Relevance.The World Health Organization (WHO) defines oral health as "a condition characterized by the absence of chronic pain in the mouth and face, oral and throat cancer, infections and oral ulcers, periodontal (gum) disease, dental caries, and tooth loss, as well as other diseases and health disorders that limit a person's ability to bite, chew, smile and speak, and affect his psychosocial well-being" [1, 2, 3]. For timely and correct differential diagnosis of pathological processes of the oral mucosa, not only knowledge of the normal anatomy and physiology of the oral mucosa is required, but also the features of its structure in human ontogenesis, which is important for the development of the correct treatment strategy [4, 5, 6]. Gemonov V.V., Lavrova E.N., Falin L.I., (2016) indicate only 88.9% diagnostic agreement with final pathological results for diagnoses after oral biopsy . According to many researchers, the data of modern histological analysis represent an invaluable resource for the use of molecular mechanisms involved in both resistance and tumor recurrence of the oral mucosa [8, 9, 10].
Purpose of our research isto study the development of the human oral mucosa in ontogenesis.
Material and methods. The study was performed taking into account the provisions of the Helsinki Declaration (2000, 2013) and with the permission of the ethical committee of the Far Eastern Federal University. Biopsy specimens of the oral mucosa were obtained in accordance with the order of the Ministry of Healthcare of the Russian Federation dated 04.29.94 N 82 "On the procedure for conducting pathological autopsies" and in accordance with the nomenclature of clinical laboratory studies of the Ministry of Health of the Russian Federation (order of February 21, 2000, No. 64). The clinical material for the study was obtained at the Kolot Medical Center (Vladivostok) during 2019-2020. The biological material of 10 human embryos and fetuses was investigated, the age of which was determined by ultrasound data and the Haase rule. Stained sections of biopsy specimens was performed according to classical protocol for a method using hematoxylin and eosin.
Results of own research and their discussion. It was found that at the 3rd week the wall of the oral fossa of the embryo is covered with a single-layer multilayer epithelium. The floor of the oral fossa is covered with a two-layer low prismatic epithelium, and the roof is covered with ciliated epithelium (fig. 1).
Fig. 1. Oral fossa of a human embryo of a) 3 weeks; b) 4 weeks. Staining with hematoxylin and eosin. Microphoto. Magnification: a) х200; b) х100.
Fig. 2. The oral cavity of a human embryo of 5 weeks. Staining with hematoxylin and eosin. Microphoto. Magnification. х400.
The surface of the oral mucosa is represented by stratified squamous epithelium. In the area of the tooth neck, the submerging ectodermal epithelium forms an enamel cap. A 2-layer epithelium is identified behind the tooth neck. The first is a brightly basophilic basal layer, above which a squamous epithelium with apically located nuclei is identified. The cytoplasm may be weakly or not at all colored. Nuclear-cytoplasmic relations are high.
Fig. 3. The oral cavity of a human embryo of 5 weeks. Staining with hematoxylin and eosin. Microphoto. Magnification. x200.
The mucous membrane is covered with stratified non-keratinized epithelium, under which the basement membrane is identified. In the lamina propria, blood vessels are identified, the lumen of which is filled with erythrocytes, and numerous fibroblasts in the intercellular substance are identified with a predominant content of the main substance.
We have noted an increase in the length of the connective tissue papillae protruding into the epithelial layer, a change in the nuclear-cytoplasmic relationship towards their decrease. Differentiation of epithelial cells and their specialization correspond to a gradual increase in the barrier function of the integumentary epithelium of the oral mucosa. The regenerative potential gradually decreases, the structure of the connective tissue is characterized by the appearance of collagen fibers adjacent to the epithelial layer. The reduced amount of collagen in the intercellular substance promotes the binding of fluid by collagen and hyaluronic acid in the main substance with further free migration of leukocytes. It is known that 1 g of collagen binds 5 g of water that is in the free state.
In the composition of the epithelium of the oral mucosa, cells appear, the cytoplasm of which is vacuolated, there are quite large vacuoles that displace the nucleus to the cytoplasmic membrane. Also, leukocyte infiltration of the lamina propria of the mucous membrane was observed, and within the epithelial layer, numerous monocytes, neutrophils and lymphocytes were identified, participating in the regulation of physiological regeneration of the oral mucosa. On the border of the prickly and basal layers, there were single Langerhans cells, they were mainly identified among the epithelium of the mucous membrane, which suggests and indirectly indicates the presence of antigen presentation in the oral mucosa for restructuring at the stages of maturation .
Conclusion.Physiological regeneration and maturation of the oral mucosa in human ontogenesis are associated with the proliferative activity of the structures of the oral mucosa, are under the control and regulation of this process by effector immunocytes infiltrating the oral mucosa.
The study was financially supported by the International Medical Research and Education Center (Vladivostok, Russia)
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