The upper layer of enamel consists of hydroxyapatite (HA) crystals. Hydroxyapatite is a crystal form of calcium (CA++), hydroxyl (OH), and phosphate (PO43−) ions. Tightly packed crystals form enamel prisms, which are the structural units of enamel.5-7 The upper layer of enamel is denser and more mineralized than its deeper layer, dentin. The structural integrity of enamel prisms, arranged in the enamel rods, also contributes to the contact stability of the structures in the cusps of teeth.4,8,9

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The hardness of the upper layer of enamel is primarily due to the high concentration of phosphate (PO43−) and calcium (CA++) ions. The dentin adjacent to the enamel is less mineralized due to lower concentrations of phosphate and calcium but higher concentrations of magnesium (Mg++), sodium (Na+), and potassium (K+) ions.10,11.10,11

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Mineralized enamel is difficult for microorganisms to penetrate. Although the pellicle, mucin contained in saliva, pH of the oral cavity, and specific factors of oral cavity protection create conditions hindering cariogenic microorganisms, the most reliable guarantee of tooth protection is high enamel mineralization.4,12

 

The weakening of the factors mentioned above creates conditions for easy penetration of microorganisms into the internal structures of the tooth. One of the most critical negative manifestations of enamel penetration is its demineralization.

 

During demineralization, the mineral composition of hydroxyapatites is broken by the action of acids produced by microorganisms in dental plaque. Apatite crystals are most stable when the pH of the mouth is 7.5. When the pH drops below 5.5, the crystals begin to break, and the inter-crystal spaces expand. As a result, the surface of the enamel becomes soft and porous, which leads to caries. It should not be understood as if enamel demineralization is an irreversible process that must necessarily end with the formation of a carious defect. The body's immune forces can ensure the regression of the imbalance in the structure of the teeth and the restoration of balance. This process is called biomineralization.1,13-15

 

Biomineralization is a dynamic, complex, continuous process that regulates the deposition of inorganic nanocrystals in the organic matrix of living organisms. As a result, unique hybrid biological tissues (enamel, dentin, cementum, and bone) are formed.1 As mentioned earlier, this process occurs throughout life. However, it may reverse and develop demineralization under certain conditions and external factors.16,17 Teeth and bones face these dangers throughout life. The high risk of demineralization is caused by the peculiarities of the anatomical arrangement and structure of the teeth - relief surface, natural grooves, hollows, and others. In addition, teeth are constantly affected by some components of food and drink and oral microorganisms.18,19 However, it should also be noted that due to the above reasons, teeth develop high resistance to demineralization, which bone does not have.1

 

The processes mentioned above are the basis for maintaining the health of the cool tissues of the tooth. Any deviation from the norm stimulates the mobilization of the body's protective forces and reverses the process.

 

However, such a factor as the delay time must also be considered. In other words, the long-term effect (delay) of undesirable factors on the tooth's surface. In the latter conditions, the demineralization-remineralization process, unfortunately, tends to favor the former.12,20

 

Unsurprisingly, the search for conditions and methods stimulating or inhibiting remineralization has always been a subject of special attention for dentists.

 

Maintaining the integrity of the tooth surface and selecting the best among the many pharmacological agents available on the market to achieve this goal will only be possible if the doctor (researcher) knows the essence and anatomy of the demineralization process and why demineralization is based on the change of mineral components in the structure of enamel and dentin. It is the study of the dynamics of these microelements that sheds light on the problem.21

 

The above determined the purpose of our research: to determine the composition of microelements (Ca, P, and F) in the enamel and dentin of undamaged human teeth and to determine their concentration changes during demineralization caused by experimental conditions. To achieve this goal, we set the following tasks:

• To determine the distribution of microelements in the enamel and dentine of extracted human teeth by X-ray spectral method;

• Modeling the carious process in vitro on extracted teeth and studying target microelements in enamel and dentin under these conditions.