20-30 mmHg. Art., which is significantly higher than interstitial pressure in other organs. Blood flow in the pulp vessels is faster than in many other organs.

Nerve bundles, along with blood vessels, penetrate into the pulp through the apical foramen and then through the root pulp into the crown. The diameter of the nerve fibers decreases as they approach the coronal part of the pulp. Reaching the coronal part of the pulp, they form a plexus of individual nerve fibers, called Rozhkov's plexus. The pulp contains mainly myelinated and unmyelinated nerve fibers.

Coronal pulp– loose connective tissue rich in vessels and nerves. Contains different cells, odontoblasts have a prismatic or pear-shaped shape, arranged in several rows.

Root pulp- contains connective tissue with a large number of collagen fibers and has a higher density than in the crown.

In the coronal pulp, secondary dentin is provided with tubules, without a radial direction. In the root pulp, ODB (odontoblasts) produce amorphous dentin, weakly canalized

№ 71 Gums. Dentogingival junction. Attachment epithelium.

The dentogingival junction (the connection between the tooth surface and the gum tissue) includes a complex of structures consisting of the attachment epithelium and the gingival epithelium.

The gingival epithelium passes into the non-keratinizing epithelium of the gingival sulcus and the attachment epithelium, which fuses with the cuticle of the tooth enamel.

The sulcular epithelium (sulcular epithelium) does not come into contact with the surface of the tooth and a space is formed between them - a gingival sulcus or gingival crevice. The stratified squamous non-keratinizing epithelium of the sulcus is a continuation of the stratified keratinizing epithelium. The sulcal epithelium in the area of the bottom of the fissure passes into the attachment epithelium.

The structure of the gums corresponds to the high mechanical loads to which it is exposed during the process of chewing food. It contains two layers - the epithelium and the lamina propria. The submucosa, which is present in other parts of the oral cavity, is absent in the gums.

The keratinizing epithelium covering the surface of the gums consists of four layers: 1) basal, 2) spinous, 3) granular and 4) horny

The gum is the only periodontal structure that is normally visible to the eye. This is the mucous membrane covering the alveolar processes of the upper and lower jaws. From the oral surface, the gum passes into the mucous membrane of the hard palate on the upper jaw and the floor of the mouth on the lower jaw. There are free (marginal) gums adjacent to the neck of the tooth and attached (alveolar) gums covering the alveolar process. The marginal gum is the outer wall of the gingival groove; it surrounds the necks of the teeth. The width of the marginal gum zone depends on the depth of the gingival sulcus. It is not the same in the area different groups teeth, but on average ranges from 0.5 mm in the frontal area to 1.5 mm in the molar area. The marginal zone also includes the interdental papilla. The interdental gingival papilla is formed by the connection of the vestibular and oral parts of the gums through connective tissue fibers, and on a cross section all papillae have the appearance of a saddle. The shape of the papillae in the area of different groups of teeth is different: triangular - in the frontal areas and trapezoidal - in the lateral areas. The free, or marginal, gum borders the zone of the attached gum. This border on the outer surface appears as a scalloped, slightly depressed line that generally corresponds to the bottom of the gingival sulcus. The gum consists of three layers: stratified squamous epithelium, the mucous membrane itself and the submucosal layer. The zone of attached gum, or alveolar gum, is devoid of a submucosal layer and fuses with the periosteum. The epithelium of the gums is multilayered flat; unlike the skin, it does not have a shiny layer of cells. Under normal conditions, keratinization and parakeratosis are observed in the gum epithelium, which provide protection from mechanical, chemical and physical influences. This epithelium is called oral (oral). In addition, a distinction is made between sulcular (sulcular) and connective (epithelial attachment) epithelium.

No. 72 Desna. Free and attached part of the gum. Gingival crevice (groove), its role in the physiology of the tooth. Epithelial attachment.

The free gum covers the cervical area and has a smooth surface. Free gum width - 0.8-2.5 mm

Width attached parts of the gum - 1-9 mm, and with age it can increase. Through connective tissue fibers, the gum is firmly connected to the alveolar bone and root cement.

The epithelium of the gums is a multilayered squamous epithelium, into which high connective tissue papillae of the lamina propria of the mucous membrane are embedded. Gingival sulcus(gap) - a narrow slit-like space between the tooth and the gum, located from the edge of the free gum to the attachment epithelium

The gingival sulcus and epithelial attachment, while performing a protective function for the periodontium, have some structural features of the epithelium and blood supply that ensure the performance of this function.

The epithelium of this section never keratinizes and consists of several layers of cells located parallel to the surface of the tooth and quickly renewing themselves (every 4-8 days). The surface cells of the connective epithelium are connected to the apatite crystals of the tooth surface through a thin layer of organic material. The epithelial attachment is not adjacent to the tooth surface, but fuses tightly with it, and as long as this barrier is intact, the underlying periodontal tissues are not infected.

The attachment epithelium, lining the bottom of the gingival sulcus, is adjacent to the surface of the tooth and fuses tightly with the enamel cuticle. After tooth eruption, the epithelial attachment is located in the cervical region of the anatomical crown of the tooth, at the level of the enamel. During passive eruption it comes into contact with cement. The attachment epithelium has a number of structural features. Its internal basement membrane, adjacent to the tooth tissues, continues into the outer basement membrane, under which the lamina propria of the mucous membrane is located. The epithelium is considered “immature” because it contains certain cytokines that prevent the differentiation of epithelial cells. A distinctive feature is that cells located under the surface layer are subject to desquamation. They are the ones who die and move towards the gingival sulcus. The intercellular spaces of the attachment epithelium are expanded, so it has high permeability and ensures the transport of substances in both directions.

No. 73 Supportive apparatus of teeth. The concept of periodontium. Periodontium. Features of the location of fibers in different parts of the periodontium. Dental alveolus.

Periodontium- this is a complex of tissues that surround the tooth, ensure its fixation in the jaw and function. The periodontal structure includes: alveolar bone, in the sockets of which the roots of the teeth are located; ligamentous apparatus of the tooth, or periodontium; connective epithelium; cement of tooth roots. On the outside, this entire fixing complex is covered with gum. The listed periodontal structures constitute a complex that is unified not only functionally, but also genetically (with the exception of the gums).

Features of the cellular composition of the periodontium- the presence of cementoblasts and osteoblasts, which ensure the construction of cement and bone tissue. Malasse epithelial cells were found in the periodontium, apparently involved in the formation of cysts and tumors.

The bone tissue of the alveolar process consists of a compact substance (osteon system, bone plates), located on the oral and vestibular surfaces of the roots of the teeth. Between the layers of the compact substance there is a spongy substance consisting of bone trabeculae. The bone marrow cavities are filled with bone marrow: red in young people and yellow fat in adults. There are also blood and lymphatic vessels, nerve fibers. The compact substance of the alveolar bone tissue along the entire length of the tooth root is penetrated by a system of perforated tubules through which blood vessels and nerves penetrate into the periodontium. Thus, the close relationship of periodontal elements is ensured through the connection of periodontal collagen fibers with the gum, alveolar bone tissue and tooth root cement, which ensures the performance of diverse functions

No. 74 Supporting apparatus of the tooth, its composition. Periodontium, sources of development, structure, function. Connection with the bone alveolus, cement, gum.

Supporting apparatus of the tooth (periodontium) includes: cement; periodontium; wall of the dental alveolus; gum.

Functions of the periodontium:Support and shock-absorbing– holds the tooth in the alveolus, distributes the chewing load and regulates pressure during chewing. Barrier– forms a barrier that prevents the penetration of microorganisms and harmful substances into the root area. Trophic– provides nutrition to cement. Reflex– due to the presence of a large number of sensitive nerve endings in the periodontium.

Periodontium– a ligament that holds the tooth root in the bony alveolus. Its fibers in the form of thick collagen bundles are woven into the cement at one end and into the alveolar process at the other. Between the fiber bundles there are spaces filled with loose fibrous unformed (interstitial) connective tissue containing blood vessels and nerve fibers

The periodontium is located between the cementum of the root and the bone tissue of the alveoli, contains blood vessels, lymphatic vessels and nerve fibers. The cellular elements of the periodontium are represented by fibroblasts, cementoclasts, dentoclasts, osteoblasts, osteoclasts, Malasse epithelial cells, protective cells and neurovascular elements. The periodontium fills the space between the root cement and the bone tissue of the socket.

Functions of periodontium: Proprioceptive- due to the presence of numerous sensory endings. Mechanoreceptors that perceive loads regulate chewing forces. Trophic– provides nutrition and vitality of cement and dental pulp. Homeostatic– regulation and functional activity of cells, processes of collagen renewal, resorption and repair of cement, restructuring alveolar bone. Reparative– participates in restoration processes through the formation of cement both during tooth root fracture and during resorption of its surface layers. Has great potential for self-recovery after damage. Protective– provided by macrophages and leukocytes.

Development of periodontal tissues closely related to embryogenesis and teething. The process begins in parallel with the formation of the tooth 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.

Cellular elements included in the periodontium: fibroblasts-they are located along the collagen fibers. Cementocytes And cementoblasts, the latter are directly adjacent to the surface of the cement of the tooth root and participate in the construction of secondary cement. Osteoblasts located on the surface of the alveoli and perform the function of bone formation. In addition, small amounts are found in periodontal tissues. osteoclasts, odontoclasts, macrophages and cellular elements of a specific link immune system (lymphocytes and plasma cells).

No. 75 The concept of periodontium. Periodontium, as its component. Tissue composition of the periodontium. Cells and intercellular substance. The main groups of fibers of the periodontal ligament. Nervous elements and vessels of the periodontium.

P arodont- this is a complex of tissues that surround the tooth, ensure its fixation in the jaw and function. The periodontal structure includes: alveolar bone, in the sockets of which the roots of the teeth are located; ligamentous apparatus of the tooth, or periodontium; connective epithelium; cement of tooth roots. On the outside, this entire fixing complex is covered with gum.

The periodontium is represented mainly by bundles of collagen fibers consisting of type I collagen, located in the periodontal fissure (between the root cement and the compact lamina of the alveoli). In addition to them, there is a small amount of thin reticulin and immature elastic - oxytalan fibers, which are usually loosely located near the vessels. Collagen fibers are attached at one end to the cementum of the tooth root, and at the other to the bone tissue of the alveoli (Fig. 14-2). Their location is horizontal in the area of the neck of the teeth and the edge of the alveolar processes, oblique along the length of the root, perpendicular in the area of the root apexes. Thanks to this, the tooth is suspended inside the alveolus, and the pressure on it in different directions is not transmitted directly to the alveolar bone and does not damage it while the periodontal structures are preserved. It is characteristic that there are no elastic fibers in the periodontium, and the collagen fibers themselves are incapable of stretching. Therefore, their shock-absorbing effect is determined by spiral bends, which allows them to straighten when the load on the tooth increases, and to curl again when the load decreases. This is what determines the physiological mobility of the tooth. Between the fiber bundles there is loose connective tissue with intercellular substance, blood and lymphatic vessels and nerve elements.

