[Influence of the crystal index on the formation of tooth enamel resistance]

The purpose is to substantiate the prospects of calculating the crystallinity index of tooth enamel as a criterion of individual potential risk of dental caries.

120 enamel samples of intact premolars of the upper jaws were examined, removed according to orthodontic indications in persons aged 18-35 years living in Omsk, previously genotyped by polymorphisms G/G, G/A and A/A of the kallikrein-4 gene at mutation points G2664153A and G2142A. The following parameters of the oral fluid of the examined were analyzed: pH, Ca²⁺ using ion-selective electrodes on the pH meter OP2/208/01 and the potentiometer EV-74, the product of the solubility of hydroxyapatite (mineralizing potential) and the degree of oversaturation with hydroxyapatite was calculated, the protein concentration in the oral fluid was determined by the method using a biuretic reaction. The crystallographic features of hydroxyapatite of tooth enamel were studied using transmission electron microscopy methods using the JEM-2100 «JEOL» apparatus (accelerating voltage 200 kV, crystal lattice resolution 0.14 nm) and infrared spectroscopy using the Nicolet- 5700 «Thermo Electron Corp.» apparatus (the number of spectra accumulation is 30cm-1, resolution is 4cm-1). Based on the data obtained, the crystallinity index of tooth enamel is calculated. Protein determination in tooth enamel was carried out according to the Barnstein method.

Differences in the values of the crystallinity index of intact tooth enamel of individuals were revealed, which is due to a certain degree of ordering of the structure and relative size of crystallites in the studied samples of tooth enamel. With the crystallinity index of enamel samples equal to 3.54, the relative size of the crystallites and the degree of ordering of the crystal lattice of hydroxyapatite are higher than enamel samples with a more defective crystallite structure, the crystallinity index of which is 3.27. With a crystallinity index equal to 3.27, there is a predominance of pathological homozygote A/A of the kallikrein-4 gene in both studied mutation points, which is accompanied by a significant increase in the mass fraction of enamel protein, as well as a number of indicators of the supraventricular oral fluid involved in mineralization processes: phosphorus content, active concentration of calcium, protein, the product of hydroxyapatite solubility and the degree of oversaturation hydroxyapatite.

The crystallinity index of tooth enamel, being an integral indicator of the geometric structure of apatites, can serve as an indirect criterion for determining the resistance of tooth enamel. Determination of the crystallinity index of tooth enamel is possible by indirect signs, namely, the predominance of homozygous polymorphism A /A of the kallikrein-4 gene at mutational points G2664153A and G2142A in combination with an increase in the oral fluid of the examined phosphorus content, active concentration of calcium, protein, the product of hydroxyapatite solubility and the degree of hydroxyapatite oversaturation.