In vitro biofilm formation on experimental composites containing calcium-phosphate nanoparticles

Purpose: The aim of this study was to evaluate the influence of experimental RBCs filled with TEGDMA-functionalized DCPD nanoparticles (DCPD-NP) on in vitro Streptococcusmutans (S. mutans) biofilm formation. The microbiological performances of the tested materials were compared with their surface properties. The null hypotheses were that (i) the presence of DCPD-NP would not reduce biofilm development on the experimental RBC surfaces when compared to control experimental RBC without DCPD-NP; (ii) functionalization of DCPD-NP would not affect RBC microbiological behavior when compared to non-functionalized DCPD-NP. Methods andmaterials: Specimenswere prepared from the following materials: (A) RBC filled with 20 vol.% functionalized DCPD nanoparticles (CaHPO4·2H2O); (B) RBC filled with 20 vol.% non-functionalized (“bare”) DCPD nanoparticles; (C) RBC filled with 20 vol.% silica; (D) Neat resin (unfilled). A standardized amount of RBC was placed into a custom-made steel mould and light-cured for 40 s at 1200mW/cm2 light intensity. All specimens were subjected to a standardized polishing protocol. Subsequently, surface roughness (SR, profilometry), surface free energy (SFE, sessile drop method) and surface chemical composition (energy-dispersive X-ray spectroscopy, EDX) were determined. A modified drip-flow reactor (MDFR) was used to obtain a monospecific S. mutans biofilm on the surfaces of the specimens. Adherent, viable biomasswas evaluated after 48h using the MTT assay. Data were statistically analyzed using one-way ANOVA and Student–Newman–Keuls post-hoc test setting the level of significance (a) to 0.05. Results: Results are displayed in Table 1. The null hypothesis (i) cannot be rejected since biofilm formation on both DCPD-NP filled RBCs was not significantly different to that of the silica-filled RBC. The null hypothesis (ii) can be rejected since DCPD-NP functionalization caused a significant reduction in biofilm formation. Neat resin specimens showed the lowest biofilm formation. Even if SR data may partly explain the microbiological results, no clear correlations between surface characteristics and biofilm formation results could be identified. Conclusion: Within the experimental conditions applied, DCPD-NP functionalization influences RBCs microbiological performances, even if DCPD-NP addition to RBCs does not seem to show a relevant antibacterial activity.