The width of the periodontal gap in different areas is not the same: the widest gap is in the cervical and apical regions of the tooth root: 0.24 and 0.22 mm, the smallest in the middle part of the root: 0.1–0.11 mm. This hourglass-like shape is determined by the adaptation of ligamentous structures to functional loads. In the middle part of the periodontium there is the Sickher plexus, which is of great importance in the regeneration of the periodontium during orthodontic tooth movements. However, opinions on its origin vary. According to some authors, collagen fibers do not directly connect the tooth root and the alveolar bone: it is believed that they are not one whole: one part begins to form from the root cement, and the other from the alveolar side, and both of these parts reach the middle of the periodontal fissure, where and are connected to each other using less mature collagen fibers. This plexus disappears after 25 years, which is important to consider when planning orthodontic treatment for adults. Features of cellular composition periodontal - the presence of cementoblasts and osteoblasts, which ensure the construction of cement and bone tissue. Malasse epithelial cells were found in the periodontium, apparently involved in the formation of cysts and tumors.

No. 76 The concept of periodontal disease. General morphofunctional characteristics of its components. Cement and its role in the composition of the tooth supporting the apparatus.

Periodontium- this is a complex of tissues surrounding the tooth. It includes: gums, periosteum, bone tissue of the socket and alveolar process, periodontium, root cement. Periodontal tissues hold the teeth in the jaw bone, provide interdental communication in the dental arch, and preserve the epithelial lining of the oral cavity in the area of the erupted tooth.

Gum- mucous membrane covering the alveolar process of the jaw and the neck of the tooth, tightly adjacent to them (attached gums). The marginal (free) part of the gum is freely located at the neck of the tooth and has no attachment to it.

The periosteum covering the alveolar process and the bone tissue of the alveolar process. The bone tissue of the alveolar process is divided into two parts: the alveolar bone itself and the supporting alveolar bone.

Root cement covers the surface of the root and is the connecting link between the tooth and the surrounding tissues. According to its structure, cement is divided into two types: acellular and cellular. Cellular cement covers the apical and furcation parts, acellular cementum covers the remaining parts of the root.

Cement together with periodontal fibers, alveoli and gums, it forms the supporting-retaining apparatus of the tooth. Cement is the calcified part of the tooth, similar in structure to bone tissue, but unlike it, it is devoid of blood vessels and is not subject to constant restructuring. Cement is firmly connected to dentin, unevenly covering it in the area of the root and neck of the tooth. The thickness of the cement is minimal in the area of the neck of the tooth and maximum at the apex of the tooth. The thickest layer of cement covers the roots of the chewing teeth. On the outside, the cement is firmly bound to the tissues of the ligamentous apparatus of the tooth.

Due to the rhythmic deposition of cement layers on the surface of the tooth root that continues throughout life, its volume increases several times.

Cement performs a number of functions: it is part of the supporting (ligamentous) apparatus of the tooth, providing attachment of periodontal fibers to the tooth; protects dentin tissue from damage.

No. 77 Development of the oral cavity and dental system. Oral pit. Primary oral cavity. Gill apparatus and its derivatives.

Initially, the entrance to the oral bay has the form of a slit, limited by 5 ridges or processes: from above in the center - the frontal process, from above on the sides - the maxillary processes, from below - the mandibular processes. Then, in the lateral part of the frontal process, 2 olfactory pits (placodes) are formed, surrounded by a ridge-like thickening, ending in the medial and lateral nasal processes. Next, the medial nasal processes fuse with each other and form the middle part of the upper jaw, bearing the incisors, and the middle part of the upper lip. Simultaneously with the medial nasal processes, the lateral nasal processes and maxillary processes fuse. If the fusion of the maxillary processes with the medial nasal processes is disturbed, a lateral cleft of the upper lip is formed, and if the fusion of the medial nasal processes with each other is disturbed, a median cleft of the upper lip is formed. The development of the palate and the division of the first oral cavity into the final oral and nasal cavities begins with the formation of the palatine processes on the inner surface of the maxillary processes. Initially, the palatine processes are directed obliquely downwards; further, as a result of an increase in the size of the lower jaw, the volume of the oral cavity increases and therefore the tongue sinks to the bottom of the oral cavity, while the palatine processes rise and occupy a horizontal position, approach each other and grow together, forming the hard and soft palate. Violation of the fusion of the palatine processes leads to the formation of a cleft of the hard and soft palate, which disrupts the child’s nutrition and breathing.

In the area of the pharynx, in the embryonic period, the gill apparatus is formed, which takes part in the development of some organs of the dentofacial apparatus. The gill apparatus is represented by 5 pairs of gill pouches and gill slits and 5 pairs of gill arches between them. Gill pouches are protrusions of the endoderm in the area of the lateral walls of the pharyngeal portion of the primary intestine. Invaginations of the ectoderm of the cervical region - gill slits - grow towards the gill pouches. Gill pouches and slits in humans do not break through; they are separated from each other by gill membranes. The material between adjacent gill pouches and slits is called gill arches - there are 4 of them, because. 5th rudimentary. The first branchial arch is called the mandibular arch, it is the largest, and subsequently differentiates into the rudiments of the lower and upper jaws. The second arch (hyoid) turns into the hyoid bone, the third arch participates in the formation of the thyroid cartilage. In addition, the I-III gill arches are involved in the formation of the tongue. The fourth and fifth arches merge with the third. The external auditory duct is formed from the first branchial cleft, and the tympanic membrane is formed from the first branchial membrane. The first gill pouch turns into the middle ear cavity and the Eustachian tube, the palatine tonsils are formed from the second gill pouches, and the parathyroid gland and thymus are formed from the third-fourth gill pouches.

Primary oral cavity

a narrow slit at the cephalic end of the embryo, bounded by five processes of the gill arches (unpaired frontal and paired maxillary and mandibular).

Stomodeum is the oral fossa of the embryo, which is a depression lined with a layer of ectoderm, from which teeth subsequently develop. The membrane separating it from the foregut of the embryo disappears at the end of the first month of pregnancy. From the ectoderm of the stomodeum only tooth enamel develops; in addition, other derivatives of the epithelium of the walls of the oral cavity develop from it.

No. 78 Gill apparatus, its derivatives. Formation of the oral cavity and jaw apparatus. The development of the oral cavity, associated with the formation of the face, occurs as a result of the interaction of a number of embryonic rudiments and structures.

At the 3rd week of embryogenesis, at the cephalic and caudal ends of the body of the human embryo, as a result of invagination of the skin epithelium, 2 pits are formed - the oral and the cloacal. Oral pit or bay (stomadeum), represents the rudiment of the primary oral cavity,

Plays an important role in the development of the oral cavity gill apparatus, which consists of 4 pairs of gill pouches and the same number of gill arches and slits.

Gill slits- invaginations of the skin ectoderm of the cervical region, growing towards the protrusions of the endoderm. The places of contact of both are called gill membranes. In humans they do not break through.

Areas of mesenchyme located between adjacent pockets and crevices grow and form roller-like elevations on the anterior surface of the embryo's neck - gill arches

The gill arches are covered on the outside with cutaneous ectoderm, and on the inside are lined with the epithelium of the primary pharynx. Subsequently, an artery, nerve, cartilage and muscle tissue are formed in each arch.

The first gill arch - the mandibular - is the largest, from which the rudiments of the upper and lower jaws are formed. From the second arch - the hyoid - the hyoid bone is formed. The third arch is involved in the formation of the thyroid cartilage.

Subsequently, the first gill slit turns into an external ear canal. From the first pair of gill pouches arise the cavities of the middle ear and eustachian tube. The second pair of gill pouches is involved in the formation of the palatine tonsils. From the III and IV pairs of gill pouches, the anlage of the parathyroid glands and thymus is formed. In the region of the ventral sections of the first 3 gill arches, the rudiments of the tongue and thyroid gland appear

With the development of the oral cavity, the first branchial arch is divided into 2 parts - the maxillary and mandibular.

No. 79 Development of the dental system. Development and growth of primary teeth. Formation of the buccolabial and primary dental plate. Formation of tooth germs. Differentiation of tooth germs.

Initially, the entrance to the oral bay has the form of a slit, limited by 5 ridges or processes: from above in the center - the frontal process, from above on the sides - the maxillary processes, from below - the mandibular processes. Then, in the lateral part of the frontal process, 2 olfactory pits (placodes) are formed, surrounded by a ridge-like thickening, ending in the medial and lateral nasal processes. Next, the medial nasal processes fuse with each other and form the middle part of the upper jaw, bearing the incisors, and the middle part of the upper lip. Simultaneously with the medial nasal processes, the lateral nasal processes and maxillary processes fuse. If the fusion of the maxillary processes with the medial nasal processes is disturbed, a lateral cleft of the upper lip is formed, and if the fusion of the medial nasal processes with each other is disturbed, a median cleft of the upper lip is formed. The development of the palate and the division of the oral cavity into the final oral and nasal cavities begins with the formation of the palatine processes on the inner surface of the maxillary processes. Initially, the palatine processes are directed obliquely downwards; further, as a result of an increase in the size of the lower jaw, the volume of the oral cavity increases and therefore the tongue sinks to the bottom of the oral cavity, while the palatine processes rise and occupy a horizontal position, approach each other and grow together, forming the hard and soft palate. Violation of the fusion of the palatine processes leads to the formation of a cleft of the hard and soft palate, which disrupts the child’s nutrition and breathing.

The formation of primary teeth occurs at the end of the second month of embryogenesis. In this case, the process of tooth development occurs in stages. There are three periods in it:

period of formation of tooth germs;

period of formation and differentiation of tooth germs;

period of histogenesis of dental tissues.

