Timing of eruption of permanent teeth. X-ray characteristics of the process of mineralization of teeth and roots

• Lecture

• for 2nd year students of the Faculty of Dentistry on the topic:

• "Anatomy-morphological, histological and radiological features of the dentofacial system in children at different age periods."

Periods of development and formation of temporary teeth

• 1st – intrauterine development

• formation of tooth buds

• histogenesis

• 2nd – teething

• 4th - stabilization

• 5th - root resorption

Periods of development and formation of permanent teeth

• 1st – intrauterine development

• formation of tooth buds

• differentiation of tooth germs

• histogenesis

• mineralization of hard tooth tissues

• 2nd – teething

• 3rd – formation and growth of roots and periodontium

• 4th - stabilization

Stages of root formation

• Unformed tip stage

• Unclosed apex stage

• Stage of formed root and periodontium

• Stage of periodontal formation

Stages of root formation

• Bell stage (stage of root growth in length)

^ TYPES OF TEETH ROOT RESORPTION

• Physiological resorption

• Pathological resorption

• Idiopathic resorption

• Uniform resorption of all roots

^ PULP STRUCTURE

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

• Neighboring ODB are connected by intercellular connections, thanks to which the ODB layer is able to perform a barrier function, regulating the movement of molecules and ions between the pulp and predentin.

• 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. Signs of high activity are characteristic of FB in the teeth of young people.

Lymphocytes

• Lymphocytes (Lc) - in small quantities, during inflammation their content increases sharply. Pulp cells belong to different subpopulations of T cells; cytotoxic suppressors predominate. B cells are not normally found, but during inflammation they become numerous. These cells actively synthesize immunoglobulins (mainly IgG) and provide reactions humoral immunity.
• Mast cells (Tc) - located perivascularly, characterized by the presence in the cytoplasm of large granules containing biologically active substances: heparin, histamine, eosinophil chemotactic factor and leukotriene C. On the outer membrane of the Tc there are receptors for IgE. MC degranulation promotes increased vascular permeability and reduction of smooth myocytes.

• For baby teeth:

• 1st period – development of the functional activity of the pulp (tooth root formation);

• 2nd period – functional maturity of the pulp (stabilization of the formed tooth root);

• 3rd period – fading of the functional properties of the pulp (resorption of the tooth root).

Pulp of primary teeth

• Higher cell content, especially in the central layer, with fewer collagen fibers.

• The volume of the pulp chamber and the pulp itself is larger in primary teeth.

• Thinner layers of enamel and dentin - the pulp is closer to the external environment than in permanent teeth.

• The differences between the structure of the coronal and root pulp are unclear.

The period of development of the functional activity of the pulp (the period of tooth root formation).

• The cavity of an erupted milk tooth does not have a constant shape and size due to the ongoing formation of roots.

• In the peripheral layer, the ODB are located in 3-4 rows. In the central layer there are numerous poorly differentiated cells.

• The main substance of the pulp is dominated by acidic MPS and hyaluronic acid. Under the ODB layer are precollagen and reticulin fibers. Collagen fibers are almost absent.

• In the first years of tooth growth, when the pulp morphologically resembles embryonic tissue, plastic properties pulps are especially pronounced.

The period of extinction of the functional properties of the pulp is the period of resorption of tooth roots.

• The pulp undergoes involutive changes: the cellular composition decreases and the amount of collagen fibers, intermediate substance and tissue fluid increases.

• Reticular or fatty degeneration and fibrosis occur in the pulp.

• Some of the blood vessels are reduced, their walls thicken, congestive hyperemia occurs, and the nerve elements of the pulp change.

• The vitality of the pulp is maintained thanks to the resorption organ, from where nutrients are delivered.

For permanent teeth:

• 1st period – formation of functional maturity of the pulp (formation of the tooth root);

• 2nd period – the onset of functional maturity (fully formed tooth roots without signs of aging);

• 3rd period – decrease in the functional activity of the pulp (fully formed roots with signs of tooth aging).

^ PULP OF PERMANENT TEETH.

• The period of formation of the functional maturity of the pulp is the period of formation of the tooth root.

• Predentine in teeth with unformed roots is represented by a wide strip of equal thickness.

• The ODB layer in teeth with developing roots is massive and includes 8-12 rows of cells located compactly. The number of cell rows depends on the function - there are more of them in places of intense dentinogenesis.

