Tooth enamel: tooth structure, main characteristics of the enamel layer

From this article you will learn:

structural components of enamel,
the structure of its organic and inorganic matrix,
electron microscopy images.

Tooth enamel (enamelum) is the outer shell of the crown of the tooth, representing the hardest tissue in the human body. This hardness is explained by the fact that 95-97% of tooth enamel consists of mineral components (mainly calcium phosphate in the form of hydroxyapatite crystals). Organic matter accounts for only 1-2%, plus about 2-3% water. The strongest are the surface layers of enamel - especially on the occlusal surfaces of the teeth, and towards the enamel-dentin border, as well as when approaching the neck of the tooth - its hardness decreases.

The hardness of enamel is 397.6 kg/mm², which is comparable to quartz. Such hardness allows it to withstand extreme mechanical loads, but on the other hand, it makes it very fragile. The enamel of human teeth does not crack or chip only due to the presence under the enamel layer - a layer of dentin, which has a moderate elasticity coefficient. However, despite its hardness, enamel has good permeability to calcium and fluoride ions contained in saliva (or toothpastes and mouthwashes), as well as to pigments contained in food and drinks.

Structure and development of tooth enamel –

Tooth enamel can have different shades - from yellow to various shades of gray and white, which depends on its transparency coefficient. The more transparent the enamel, the more the underlying layer of dentin, which is physiologically yellow, will be visible through it. In addition, the enamel may have a blue tint - at the cutting edges of the incisors (where there is no underlying dentin layer), as well as at baby teeth. The transparency of enamel depends on the degree of its mineralization and homogeneity, which is associated with the ratio of its organic and inorganic matrices. Transparency also depends on the thickness of the enamel layer.

The thickness of the enamel will vary on different surfaces of the tooth crown. For example, in permanent teeth, the thickness of the enamel ranges from 1.7 to 2.5 mm in the area of the chewing cusps of the molars, and to only 0.01 mm in the cervical part of the tooth (where the enamel borders the root cement). Thus, the closer to the neck of the tooth, the less its thickness will decrease. In baby teeth, the thickness of the enamel will be two times less than in permanent teeth, not exceeding 0.8-1.0 mm.

Composition of tooth enamel

Dental enamel is the most durable, wear-resistant and hard component in the human body. It represents the outer or surface layer of the teeth, completely covers its coronal and partially cervical part, and also performs protective functions. The main characteristics of enamel include:

The color of tooth enamel varies from white to yellowish, and it can change shade (color) depending on a person’s dietary habits or bad habits.
The thickest areas of enamel cover the chewing molars in the area of their anatomical tubercles; their thickness varies between 2.3-3.5 mm;
The thinnest areas of tooth enamel are localized in paroxysmal areas (places of contact in their lateral projection), here the thickness of the protective layer reaches approximately 1.3 mm;
The enamel that covers all the teeth in the human oral cavity is not capable of regeneration, because there are no living cellular structures in the tissues of this protective layer;
Depending on the characteristics of each person’s body, up to 95% of the chemical composition of tooth enamel is presented in the form of mineral compounds. The remaining percentage is divided between water and organic matter in approximately a 2:1 ratio, respectively. In addition, depending on the percentage of mineral content of tooth enamel, it can be more or less transparent (the higher the percentage of minerals, the more transparent the enamel becomes).

Development of cement (cementogenesis) –

The formation of cement occurs in two stages. At stage 1, the synthesis of an organic matrix (cementoid or primary cement) occurs. At stage 2, mineralization of the cementoid occurs - with the formation of secondary cement. Let's look at how this all happens.

First, the cells of the dental papilla (as a result of the inducing influence of the epithelial sheath) differentiate into root odontoblasts, which form root dentin. Next, the cementoblasts of the dental sac begin to produce the organic cement matrix (cementoid), as well as collagen fibers and the main amorphous substance. As a result, cementoid is deposited on the surface of the root dentin - in the form of a highly mineralized structureless “Hopewell-Smith” layer (this layer contributes to the strong attachment of cement to the root dentin).

