Introduction: Dental caries is the most widespread disease in the world. Reorganization of dental health care has led to increase of the KEP index in the Republic of Croatia. Objective: Find out the prevalence, degree of sanation and caries incidence before and after conducting a preventive dental project during the period of early mixed dentition. Respondents and methods: The research includes a sample of 400 respondents which who took part in the project „Razred najljepših osmijeha“ in the academic year 2017./2018.. Results: The sample consisted of 49% girls and 51% boys. The results have been calculated before and after conducting the preventive project. The KIO index descreased from 76,5% to 75,25%. The value of the kp index was reduced from 2,7 to 2,5. The KEP index hasn't changed (0,6). The CI index of the primary dentition has increased from 14,3% to 36,5%. The CI index of the permanent dentition has increased from 29,2% to 57,5%. The TNI index of the primary dentition has descreased from 602% to 174% while the TNI index of the permanent dentition has descreased from 242,9% to 73,9%. Considering the total share of respondents, the percentage of respondents with caries has descreased from 70% to 55%. The percentage of respondents with a filling has increased from 7% to 20%. The percentage of CF respondents has increased from 23% to 25%. Considering the total number of teeth, the percentage of teeth with caries has descreased from 12% to 8%. The percentage of teeth with a filling has increased from 2% to 5%. The percentage of CF teeth has increased from 86% to 87%. Conclusion: The prevalence of caries is higher than that of the Western European countries. At the time of the preventive project the sanation of caries has increased while the incidence of caries wasn't documented