• The pododontoblastic layer is represented by the TC, FB, preODB, and MK of the pulp.

• Reticulin fibers are represented mainly by precollagen fibers, turning into collagen fibers.

• Thus, the pulp of teeth with unformed roots can be characterized as unformed maturing connective tissue.

The period of functional maturity of the pulp (the period of a fully formed tooth root).

• The ODB layer is compact. Intensive dentin formation continues until the onset of signs of tooth aging.

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

After the formation of the apical foramen, the coronal pulp is rich in intermediate substance, in which well-developed fibrillar structures are immersed. The pulp contains a sufficient amount of energy material - glycogen, acidic and neutral MPS, ensuring normal fiber formation processes, as well as RNA and DNA involved in protein metabolism. The pulp during this period is well supplied with blood, its functions of dentin formation, protection, and trophism are clearly expressed. The structure of the pulp of a fully formed tooth corresponds to mature connective tissue with established high physiological activity.

Source for formation permanent teeth serves as an epithelial dental plate. The timing of their formation is somewhat behind those for baby teeth. Root rudiments begin to appear only by the fifth month of intrauterine development.

Permanent teeth are divided into 2 groups:

• Substituting, which have analogues in the milk kit. These include incisors, canines and premolars.
• Additional, which have no temporal predecessors. These teeth are represented by molars.

The rudiments of permanent replacement teeth begin to grow in the same alveolus with milk teeth, located behind their lingual surface. And only after some time they are completely isolated by bone tissue.

The formation of additional teeth begins even later, only after a year, which is associated with the need to increase the size of the jaw.

Molars in most cases complete their growth by 15-18 years

At what age do they appear?

The start and end times of the replacement of baby teeth with a permanent set are approximately the same for all children. Slight fluctuations from the average age indicators can be observed among representatives of different regions. It is believed that the hotter the climate, the earlier the child’s molars grow.

The table presents age indicators reflecting the time when teeth from the permanent set begin to erupt according to various authors.

Disagreements in the timing of molar eruption according to various authors are explained by the fact that the studies were carried out in different regions and several decades apart.

Teething order

Most parents are sure that the first permanent teeth that appear in a child’s mouth are the incisors, which grow to replace the milk teeth. But that's not true. Before the temporary teeth begin to fall out, children aged about 5-6 years have their first molars, which are not present in the primary dentition, emerge.

• the lower and then the upper central incisors appear;
• then the lateral incisors emerge on the lower and upper jaws;
• after the incisors, the upper and lower first premolars erupt;
• the next ones to change are the fangs;
• then the second premolars appear above and below;
• The second and third molars are the last to erupt, while “wisdom teeth” may never appear on the surface of the gums.

This sequence of appearance of molars in a child is not accidental. In it, nature took into account all the necessary growth rates of the maxillofacial system. Therefore, if this order is not violated, the correct bite is formed.

How long do they grow?

In most cases, a child of 12-13 years old has already lost his last milk teeth, although the resorption of their roots occurs somewhat earlier. At this point, the oral cavity contains teeth from permanent dentition, which continue to grow and have varying degrees root formation.

Knowledge normal terms growth and formation of roots is important in the event of any pathologies, since these parameters are decisive when choosing treatment tactics.

In the process of tooth root development, it is customary to distinguish 2 stages:

1. Stage of unformed apex.
2. Unclosed apex stage.

At the first stage the root reaches its maximum length, but at the same time its walls are located parallel to each other. The root canal is quite wide and ends in a bell in the area of ​​the future apex. In this case, the periodontal gap is noticeable only on the sides of the root.

At the second stage There is a gradual formation of the apex of the tooth root. The root walls gradually come closer together, the periodontal fissure is finally distinguished, which is somewhat expanded in the apical region.

The completion of the formation of dental roots has its own timing for different teeth:

Since the eruption of third molars does not have a clear timing, it is not possible to determine the specific age of formation of their roots.

The fact that the dental roots are fully formed can only be judged by the results of radiography. The main criteria are the absence of the apical foramen and the presence of a clear periodontal contour.

Thus, the final growth of dental elements and their full maturation ends only by 15-18 years, when maxillofacial apparatus the child reaches adult size.

Before the start of tooth eruption, the intramaxillary development of the tooth crown is completed and the formation of its root begins. This physiological process actively occurs during tooth eruption, and most actively after its eruption.