Next, primary cementum, which does not contain cells, is the first to form. It is slowly deposited as the tooth erupts, covering 2/3 of the root surface (closer to the crown of the tooth). Next, mineralization of the cementoid occurs, which is associated with the deposition of phosphates and calcium carbonate. This process occurs in waves, and then in the apical third of the root and the furcation zone, a cell is formed, i.e. secondary cement. We hope that our article was useful to you!

Sources:

1. Higher professional education of the author in dentistry, 2. The European Academy of Paediatric Dentistry (EU), 3. “Anatomy of human teeth” (Gayvoronsky, Petrova). 4. “Therapeutic dentistry” (Politun, Smolyar), 5. “Histology of the oral cavity” (Glinkina V.V.).

Other components in the enamel

In addition to the already mentioned main components of the enamel layer of the tooth, its chemical composition also contains a set of other components:

Neonatal line - present exclusively on baby teeth, it looks like a dark-colored stripe (almost black). This line is located in the area of contact between two types of enamel, the first of which was formed before the baby was born, and the second after.
Bundles and plates of dental enamel are special enamel formations containing prisms of a hypomineralized type, between which the interprismatic substance consists of the same material. It is noteworthy that the molecular structure of this material involves a large number of protein compounds. Many dentists are of the opinion that through the mentioned bundles and plates, various microorganisms penetrate into the enamel from the oral cavity, making their way to deeper dental tissues, causing caries, etc.
Gunter-Schräger stripes are lines that stand out on the tooth enamel in a darker or lighter shade, the width of which does not exceed 100 microns. They are located perpendicular to the surface of the enamel layer and are formed as a result of opening its prisms.
Retzius lines - in shape they resemble arches offset from the central one, located symmetrically in relation to each other. When cut across a tooth , these formations resemble rings inside a tree trunk. The formation of Retzius lines corresponds to different periods of mineralization of the enamel layer.

Teething

This stage is characterized by the active movement of temporary teeth from their places of origin inside the jaw until the crown completely exits into the oral cavity. This process is accompanied by active changes in the surrounding tissues, increased development of the root part, restructuring of the alveolar bone structure, as well as the formation and strengthening of the periodontium.

The first temporary teeth, which are usually the lower central incisors, erupt at the age of 5-6 months. Behind them appear the upper antagonists, other incisors and first primary molars. The last to erupt are the lower and upper canines. Typically the process lasts from 4-6 months to 2-2.5 years. With late eruption, the timing of the appearance of temporary teeth shifts from 8-10 months. up to 3.5 years.

Features of the structure of the enamel of baby teeth

The main distinguishing feature of the enamel layer of children's teeth is that it is less durable and also much thinner than the enamel of permanent teeth. This is explained by the lower content of mineral compounds in teeth in relation to water and organic substances. Considering these features, if you examine baby teeth and their enamel layer under a microscope, you will notice the following differences:

Due to the fact that the service life, as well as periods of mineralization and the tendency towards this process are shorter, the Retzius lines are much less pronounced in the structure of primary dental units.
If in permanent teeth enamel prisms are located apically, then in milk teeth their direction is completely different, they are located horizontally.
In children's primary teeth, the final enamel layer is much less pronounced; prisms are clearly visible on its surface, while its structure is much more porous, with microscopic cracks present.

Under the influence of each of these features, tooth enamel in children is more susceptible to wear and damage. For this reason, children develop caries much more often and it progresses faster, which is why it is important to visit the dentist regularly and have their teeth treated in a timely manner.

Topography of cement in the area of the tooth neck –

There are 3 options for connecting cement and tooth enamel. It can be either “joint to joint”, or the cement may extend slightly onto the enamel, or there may be a strip of exposed dentin (Fig. 8). Studies have shown that enamel and cement border “joint to joint” - only in 30% of cases. At the same time, 60% of teeth have a layer of cement on the edge of the tooth enamel (Fig. 9), and a strip of exposed dentin is found in 10% of cases.

