Background -Changes in the molecular composition of mixed human saliva using endogenous and exogenous methods of caries prevention were studied and the duration of these changes in relation to the initial state of the oral fluid was determined. Material and Methods -In total, 200 European healthy, addiction-free, university-educated males and females, aged 22-30 were recruited for the study. Participants collected their mixed saliva samples after the use of a multi-mineral toothpaste (exogenous prevention) and after three days of taking a calcium glycerophosphate tablet (endogenous prevention). In the first stage of the study, samples of mixed saliva were analysed by infrared (IR) lab spectrometer and equipment of infrared microspectroscopy beamline at the Australian Synchrotron (Victoria, Australia) was used in the second stage of study. Results -Based on the experimental data obtained by IR-spectroscopy technique, the mineral/organic and carbon/phosphate ratios were calculated. The changes in the organic mineral balance of the oral cavity induced by these two preventive methods were analysed. The statistical significance of the results for the confidence level of p is indicated. The data shows that changes in the molecular composition of mixed saliva when using an exogenous method of caries prevention only provides a short-term effect, continuing for the first 30 minutes after the preceding prevention. Moreover, calcium glycerophosphate tablets can change the organic-mineral balance in mixed saliva, increasing the content of mineral groups and complexes. The content of endogenous, biologically accessible phosphate groups and complexes in the mixed saliva exceeds by approximately 12% that of the mixed saliva before the use of the prevention agents. Conclusion -Use of calcium glycerophosphate tablets in combination with brushing (a combination of endogenous and exogenous prevention methods) leads to the long-term presence of high concentrations of ions, mineral complexes and groups (phosphates) in the oral fluid.