During the formation of the tooth root, cementum develops. The formation of cement begins in the postembryonic period immediately before tooth eruption and occurs according to the type of periosteal osteogenesis. The structure of cementum is similar to coarse-fibered bone. Cemengoblasts are practically no different in structure from osteoblasts. They form collagen fibers and the ground substance is mineralized to form hydroxyapatite crystals. After the cells develop the substance, cementoblasts turn into cementocytes, the bodies of which are localized in the lacunae, and the processes in the tubules.

Dental pulp develops from the mesenchyme of the dental papilla. This process begins from its apex, where denginoblasts first appear. At the same time, differentiation of mesenchymal cells begins in the central part of the dental papilla. They increase in size and move away from each other. Gradually mesenchyme central departments turns into loose connective tissue, rich in fibroblasts, macrophages (histiogtitis) and other pulpocytes. With the development of the tooth germ, the process of differentiation of the mesenchyme of the dental papilla and its transformation into loose connective tissue expands from its apex to the base. Together this connective tissue grows blood vessels and nerves.

Periodontal formations comes from the mesenchyme of the dental sac simultaneously with the formation of the tooth root. After the formation of cement from the mesenchymal cells of the inner layer of the dental sac, the remaining cells contained in the outer layer give rise to dense periodontal connective tissue. collagen fibers periodontal (pericemental) one end is embedded in the main substance of cement, the other goes to the main substance alveolar bone. Thanks to this, the roots are tightly attached to the wall of the bone socket.

Growth, development, formation of the tooth root and periodontal tissues after eruption averages 1.5-2 years for temporary teeth and 3-5 years for postmortary teeth.

The growth, development and formation of roots has three stages:

1) incomplete root growth - “bell”;

2) unformed root apex;

3) uncovered root apex (Fig. 7).

Rice. 7. Schematic representation of the formation of a tooth root: 1 - stage of incomplete root growth - “bell”, 2 - unformed root apex, 3 - unclosed root apex.

At the first stage of incomplete root growth - the “bell”, the length of the root corresponds to the length of the crown, which is approximately 1/2 of its future length. The walls of the root are thin and expanded on the intra-pulp side, in the direction from anatomical neck tooth to the apex of the root. The sprout zone is massive and clearly limited by the cortical plate of the socket.

For the second stage - unformed root apex, it is characteristic that the root walls are thin, parallel to each other, the root canal is wide, expands towards the apex and passes into the growth zone, which is radiologically represented by rarefaction bone tissue with a clear limitation along the periphery by the cortical plate of the alveoli.

In the third stage - the unclosed root apex, the canal walls are formed, the canal narrows at the apical foramen, the apical foramen is wide, the germinal zone near the apex is absent, and in place of the germinal zone, the periodontal fissure is slightly expanded.

Phylogenetically, the root arose later than the stem and leaf - in connection with the transition of plants to life on land and probably originated from root-like underground branches. The root has neither leaves nor buds arranged in a certain order. It is characterized by apical growth in length, its lateral branches arise from internal tissues, the growth point is covered with a root cap. The root system is formed throughout life plant organism. Sometimes the root can serve as a storage site for nutrients. In this case, it changes.

Types of roots

The main root is formed from the embryonic root during seed germination. Lateral roots extend from it.

Adventitious roots develop on stems and leaves.

Lateral roots are branches of any roots.

Each root (main, lateral, adventitious) has the ability to branch, which significantly increases the surface of the root system, and this contributes to better strengthening plants in the soil and improving its nutrition.

Types of root systems

There are two main types of root systems: taproot, which has a well-developed main root, and fibrous. The fibrous root system consists of a large number of adventitious roots, equal in size. The entire mass of roots consists of lateral or adventitious roots and has the appearance of a lobe.

The highly branched root system forms a huge absorbent surface. For example,

• the total length of winter rye roots reaches 600 km;
• length of root hairs - 10,000 km;
• the total root surface is 200 m2.

This is many times the area of ​​the aboveground mass.

If the plant has a well-defined main root and adventitious roots develop, then a mixed type root system (cabbage, tomato) is formed.

External structure of the root. Internal structure of the root

Root zones

Root cap

The root grows in length from its apex, where the young cells of the educational tissue are located. The growing part is covered with a root cap, which protects the root tip from damage and facilitates the movement of the root in the soil during growth. The latter function is carried out due to the property of the outer walls of the root cap being covered with mucus, which reduces friction between the root and soil particles. They can even push soil particles apart. The cells of the root cap are living and often contain starch grains. The cells of the cap are constantly renewed due to division. Participates in positive geotropic reactions (direction of root growth towards the center of the Earth).