Variants of the enamel-cementum boundary (scheme and histology) –

Fig. 8, where 1 – enamel, 2 – dentin, 3 – cement, and options for joining enamel and cement (I – cement partially touches the tooth enamel; II – cement joins the enamel, III – cement does not reach the tooth enamel).

Types of damage to tooth enamel

Over the course of life, even if you provide your teeth with proper care and follow the rules of oral hygiene prescribed by dentists, the enamel layer gradually wears out and is destroyed. This contributes to the occurrence of various diseases of the oral cavity; it is influenced by the food a person eats, etc.

Among the main causes of damage and destruction of tooth enamel, dentists identify:

Erosion is damage to the enamel layer, and then dentin, which is not associated with carious lesions of the teeth . The essence of this pathological process lies in disorders of mineral metabolism. As a result, disturbances occur in the crystalline structure of the enamel, which is manifested by its focal thinning and destruction. Externally, erosions look like local darkening on a round or oval tooth. The occurrence of erosions is provoked by the consumption of foods with high acidity levels, pathologies of the gastrointestinal tract, the use of certain medications, and the use of aggressive tooth powder or paste.
Excessive sensitivity of tooth enamel - this disorder is especially pronounced in the form of painful sensations when the teeth cold or hot food, drinks, and even as a result of contact with cool air. The sensitivity of tooth enamel develops due to its thinning under the influence of the factors already described above. A thinned enamel layer puts teeth at increased risk of caries and other dental pathologies.
Necrosis - this term characterizes multiple lesions of the hard tissues of the tooth, especially the enamel layer and dentin. The pathological process is initially expressed in the appearance of small light spots on the surface of the tooth , which subsequently darken and deepen. The progression of pathology threatens tooth destruction and is accompanied by a number of other oral diseases. The main reasons for the development of necrosis include gastrointestinal diseases, hormonal imbalances, metabolic disorders in the body, and work in hazardous industries.

Caries is a carious lesion that threatens teeth , primarily affecting the enamel layer of the structure , gradually destroying it and spreading to deeper tissues. There are many reasons for the development of caries, from non-compliance with the rules of oral hygiene and irregular tooth brushing, to pathologies of the structures of the oral cavity, diseases of the gastrointestinal tract and metabolic disorders. If you start caries treatment at the stage when the lesions have affected only the enamel layer, you can only get by installing a filling or even restoring the enamel. But progressive caries is dangerous for teeth due to destruction, which may lead to the need for its complete removal.
Mechanical damage - due to the fact that the main function of the enamel layer is to provide protection to the teeth , it primarily suffers from the effects of external adverse factors. Mechanical damage to the enamel includes cracks and other violations of its integrity due to blows, bruises, eating too hard food, etc. If the enamel of at least one tooth has been subjected to aggressive mechanical action, you should consult a doctor for an examination and, if necessary, subsequent treatment.
Wedge-shaped defect – this term characterizes the pathological process in which the area of the dental neck is exposed. In such cases, the thinnest and most vulnerable areas of the enamel layer, located at the base of the teeth, are negatively affected. In addition to visible receding gums, damage to the enamel is indicated by a change in its color, as well as an acute reaction to hot and cold.

Organic and inorganic enamel matrices –

Tooth enamel is quite unique, and in many ways is absolutely unlike other hard tooth tissues. Firstly, enamel is the only dental tissue that comes from the ectoderm (the development of all others is associated with the mesoderm). Secondly, if the organic matrix of other dental tissues is formed mainly by collagen fibers, then the organic enamel matrix does not contain collagen and is formed by the so-called “enamel proteins”. Thirdly, hydroxyapatite crystals in tooth enamel are much larger than in other mineralized tooth tissues.