PERIOD OF DENTAL EMPLOYMENTS

Dental plate. At the 6th week of intrauterine development, the multilayered epithelium lining the oral cavity forms a thickening along the entire length of the upper and lower jaws due to the active proliferation of its cells. This thickening (primary epithelial cord) grows into the mesenchyme, almost immediately dividing into two plates - vestibular and dental. The vestibular plate is characterized by rapid proliferation of cells and their immersion in the mesenchyme, followed by partial degeneration in the central areas, as a result of which a gap begins to form ( buccolabial groove), separating the cheeks and lips from the area where future teeth are located and delimiting the actual oral cavity of its vestibule. The dental plate has the shape of an arch or a horseshoe, located almost vertically with a slight tilt back. The mitotic activity of mesenchymal cells directly adjacent to the developing dental plate is also enhanced. Formation of enamel organ primordia. At the 8th week of embryonic development, round or oval protrusions (tooth buds) are formed in each jaw on the outer surface of the dental plate (facing the lip or cheek) along the lower edge at ten different points, corresponding to the location of future temporary teeth - the anlage of the enamel organs. These anlages are surrounded by clusters of mesenchymal cells, which carry signals that induce the formation of a dental plate by the oral epithelium, and subsequently the formation of enamel organs from the latter. Formation of tooth germs. In the area of the dental buds, epithelial cells proliferate along the free edge of the dental plate and begin to penetrate the mesenchyme. The growth of the enamel organ primordia occurs unevenly - the epithelium seems to overgrow condensed areas of mesenchyme. As a result, the developing epithelial enamel organ initially takes on the appearance of a “cap”, which covers an accumulation of mesenchymal cells – the dental papilla. The mesenchyme surrounding the enamel organ also condenses to form the dental sac (follicle). The latter subsequently gives rise to a number of tissues of the supporting apparatus of the tooth. The enamel organ, dental papilla and dental sac together form the tooth germ.

DIFFERENTIATION OF DENTAL RUDIA.

As the enamel organ grows, it becomes more voluminous and elongates, acquiring the shape of a “bell,” and the dental papilla that fills its cavity lengthens. At this stage, the enamel organ consists of:

outer enamel cells (outer enamel epithelium);

inner enamel cells (inner enamel epithelium);

intermediate layer;

pulp of the enamel organ (stellate reticulum).

At this stage, the enamel organ is accompanied by:

enamel nodule and enamel cord;

dental papilla;

dental sac.

No. 80 Stages of tooth development, their characteristics. Development of the enamel organ: dental sac, dental papilla, their structure. Derivatives of the enamel organ.

There are several stages in tooth development:

1.laying and formation of primordia. In the seventh to eighth week, 10 flask-shaped outgrowths-caps are formed on the cervicolabial surface of the dental plate along its lower edge, which are the rudiments of the enamel organs of future milk teeth. At the tenth week, a dental papilla from the mesenchyme grows into each enamel organ. Along the periphery of the enamel organ is the dental sac (follicle). Thus, the tooth germ consists of three parts: the epithelial enamel organ and the mesenchymal dental papilla and dental sac;

2. differentiation of tooth germ cells. The cells of the enamel organ, which are adjacent to the surface of the dental papilla, form a layer of internal enamel cells, which then become anameloblasts. The outer layer of epithelial cells of the enamel organ forms the enamel cuticle;

3. histogenesis of dental tissues. This period begins from the moment nerves and blood vessels grow into the dental papilla (4 months) and lasts longer. By the 14-15th week of intrauterine life, dentin begins to form by preodontoblasts and odontoblasts. With further development, the central part of the dental papilla turns into dental pulp

The period of formation and differentiation of tooth germs begins with a process during which each tooth bud turns into epithelial enamel organ, and the mesenchyme interacting with them - in dental papilla(fills the cavity of the enamel organ) and dental sac(condenses around the enamel organ). These three components together form tooth germ.

The enamel organ initially looks like hats, later, stretching out, it becomes similar to bell. At the same time, it differentiates, dividing into a number of clearly distinguishable structures 1) cubic outer enamel epithelium, covering its convex surface; 2) inner enamel epithelium, directly lining its concave surface and bordering the dental papilla; 3) intermediate layer from a layer of flattened cells between the inner enamel epithelium and the pulp of the enamel organ; 4) pulp of the enamel organ (stellate reticulum) - a network of process cells in the central part of the enamel organ between the outer enamel epithelium and the intermediate layer.

The cells of the inner enamel epithelium initially have a cubic shape, later they turn into tall columnar ones preenameloblasts- predecessors enameloblasts- cells that produce enamel. In the peripheral layer of the dental papilla differentiate preodontoblasts - predecessors odontoblasts- cells that produce dentin. The preodontoblast layer is directly adjacent to the preenameloblast layer. Thus, as the tooth germs grow and differentiate, they are prepared for the formation of hard tooth tissues - dentin and enamel.

No. 81 Tooth development. Histogenesis of the tooth. Odontoblasts and tooth formation. Mantle and peripulpal dentin. Predentin.

Dentin formation begins in the final stages of the bell stage with the differentiation of peripheral cells of the dental papilla, which turn into odontoblasts, which begin to produce dentin. Deposition of the first dentin layers induces the differentiation of the inner cells of the enamel organ into secretory-active anameloblasts, which begin to produce enamel on top of the resulting dentin layer. At the same time, enameloblasts themselves previously differentiated under the influence of cells of the inner enamel epithelium. Such interactions, as well as the interactions of mesenchyme from the epithelium at earlier stages of tooth development, are examples of reciprocal (mutual) inductive influences. In the prenatal period, the formation of hard tissues occurs only in the crown of the tooth, while the formation of its root occurs after birth, beginning shortly before eruption and being completely completed (for different temporary teeth) by 1.5 - 4 years.

Dentin formation in the tooth crown Dentin formation (detinogenesis) begins at the apex of the dental papilla. In teeth with several masticatory cusps, dentin formation begins independently in each of the areas corresponding to the future tips of the cusps, spreading along the edges of the cusps until the fusion of adjacent centers of dentin formation. The dentin formed in this way forms the crown of the tooth and is called coronal. Secretion and mineralization of dentin do not occur simultaneously: odontoblasts initially secrete organic base (matrix) dentin ( predentin), and subsequently it is calcified. Predentin on histological preparations appears as a thin strip of oxyphilic material located between the odontoblast layer and the inner enamel epithelium. During dentinogenesis, it is first produced mantle dentin– outer layer up to 150 microns thick. Further education occurs peripulpal dentin, which makes up the bulk of this tissue and is located inward from the mantle dentin. The processes of formation of mantle and peripulpar dentin have both a number of patterns and a number of features. Formation of mantle dentin. The first collagen, synthesized by odontoblasts and released by them into the extracellular space, has the form of thick fibrils, which are located in the ground substance directly under the basement membrane of the inner enamel epithelium. These fibrils are oriented prependicular to the basement membrane and form bundles called radial Corf fibers . Thick collagen fibers together with amorphous substance form an organic matrix mantle dentin, the layer of which reaches 100-150 microns.

Formation of peripulpar dentin occurs after completion of the formation of mantle dentin and differs in some features. Collagen secreted by odontoblasts forms thinner and denser fibrils, which intertwine with each other and are located mainly perpendicular to the course of the dentinal tubules or parallel to the surface of the dental papilla. The fibrils arranged in this way form the so-called Ebner tangential fibers. The main substance of peripulpal dentin is produced exclusively by odontoblasts, which by this time have already completely completed the formation of intercellular connections and thereby separate predentin from the differentiating dental pulp. The composition of the organic matrix of peripulpal dentin differs from that of mantle dentin due to the secretion by odontoblasts of a number of previously unproduced phospholipids, lipids and phosphoproteins. Calcification of peripulpar dentin occurs without the participation of matrix vesicles.

See question 77

No. 82 Tooth development. Stage of histogenesis of dental tissues. Enamel formation. Enameloblasts. The emergence of enamel prisms. Calcification of enamel.

Dentin forms the earliest of the hard tissues of the tooth. The connective tissue cells of the dental papilla adjacent to the internal cells of the enamel organ (future ameloblasts) turn into dentinoblasts, which are arranged in one row like epithelium. They begin to form the intercellular substance of dentin - collagen fibers and ground substance, and also synthesize the enzyme alkaline phosphatase. This enzyme breaks down blood glycerophosphates to form phosphoric acid. As a result of the connection of the latter with calcium ions, hydroxyapatite crystals are formed, which are released between collagen fibrils in the form of matrix vesicles surrounded by a membrane. Hydroxyapatite crystals increase in size. Dentin mineralization gradually occurs.

Internal enamel cells, under the inductive influence of dentinoblasts of the dental papilla, transform into ameloblasts. At the same time, a reversal of physiological polarity occurs in the internal cells: the nucleus and organelles move from the basal part of the cell to the apical part, which from this moment becomes the basal part of the cell. On the side of the cell facing the dental papilla, cuticle-like structures begin to form. They then undergo mineralization with the deposition of hydroxyapatite crystals and turn into enamel prisms- basic enamel structures. As a result of the synthesis of enamel by ameloblasts and dentin by dentinoblasts, these two types of cells move further and further away from each other.

Enameloblasts are the cells that form enamel; they arise as a result of the transformation of pre-enameloblasts, which differentiate from the cells of the inner enamel epithelium.

Plan

PERIODS OF DEVELOPMENT OF MILK TEETH

^ PERIOD OF DENTAL EMPLOYMENTS

DIFFERENTIATION OF DENTAL RUDIA.

HISTOGENESIS OF THE TOOTH

Dentin formation (dentinogenesis)

Clinical significance of dentinogenesis disorders

Enamel formation (enamelogenesis)

Clinical significance of amelogenesis disorders

Formation of cement, development of periodontium and dental pulp

Tissue changes during tooth eruption

PERIODS OF DEVELOPMENT OF MILK TEETH

The continuous process of tooth development is divided into three main periods:

period of formation of tooth germs;
period of formation and differentiation of tooth germs;
the period of formation of dental tissues (histogenesis of dental tissues).

PERIOD OF DENTAL EMPLOYMENTS

Dental plate. At the 6th week of intrauterine development, the multilayered epithelium lining the oral cavity forms a thickening along the entire length of the upper and lower jaws due to the active proliferation of its cells. This thickening (primary epithelial cord) grows into the mesenchyme, almost immediately dividing into two plates - vestibular and dental. Vestibular plate characterized by rapid proliferation of cells and their immersion into the mesenchyme, followed by partial degeneration in the central areas, as a result of which a gap begins to form ( buccolabial groove), separating the cheeks and lips from the area where future teeth are located and delimiting the actual oral cavity of its vestibule.

^ Dental plate has the shape of an arc or horseshoe, located almost vertically with a slight tilt back. The mitotic activity of mesenchymal cells directly adjacent to the developing dental plate is also enhanced.

^ Formation of bookmarks of enamel organs . At the 8th week of embryonic development, round or oval protrusions (tooth buds) are formed in each jaw on the outer surface of the dental plate (facing the lip or cheek) along the lower edge at ten different points, corresponding to the location of future temporary teeth - the anlage of the enamel organs. These anlages are surrounded by clusters of mesenchymal cells, which carry signals that induce the formation of a dental plate by the oral epithelium, and subsequently the formation of enamel organs from the latter.

