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 usingStreptococcus mutans(S. mutans) biofilms. Methods.S. mutansbiofilms 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, viableS. mutanscells, 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.