The last point is that other hard dental tissues continue to be synthesized by cells during the life of an individual (odontoblasts and cementoblasts, respectively), but in mature enamel there are no cellular elements, and therefore, after its maturation, no growth can occur. This is due to the resorption of enameloblast cells during the process of enamelogenesis.

1) Organic matrix of tooth enamel –

We have already said above that the organic matrix of tooth enamel consists of non-collagenous proteins (proteins), which are the product of secretion of enameloblasts, and they are called the term “enamel proteins”. The function of the organic matrix is to adsorb minerals, resulting in the formation of apatite crystals around the enamel proteins. However, as the enamel matures, the organic matrix is almost completely lost.

All enamel proteins are conventionally divided into four types - 1) enamelins and 2) amelogenins, 3) ameloblastins and 4) taftelins. Enamelins are acidic glycoproteins with a large molecular weight, which are characterized by a high content of glycine, serine, aspartic and gamma-carboxyglutamic acids. In turn, amelogenins are hydrophilic glycoproteins (2 times less molecular weight), enriched with proline, leucine, histidine and gamma-carboxyglutamic acid.

Ameloblastins and taftelins occur only during the period of amelogenesis (enamel formation). In addition to enamelins and amelogenins, the organic matrix of mature enamel also contains glycosaminoglycans, proteoglycans, as well as various classes of lipids. All these organic substances are one way or another involved in the processes of mineralization of the organic matrix (protein calcification).

2) Inorganic enamel matrix –

According to research by E.V. Borovsky, tooth enamel contains the following inorganic compounds (average values):

hydroxyapatite [Ca10(PO4)6(OH)2] – 75.04%
carbonate-apatite [Ca10(PO4)6(CaCO3)2] – 12.06%,
chlorapatite [Ca10(PO4)6(Cl)2] – 4.39%,
fluorapatite [Ca10(PO4)6(F)2] – 0.66%,
calcium carbonate – 1.33%,
magnesium carbonate – 1.62%.

These compounds contain about 37% calcium and about 17% phosphorus. Thus, the main mineral salt in the composition of enamel (as well as dentin and tooth root cement) is “calcium phosphate” in the form of apatite crystals, which will additionally contain either hydroxyl residues, or a carbonate group, or chlorine or fluorine. But in addition to these elements and compounds, lead, zinc, aluminum, copper, molybdenum, sodium, strontium, sulfur, tin and titanium are also included in enamel apatite crystals (in extremely small quantities).

In the superficial layers of enamel there are more apatite crystals containing fluorine, lead or zinc, but in the deep layers of enamel their content will be less. At the same time, on the contrary, there will be more apatite crystals containing sodium, magnesium or carbonates in the area of the enamel-dentin junction, and fewer in the surface layers of enamel (24stoma.ru). This "ion gradient" has a certain meaning. For example, apatites with inclusions of sodium, magnesium or carbonates are highly resistant to splitting along the enamel-dentin junction.

More superficially located apatites with inclusions of fluorine, lead and zinc - thanks to these elements, they acquire special strength and resistance to acids. Enamel containing such apatite crystals (such as fluorapatite) is significantly resistant to caries, because fluorapatite begins to degrade at a lower pH value compared to ordinary hydroxyapatite. For example, for ordinary hydroxyapatite the critical pH value will be 5.5, but for fluorapatite – pH 4.6.

In addition, it should be noted that enamel hydroxyapatite crystals (compared to dentin and cement) will have a significantly larger size. For example, in dentin, hydroxyapatite crystals are 20 nm long, 18-20 nm wide, and 3.5 nm thick, which indicates their small size and needle-shaped shape. In turn, in enamel, hydroxyapatite crystals look like hexagonal plates with a length of about 200 nm (but crystals with a size of 500 to 600 nm can also be found), a width of 40–90 nm and an average thickness of 25–40 nm.