Cells of the division zone are actively dividing, the length of this zone is different types and different roots of the same plant are not the same.

Behind the division zone is an extension zone (growth zone). The length of this zone does not exceed a few millimeters.

As linear growth completes, the third stage of root formation begins—its differentiation; a zone of cell differentiation and specialization (or a zone of root hairs and absorption) is formed. In this zone, the outer layer of the epiblema (rhizoderm) with root hairs, the layer primary cortex and the central cylinder.

Root hair structure

Root hairs are highly elongated outgrowths of the outer cells covering the root. The number of root hairs is very large (per 1 mm2 from 200 to 300 hairs). Their length reaches 10 mm. Hairs form very quickly (in young apple tree seedlings in 30-40 hours). Root hairs are short-lived. They die off after 10-20 days, and new ones grow on the young part of the root. This ensures the development of new soil horizons by the roots. The root continuously grows, forming more and more new areas of root hairs. Hairs can not only absorb ready-made solutions of substances, but also contribute to the dissolution of certain soil substances and then absorb them. The area of ​​the root where the root hairs have died is able to absorb water for a while, but then becomes covered with a plug and loses this ability.

The hair shell is very thin, which facilitates the absorption of nutrients. Almost the entire hair cell is occupied by a vacuole, surrounded by a thin layer of cytoplasm. The nucleus is at the top of the cell. A mucous sheath is formed around the cell, which promotes the gluing of root hairs to soil particles, which improves their contact and increases the hydrophilicity of the system. Absorption is facilitated by the secretion of acids (carbonic, malic, citric) by root hairs, which dissolve mineral salts.

Root hairs also play a mechanical role - they serve as support for the root tip, which passes between the soil particles.

Under a microscope, a cross section of the root in the absorption zone shows its structure at the cellular and tissue levels. On the surface of the root there is rhizoderm, under it there is bark. The outer layer of the cortex is the exodermis, inward from it is the main parenchyma. Its thin-walled living cells perform a storage function, conducting nutrient solutions in a radial direction - from the suction tissue to the vessels of the wood. They also contain the synthesis of a number of vitally important substances for the plant. organic matter. Inner layer cortex - endoderm. Nutrient solutions entering the central cylinder from the cortex through endodermal cells pass only through the protoplast of cells.

The bark surrounds the central cylinder of the root. It borders on a layer of cells that retain the ability to divide for a long time. This is a pericycle. Pericycle cells give rise to lateral roots, adventitious buds and secondary educational tissues. Inward from the pericycle, in the center of the root, there are conductive tissues: bast and wood. Together they form a radial conductive bundle.

The root vascular system conducts water and minerals from the root to the stem (upward current) and organic matter from the stem to the root (downward current). It consists of vascular-fibrous bundles. The main components of the bundle are sections of phloem (through which substances move to the root) and xylem (through which substances move from the root). The main conducting elements of phloem are sieve tubes, xylem is trachea (vessels) and tracheids.

Root life processes

Transport of water in the root

Absorption of water by root hairs from the soil nutrient solution and conduction of it in a radial direction along the cells of the primary cortex through passage cells in the endoderm to the xylem of the radial vascular bundle. The intensity of water absorption by root hairs is called suction force (S), it is equal to the difference between osmotic (P) and turgor (T) pressure: S=P-T.

When osmotic pressure is equal to turgor (P=T), then S=0, water stops flowing into the root hair cell. If the concentration of substances in the soil nutrient solution is higher than inside the cell, then water will leave the cells and plasmolysis will occur - the plants will wither. This phenomenon is observed in conditions of dry soil, as well as with excessive application of mineral fertilizers. Inside the root cells, the suction force of the root increases from the rhizoderm towards the central cylinder, so water moves along a concentration gradient (i.e. from a place with a higher concentration to a place with a lower concentration) and creates root pressure, which raises the column of water through the xylem vessels , forming an ascending current. This can be found on leafless trunks in the spring when the “sap” is collected, or on cut stumps. The flow of water from wood, fresh stumps, and leaves is called “crying” of plants. When the leaves bloom, they also create a suction force and attract water to themselves - a continuous column of water is formed in each vessel - capillary tension. Root pressure is the lower driver of water flow, and the suction force of the leaves is the upper one. This can be confirmed using simple experiments.

