To investigate the effectiveness of fluoride varnish in preventing primary caries in 3-5 years old children in the kindergarten collective environment and provide necessary information for oral health care plans.

Children aged 3-5 years old were randomly assigned into two study groups. The test group was treated with fluoride varnish and given oral hygiene instruction semi-annually for 4 times; the control group was only given oral hygiene instruction semi-annually. Follow-up examinations were conducted after 4 interventions to monitor primary caries increment among these children.

After intervention, the caries prevalence of test group raised from 51. 61% to 59. 14%, with incidence of 7. 53% at last. In the control group, the prevalence before and after was 52. 61% and 73. 93%, with the incidence of 21. 33%. The differences of the prevalence, the dmft value and the incidence between the test group and control group were significant.

Semi-annual application of fluoride varnish is effective in the prevention of dental caries in primary teeth of children and can improve the oral health of children.