Laboratory evaluation of mixed-species biofilm formation by Streptococcus mutans and Lactobacillus casei on three...

To evaluate the biofilm-forming potential of mixed-species bacteria on three commercially available dental restorative composites and compare their resistance to biofilm accumulation. Given the increasing emphasis on bioactive and fluoride-releasing materials in caries prevention, the study specifically assessed the difference between restorative with and without fluoride content.

Three restorative materials, Activa (bioactive fluoride releasing), Filtek Bulk Fill (non-fluoride releasing) and TPH (non-fluoride containing) were tested in the laboratory. Standardized resin-discs were fabricated, saliva-coated to simulate oral conditions, and inoculated with a 1:1 mixed culture of Streptococcus mutans and Lactobacillus casei. Biofilm development was assessed at 24- and 48-hours using colony forming unit (CFU) quantification. Statistical analysis was performed using one-way ANOVA and Tukey's post hoc test (α= 0.05).

Significant differences in biofilm accumulation were observed among materials at both points (P< 0.05). TPH exhibited the highest CFU counts at 24 hours (0.24 ± 0.03 x 10⁷ CFU/mL) and 48 hours (1.07 ± 0.12 x 10⁷ CFU/mL). In contrast, Activa and Filtek showed significantly lower biofilm formation at both points (24 hours: 0.093 ± 0.05 x 10⁷ CFU/mL; 48 hours: 0.47 ± 0.31 and 0.53 ± 0.12 x 10⁷ CFU/mL, respectively), with no significant difference between them.

The restorative materials tested demonstrated varying degrees of resistance to biofilm formation. Activa and Filtek showed reduced biofilm accumulation compared to TPH at both early and mature stages of growth. The selection of restorative materials should consider their potential to resist bacterial colonization, especially in high-caries-risk patients and restorations placed near gingival margins.