A defined-multispecies microbial model for studying enamel caries development

The aims of this study were to describe and validate an in vitro multispecies microbial biofilm model for caries development by evaluating the effects of varying medium concentration of sucrose (0.5 and 1.0%) and fluoride (0.4, 0.8 and 1.0 ppm F) in study 1, and calcium (1.0 and 2.0 mM Ca) in study 2. Defined-multispecies biofilms, formed by Lactobacillus casei, Streptococcus mutans, S. salivarius and S. sanguinis, were grown on the surface of salivary-pellicle-coated enamel slabs, with known baseline surface hardness; growth medium was changed daily. Counts of viable cells on biofilms and the percentage of surface microhardness change (%SMC), lesion depth (LD) and integrated mineral loss (IML) on enamel slabs were assessed after 4 days of biofilm formation under the tested conditions. Counts of viable cells on biofilms were significantly affected by sucrose, fluoride and calcium concentrations (p < 0.05). There was a decrease in %SMC in response to increased fluoride and calcium concentrations (p < 0.001). Lower IML (p < 0.001) and LD (p < 0.05) were found in the presence of 0.8 and 1.0 ppm F. A negative correlation was found between the response variables (%SMC, LD and IML) and fluoride and calcium concentrations. The results suggest that the microbial caries model developed was able to show distinct levels of caries inhibition in response to fluoride and calcium concentrations, corroborating clinical observations. An effect of sucrose concentration on caries development was found only in the presence of the lowest fluoride concentration.