Absorption of water by roots

Target: find out the basic function of the root.

What we do: plant grown on wet sawdust, shake off its root system and lower its roots into a glass of water. Pour a thin layer over the water to protect it from evaporation. vegetable oil and mark the level.

What we see: After a day or two, the water in the container dropped below the mark.

Result: consequently, the roots sucked up the water and brought it up to the leaves.

You can also do one more experiment to prove the absorption of nutrients by the root.

What we do: cut off the stem of the plant, leaving a stump 2-3 cm high. We put a rubber tube 3 cm long on the stump, and on the upper end we put a curved glass tube 20-25 cm high.

What we see: The water in the glass tube rises and flows out.

Result: this proves that the root absorbs water from the soil into the stem.

Does water temperature affect the intensity of water absorption by roots?

Target: find out how temperature affects root function.

What we do: one glass should be with warm water(+17-18ºС), and the other with cold (+1-2ºС).

What we see: in the first case, water is released abundantly, in the second - little, or stops altogether.

Result: this is proof that temperature greatly influences root function.

Warm water is actively absorbed by the roots. Root pressure increases.

Cold water is poorly absorbed by the roots. In this case, root pressure drops.

Mineral nutrition

Physiological role minerals very big. They are the basis for the synthesis of organic compounds, as well as factors that change physical state colloids, i.e. directly affect the metabolism and structure of the protoplast; act as catalysts for biochemical reactions; affect cell turgor and protoplasm permeability; are centers of electrical and radioactive phenomena in plant organisms.

It has been established that normal plant development is possible only if there are three non-metals in the nutrient solution - nitrogen, phosphorus and sulfur and four metals - potassium, magnesium, calcium and iron. Each of these elements has an individual meaning and cannot be replaced by another. These are macroelements, their concentration in the plant is 10 -2 -10%. For normal development plants need microelements, the concentration of which in the cell is 10 -5 –10 -3%. These are boron, cobalt, copper, zinc, manganese, molybdenum, etc. All these elements are present in the soil, but sometimes in insufficient quantities. Therefore, mineral and organic fertilizers are added to the soil.

The plant grows and develops normally if the environment surrounding the roots contains all the necessary nutrients. This environment for most plants is soil.

Breathing of roots

For normal growth and development of the plant, it is necessary that the root receives Fresh air. Let's check if this is true?

Target: Does the root need air?

What we do: Let's take two identical vessels with water. Place developing seedlings in each vessel. Every day we saturate the water in one of the vessels with air using a spray bottle. Pour a thin layer of vegetable oil onto the surface of the water in the second vessel, as it delays the flow of air into the water.

What we see: After some time, the plant in the second vessel will stop growing, wither, and eventually die.

Result: The death of the plant occurs due to a lack of air necessary for the root to breathe.

Root modifications

Some plants store reserve nutrients in their roots. They accumulate carbohydrates, mineral salts, vitamins and other substances. Such roots grow greatly in thickness and acquire an unusual appearance. Both the root and the stem are involved in the formation of root crops.

Roots

If reserve substances accumulate in the main root and at the base of the stem of the main shoot, root vegetables (carrots) are formed. Plants that form root crops are mostly biennials. In the first year of life, they do not bloom and accumulate a lot of nutrients in the roots. On the second, they quickly bloom, using the accumulated nutrients and forming fruits and seeds.

Root tubers

In dahlia, reserve substances accumulate in adventitious roots, forming root tubers.

Bacterial nodules

The lateral roots of clover, lupine, and alfalfa are peculiarly modified. Bacteria settle in young lateral roots, which promotes the absorption of gaseous nitrogen from the soil air. Such roots take on the appearance of nodules. Thanks to these bacteria, these plants are able to live in nitrogen-poor soils and make them more fertile.

Stilates

Ramp, which grows in the intertidal zone, develops stilted roots. They hold large leafy shoots on unstable muddy soil high above the water.

Air

Tropical plants living on tree branches develop aerial roots. They are often found in orchids, bromeliads, and some ferns. Aerial roots hang freely in the air without reaching the ground and absorb moisture from rain or dew that falls on them.

Retractors

In bulbous and corm plants, such as crocuses, among the numerous thread-like roots there are several thicker, so-called retractor roots. By contracting, such roots pull the corm deeper into the soil.