^ Formation of tooth germs . In the area of the dental buds, epithelial cells proliferate along the free edge of the dental plate and begin to penetrate the mesenchyme. The growth of the enamel organ primordia occurs unevenly - the epithelium seems to overgrow condensed areas of mesenchyme. As a result, the developing epithelial enamel organ initially takes on the appearance of a “cap”, which covers an accumulation of mesenchymal cells – the dental papilla. The mesenchyme surrounding the enamel organ also condenses to form the dental sac (follicle). The latter subsequently gives rise to a number of tissues of the supporting apparatus of the tooth.

The enamel organ, dental papilla and dental sac together form the tooth germ.

DIFFERENTIATION OF DENTAL RUDIA.

outer enamel cells (outer enamel epithelium);
inner enamel cells (inner enamel epithelium);
intermediate layer;
pulp of the enamel organ (stellate reticulum).

At this stage, the enamel organ is accompanied by:

enamel nodule and enamel cord;
dental papilla;
dental sac.

HISTOGENESIS OF THE TOOTH

Dentin formation (dentinogenesis)

In the prenatal period, the formation of hard tissues occurs only in the crown of the tooth, while the formation of its root occurs after birth, beginning shortly before eruption and being completely completed (for different temporary teeth) by 1.5 - 4 years.

^ Formation of dentin in the crown of a tooth

Dentin formation (detinogenesis) begins at the apex of the dental papilla. In teeth with several chewing cusps, dentin formation begins independently in each of the areas corresponding to the future tips of the cusps, spreading along the edges of the cusps until the fusion of adjacent centers of dentin formation. The dentin formed in this way forms the crown of the tooth and is called coronal.

Secretion and mineralization of dentin do not occur simultaneously: odontoblasts initially secrete organic base (matrix) dentin ( predentin), and subsequently it is calcified. Predentin on histological preparations appears as a thin strip of oxyphilic material located between the odontoblast layer and the inner enamel epithelium.

During dentinogenesis, it is first produced mantle dentin– outer layer up to 150 microns thick. Further education occurs peripulpal dentin, which makes up the bulk of this tissue and is located inward from the mantle dentin. The processes of formation of mantle and peripulpar dentin have both a number of patterns and a number of features.

^ Formation of mantle dentin. The first collagen, synthesized by odontoblasts and released by them into the extracellular space, has the form of thick fibrils, which are located in the ground substance directly under the basement membrane of the inner enamel epithelium. These fibrils are oriented prependicular to the basement membrane and form bundles called radial Corf fibers . Thick collagen fibers together with amorphous substance form an organic matrix mantle dentin, the layer of which reaches 100-150 microns.

^ Calcification of dentin begins at the end of the 5th month of intrauterine development and is carried out by odontoblasts through their processes. The formation of the organic matrix of dentin precedes its calcification, so its inner layer (predentin) always remains unmineralized. In the mantle dentin, matrix vesicles containing hydroxyapatite crystals appear between the collagen fibrils, surrounded by a membrane. These crystals grow rapidly and, breaking the membranes of the vesicles, grow in the form of crystal aggregates in various directions, merging with other clusters of crystals.

^ Formation of peripulpar dentin occurs after completion of the formation of mantle dentin and differs in some features. Collagen secreted by odontoblasts forms thinner and denser fibrils, which intertwine with each other and are located mainly perpendicular to the course of the dentinal tubules or parallel to the surface of the dental papilla. The fibrils arranged in this way form the so-called Ebner tangential fibers.

The main substance of peripulpal dentin is produced exclusively by odontoblasts, which by this time have already completely completed the formation of intercellular connections and thereby separate predentin from the differentiating dental pulp. The composition of the organic matrix of peripulpal dentin differs from that of mantle dentin due to the secretion by odontoblasts of a number of previously unproduced phospholipids, lipids and phosphoproteins. Calcification of peripulpar dentin occurs without the participation of matrix vesicles.

^ Mineralization of peripulpal dentin occurs by deposition of hydroxyapatite crystals on the surface and inside collagen fibers, as well as between them (without the participation of matrix vesicles) in the form of rounded masses - globules (calcospherites). The latter subsequently increase and merge with each other, forming a homogeneous calcified tissue. This type of calcification is clearly visible in the peripheral areas of peripulpar dentin near mantle dentin, where large globular masses do not completely merge, leaving hypomineralized areas called interglobular dentin . The size of the globules depends on the rate of dentin formation. An increase in the volume of interglobular dentin is characteristic of dentinogenesis disorders associated with calcification defects, for example, due to vitamin D deficiency, calcitonin deficiency, or exposure to elevated fluoride concentrations.

The duration of the period of activity of odontoblasts, which carry out the deposition and mineralization of dentin, is approximately 350 days in temporary teeth, and about 700 days in permanent teeth. These processes are characterized by a certain periodicity, thanks to which it is possible to detect so-called growth lines in dentin. Their appearance is due to small periodic changes directions of collagen fiber deposition. Thus, with an average interval of 4 µm, daily growth lines are revealed; at a distance of about 20 µm more clearly defined Abner's growth lines indicating the existence of cyclical dentin deposition with a period of about 5 days (infradian rhythm). Mineralization of dentin also occurs rhythmically with a period of about 12 hours (ultradian rhythm), independent of the cyclicity of the production of the organic matrix.

^ Formation of peritubular dentin. At the beginning of dentin formation, the dentinal tubules have a significant lumen, which subsequently decreases. This occurs due to deposition from the inside on their walls peritubular dentin, which would be more correctly called intratubular dentin. Peritubular dentin differs from intertubular dentin by its higher content of hydroxyapatite. Its secretion is carried out by processes of odontoblasts located in the dentinal tubules. Mineralization of the secreted organic base of dentin is ensured by calcium transfer in three ways:

as part of matrix vesicles, which are located along the periphery of the cytoplasm of the processes and are released into the extracellular space;
by intratubular (dentinal) fluid;
in chemical connection with phospholipids of the process membrane.

Peritubular dentin is found in small quantities in the teeth of young people; it is absent in interglobular dentin.

^ Formation of dentin at the root of a tooth

The formation of dentin in the root of a tooth proceeds in essentially the same way as in the crown, but it occurs at later stages, starting before and ending after the eruption of the tooth. During the formation of the crown, most of the enamel organ involved in the formation of the crown has already undergone regressive changes. Its components have lost their characteristic differentiation and have become several layers of flattened cells, forming a reduced enamel epithelium that covers the crown of the tooth. The zone of activity of the enamel organ at this stage moves to the region of the cervical loop, where the cells of the inner outer epithelium connect. Hence, due to the proliferation of these cells, a two-layer epithelial cord of cylindrical shape grows into the mesenchyme between the dental papilla and the dental sac - epithelial (Hertwig) root sheath . This vagina gradually descends in the form of an elongating skirt from the epithelial organ to the base of the papilla. Unlike the internal epithelium of the enamel organ, the internal cells of the root sheath do not differentiate into anameloblasts and retain a cubic shape. As the epithelial root sheath encloses the elongating dental papilla, its internal cells induce the differentiation of peripheral papillary cells, which develop into dental root odontoblasts. The inwardly curved edge of the root sheath, called the epithelial diaphragm, encloses the epithelial opening. When the roots of multi-rooted teeth are formed, the initially existing root canal is divided into two or three narrower canals due to the edges of the epithelial diaphragm, which, in the form of two or three tongues, are directed towards each other and ultimately merge together.

After odontoblasts form root dentin along the edge of the epithelial sheath, connective tissue grows into the vaginal epithelium in its various parts. As a result, the root sheath breaks up into numerous small anastomosing cords called epithelial remnants (islets) of Malasse (see lecture “Structure of the periodontium”). While the areas of the epithelial sheath closest to the crown undergo decay, the apical areas continue to grow into the connective tissue, inducing odontoblast differentiation and determining the shape of the tooth root. The epithelial remains of Malasse, which, along with the material of the decayed root sheath, also include the remains of the dental plate, can play an important role in pathology, since they can serve as centers for the formation of cementicles and a source of the development of cysts and tumors ( see lecture “Structure of the periodontium”).

During root formation, the growing edge of the epithelial sheath may encounter a blood vessel or nerve along its path. In this case, it grows along the edges of these structures, and in the area of their location, the peripheral cells of the dental papilla do not come into contact with the inner layer of the epithelial vagina. For this reason, they do not turn into odontobrasts and, in this area the root will have a dentin defect - accessory (lateral) root canal , connecting the pulp with the periodontal connective tissue surrounding the tooth. Such channels can serve as routes for the spread of infection. In some cases, individual internal cells of the epithelial root sheath, in contact with dentin, are able to differentiate into anameloblasts, which will produce small droplets of enamel associated with the root surface or located in the periodontium (“enamel pearls”) .

Root dentin differs from coronal dentin chemical composition some organic components, a lower degree of mineralization, lack of strict orientation of collagen fibers and a lower rate of deposition.

The final formation of root dentin is completed only after teeth eruption, in temporary teeth after approximately 1.5-2 years, and in permanent teeth, on average, after 2-3 years from the start of eruption.

In general, dentin formation continues until the teeth acquire their final anatomical shape; such dentin is called primary, or physiological. The slower formation of dentin in a fully formed tooth (secondary dentin) continues throughout life and leads to a progressive reduction in the pulp chamber. Secondary dentin contains lower concentrations of glycosaminoglycans and is characterized by weaker mineralization than primary dentin. A distinct line of rest can be identified between primary and secondary dentin. Tertiary dentin, or reparative dentin, is deposited in specific areas in response to damage to the tooth. The rate of its deposition depends on the degree of damage: the more significant the damage, the higher it is (reaches 3.5 µm/day).

Clinical significance of dentinogenesis disorders

Disruption of dentinogenesis can occur during the formation of its organic matrix, during mineralization, or at both of these stages. Matrix abnormalities are characteristic of a hereditary disease called dentinogenesis imperfecta. In this disease, the structure of the enamel is not changed, but its connection with dentin is fragile, as a result of which the enamel breaks off. When calcification is disturbed, calcospherites are revealed that do not merge with each other, leaving very large zones of interglobular dentin.

