Tooth enamel - functions, composition and structure. The structure of tooth enamel and the consequences of its destruction

Hard tooth tissues are composed of organic, inorganic substances and water.
By chemical composition enamel consists of 96% inorganic substances, 1% organic substances and 3% water.

Mineral enamel base make up crystals of apatite. In addition to the main thing - hydroxyapatite (75%), enamel contains carbonatapatite (19%), chlorapatite (4.4%), fluorapatite (0.66%). Less than 2% of the mass of mature enamel are non-apatite forms.

The main components of enamel are hydroxyapatite Ca 10 (PO 4) in (OH) 2 and octalcium phosphate - Ca 8 H 2 (PO 4) 6 x 5H 2 0. There may be other types of molecules in which the content of calcium atoms varies from 6 to 14. Molar the Ca / P ratio in hydroxyapatite is 1.67. However, in nature there are hydroxyapatites with a Ca / P ratio from 1.33 to 2.0.
One of the reasons for this is the substitution of Ca in the hydroxyapatite molecule for Cr, Ba, Mg, and other elements.

Of great practical importance is fluorine substitution reaction, as a result of which hydroxyfluoroapatite is formed, which is more resistant to dissolution. It is with this ability of hydroxyapatite that the prophylactic effect of fluorine is associated.

Enamel organic matter consist of proteins, lipids, carbohydrates. Water occupies free space in the crystal lattice and is also located between crystals.

Dentine consists of about 70% inorganic substances in the form of apatites and about 30% organic substances and water. The organic basis of dentin is collagen and a small amount of mucopolysaccharides and fat.

Hardness cement significantly inferior to enamel and partly to dentin. It consists of 66% inorganic substances and 32% organic substances and water. Of the inorganic substances, salts of phosphate and calcium carbonate predominate. Organic matter is represented mainly by collagen.

General information about the periodontium

A combination of several surrounding and supporting tissues of the tooth, related in their development, topography and function.
includes the gum, cement, periodical ligament and the alveolar bone proper. It can be conditionally divided into two large groups: attachment apparatus and gum.

The chemical composition of tooth enamel

Tooth enamel is formed from ameloblasts. During the development period, its cyclical mineralization occurs. Crystallization of calcium phosphate compounds during mineralization and subsequent crystal growth is defined as pre-eruptive enamel maturation. At the same time, growth lines formed as a result of uneven mineralization of the enamel are preserved. Each crystal of enamel has a hydration layer due to which ion exchange is carried out.

After the eruption of teeth, porosity and heterogeneity are leveled due to the post-eruptive maturation of the enamel. Formed tooth enamel is a non-regenerating tissue that does not contain cells or cellular elements.
Tooth enamel is the hardest tissue in the human body.

On average, its thickness varies between 2.8 and 3.0 mm, depending on the degree of maturity, chemical composition and topography.

The hardness of the enamel ranges from 250 KHN (Knoop-hardness numbers) at the enamel-dentin border to 390 KHN at its surface.

The main structural element of tooth enamel is inorganic substances, and the data on their amount differ depending on the analysis method and sample (93-98% of the mass). The second by volume component of enamel is water: data on its amount fluctuate between 1.5 and 4% of the mass. Enamel also contains organic compounds such as proteins and lipids.

The composition of the enamel is influenced by nutrition, age and other factors. Its constituent parts are apatite of several types, the main of which is hydroxyapatite. In addition, over 40 microelements have been identified in the tooth enamel. Some of these trace elements enter the oral cavity only as a result of dental interventions, others (for example, tin and strontium) can be considered as a result of environmental influences.

The composition of the enamel differs depending on its topography, due to fluctuations in the concentration of individual elements. Thus, the concentration of fluorides, iron, zinc, chlorine and calcium decreases from the enamel surface towards the enamel-dentin border. The concentration of fluorides in this area increases, and the concentration of water, carbonate, magnesium and sodium decreases from the enamel-dentin border to the enamel surface.
Apparently, the content of magnesium and carbonate affects the density of the enamel.
In areas with a high concentration of magnesium, near the dentin cusps and directly under the central fissure of the teeth, there is a lower density than, for example, in the mineralized areas of the buccal and lingual surfaces.

