Resin composite blocks for dental CAD/CAM applications reduce biofilm formation in vitro

Objectives: Modern dentistry is increasingly focusing on digital procedures, including CAD/CAM technologies. New materials have to resist in a demanding environment that includes secondary caries occurrence. The current study hypothesized that the microbiological behavior of different RBCs for CAD/CAM applications is better than that of their counterparts for direct restorations due to differences in the surface characteristics. Methods: Both direct and CAD/CAM RBCs were tested. Specimens were obtained from each group, polished, cleaned, stored in artificial saliva (1 w), then sterilized under UV (24 h). Specimens’ surface was assessed using profilometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction; resin/filler content was assessed using thermogravimetry. After pre-incubation with sterile human saliva (24 h), the microbiological behavior of the materials was assessed using four models: Streptococcus mutans adherence (2 h), S. mutans biofilm formation in an orbital shaking bioreactor (24 h), S. mutans biofilm formation in a continuous-flow bioreactor simulating shear forces (24 h), and mixed-plaque formation in the bioreactor (24 h). The viable biomass adhering to the specimens’ surfaces was measured using a tetrazolium dye-based test. Statistical analysis included verification of normality of distribution and homoscedasticity, then Oneway ANOVA and Tukey's test (α = 5%). Results: When using the bioreactor setup, CAD/CAM RBCs generally yielded lower S. mutans and mixed-plaque biofilm formation compared to direct RBCs. This difference was not evidenced in the first two microbiological models. Differences in manufacturing and curing processes rather than in materials’ surface roughness and composition could explain these results. Significance: CAD/CAM RBCs are promising materials from a microbiological point of view, featuring reduced biofilm formation on their surfaces when shear conditions similar to in vivo ones are present.