Enamel formation (enamelogenesis)

Enamel is a secretory product of the epithelium, and its formation differs significantly from the development of all other hard tissues of the body, which are derivatives of mesenchyme. Amelogenesis occurs in three stages:

stage of secretion and primary mineralization of enamel;
stage of maturation (stage of secondary mineralization) of enamel;
stage of final maturation (stage of tertiary mineralization) of enamel

During the first of them is the stage of secretion and primary mineralization of enamel– enameloblasts secrete the organic basis of the enamel, which almost immediately undergoes primary mineralization. However, the enamel thus formed is relatively soft fabric and contains a lot of organic matter. During the second stage of amelogenesis – the stage of maturation (secondary mineralization) of enamel it undergoes further calcification, which occurs not only as a result of the additional inclusion of mineral salts in its composition, but also by removing most of the organic matrix. The third stage of anamelogenesis is the stage of final maturation(tertiary mineralization) of enamel occurs after tooth eruption and is characterized by the completion of enamel mineralization mainly through the entry of ions from saliva.

Enameloblasts

Cells that form enamel - enameloblasts arise due to the transformation of pre-enameloblasts, which in turn differentiate from the cells of the inner enamel epithelium. The differentiation of enameloblasts at the beginning of amelogenesis is preceded by changes in the enamel organ, affecting all its layers. The cells of the outer enamel epithelium turn from cubic to flat. Changes and general shape enamel organ - its smooth outer surface becomes uneven, scalloped due to the pressing into it in many areas of the surrounding mesenchyme of the dental sac and capillary loops. In this case, the surface area of contact between the mesenchyme and the outer epithelium increases, the capillaries growing from the side of the mesenchyme approach the inner enamel epithelium, and the pulp of the enamel organ separating them decreases in volume. These changes contribute to increased nutrition of the layer of differentiating enameloblasts from the side of the dental sac. This compensates for the cessation of the supply of metabolites to them from the dental papilla, which previously served as the main source of nutrition for preenameloblasts, and is now cut off from them due to the deposition of a dentin layer between them. At the same time, a change in polarity occurs in the epithelial cells of the internal enamel organ, as a result of which the basal and apical poles change their places. The Golgi complex and the centrioles of preenameloblasts, located at the pole facing the intermediate layer (previously apical), are displaced to the opposite pole of the cell (which now becomes apical). Mitochondria, which were initially diffusely scattered throughout the cytoplasm, are concentrated in the region formerly occupied by the Golgi complex and becoming the basal part of the cell.

Enameloblasts differentiate only 24-36 hours after the completion of functional maturation of the adjacent odontoblasts. The final signal for this process is the beginning of the formation of predetin, in particular, its collagen and (or) proteoglycans. This explains why amelogenesis always lags behind dentinogenesis. For the same reason, the first secretory-active anameloblasts are formed where dentin deposition begins - in the area of the future cutting edge of the crown of the anterior or chewing cusps of the posterior ones. From here, the wave of enameloblast differentiation spreads towards the edge of the enamel organ to the cervical loop. The connection between the differentiation of enameloblasts and the formation of dentin serves as another example of mutual induction, since the induction of odontoblast development was carried out by the internal cells of the enamel organ.

The secretory-active odontoblast is a tall prismatic cell (length to width ratio up to 10:1) with highly differentiated cytoplasm. The apical part contains the large Golgi complex, cisterns of the granular endoplasmic reticulum, and mitochondria. Polarization is accompanied by a reorganization of the cytoskeleton and ends with the appearance of Toms' process in their apical part. Functionally, the differentiation of preenameloblasts into enameloblasts is accompanied by inhibition of the ability to synthesize glycosaminoglycans and type IV collagen (a component of the basement membrane) and the emergence of the ability to synthesize specific enamel proteins - enamelins And amelogenins .

Secretion and primary mineralization of enamel

Secretion of enamel by enameloblasts begins with the release of organic matter between dentin and the apical surface of enameloblasts in the form of a continuous layer 5-15 microns thick, in which calcification processes occur very quickly due to the deposition of hydroxyapatite crystals. In this case, a layer is formed initial enamel . Enamel deposition begins in the area of the future cutting edge of the front teeth and the chewing tubercles of the rear teeth, spreading towards the neck.

A feature of enamel that distinguishes it from dentin, cement and bone is that its mineralization occurs very quickly after secretion - the time period separating these processes is only minutes. Therefore, when enamel is deposited, it has virtually no non-mineralized precursor (pre-enamel). Enamel mineralization is a two-step process involving mineralization and subsequent crystal growth.

Enameloblasts control the transport of inorganic ions from the capillaries of the dental sac to the enamel surface. An important role in the mineralization of enamel is played by proteins produced by enameloblasts, which perform a number of functions:

participate in the binding of Ca 2+ ions and regulation of their transport by secretory enameloblasts;
create initial sites of nucleation (initiation) during the formation of hydroxyapatite crystals;
promote the orientation of growing hydroxyapatite crystals;
form an environment that ensures the formation of large hydroxyapatite crystals and their dense placement in the enamel.

Enamel proteins are non-collagenous, which also distinguishes enamel from other calcified human tissues. The main proteins during its secretion are amelogenins , making up 90% of the proteins secreted by enameloblasts. Amelogenins are hydrophobic proteins. They contain a large number of proline, glutamine And histidine and are formed due to the cleavage of a secreted large glycoprotein molecule. Amelogenins are mobile and not associated with crystals. It is believed that they are modified and migrate along the enamel, participating in the regulation of crystal growth in length, width and thickness. To continue the growth of crystals after formation, some of the proteins must be removed. This is achieved in two ways:

due to the pressure created by the growing crystals, amelogenins are forced out of the space between the crystals towards the enameloblasts;
Some of the proteins remaining between the rapidly growing crystals are cleaved to low molecular weight substances due to the action of proteolytic enzymes secreted by anameloblasts.

The second group of proteins found in enamel are enamelines , which bind to hydroxyapatite crystals and are characterized by a high content glutamine, aspartic acid And serine. Enamelins are probably not an independent secretory product, but the result of polymerization of the digestion products of amelogenins.

In the initial enamel, small hydroxyapatite crystals are arranged randomly (mainly perpendicular to the dentin surface) and interdigitate with dentin crystals. According to some authors, denine crystals are nucleation (initiation) sites for the formation of crystals in enamel.

After deposition of the first layer of initial (non-prismatic) enamel, enameloblasts move away from the dentin surface and form shoots Toms , which serves as a sign of the complete completion of their functional differentiation. Although the cytoplasm of the enameloblast directly passes into the cytoplasm of the process, their conditional boundary is considered to be the level of the apical complex of intercellular junctions. The cytoplasm of the cell body contains mainly organelles of the synthetic apparatus, and the cytoplasm of the process contains secretory granules and small vesicles.

Subsequent portions of the resulting enamel fill the intercellular spaces between the Toms processes. This enamel is secreted by the peripheral portions of enameloblasts at the base of their processes at the level of the apical junctional complexes. In the future, it will turn into interprismatic enamel. As a result, a cellular structure appears in the form of a honeycomb, the walls of which are formed by future interprismatic enamel, and inside each cell there is a Toms’ process. Once formed, such a cellular structure will determine the nature of the enamel structure, including the shape, size and orientation of the enamel prisms that will be formed by Toms' processes and fill the holes in the cells. Thus, interprismatic enamel has an initial organizing influence on the structure of the entire resulting enamel.

There is disagreement on the issue of the mechanisms of formation of enamel prisms and the fate of Toms' process. The most common idea is that secretory-active anameloblasts, together with their processes, are constantly pushed back by the newly formed enamel to its periphery. The displacement occurs at an angle to the dentinal-enamel boundary. According to other views, the process remains in place and is compressed by the growing prism. In this case, during enamelogenesis, the part of the process that is more distant from the cell body continuously dies, and the part located near the cell body grows.

With an arched configuration of enamel prisms, each of them is formed by more than one enameloblast; in fact, four cells take part in its formation, with one of them forming the “head” of the prism, and the other three together forming the “tail” (interprismatic enamel). In turn, each enameloblast participates in the formation of four prisms: it forms the “head” of one prism and the “tails” of the other four.

The orientation of crystals in the resulting prisms differs from that in the interprismatic areas. In prisms, especially in its central sections, most of the crystals are located parallel to their axis, and in the peripheral sections they deviate from it. In the interprismatic areas, the crystals lie at right angles to the crystals in the central part of the prism.

The growth of enamel prisms occurs cyclically, as a result of which, on each of them, with an interval of 4 microns, transverse striations are detected, corresponding to the 24-frequency rhythm of secretion and mineralization of enamel. During the formation of enamel, a slower (about a week) rhythm of its deposition is also noted, which is manifested by the appearance of enamel growth lines (Retzius lines). On longitudinal sections they are visible as brown lines running obliquely from the surface of the enamel to the dentin-enamel boundary, on transverse sections they are visible as concentric circles corresponding to the fronts of enamel deposition. These lines are associated with the periodicity of calcification (according to other sources, the formation of an organic matrix) of the enamel. According to the latest data, the appearance of Retzius lines is associated with periodic bending of the enamel prisms due to compression of the Thoms processes, combined with an increase in the secretory surface forming the interprismatic enamel.

Enamel proteins are found in all areas of newly formed enamel, however, as it matures, their highest concentration remains in the peripheral layer of enamel prisms, traditionally called shell. This is due to the fact that hydroxyapatite crystals in the shells are located at different angles, as a result of which they are not packed tightly, and the proteins filling the spaces between them are not completely removed. Thus, shells are not independent education, but only the peripheral sections of the enamel prisms themselves with a less ordered arrangement of crystals and an increased content of proteins.

The formation of enamel in the form of enamel prisms begins at the initial enamel (near the dentin surface) and is pumped up at the outer surface of the enamel, where a layer is formed ultimate enamels . In its structure, the final enamel is similar to the initial one and also does not contain prisms.

During amelogenesis, the cells of the outer enamel epithelium, the pulp of the enamel organ and the intermediate layers lose their individual morphological characteristics and form a single layer of multilayered epithelium adjacent to the enameloblasts.

^ Maturation (secondary mineralization) of enamel

Enamel formed by secretory enamaloblasts and subjected to primary mineralization , is immature . It consists of 70% mineral salts and 30% organic matrix. This enamel has the consistency of cartilage and is unable to perform its function. It persists after decalcification and is therefore clearly visible on histological preparations. The only area of more mineralized enamel is its innermost layer. Its thickness is several micrometers (initial enamel).

Mature enamel 95% is formed by mineral salts and 1.2% by organic substances. Almost all of it consists of densely spaced crystals of hydroxyapatite. The organic (protein) matrix of enamel has the form of a three-dimensional network of fibrillar structures about 8 nm thick, connected to each other and to hydroxyapatite crystals. During decalcification, the enamel almost completely dissolves and, therefore, on histological sections, empty spaces correspond to its location.

