Background: Pediatric dentistry is looking for new methods to influence the cariogenic microorganisms of dental biofilm without the use of antiseptics and antibiotics, which often have negative side effects. Photodynamic therapy (PDT) is a promising and effective method to influence on the cariogenic microorganisms without using antiseptics and antibiotics. Material and methods: Forty five children aged 7 to 12 years with high risk of dental caries and pathology of central nervous system were observed during three years of the complex preventive measures, including multivitamins, minerals, antioxidants and PDT of dental biofilm. The activity of glutathione S-transferase (GST), content of reduced glutathione (GSH), thiocyanate (SCN) and total protein in the oral liquid (OL) were determined by spectrophotometry (Diasys Diagnostics, DE). The results were statistically processed using the program Excel Microsoft: Microstat 2007. Results: In three years the protein content in OL of the children was below the initial content in all groups that may be the confirmation of PDT bacteriostatic effect. In all periods of the study significant changes in the content of GSH, thiocyanate and activity of GST in OL in the children were not observed. Conclusions: Our results are indicating that complex preventive measures including the non-invasive method of PDT were effective, without any negative side effects and had bacteriostatic action. These complex preventive measures may be recommended for children with high risk of caries and pathology of CNS.