The aim of the paper was to study the microcrystallization of oral fluid and to affect children through tooth decay. 148 children between the ages of 7 and 10 were clinically examined. Indices of tooth decay frequency and carious experience were estimated. Salivary flow rate, saliva pH and salivary buffering capacity were studied using the Saliva–Check Buffer Kit, GC. The study of microcrystallization of oral fluid (OF) was performed by the method of drop dehydration. The study was performed in accordance with the requirements of the Code of Ethics in scientific research. A direct relationship was established between intense carious activity and the decrease of the degree of microcrystallization of OF. Conclusions: the main advantages of the research of the crystallographic properties of OF are the non–invasiveness, the simplicity of the realization and the accessibility of the sampling of the studied substrate, thus offering new perspectives in clinical trials. The study of OF microcrystallization in children with dental caries elucidated a series of markers of changes in the oral cavity that can be used later in screening research, in dental practice, in the development of preventive measures and evaluation of their effectiveness.