Columnar

Ficus plants develop columnar above-ground roots, or support roots.

Soil as a habitat for roots

Soil for plants is the medium from which it receives water and nutrients. The amount of minerals in the soil depends on the specific characteristics of the parent rock, the activity of organisms, the life activity of the plants themselves, and the type of soil.

Soil particles compete with roots for moisture, retaining it on their surface. This is the so-called bound water, which is divided into hygroscopic and film water. It is held in place by the forces of molecular attraction. The moisture available to the plant is represented by capillary water, which is concentrated in the small pores of the soil.

An antagonistic relationship develops between moisture and the air phase of the soil. The more large pores there are in the soil, the better the gas regime of these soils, the less moisture the soil retains. The most favorable water-air regime is maintained in structural soils, where water and air exist simultaneously and do not interfere with each other - water fills the capillaries inside the structural units, and air fills the large pores between them.

The nature of the interaction between plant and soil is largely related to the absorption capacity of the soil - the ability to hold or bind chemical compounds.

Soil microflora decomposes organic matter into simpler compounds and participates in the formation of soil structure. The nature of these processes depends on the type of soil, chemical composition plant residues, physiological properties microorganisms and other factors. Soil animals take part in the formation of soil structure: annelids, insect larvae, etc.

As a result of a combination of biological and chemical processes in the soil, a complex complex of organic substances is formed, which is combined with the term “humus”.

Water culture method

What salts the plant needs, and what effect they have on its growth and development, was established through experience with aquatic crops. The water culture method is the cultivation of plants not in soil, but in aqueous solution mineral salts. Depending on the goal of the experiment, you can exclude a particular salt from the solution, reduce or increase its content. It was found that fertilizers containing nitrogen promote plant growth, those containing phosphorus promote the rapid ripening of fruits, and those containing potassium promote the rapid outflow of organic matter from leaves to roots. In this regard, it is recommended to apply fertilizers containing nitrogen before sowing or in the first half of summer; those containing phosphorus and potassium - in the second half of summer.

Using the water culture method, it was possible to establish not only the plant’s need for macroelements, but also to clarify the role of various microelements.

Currently, there are cases where plants are grown using hydroponics and aeroponics methods.

Hydroponics is the growing of plants in containers filled with gravel. Nutrient solution containing necessary elements, is fed into the vessels from below.

Aeroponics is the air culture of plants. With this method, the root system is in the air and is automatically (several times within an hour) sprayed weak solution nutrient salts.

The process of teething is understood as the complex process of their vertical movement from the place of origin and development inside jaw bones before the crown erupts in the dentition.

The process of teething begins at the time of the final formation of the tooth crown and is accompanied by its further development, growth and development of the jaw bones.
The main changes that occur in the tissues surrounding the tooth during its eruption include (V.L. Bykov, 1998): development of the tooth root; periodontal development; alveolar bone remodeling; changes in the tissues covering the tooth (Fig. 76).

The development of the tooth root is associated with the ingrowth of the epithelial root sheath of Hertwig into the mesenchyme of the dental papilla. Its cells determine the production and development of odontoblasts that produce root dentin. With the reduction of Hertwig's sheath, the cells of the dental sac undergo differentiation and produce cementum over the root dentin.
The development of periodontium is expressed in the growth of its fibers, both from the root cementum and from the alveoli. These processes become more intense immediately before tooth eruption.

Restructuring of the alveolar bone is accompanied by complex processes osteoapposition and osteoresorption. The intensity of alveolar bone restructuring is varied and depends on many factors, including: localization, group affiliation of teeth. When the tooth root forms, it reaches the bottom of the bone alveolus and causes its resorption in the compression zone. At the same time, intensive processes of bone formation continue at the site of contact with the alveolus.

In multi-rooted teeth, bone deposition occurs most intensively in the area of ​​the developing interradicular septum. In single-rooted teeth, the zone of increased bone tissue deposition is the bottom of the socket on the lingual surface.

Resorption of bone tissue during tooth eruption provides a local decrease in the strength properties of the bone and weakens its resistance.

Changes in the tissues covering the erupting tooth. As the tooth approaches the mucous membrane of the oral cavity, regressive changes occur in the connective tissue separating the tooth from the epithelium of the mucous membrane, this is facilitated by the reduced enamel epithelium covering the crown of the tooth (Fig. 76, 1).

