Time-dependent interfacial tension of whole saliva and saliva-bacteria mixes

Using a tensiometer in accordance with the drop volume principle, the surface tension decrease with time was determined for whole and for 2%, 10%, and 50% aqueous solutions of saliva from one healthy donor. The reduction of surface tension with time was also measured for 10% and 20% saliva solutions with added samples of Streptococcus salivarius KRF2, S. sanguis KRF3, and Actinomyces naeslundii 2t-55. The results show that 1) there is a time dependence of the surface tension reduction of both whole saliva and diluted saliva, 2) an increase of the concentration of whole saliva in salivary solutions gives rise to larger and more rapid surface tension reduction, 3) the proteinaceous components of saliva appear to have a dominant contribution on surface tension in whole saliva and diluted saliva, and 4) the surface-active proteinaceous components in saliva have the ability to dominate the air-saliva interface also in the presence of high concentrations of salivary bacteria.