The aim of our study is to evaluate the oral microbiome in distinct areas of the mouth of children with dental cavities (specifically the planktonic phase in saliva, the biofilm on the tooth and over the gingival epithelium) and understand whether or not the oral microbiome can be modulated through the use of probiotic Streptococcus Salivarius M18. The oral microbiome is also compared to the intestinal microbiome in order to understand if it exist a link between the two microbial communities and whether the changes in one of the two communities could affect the other