Approaching the epithelium lining the oral cavity, the reduced enamel epithelium merges with it (Fig. 76, 3). The latter stretches and breaks through in the central areas (Fig. 76, 4). Through the resulting hole, the crown of the tooth erupts into the oral cavity (Fig. 76, 5). In this case, there is no bleeding, since the crown moves through a canal lined with epithelium.

Having erupted into the dentition, the crown continues to erupt at the same speed until the tooth is established in the correct occlusal relationships with antagonists and neighboring teeth (Fig. 76, 6).

The reduced enamel epithelium remains attached to the enamel in the part where the crown has not erupted; it is called the primary attachment epithelium. It is subsequently replaced by secondary attachment epithelium, which is part of the gum.

In modern literature, there are four main theories that explain the mechanism of teething (V.L. Bykov, 1998):

1. The theory of tooth root growth.
2. Increased hydrostatic pressure in the periapical zone or dental pulp.
3. Restructuring of bone tissue.
4. Periodontal traction.

The eruption and replacement of temporary teeth by permanent ones is a complex physiological process. Signs of correct teething are: consistency, pairing and symmetry.

First, teeth erupt on the lower jaw, then on the upper jaw. Teething is an indicator of the correct development of the child; it is closely related to general condition his health. It should be noted that the process normal eruption teeth are individual, therefore only sharp deviations from natural ones are considered anomalies.

The beginning of teething in the temporary occlusion dates back to the second half of the child’s 1st year of life (Table 4).

Table 4.
Average time for eruption of primary teeth

Teething begins with the formation of dense protrusions on the gums, corresponding to the future crowns of temporary teeth.

At 6-8 months of life, the cutting edges of two central incisors appear on the surface of the gum: first on the lower, then on the upper jaw.

By one year, 4 incisors should erupt in the upper and lower dentition of the child, i.e. 8 teeth in the oral cavity.

By 30 months, the child has formed a temporary bite.

The development of permanent teeth generally resembles the development of primary teeth. The source of formation of the enamel organs of permanent teeth is the dental plate.
The anlages that will give rise to permanent replacement teeth (incisors, canines, premolars) arise as a result of increased proliferation of cells of the dental plate near the enamel organs of temporary teeth and its growth in the form of a replacement dental plate. They are located on the lingual surface of temporary teeth.

Permanent molars do not have temporary predecessors, which is why they are called additional molars. Their initial development differs from the development of permanent replacement teeth.
During the eruption of permanent replacement teeth, destruction and loss of temporary teeth occurs, which also includes progressive resorption of the roots of temporary teeth and their alveoli (Fig. 77).

Due to pressure permanent tooth differentiation of osteoclasts begins on the alveolus of a temporary tooth, which are actively involved in the processes of bone tissue resorption.
The localization of the zones of physiological resorption of the roots of temporary teeth varies depending on the group affiliation of the tooth: in single-rooted teeth it is located in the area of ​​the apex of the tooth on the lingual side, and in multi-rooted teeth - in the zone of root bifructation.

Timing of eruption of permanent teeth proper development of the child coincide with the time of loss of primary teeth (Table 5).

The process of temporary tooth loss occurs synchronously with the process of permanent tooth eruption.

Clinically, after the loss of a temporary tooth, cusps or part of the cutting edge of the erupting permanent teeth are detected.

The eruption of permanent teeth begins with the first permanent molar at 6 years of age. Then, sequentially at the age of 6 - 8 years, the central and lateral incisors erupt.

At 9 - 10 years old, the first premolars erupt, most often followed by canines (10 - 11 years) and second premolars (11 - 12 years).

At 12 - 13 years old, the second permanent molars erupt. Thus, by the age of 12 - 13 years, all temporary teeth are replaced by permanent ones. The final formation of roots is completed by 15 years.

Replacement teeth have a special anatomical structure that facilitates their eruption - a conductive canal, which contains a conductive cord.

The anlage of such a permanent tooth is initially located in a common bone alveolus with its temporary predecessor.

It is subsequently completely surrounded by alveolar bone, with the exception of a small canal containing the remains of the dental plate and connective tissue. Together, these structures help guide the movement of the permanent tooth as it erupts.

Table 5.
Timing of formation and eruption of permanent teeth.

Orthodontics
Edited by prof. IN AND. Kutsevlyak