In progress maturation (secondary mineralization ) enamels , occurring upon completion of its secretion and primary mineralization, the content of mineral salts in it increases significantly, which leads to a sharp increase in its hardness. This is accomplished by the influx and inclusion of mineral salts into the enamel while simultaneously removing organic compounds (mainly proteins) and water from it. The maturation of enamel, as well as its secretion, begins along the cutting edge of the front teeth and on the chewing cusps of the rear teeth, spreading towards the neck of the tooth.

As a result of the maturation process, the highest level of enamel mineralization is achieved in its surface layer, and in the direction of the dentin-enamel boundary it decreases down to the innermost layer of the initial enamel, which is also characterized by an increased mineral content.

Secondary mineralization of enamel is ensured due to the active activity of enameloblasts ( enameloblasts stage of maturation ), which are formed as a result of structural and functional transformations secretion stage enameloblasts (secretory-active enameloblasts) (check!) who have completed their activities. The last product of the synthesis of secretory-active enameloblasts is a material that forms a structure similar to the basement membrane. This material is deposited on the surface of the enamel and serves as an attachment site for hemidesmosomes of enameloblasts. (primary cuticle of enamel, or Nasmyth's shell) . Upon completion of enamel secretion, enameloblasts undergo a short transition phase, during which they shorten, lose Thoms' processes, and are included in the process of enamel maturation. Excess organelles involved in secretion processes undergo autophagy and are digested by lysosomal enzymes. Some enamaleblasts die by apoptosis and are phagocytosed by neighboring cells.

The cyclical nature of the enamel maturation process is reflected in the morphological characteristics of enameloblasts. Among the latter, two types of cells are found that are capable of mutual transformations.

Enameloblasts type 1 characterized by the appearance of a striated edge on the apical surface. Their basal (remote from the enamel) complexes of intercellular junctions have significant permeability, and their apical (adjacent to the enameloblasts) have a high density. It has been established that these cells participate predominantly in the active transport of inorganic ions, which are transported through their cytoplasm and released on the apical surface. They have a very high concentration of calcium-binding proteins. Absorption of breakdown products of enamel proteins also occurs through the striated edge.

Enameloblasts of the second type have a smooth apical surface. Their basal junction complexes are impermeable, while their apical complexes are highly permeable. These cells take a major part in removing organic substances and water from the enamel. The molecules of these substances easily penetrate into the intercellular space at the apical ends of cells and are then transported by vesicles formed on their lateral surfaces.

After enamel maturation is completed, the layer of enameloblasts and the adjacent epithelial layer (formed by the outer enamel epithelium, collapsed pulp and the intermediate layer of the enamel organ) together form reduced dental epithelium (secondary enamel cuticle), which covers the enamel and plays a protective role, especially significant before tooth eruption.

^ Final maturation (tertiary mineralization) of enamel

The maturation of enamel, associated with an increase in the content of mineral substances in it, is not completely completed in the formed crown of an unerupted tooth. The final maturation of enamel occurs after tooth eruption, especially intensively during the first year that the crown is in the oral cavity. The main source of inorganic substances entering the enamel is saliva, although some of them can come from the dentin. In this regard, the mineral composition of saliva, including the presence in it of the required amount of ions, calcium, and fluorine phosphorus, is of particular importance for the complete mineralization of enamel during this period. The latter are included in the hydroxyapatite crystals of the enamel and increase its acid resistance. Subsequently, throughout life, enamel participates in ion exchange, undergoing processes of demineralization (removal of minerals) and remineralization (intake of minerals), balanced under physiological conditions.

Clinical significance of amelogenesis disorders

Enamaloblasts are sensitive to external influences, which lead to deviations in the normal course of amelogenesis. Even small impacts can manifest themselves as morphologically noticeable changes in the composition of the enamel and its quantity. More significant lesions can lead to profound disturbances in enamelogenesis and even death of enameloblasts.

If the impact of a damaging factor occurs during the period of enamel secretion, then the amount of enamel formed (the thickness of its layer) in this area decreases. This violation is called hypoplasia enamel, or its underdevelopment.

If the impact occurs during the period of enamel maturation, its mineralization is disrupted to a greater or lesser extent. This condition is called hypocalcification enamels. At the same time, enamel with a reduced content of mineral substances is easily subject to decalcification and caries.

Hypoplasia and hypocalcification of enamel can affect one, several teeth, or all teeth. In these cases, the causes of the disorder are local, systemic or hereditary in nature, respectively. The most common systemic factors are endocrinopathies, diseases accompanied by febrile conditions, nutritional disorders and the toxic effects of certain substances.

Local enamel hypoplasia may affect one tooth or part of it. It is usually caused by local disorders, such as trauma, osteomyelitis. In a permanent tooth, it can be caused by a periapical infection of the corresponding primary tooth.

Systemic enamel hypoplasia develops under different infectious diseases and metabolic disorders, covering several teeth in which enamel formation occurred during the disease. Upon recovery, the normal process of amelogenesis resumes. As a result, stripes of hypoplastic enamel alternating with normal enamel are clinically visible on the teeth. If the normal development of enamel is interrupted several times due to metabolic disorders, multiple enamel hypoplasia occurs.

Enamel defects can be caused by taking tetracycline antibiotics. Tetracyclines are incorporated into calcifying tissues, leading to enamel hypoplasia and brown pigmentation. The degree of enamel damage depends on the dosage of the antibiotic and the duration of its use.

Hereditary (congenital) enamel hypoplasia, or amalogenesis imperfecta , affects all teeth (both temporary and permanent), in which the entire crown is affected. Since the thickness of the enamel decreases sharply, the teeth have a yellow-brown color. Amalogenesis imperfecta can be combined with dentinogenesis imperfecta.

Local enamel hypocalcification , as a rule, is caused by local disturbances. Systemic hypocalcification covers all teeth in which the action of a damaging factor occurred during the period of enamel maturation. The most common example of such a disorder would be abnormal calcification of the enamel due to an increase in fluoride content in drinking water(5 or more times higher than its concentration in fluoridated water), leading to the development of a disease called fluorosis. It is characterized by the formation of so-called “moth-eaten” enamel, in which multiple areas of hypomineralization are found.

Congenital hypocalcification of enamel – a hereditary disease in which irregularities are detected in all teeth. Immediately after eruption, the crown has a normal shape, but the enamel is soft, dull in color, and quickly wears off or separates in layers.

Formation of cement, development of periodontium and dental pulp

Formation of cement (cementogenesis)

During tooth root formation, dentin is deposited in the inner surface of the epithelial (Hertwig's) root sheath, which separates the dental papilla from the dental sac. During dentinogenesis, the root sheath breaks up into separate fragments (epithelial remnants of Malasse), as a result of which poorly differentiated connective tissue cells of the dental sac come into contact with dentin and differentiate into cementoblasts - cells that form cement. Cementoblasts are cubic cells with a high content of mitochondria, a large Golgi complex, and a well-developed hydroelectric power station.

Cementoblasts begin to produce an organic matrix (cementoid), which consists of collagen fibers and ground substance. Cementoid is deposited on top of the root dentin and around the fiber bundles of the developing periodontium. According to some information, however, the deposition of cementoid does not occur directly on the surface of the mantle dentin, but on top of a special highly mineralized structureless layer ( Hopewell-Smith hyaline layer) 10 µm thick, covering the root dentin and formed, presumably, by the cells of the epithelial root sheath before its disintegration. This layer probably contributes to the strong attachment of cementum to dentin and periodontal ligament fibers to cementum.

The second phase of cement formation involves the mineralization of the cementoid by the deposition of hydroxyapatite crystals into it. Crystals are deposited first in matrix vesicles, followed by mineralization of collagen fibrils of cement. Cementum deposition is a rhythmic process in which the formation of a new cementoid layer is combined with the calcification of a previously formed layer. The outer surface of the cementoid is covered with cementoblasts. Between them, connective tissue fibers of the periodontium, consisting of numerous collagen fibers, called Sharpey's fibrils, are woven into the cement.

As cement forms, cementoblasts either move to its periphery or become immured in it, settling in lacunae and turning into cementocytes . The first to form is cementum, which does not contain cells ( acellular , or primary ), it is slowly deposited as the tooth erupts, covering 2/3 of the surface of its root closest to the crown.

After tooth eruption, cementum containing cells ( cellular , or secondary ). Cell cement is located in the apical 1/3 of the root. Its formation occurs faster than acellular cement; in terms of the degree of mineralization, it is inferior to it. The matrix of cellular cement contains internal (intrinsic) collagen fibers formed by cementoblasts, and external (external) fibers penetrating into it from the periodontium. External fibers penetrate the cement at an angle to its surface, and their own fibers are located along the surface of the root, weaving a network of external fibers. The formation of secondary cement is a continuous process, as a result of which the cement layer thickens with age. Secondary cement is involved in the adaptation of the supporting apparatus of the tooth to changing loads and in reparative processes.

^ Periodontal development

The periodontium develops from the dental sac soon after the formation of the tooth root begins. The cells of the pouch proliferate and differentiate into fibroblasts, which begin to form collagen fibers and ground substance. Already at the most early stages During the development of the periodontium, its cells are located at an angle to the surface of the tooth, as a result of which the resulting fibers also acquire an oblique course. According to some reports, the development of periodontal fibers occurs from two sources - from the cementum and from the alveolar bone. The growth of fibers from the first source begins earlier and occurs rather slowly, with only some fibers reaching the middle of the periodontal space. The fibers growing from the side of the alveolar bone are thick, branched and, in terms of their growth rate, are significantly ahead of the fibers growing from the cement; they meet with them and form a plexus.

Before the tooth erupts, its cemento-enamel boundary is located significantly deeper than the crest of the developing dental alveolus, then, as the root forms and the tooth erupts, it reaches the same level, and in a fully erupted tooth it becomes higher than the crest of the alveolus. In this case, the fibers of the developing periodontium associated with the ridge, following the movement of the root, are first located obliquely (at an acute angle to the alveolar wall), then occupy a horizontal position (at a right angle to the alveolar wall) and ultimately again take an oblique direction (at an obtuse angle). angle to the alveolar wall). The main groups of periodontal fibers are formed in a certain sequence.

The thickness of the periodontal fiber bundles increases only after the tooth erupts and begins to function. Subsequently, throughout life, there is a constant restructuring of the periodontium in accordance with changing load conditions.

^ Dental pulp development

The pulp develops from the dental papilla, formed by ectomesenchyme. The papilla initially consists of branched mesenchymal cells separated by large spaces. The process of differentiation of the papilla mesenchyme begins in the region of its apex, from where it further spreads to the base. The vessels begin to grow into the papilla even before the appearance of the first odontoblasts; nerve fibers, however, grow into the papilla relatively late - with the beginning of dentin formation.

