Objective. evaluation of oral hygiene to enhance the prophylaxis of complications specifically of dental caries in children with disturbances in tooth formation (DTF) who live on radiologically contaminated territories after the Chornobyl NPP (ChNPP) accident. Materials and methods. Children aged 6–14 years (n = 1470) with DTF were the study subjects examined in 2012– 2016. Among them there were (n = 528) residents of the zones III and IV of radiological contamination after the ChNPP accident with 137Cs soil contamination density 1-15 Ci/km2. The effective radiation dose in them was not exceeding 1 mSv/year. The Green-Vermillion and Silness-Loe oral hygiene indices were assesses within clinical examination methods. Results. The worth oral hygiene was revealed in children having got the DTF, compensated chronic diseases of organs and systems, and in those with burdened radiation history. The Green-Vermilion and Silness-Loe indices were 1.7 ± 0.51 and 1.65 ± 0.46 respectively. Conclusions. A significant deterioration in oral hygiene confirmed by the highest values of the Green-Vermillion index (1.7 ± 0.51; p < 0.001 – «unsatisfactory oral hygiene» criterion) and Silness-Loe index (1.65 ± 0.46; p < 0.001 – «poor oral hygiene» criterion) was found in children with DTF aged 6-14 years being residents of contaminated areas as a result of the Chernobyl accident. The revealed deterioration may be due to a set of negative factors, including the impact of ionizing radiation in low doses and peculiarities of social status. Results of the questioning of surveyed pediatric contingents both having got an DTF and with no defects of the hard tissues of teeth indicate an insufficient level of knowledge and skills in hygienic care of oral cavity regardless of the area of residence. Development of a set of measures to prevent the DTF complications in children should be carried out taking into account the state of oral hygiene, level of knowledge and skills in oral care, and include the use of hygiene products, namely toothpastes and anti-caries mouthwashes. Key words: children, disturbances in tooth formation, systemic hypoplasia of enamel, molar-incisor enamel hypomineralization, hygienic indices, ionizing radiation, ChNPP accident.

Background. Odontological effects of ionizing radiation (IR) as a result of radiotherapy, the consequences of acci-dents at nuclear power plants and industry, individual occupational exposure, etc. deserve significant attention interns of radiation medicine and radiation safety. Objective: to analyze and summarize clinical and experimental data on the odontological radiation effects. Materials and methods. Object: the pathological changes in the hard tissues of teeth, pulp, periodontium, mucous membranes of the mouth and jaws due to exposure to IR. Method: search in the PubMed / MEDLINE, Google Scholar abstract medical and biological databases, scientific libraries of the relevant sources of scientific information. Results. Radiobiological effects of IR due to its direct and indirect action are manifested throughout the period of odontogenesis and formation of the facial skeleton. Experimental and clinical data (in children and adults) indicate the increased risk of dental caries, reduction of pain threshold and vascularization of tooth pulp along with its fibrosis and atrophy, periodontal dysfunction, which predispose to a high probability of tooth loss. Abnormalities in the activity of osteoblasts and cementoblasts of dental periosteum and osteoblasts of alveolar process in combination with circulatory disorders due to endothelial cell death, hyalinization, thrombosis and vascular obliteration increase the risk of jaw osteoradionecrosis. Children who have undergone a prenatal exposure to IR as a result of the Chornobyl NPP accident have a premature change of teeth. Deterioration of periodontal tissues and early development of acute and complicated dental caries are typical for children and adults affected by the Chornobyl disaster. Conclusions. Summarized data on the effects of radiation exposure under different conditions on teeth primordia (i.e. immature teeth), their formation and eruption in experimental and clinical settings, as well as on the odontological radiation effects in adults are summarized. Condition of the teeth in the Chornobyl NPP accident survivors is described. Understanding and taking into account the radiobiological odontological effects is necessary in the light of planning, preparing, and conducting local radiation therapy and developing the standards of radiation safety and measures to protect professionals and the public in the event of possible radiation accidents at the nuclear power plants and industry facilities. Key words: ionizing radiation, radiation therapy, Chornobyl NPP accident, odontology, tooth enamel, dentin, pulp, periodontium, caries, odontogenesis.

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Objective: to determine the severity of gingivitis in children with teeth formation disorders - residents of the territories contaminated with radionuclides as a result of Chornobyl Nuclear Power Plant (ChNPP) accident. Materials and methods. The object of the study is 1470 children aged 6–14 years with dental malformations, 528 amomg them are residents of areas contaminated with radionuclides as a result of the ChNPP with the identified types of disorders of teeth formation (DTF) (systemic enamel hypoplasia (SEH) and molar-incisor hypomineralization (MIH)), and different stages of the severity of gingivitis. Results. Determining of the degree of severity of gingivitis in children with DTF indicates the presence of its lesion of a moderate degree of the severity with a prevalence in persons with SEH or MIH and chronic diseases of internal organs suffered after the ChNPP accident. Conclusions. In irradiated children with DTF, an average degree of severity of gingivitis was established (РМА = (43.03 ± 19.64) %, p > 0.001), which may be due to the effect of a complex of negative factors, in particular the influence of low doses of ionizing radiation, the peculiarities of the social status of the examined persons (imbalanced nutrition), unsatisfactory oral hygiene. In children suffered after the ChNPP accident with SEH, the indicators of the PMA index were reliable (p > 0.05) higher compared to individuals with MIH, which indicates a more pronounced degree of periodont damage. Revealed damage to periodont, in particular gingivitis, in children with DTF residents of the contaminated territories, probably caused by the action of a complex of negative environmental factors, in particular the influence of low doses of ionizing radiation, and the peculiarities of the social status of children, which requires a comprehensive approach to the prevention of complications of defects of hard tissues of the teeth. Key words: children, gingivitis, systemic enamel hypoplasia, molar-incisor hypomineralization, ionizing radiation.