Important: due to the absence of enameloblasts in mature enamel, enamel does not have the ability to regenerate (like tooth root cement or dentin). However, despite this, the inorganic enamel matrix is in the process of constant remodeling - thanks to the ongoing processes of mineralization / demineralization. Moreover, the entry of calcium, phosphorus, and fluorine ions into the enamel occurs not only from saliva, but also from the dentin and pulp of the tooth (thanks to the so-called “enamel spindles”).

Strengthening tooth enamel

Today in dental practice there are many effective ways to strengthen the enamel, which allows you to maintain its integrity and prevent destruction and diseases of the dentition. At the same time, methods of strengthening and protecting the enamel layer are divided into two groups, the first are intended for adults, the second for children.

Resorption and preparation for shift

At the age of 5-6 years, the process of completely replacing the temporary bite begins. This period begins immediately after the resorption of milky roots and the beginning of the growth of permanent rudiments. Temporary teeth begin to undergo resorption and ejection from the alveoli. Odontoclasts, which carry out demineralization and intracellular destruction, as well as pulp tissues that secrete osteoclast-like cells, which are responsible for the destruction of dentin and predentin from the internal side, actively participate in the process. Removal of the crown of temporary teeth, as a rule, occurs under the influence of chewing pressure. The root remaining in the hole undergoes a natural process of destruction and resorption. The location of the crown is quickly epithelialized due to granulation tissue.

The process of loss of temporary teeth occurs symmetrically on both jaws and ends with the appearance of permanent teeth. The individual nature of its course is determined genetically.

Strengthening baby teeth enamel

As was said earlier in relation to baby teeth, their enamel is more vulnerable. To protect it, saving the child from premature loss of dental units and problems in the future, doctors perform the following actions to provide temporary protection:

Fluoridation involves treating teeth with special fluoride-based compounds; it is recommended to repeat this procedure 2-3 times a year.
Fissure sealing - the dentist performs the procedure of filling the recesses and grooves of chewing teeth with temporary filling material, protecting the dental structures from the negative effects of harmful microorganisms and other unfavorable factors.
Application gels and preventive mouth guards for teeth - the method is based on enriching the enamel layer with useful components (fluorine, calcium, vitamins) through the use of special products.

Stabilization

This period is characterized by a complete stop of all processes of tissue formation and development. The crown and root reach the required shape, size and level of strength that allows them to perform their basic functions.

The period of stabilization of primary teeth lasts on average 2.5-3 years. At this time, it is important to ensure optimal chewing load on the bite, which will ensure the normal development of facial and other muscles, as well as periodontal tissues and jaw bones. If a child has caries or other diseases, it is during this period that treatment of temporary teeth will be most effective in terms of preserving them, preventing the spread of infection and ensuring normal conditions for changing the bite.

Strengthening the enamel of molars

There are more methods to preserve molars and maintain the condition of their enamel layer. Firstly, this is due to fewer contraindications for adults. Secondly, molars require long-term strengthening.

The main methods of strengthening the enamel of permanent teeth include:

Drug therapy is based on the use of vitamin complexes containing vitamins of groups B6, B12, D. In addition, the patient is selected drugs that promote better absorption of calcium and fluoride by the body.
Special gels and oral hygiene products – this technique uses specialized toothpastes and gels containing components necessary for teeth to strengthen and maintain the condition of the enamel layer. Also, teeth are subjected to unimaginative cleaning in a dental office.
Mineralization and preventive cleaning – mineralization is performed using special means to increase the strength of the enamel and reduce its susceptibility to a number of negative factors. As for cleaning, such procedures are performed by dentists in the clinic using special equipment. During cleaning, plaque and tartar are eliminated , pathogenic bacteria and microorganisms that can harm the enamel layer are removed.
Home prevention - to maintain healthy teeth and enamel, patients are advised to perform a light massage of the gums, enrich the diet with fresh vegetables and fruits rich in vitamins.

Author: Zhukov M.A.