The cells of the peripheral layer of the papilla, adjacent to the inner enamel epithelium, turn into preodontoblasts. And later - odontoblasts, which begin to form dentin. The course of odontoblast differentiation is described above. In the central areas of the pulp, the mesenchyme gradually differentiates into loose, unformed connective tissue. Most of the mesenchymal cells turn into fibroblasts, which begin to secrete components of the intercellular substance. The latter accumulates collagen types I and III. Despite the progressive increase in collagen content in the developing pulp, the ratio between collagen types I and III remains unchanged, and type III collagen is present in the pulp in an unusually high concentration for connective tissue. Collagen is first detected in the form of isolated fibrils, lying without strict orientation; later the fibrils form fibers that fold into bundles. As the pulp matures, its glycosamyoglycan content decreases.

At the same time, active proliferation of blood vessels occurs in the connective tissue of the pulp. Larger arterioles and venules are located in the center of the developing dental pulp; an extensive capillary network develops at the periphery, including both fenestrated capillaries and capillaries with a continuous vascular wall. The development of blood vessels is combined with the proliferation of nerve fibers and the formation of their networks.

Tissue changes during tooth eruption

Once crown formation is complete, the developing tooth undergoes small movements in conjunction with jaw growth. During the process of eruption, the tooth travels a considerable distance in the jaw. Moreover, its migration is accompanied by changes, the main of which are:

tooth root development;
periodontal development;
alveolar bone remodeling;
changes in the tissues covering the erupting tooth.

Tooth root development associated with the ingrowth of the epithelial root sheath into the mesenchyme of the dental papilla, extending from the cervical loop of the enamel organ. Vaginal cells induce the development of root odontoblasts, which produce its dentin. As the sheath is destroyed, the mesenchymal cells of the dental sac differentiate into cementoblasts, which begin to deposit cementum on top of the root dentin.

^ Periodontal development includes the growth of its fibers from the cementum and dental alveoli and becomes more intense immediately before tooth eruption.

Alveolar bone remodeling combines rapid deposition of bone tissue in some areas with its active resorption in others. The localization of changes in the alveolar bone and their severity varies at different times and is not the same in different teeth. When a tooth root is formed, it reaches the bottom of the bone cell and causes resorption of bone tissue, resulting in freeing up space for the final formation of the root end. Bone deposition usually manifests itself as the formation of bony trabeculae separated by wide spaces.

In multi-rooted teeth, bone deposition occurs most intensively in the area of the future interradicular septum. In premolars and molars, such areas are the bottom and distal wall of the socket (which indicates their additional medial displacement during axial movement during eruption). In incisors, areas of increased deposition of bone beams are the bottom and lingual surface of the socket (which indicates their subsequent displacement towards the lips during eruption). Bone deposition occurs in those areas of the bone socket from which the tooth is displaced, and resection occurs in those areas towards which the tooth migrates. Resorption of bone tissue frees up space for the growing tooth and reduces resistance to its movement.

LITERATURE

Bykov V.P. Histology and embryology of human oral cavity organs: Tutorial 2nd ed. –SPb. – 1999
Histology textbook / Ed. Yu.I. Afanasyeva, N.A. Yurina - 5th ed., revised. and additional – M.: Medicine, 2006.
Histology textbook / Edited by E.G. Ulumbekova, Yu.A. Chelysheva. – “th ed., revised. and additional – M.: GOETAR MED, 2009.
Dzhulay M.A., Yasman S.A., Baranchugova L.M., Pateyuk A.V., Rusaeva N.S., V.I. Obydenko Histology and embryogenesis of the oral cavity: Textbook.-Chita: IRC ChSMA. - 2008.- 152 p.
V.I.Kozlov, T.A.Tsekhmistrenko Anatomy of the oral cavity and teeth: Textbook Publisher: RUDN IPK - 2009 -156 p.
Myadelets O.D. "Histophysiology and embryogenesis of the oral cavity organs." Vitebsk, VSMU. Educational and methodological manual VSMU - Vitebsk State medical University- Publishing house 2004.-158 p.
Histology of the oral cavity: Educational manual / Compiled by Yu.A. Chelyshev. - Kazan, 2007. - 194 p.: ill. Educational and methodological, designed for intensive training of students of the Faculty of Dentistry in the histology of the oral cavity.
Danilevsky N.F., Lenontiev V.K., Nesin A.F., Rakhniy Zh.I. Diseases of the oral mucosa Publisher: OJSC "Dentistry" -: 2007- 271 p.: Ch. 1. Oral cavity - concept, features of structure, function and processes; Ch. 2 Histological structure oral mucosa

Teeth are derivatives of the fetal oral mucosa. Tooth enamel develops from the epithelium of this mucous membrane. Dentin, cement, dental pulp, as well as periodontal tissues (periodontium) are derivatives of mesenchyme. Dental development is a complex and lengthy process that begins in the early stages of embryogenesis and continues until 18-20 years of postnatal life, and the last large molars (wisdom teeth) erupt at the age of 23 and even 25 years.

The fundamental diagram of the development of milk and permanent teeth is the same, but the timing of their formation, eruption and replacement is different; they are an important criterion for judging the physical development and health of the child.
D evelopment of baby teeth. Initial signs The appearance of the rudiments of teeth in humans refers to the end of the second month of embryonic life, when the oral cavity has not yet separated and the vestibule of the oral cavity has not formed. The first stages of dental development proceed in parallel with the separation of the oral cavity, with the formation of the vestibule of the oral cavity. Three main periods can be distinguished in the development of primary teeth. The first period is the formation and formation of tooth germs.
The second period is differentiation of tooth germs. The third is the period of histogenesis of dental tissues.

The period of formation and formation of tooth germs. The beginning of the development of baby teeth in human embryos dates back to 6-8 weeks of intrauterine life. The stratified squamous epithelium lining the oral fossa forms a thickening located along the upper and lower edges of the primary oral fissure. The resulting thickening gradually grows into the underlying mesenchyme, forming an epithelial plate, which splits into two parts: the anterior, or buccal-labial, plate and the dental plate located at a right angle to it. The anterior, or buccolabial, plate then splits, turning into a groove that separates the anlage of the lips and cheeks from the rudiments of the gums, i.e. gives rise to the vestibule of the mouth. The appearance of a slit-like cavity in this epithelial plate means that the rudiment or lip or cheek is isolated in front of it, and the rudiments of the upper or lower jaws are located behind it.

The dental plate gradually takes on the shape of an arch embedded in the mesenchyme of the upper and lower jaws. It is an epithelial cord starting from either back surface buccolabial plate and growing posteriorly into the underlying mesenchyme, or directly from the epithelium covering the upper or lower jaw. First growing posteriorly in a horizontal direction, the dental plate then turns downwards and takes on a more vertical position. Its shape corresponds to the shape of the lower or upper jaw and it is formed throughout the rudiments of the jaws.

On the front surface of the dental plates facing the lip or cheek, near the free edge, growths appear that look like colloidal protrusions connected to the edge of the dental plate by thin epithelial bridges, which are called dental buds. In each jaw, 10 such tooth buds appear, corresponding to the number of future milk teeth. At 9-10 weeks of intrauterine life, mesenchyme grows into each dental bud from below, forming a dental papilla. As a result of this, the tooth buds turn into dental buds, or, as they are often called, enamel organs, which look like caps or double-walled glasses. With further growth, the dental organs gradually become separated from the dental plates, remaining connected to them only by thin strands of epithelial cells, which are called the necks of the dental organ. Simultaneously with the separation of the tooth germs, the so-called dental sac is formed around each of them due to the compaction of the mesenchyme. Thus, during the first period of development of primary teeth, the formation of dental germs occurs, consisting of a dental or enamel organ of epithelial origin, as well as the dental papilla and dental sac - derivatives of mesenchyme.

Period of differentiation of tooth germs. The second period of development of primary teeth in human embryos is characterized by a number of complex transformations occurring both in the dental germs themselves and in the tissues surrounding them and associated with typical manifestations of differentiation. In the dental, or enamel, organ, these changes are expressed in the fact that instead of homogeneous cellular elements, cells of different shapes and functions appear here. Thus, flattened outer epithelial cells are now located on the outer surface of each dental organ. The internal cells of the dental organ, located on the border with the dental papilla, acquire a high cylindrical shape. As a result of the accumulation of protein fluid between the epithelial cells of the central enamel organ, these cells become stellate in shape, move away from each other and are connected to each other using long cytoplasmic processes. The pulp of the dental organ is formed. The part of the pulp adjacent directly to the internal cells makes up the so-called intermediate layer, where flat or cubic cells are arranged in 2-3 rows and there are small intercellular spaces between them. These cells are characterized by high mitotic activity.

Electron microscopic studies have shown that the cytoplasm of the outer cells of the enamel organ contains a well-developed lamellar complex, a granular cytoplasmic reticulum and contains a small number of mitochondria. At the border of these cells with the surrounding tissue of the dental sac there is a basement membrane with a thickness of about 10-22 nm. In the cytoplasm of the pulp cells of the dental organ, a lamellar complex is revealed, consisting of small vesicles and cisterns, tubules of a granular cytoplasmic reticulum. It has been established that the outer cells and cells of the pulp of the dental organ are connected to each other using typical desmosomes. The internal cells of the dental organ at the early stages of differentiation contain a poorly developed cytoplasmic reticulum and a fairly large number of free ribosomes. Their lamellar complex is small and consists of small vesicles. Mitochondria are scattered throughout the cytoplasm of cells. The internal cells are arranged in a single row on the basement membrane, which separates them from the tissue of the dental papilla and has a thickness of about 30 nm.

Histochemical studies show that in the early stages of development, cells of the dental organs contain a large amount of glycogen, and the cells of the intermediate layer are also distinguished by high enzymatic activity (acid phosphatase, succinate dehydrogenase, etc.).

The differentiation of the mesenchymal dental papilla is expressed in the fact that it significantly increases in size and protrudes even deeper into the dental or enamel organ. A large number of small blood vessels and nerves grow into the papilla. On the surface of the papilla, several rows of elongated cells are formed from mesenchymal cells. Their sharply basophilic cytoplasm reveals a well-developed lamellar complex, cytoplasmic reticulum and numerous mitochondria. Alkaline phosphatase activity is detected in cells. These cells are called odontoblasts because they take part in the formation of dentin.

The growth and differentiation of tooth germs is accompanied by an increase in the size of the dental sacs and their specific differentiation.