Calcium and phosphorus, as an apatite compound, are contained in the form of crystals in a ratio of 1: 1.2 (Ca10-xPO6-x) * X2 * H2O. Internal displacement reactions can lead to the formation of fluoroapatite or hydroxyapatite fluoride. They also admit the possibility of carbonate formation in the enamel minerals. The resulting apatite is less resistant to caries than hydroxy-apatite. Along with the indicated compounds, a number of calcium-phosphate compounds, for example, octacalcium phosphate, have been revealed in small amounts in enamel.

There are two forms of water in tooth enamel. The first is bound water (hydration shell of crystals), the second is free water located in microspaces.
Free water can evaporate when heated, but the enamel is able to absorb water when moisture enters. This property can be used as an explanation for certain physical phenomena in the occurrence of caries or its prevention.
Tooth enamel functions as a "molecular sieve" and the enamel fluid serves as a carrier of molecules and ions.

A smaller part of the organic matter of mature enamel consists of protein (= 58%), lipids (= 48%) and insignificant amount carbohydrates, citrate and lactate. Most of the organic matter is found in the inner third of the enamel shell in the form of enamel bundles.

Enamel is the protective coating that covers the anatomical crown of the teeth. In different areas, it has a different thickness: for example, in the area of ​​the bumps it is thicker (up to 2.5 mm), and in the cement-enamel joint it is thinner.

Despite the fact that it is the most mineralized and hardest tissue in the body, at the same time, it is very fragile.

Enamel is the most hard cloth in the human body, which is explained by the high content of inorganic substances - up to 97%. There is less water in the tooth enamel than in other organs, 2-3%. The hardness reaches 397.6 kg / mm² (250-800 Vickers). The thickness of the enamel layer differs in different parts of the coronal part of the tooth and can reach 2.0 mm, while at the neck of the tooth it disappears.

Proper care of tooth enamel is one of the key points of a person's personal hygiene.

The enamel of permanent teeth is a translucent tissue, the color of which varies from yellowish to gray-white shades. Due to this very translucency, the color of the tooth depends on the color of the dentin more than on the color of the enamel. This is why almost everyone modern methods teeth whitening aims to brighten the dentin.

As for milk teeth, here the enamel looks whiter due to the high content of opaque crystalline forms.

Chemical composition

Enamel has next lineup: inorganic substances - 95%, organic - 1.2%, water - 3.8%. A more detailed one will be presented below. chemical composition tooth enamel.

Tooth enamel consists of many types of apatite, the main of which is hydroxyapatite Ca10 (PO4) 6 (OH) 2. The composition of the enamel inorganic substance is presented: hydroxyapatite - 75.04%, carbonapatite - 12.06%, chlorapatite - 4.39%, fluorapatite - 0.663%, calcium carbonate - 1.33%, magnesium carbonate - 1.62%. In the composition of chemical inorganic compounds, calcium 37%, and phosphorus - 17%. The Ca / P ratio largely determines the condition of the tooth enamel. It is impermanent and can change from action various factors moreover, it can vary within one tooth.
More than 40 microelements have been identified in the enamel of the teeth; their location in the enamel is uneven. In the outer layer, a high content of fluorine, lead, iron, zinc was revealed with a lower content of sodium, magnesium, carbonates. Strontium, copper, aluminum and potassium have a more uniform arrangement over the layers.

In enamel, organic matter is represented by proteins, lipids and carbohydrates. The total amount of proteins is 0.5%, lipids - 0.6%. Also, citrates (0.1%) and very few polysaccharides (0.00165%) were found in the enamel.

Tooth enamel structure

Enamel prisms are the main structural formation of enamel, their diameter is only 4-6 microns, but due to their sinuous shape, the length of the prism exceeds the thickness of the enamel. The enamel prisms, gathering in beams, form s-shaped bends. Due to this, dark and light stripes are found on the enamel thin sections: in one area the prisms are cut in the longitudinal direction, and in the other - in the transverse direction (Gunther-Schroeger stripes).

On the thin sections of the enamel, you can see lines going in an oblique direction and reaching the surface of the enamel - these are the Retzius lines, they are especially clearly visible when the enamel is treated with acid. Their formation is associated with the cyclical nature of enamel mineralization in the process of its formation. And just in these areas mineralization is less pronounced, therefore, during acid etching in the Retzius lines, the earliest and most pronounced changes occur.

