Aim: Although still debatable, bovine milk has cariogenic and anticariogenic properties due to lactose and protein composition, respectively. The objective of this study was, therefore, to evaluate the effect of milk on S. mutans biofilm composition and its effect on enamel and dentin demineralization. Materials and methods: S. mutans UA159 biofilms were grown on enamel and dentin bovine slabs immersed in culture medium ultrafiltered tryptone-yeast extract
broth containing 0.10 mM glucose. Enamel and dentine slabs (n=27) of known surface hardness (SH) were allocated to 3 groups of treatment: Group I: Sucrose 10% (positive control), Group II: bovine milk (test), Group III: 4.5% lactose (bovine milk concentration, active control group). Each biofilm was experimentally treated 8 times per day in triplicate. The experiments were carried out three times in three separated phases. After each phase, biofilms were collected and the values of dry weight, total protein, acidogenicity (pH), intracellular polysaccharides, soluble and insoluble extracellular polysaccharides were determined. SH of the slabs was again determined and the percentage of surface hardness change (%SHC) was calculated as indicator of demineralization. The difference between the treatment groups was assessed by ANOVA followed by Tukey test.
Results: In enamel, Group I (sucrose) showed significantly higher values of biomass, total protein, pH and %SHC than the other groups (p<0.05). In dentin, Group I exhibited significantly higher values of: biofilm formation, total protein, insoluble extracellular polysaccharide, pH and %SHC than the other groups (p<0.05). GII and GIII did not differ between them (p>0.05) for any parameter, either for enamel or dentine. Dentine demineralization was higher than enamel (p<0.05). Conclusion: These findings suggest that S.mutans biofilm formed under bovine milk exposure results less cariogenic than that formed from sucrose but this effect may not be due to milk anticariogenic properties.