Introduction: The basis of oral health in children and adults is prevention. By frequently performing preventive procedures, it is possible to maintain oral health, i.e. prevent the development of caries. The most intensive period for carrying out preventive procedures in children is primary school age, because this is the time of formation of permanent dentition. During this period, children should be made aware of the importance of maintaining oral hygiene, proper nutrition and cooperation with their doctor of dental medicine. Along with children, parents/guardians should be involved in all procedures, because without their support, children of elementary school age are not able to carry out all procedures correctly. It is the duty of dental medicine doctors to continuously perform check-ups and educate patients and carry out preventive procedures that patients are unable to perform at home, namely professional teeth cleaning, fluoridation and preventive sealing of pits and fissures. Pit and fissure sealing of permanent molars, according to the literature, is the most effective way to prevent caries in these teeth. Aim. The aim of this research was to experimentally compare the retentive properties and the caries-protective effect of four materials for sealing pits and fissures: two filled composite resins, one unfilled composite resin and glass ionomer cement. As part of the same research, the influence of oral hygiene and dietary habits on the oral health of the examined children was observed. Material and Methods. For easier statistical processing and analysis, the research is divided into two parts: Research no. 1 - the influence of dietary and hygiene habits on the oral health of children and Research no. 2 - retention and the caries-protective effect of four different materials for sealing pits and fissures. In Research no. 1,143 children participated, students of the Blato Elementary School on Korčula, aged 6 to 13 years. They filled a questionnaire of nutrition and oral hygiene habits, a dental examination was performed on them, and their plaque index was determined. Research no. 2 included 80 respondents from Research no. 1 who met the pre-set criteria for participation in the second research. For them, the condition of the first and second permanent molars was determined using the visual tactile method and the DIAGNOdent device, and sealing materials were placed on the healthy molars according to a predetermined random arrangement using the split-mouth method. Results. The results of Research no. 1 indicate that, regardless of age and gender, there are no statistically significant differences in the consumption of sweets, sweetened beverages and cakes among children. There is no statistically significant difference in the frequency of tooth brushing or in the value of the plaque index, which for all children is: 32.18 ± 20.92 (mean value ± standard deviation). Older children have a statistically significantly higher KEP index (2.66), i.e. worse oral health, than younger children (KEP =1.08), P<0.001. From the results of Research no. 2 it is certain that filled composite resins have statistically better retention (M2 = 69.2%, 56.9%, 46.2% for 6 months, 1 year, 2 years respectively, and M4=72.4%, 65.5% , 46.6% for 6 months, 1 year, 2 years) than unfilled composite resins and glass ionomer cement (M1=48.1%, 34.6%, 19.2% for 6 months, 1 year, 2 years and M3 = 43.1 %, 29.3%, 20.7% for 6 months, 1 year, 2 years), P<0.001. There was no statistically significant difference in the occurrence of caries on sealed teeth among the materials used in the time intervals. However, teeth sealed with materials M1 and M3 developed a higher proportion of teeth with caries than teeth sealed with materials M2 and M4 (M1-26.9%, M3- 24.1% vs., M2=10.8%, M4 19 .0%, P=0.126). Oral health deteriorates with age, as can be seen from the value of the KEP index (KEP: first examination 1.19±1.86; 2 years from the first examination 2.07±2.28, P=0.033). Conclusions. In both parts of this research, time was shown to be the most important factor in children's oral condition. Over time, dental health deteriorates. A healthy diet, frequent tooth brushing and frequent visits to the dentist can contribute to maintaining oral health. Also, sealing the molars is effective in preventing tooth decay. As long as the sealing material is retained on the teeth, it protects the occlusal surface from the development of caries. Due to better retention, filled composite resins have proven to be more effective sealing materials than unfilled composite resins and glass ionomer cement.