Period of dental histogenesis. The period of differentiation of tooth germs at the end of the 4th month of intrauterine life is replaced by a period of histogenesis, during which dentin, enamel and pulp of the crowns of primary teeth appear. The development of the roots of primary teeth occurs in the postembryonic period and coincides in time with the beginning of teething. The first tissue that is formed during tooth histogenesis is dentin. It is believed that the initial components for building the fibrous structures of dentin are secreted by odontoblasts, and the formation of fibrils takes place outside the cytoplasm of the cells. Immediately before the formation of dentin, the structure of odontoblasts undergoes a number of changes. Thus, the odontoblast nucleus moves to the basal part of the cell. The cytoplasmic reticulum becomes more complex and takes on the appearance of convoluted tubules. This organelle, together with the lamellar complex, is located above the nucleus. A sign of the onset of dentin-forming activity of odontoblasts is the appearance near these cells of thin pre-collagen fibers with a radial direction. These fibers are included in the ground substance of uncalcified dentin, or predentin.
Subsequently, thin pre-collagen fibers gradually transform into thicker collagen fibers (the so-called Korff fibers). When the layer of predentin with radial fibers reaches a thickness of 60-80 micrometers, the formation of new layers of predentin begins, in which the fibers no longer have a radial, but a tangential direction, i.e. run parallel to the surface of the dental papilla. These are the so-called Ebner fibers.

Unlike Korff fibers, Ebner fibers do not go through the precollagen stage in their development, but appear immediately as collagen fibers. A feature of the development of dentin is that already in the first stages of its formation, cytoplasmic processes appear in the odontoblasts, which penetrate into the ground substance of non-calcified dentin and are gradually immured in it in the so-called dentinal tubules. The odontoblasts themselves constantly remain in the outer parts of the dental papilla. Dentin mineralization begins at the end of the 5th month of intrauterine life. In the process of calcification of dentin, an important role is played by odontoblasts, which, with the help of their processes, participate in the transport of minerals from the blood into the main substance of dentin. Inorganic salts in the form of hydroxyapatite crystals are deposited in the main substance of dentin along the collagen fibers. In addition, some crystals are deposited in the form of spheres or alcospherites. Enamel begins to develop soon after the formation of dentin begins, but before the development of enamel begins, a number of changes occur in the internal cells of the dental organ, which are now called enameloblasts or adamantoblasts. In these cells, the cytoplasmic reticulum and lamellar complex become very well developed. Many free ribosomes are found in their cytoplasm. All these organelles move to the cell pole that was previously basal and facing the layer of developing dentin. This pole of the cell now becomes apical. The cell nucleus shifts to the opposite pole, which now becomes the basal pole. The change in the morphological and physiological polarity of enameloblasts is due, in particular, to the fact that these cells, after the onset of dentinogenesis, can receive the materials necessary for the construction of enamel only from the blood vessels of the inner layer of the dental sac. After this inversion, the apical pole of each enameloblast elongates and forms a finger-like process, the so-called Toms process. Before the formation of enamel, round or oval granules, surrounded by a shell and containing an electron-dense substance, accumulate in these processes. The appearance of granules appears to be the beginning of the production of ordinary enamel substance. According to modern scientific data, enamel formation occurs by secretion of the contents of these granules into the intercellular space by enameloblasts. The secretion process proceeds according to the micromerocrine type. As the basic substance of the enamel accumulates, the enameloblasts move to the periphery. Calcification of the main substance of the enamel occurs immediately after the appearance of its first portions. Calcium salts are deposited in the enamel in the form of hydroxyapatite crystals, which initially have the shape of thin plates. These plates combine into prisms as they grow. The previously existing opinion that each enameloblast turns into an enamel prism was not confirmed in electron microscopic studies. After completion of enamel formation, enameloblasts are reduced. The appearance of enamel usually leads to partial resorption of dentin in the place where these two tooth tissues contact each other. This apparently contributes to increased mineralization of the enamel and its stronger connection with dentin.

Simultaneously with the development of dentin and enamel, the process of formation of the pulp of milk teeth occurs. The mesenchyme of each dental papilla is gradually transformed into loose connective tissue, rich in cellular elements such as fibroblasts, macrophages, etc., between which precollagen and collagen fibers appear. Histochemically, in the peripheral parts of the developing dental pulp, respiratory enzymes of the Krebs cycle and enzymes that hydrolyze phosphate compounds are detected, due to which mineralization of dentin and enamel occurs. The vascular network and nervous apparatus of the developing dental pulp become more complex.

The development of the roots of baby teeth in humans begins shortly before their eruption, i.e. already in the postembryonic period. By this time, the crowns of baby teeth are almost completely formed. Each crown is covered on the outside with a cuticle, which is the remains of the dental organ, consists of several rows of flat epithelial cells and separates the tooth crown from the surrounding tissues. The reduced epithelium of the dental organ remains on the surface of the tooth crown until its eruption and, apparently, prevents the resorption of enamel and the deposition of cement on its surface (Orban, 1953).

The edges of the dental organ, i.e. its areas where the internal squamous epithelium passes into the layer of external squamous epithelial cells, by the time the tooth root develops, grow intensively and penetrate into the underlying mesenchyme, forming the so-called Hertwig epithelial root sheath. This epithelial sheath, as it were, limits the area of mesenchyme that will go into the formation of the tooth root, and determines the future shape of the root. During further development, odontoblasts are formed from the mesenchymal cells of the dental papilla, adjacent to the epithelial root sheath, which begin to produce root dentin. After the formation of the first layers of dentin, the epithelial sheath grows with mesenchymal cells of the inner layer of the dental sac. As a result, the epithelial vagina breaks up into a number of epithelial islands, most of which then disappear. From the mesenchymal cells of the inner layer of the dental sac, cementoblasts differentiate, which begin to deposit cement on the outer surface of the root dentin.

The formation of cement occurs according to the type of periosteal osteogenesis. Due to the outer layer of the dental sac, periodontium is formed, thanks to which the tooth root is firmly attached to the wall of the bony alveoli.

Eruption of baby teeth. Teething theories. As already noted, the development of the roots of baby teeth in humans coincides in time with their eruption. The child's first milk teeth erupt at 6-7 months of postnatal development.

At the beginning of eruption, the tooth compresses the gum tissue with the top of its crown, which naturally leads to gum atrophy in this area. In this case, the enamel cuticle, which covers the outside of the tooth crown and represents the remains of the epithelium of the dental organ, comes into contact with the gum epithelium. Soon, a breakthrough of the gum epithelium occurs above the top of the tooth crown, and the tooth appears in the oral cavity. As the crown of the tooth moves into the oral cavity, the epithelium of the gums seems to slide off it and only in the area of the neck of the tooth does it tightly connect to the cuticle of the enamel (nasmite membrane). This connection remains for life, forming the bottom of the so-called gum pocket. There are several theories regarding the mechanism of teething. According to one of them, teething is associated with the growth of roots. However, there are a number of observations that cannot be explained from the perspective of this theory (for example, the existence of impacted, that is, unerupted teeth with fully formed roots).

Most scientists adhere to the theory proposed by G.V. Yasvoin (1929, 1936). According to this theory, teething is associated with differentiation of the mesenchyme of the dental papilla, during which a large amount of basic substance is formed, which entails an increase in pressure inside the tooth germ. This pressure forces the tooth to move towards the free edge of the gum. The moment of complete eruption of the tooth crown coincides with the stage of development of the tooth germ when the supply of undifferentiated mesenchyme in it is completely consumed.

Many researchers believe that the restructuring of the bone alveoli plays an important role in teething. This point of view was most clearly formulated by A.Ya. Katz (1940). According to his opinion, teething is accompanied by resorption (absorption) of the bone avulveolus in those areas where the crown of a growing tooth exerts pressure, and new formation of bone tissue in the area of the alveolar bottom. Thus, the combination of the processes of resorption and new formation of bone tissue is the dominant factor in the mechanism of teething.

Permanent teeth.

Development and eruption of permanent teeth. In the development of 32 permanent human teeth, the same three main periods can be distinguished as in the development of baby teeth. The source of the formation of dental or enamel organs are the same dental plates from which the dental organs of the 20 primary teeth developed. At the end of the 4th and beginning of the 5th month of intrauterine life along the edge of the dental plate behind each rudiment baby tooth the corresponding dental organs of permanent teeth (incisors, canines and small molars) are formed. As is known, the child does not have small molars, so permanent small molars replace the molars of the primary occlusion. As for large molars, their anlages appear at a later date. Thus, the rudiment of the first large molar appears in the 5th month of intrauterine life, the rudiment of the second large molar - in the middle of the first year of a child’s life, and the rudiment of the third large molar ("wisdom tooth") - in the 4th and even 5th -year of life. This late formation of large molars is due to the fact that there is not enough space for them in the developing jaws of the fetus. The conditions for the appearance of the rudiments of these teeth arise only when intensive growth of the jaws occurs posteriorly and when dental plates grow posteriorly.

The general structure of the germ of permanent teeth does not differ from the corresponding germ of primary teeth. This rudiment contains an epithelial dental organ, a mesenchymal dental papilla and a dental sac. The development of the tissues of permanent teeth occurs in the same sequence as in milk teeth, i.e. Dentin is formed first, followed by enamel and pulp. The roots of the teeth are formed much later; the difference lies only in the time of passage of individual stages and the longer duration of development of permanent teeth. The germ of a permanent tooth and the root of the corresponding baby tooth are located in a common bone alveolus and are separated by a bone septum. During its growth, the permanent tooth germ begins to put pressure on this septum and on the root of the baby tooth. At the same time, osteoclasts appear in the surrounding connective tissue, which destroy the bone septum and begin to gradually destroy the root part of the baby tooth. The process of resorption of the roots of primary teeth begins long before the eruption of the corresponding permanent teeth and proceeds very slowly. In the end, the baby tooth is left with an empty crown, which easily falls out, and a growing permanent tooth gradually appears in its place. The eruption of large molars, which do not have predecessors, occurs in the same way as the eruption of milk teeth. The eruption of permanent teeth begins at the age of 6-8 years.

In children aged 6 months, cement appears on the roots of the primordial deciduous teeth and interradicular vaults. By 1.5-2 years, the root part of the tooth in the neck area and the upper two-thirds of it are already covered with acellular cement, and the lower part of the root and the interradicular arch are covered with primary cellular cement. The layering of secondary acellular cement on primary cellular cement is accompanied by resorption of the latter by cementoclasts. By the age of 4, the resorption process noticeably intensifies and by the age of 5-6, deep niches are formed on the lateral surfaces of the roots of the teeth, partially filled with cement. The spread of the resorption process leads to shortening of tooth roots and disruption of the connection between the tooth and the periodontium. At the same time, the partition between the milk and permanent teeth is resorbed. This creates the precondition for the loss of baby teeth.