The enamel prism has cross striation, which reflects the daily rhythm of the deposition of mineral salts. In cross-section, the enamel prism has an arcade-like shape or resembles a scale in shape, but it can be round, hexagonal or polygonal. The interprismatic enamel substance consists of the same crystals as the prism itself, but differs in their orientation. The organic matter of the enamel has the form of the finest fibrillar structures, which, according to the existing opinion, determine the orientation of the crystals of the enamel prism.
In the enamel of the tooth, there are such formations as plates, tufts and spindles. The plates (they are also called lamellae) penetrate into the enamel to a considerable depth, the bundles - to a smaller one, the spindles (processes of odontoblasts) enter the enamel through the dentine-enamel joint.

The smallest structural unit of enamel is an apatite-like substance that forms enamel prisms. In section, these crystals have a hexagonal shape, from the side they look like small rods.

Enamel crystals are the largest crystals of human hard tissue. Their length is 160nm, width is 40-70nm, and thickness is 26nm. Crystals in the enamel prism adjoin tightly to each other, the space between them does not exceed 2-3 nm, in the core of the prism the crystals are directed parallel to the axis of the prism. In the interprismal substance, the crystals are less ordered and directed perpendicular to the axis of the enamel prism.

Each crystal has a 1nm thick hydration shell. and is surrounded by a layer of proteins and lipids.
except bound water, which is part of the hydration shell, there is free water in the enamel microspaces. The total volume of water in the enamel is 3.8%.

On the surface of the crown of a human tooth, it is often found thin layer prism-free enamel. Its thickness is 20-30 microns and the crystals in it adhere tightly to each other, being parallel to the surface. Prism-free enamel is often found in milk teeth and fissures, as well as in the necks of the teeth in adults.

Tooth enamel functions

- Protection of dentin and pulp from external mechanical, chemical and thermal irritants.
- Due to its high hardness and strength, enamel allows teeth to fulfill their purpose - biting and grinding food.

Anatomical and histological structure

The main structural formation of enamel is an enamel prism (4-6 microns in diameter), consisting of hydroxyapatite crystals. The enamel interprismatic substance consists of the same crystals as the prism, but they differ in orientation. The outer layer of enamel and the inner layer at the dentino-enamel border do not contain prisms (prism-free enamel). These layers contain small crystals and larger ones - lamellar.

Also in the enamel there are enamel plates (lamellae) and beams, which represent insufficiently mineralized interprismatic substance. They pass through the entire thickness of the enamel.

The next structural element of enamel is enamel spindles - bulbous thickenings of odontoblast processes penetrating through dentinoenamel joints.

Personal hygiene

Located in oral cavity, in which the natural environment is alkaline, tooth enamel also needs to maintain an alkaline balance. After each meal, with the breakdown of carbohydrates, under the influence of a variety of bacteria that process food residues and secrete acids, alkaline environment is violated. The acid eats away at the enamel and leads to caries, for the elimination of the irreversible consequences of which it is necessary to install fillings.

To prevent tooth decay, after each meal, you should at least rinse your mouth with water, or better with a special mouthwash, brush your teeth or at least chew chewing gum sugarless.

Caries susceptibility of tooth enamel

Caries susceptibility or the resistance of the tooth surface depends on the following factors.
1. Property of the anatomical surface of the tooth: in natural fissures and in the spaces between teeth, there are favorable conditions for long-term fixation of dental plaque.
2. Saturation of tooth enamel with fluoride: the resulting fluorapatites are more resistant to acids.
3. Oral hygiene: timely removal of dental plaque prevents further development caries.
4. Diet Factor: Soft, carbohydrate-rich foods promote plaque formation. The amount of vitamins and minerals also affects general state the body and especially saliva.
5. Quality and quantity of saliva: A small amount of viscous saliva promotes the attachment of bacteria to the pellicle and the formation of dental plaque (see. Dental plaque). The buffering properties of saliva (which neutralize acids) and the amount of immunoglobulins and other protective factors in saliva have a very important effect on enamel caries resistance (see Saliva).
6. Genetic factor.
7. General condition of the body.