The aim: The paper was aimed at the study of the processes of mineralization of the enamel of the permanent tooth after its eruption. Materials and methods: To study the structure of the enamel of permanent teeth has been carried out using light and electron microscopy. The study of the process of the development of the primordia of the permanent teeth involved 10 culled puppies of 30-40 days of age. Microscopic, electron microscopic, immunohistochemical methods of research have been used to study the processes of histogenesis. Results: The studies show that in the postnatal period, the formation of the crown, externally covered with cuticular epithelium, marks the formation of the primordium of the permanent tooth at the follicle stage. After eruption of a tooth, different parts of its crown have three individual structural and functional barriers to enamel biomineralization. The first one is provided by the cuticular epithelium of the pitted areas of the crown, which ensures filtering of the salivary fluid from the protein deposit in the form of a pellicle. The second barrier is defined on the lateral and cuspidate surfaces of the enamel, where the cuticle is erased or poorly expressed. The third structural and functional barrier of enamel biomineralization is located in the cervical portion of teeth of different classes. Conclusions: Different areas of the enamel in the tooth crown have specific filtration barriers, which can be distinguished as follows: pit-and-fissure-and-groove, cuspidateand-approximal, and cervical barriers. The cuticle is poorly expressed or totally absent on the cusps of the tooth crowns in contrast to pitted areas.

The aim: Thepaper wasaimedat thestudyof thebiomineralization processesofa permanentdental crown in thepostnatal period of histogenesis. Materials and methods: The study involved 30 culled puppies aged 30-40 days. To study the histogenesis of the germs of the permanent tooth from the cuticular epithelium in the postnatal period microscopic, electron microscopic, immunohistochemical methods of study have been used. Results: The studies show that in the postnatal period, the maturation of the germ of a permanent tooth starts with the synthesis of cells of the cuticular epithelium of the organic stroma, capable of subsequent mineralization. Differentiation of the proameloblasts, located on the surface of the dental papillary mesenchyma, at the early stages of histogenesis, is strongly associated with the appearance of a specific protein taftelin. Origination of secretory ameloblasts, which produce the protein enamelin, triggers the process of secondary biomineralization of the enamel. The terminal processes of the secretory ameloblasts produce the protein in the form of layers that overlap each other at a certain angle. Such layering of the structures of enamel and dentin contributes to the S-shaped maturation of the hard tooth tissues, strengthening them considerably. At the follicle stage, maturation of the dental crown, coated with cuticular epithelium, occurs. Invaginations of the cuticular epithelium form a characteristic topography of the dental crown, and enamel projections are further formed by the ameloblasts. Epitheliocytes of the inner layer of the enamel organ have desmosomal connections that allow the filtration of the salivary fluid at the stage of the enamel trophism. Conclusions: The findings of the study suggest that, normally, due to the cuticular epithelium, filtration of the salivary fluid occurs with protein deposition on it and subsequent infiltration of the calcium salts into the subjacent enamel.

The perfect knowledge of the microscopic structure of the appropriate organ is crucial in the solution of many urgent problems of clinical medicine. Better preservation of tissue structures is achieved when the tissues are embedded into epoxy resins followed up with the semi-thin section making. In contrast to the thick sections that are used for light microscopy, due to the greater awareness and relative cost effectiveness without the need of complicated expensive equipment, the method of semithin sections today is currently used in morphological studies. The paper was aimed at the study of the prospects of using the semi-thin section method to evaluate the immobilization stress-induced structural changes in the lungs. The resulting study showed the appropriateness of the use of semi-thin sections to study structural changes in lungs, induced by the experimental stress. The study of the semi-thin sections is the beneficial technique of the morphological analysis that permits to evaluate the structure of the studied material at the tissue and cellular level.

Stress-related studies remain relevant notwithstanding its long-lasting history of research. Experimental studies are crucial in the study the impact of stress on a living organism. Currently, there is a great variety of simulation animal acute stress reaction models, in particular, cervical fold suspension of mice, which is cost effective and easy-to-use. However, there are insufficient data on using this technique to reproduce the acute stress response in rats, particularly, in studying the impact of immobilization stress on the liver. The purpose of the work was to study the impact of 6-hour-long cervical fold suspension simulation model of acute immobilization stress on the albino rats’ liver. Material and methods. Based on the international bioethical regulations, 20 male albino rats were involved into the study. The intact animals were assigned into group I (n=10) (control); the animals, exposed to 6-hour-long cervical fold suspension simulation model of acute immobilization stress were assigned to experimental group (n=10) (group II). After euthanasia, macro- and microscopic examination of the liver was performed. Micro-specimens were stained with hematoxylin and eosin. Results and discussion. The macroscopic examination of the liver did not reveal any visual differences in the rats of the experimental group compared to the control ones. Histological study of the liver specimens of group II rats showed that the experimental model of simulated acute immobilization stress in rats by atraumatic cervical fold suspension for 6 hours caused significant changes. They were especially pronounced in the bloodstream of the liver, manifested by the plethora and the phenomena of interlobular vein thrombosis. The central veins were also plethoric and a significant dilatation of the perisinusoidal spaces was noted. Changes in the hemomicrocirculation were characterized by manifestations of blood stasis and sludge in most sinusoidal capillaries. We detected the phenomena of tissue infiltration by the segmented neutrophils, as well as macrophages and lymphocytes perivascularly and in the portal tracts. Changes were also found in the liver cells, namely, the phenomena of karyopyknosis; subcapsular focal colliquational necrosis in the individual hepatocytes; hydropic dystrophy in hepatocytes located on the periphery of the liver lobuli. Conclusion. The implementation of experimental model of acute immobilization stress in rats by atraumatic cervical fold suspension caused significant histological changes in rat liver

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