 Objectives The aim of the present project is to evaluate the effect of daily administration of chewing tablets containing probiotic bacteria Probiora3 on plaque amount, gingival health and caries incidence in preschool children. In addition, information on general health will be collected. The null hypothesis is that the oral health will not differ from preschool children with a similar intake of placebo tablets. An additional aim is to monitor the microbial composition in saliva samples at baseline and during the course of intervention. 