Objective. Whether a minimum quantity of saliva is needed to inhibit the caries process is unclear. Here, we evaluated the effect of saliva dilutions on an in vitro caries model with Streptococcus mutans (S. mutans) biofilms. Methods. S. mutans biofilms were grown on enamel and root dentin slabs, in culture media containing different proportions of saliva (v/v): 0%, 5%, 10%, 25%, 50%, 75% and 100% saliva, and exposed to a 10% sucrose solution (5 min, 3x/day), with appropriate controls. After 5 (enamel) and 4 (dentin) days, demineralization, biomass, viable bacteria and polysaccharide formation were analyzed. The acidogenicity of the spent media was monitored overtime. Assays were carried out in triplicate in 2 independent experiments (n=6). Results. An inverse relationship was observed between acidogenicity, demineralization, and saliva proportion, both in enamel and dentin. A marked reduction in enamel and dentin demineralization was observed when small amounts of saliva were incorporated in the medium. For both tissues, a significant reduction in biomass, viable S. mutans cells and polysaccharides were observed when saliva was present, in a concentration-dependent manner. Conclusions. High quantities of saliva can almost completely inhibit sucrose-induced cariogenicity, but small amounts can also exert a dose-dependent caries-protective effect.

Objective. Whether a minimum quantity of saliva inhibit the caries process remains uncertain. This study aimed to investigate the impact of saliva dilutions on an in vitro caries model using Streptococcus mutans (S. mutans) biofilms. Methods. S. mutans biofilms were cultivated on enamel and root dentin slabs, in culture media containing different proportions of saliva (v/v): 0%, 5%, 10%, 25%, 50%, 75%, and 100% saliva, and exposed to a 10% sucrose solution (5 min, 3x/day), with appropriate controls. After 5 (enamel) and 4 (dentin) days, demineralization, biomass, viable bacteria, and polysaccharide formation were analyzed. The acidogenicity of the spent media was monitored overtime. Each assay was performed in triplicate across two independent experiments (n = 6). Results. In both enamel and dentin, an inverse relationship was observed between acidogenicity, demineralization, and the proportion of saliva. Even small quantities of saliva incorporated into the media led to a noticeable reduction in enamel and dentin demineralization. Saliva presence resulted in significant reductions in biomass, viable S. mutans cells, and polysaccharides, with the effects being concentration-dependent for both tissues. Conclusions. High quantities of saliva can almost completely inhibit sucrose-induced cariogenicity, while even small amounts exhibit a dose-dependent caries-protective effect.