Salivary parameters of relevance for assessing caries activity in individuals and populations

A review of the non-microbial salivary parameters with respect to their possible association with caries activity is presented. The parameters are limited to those which already are or at least in the near future will obviously be simple enough, also for clinical purposes. Salivary flow rate is undoubtedly the most important single parameter since the cariostatic activity or efficacy of practically all other salivary parameters depends on the flow rate. Flow rate as such has no linear association with dental caries but there seems to exist an individual "threshold" limit which is decisive for enhanced caries activity. This threshold limit varies among different individuals and therefore the so-called normal values for unstimulated or stimulated flow rate are more reliable on a population level than among individuals for screening purposes. In any individual a regular and longitudinal follow-up of the flow rate is of higher clinical value than only a single cross-sectional measurement. Salivary buffer effect has only a weak negative association with caries activity and again, this effect is of greater clinical significance on a population level. Since the decisive processes in caries attack occur within or under the dental plaque, the buffering effect of saliva is limited and obviously more important to screen for erosion-than caries-prone individuals. Although important for dental health, none of the salivary antimicrobial agents as such has shown any strong association with caries activity. The only ones with some evidence of a regulatory role are secretory IgA antibodies, hypothiocyanite ions, and agglutinins. However, the data are controversial and it seems that instead of measuring individual parameters, the assessment of saliva's functional properties (such as the ability to aggregate bacteria, prevent their adhesion to hydroxyapatite or sugar metabolism etc.) is more important for clinical purposes. Of the parameters involved in de- and remineralization process, only salivary fluoride content has some association with caries susceptibility but its diagnostic or predictive value is questionable.