RESIN-BASED COMPOSITES MODULATE ORAL BIOFILM FORMATION

Resin-based composites (RBCs) are increasingly used because of their excellent aesthetic properties and improved mechanical features. Nevertheless, the main reason for failure of resin composite restorations is still secondary caries. Dental caries is a very common infectious disease driven by the metabolic activity of a dysbiotic biofilm able to colonize both natural and artificial surfaces. In recent years, extensive research has been devoted to develop new restorative materials that could prevent the formation of recurrent carious lesions. Many approaches have been followed to reach this goal, particularly optimizing RBCs surfaces to obtain anti-adhesive properties, developing bioactive materials and synthesizing biomimetic materials. The aim of this PhD thesis was to explore the different approaches in order to discriminate the parameters influencing the microbiological behaviour of RBCs and therefore optimize their formulation to successfully control oral biofilms development. The three approaches were evaluated in the experimental part of the thesis. Considering the first approach, the optimization of the microbiological properties of resin- based dental materials was evaluated from different points of view. Experimental RBCs with different compositions were studied, hypothesizing that surface features and nanotexture would have influenced biofilm formation. The anti-adhesive properties of the tested materials were evaluated as a possible way to control biofilm formation without the need of antibacterial agents. The results showed that both hydrophobicity of the resin matrix of RBCs and filler amount can influence oral biofilm formation. Furthermore, different commercially available RBCs were submitted to diverse finishing and polishing protocols in order to evaluate the influence of these procedures on the surface features and on the microbiological behaviour of each material. It was therefore showed that surface chemistry seemed to play an important role in influencing biofilm formation. Regarding the second research field, the antimicrobial behaviour of experimental RBCs derived from a commercial formulation including different fractions of fluoride-releasing S- PRG filler particles was evaluated. The results of this study suggested an impact of fluoride- releasing S-PRG filler particles particularly on the early phases of biofilm formation. As the release of fluoride diminishes as a function of time, optimizing the fluoride-recharging abilities of the materials might help to control biofilm formation for longer periods. Moreover, the final polishing of the material may substantially influence the release of fluoride. The third research approach evaluated the possibility that biomimetic materials may control oral biofilm formation, without the addition of specific antimicrobial agents. In this study functionalized dicalcium phosphate dihydrate nanoparticles (nDCPD) were incorporated into an experimental RBC. Results showed that the RBC with functionalized nDCPD nanoparticles showed a reduction in biofilm formation when compared to a RBC filled with non-functionalized nanoparticles. All these approaches were effective in influencing oral biofilm formation on the tested materials. Recent studies regarding the human microbiome tend to consider biofilms as a part of the human body and show that many diseases, including dental caries, are due to an imbalance between host and biofilms. These diseases may be treated by modifying biofilms composition, without trying to eradicate biofilms. Hence, the possibility to modulate oral biofilm formation on restorations through the optimization of materials surfaces without the addition of any antibacterial agent seems to be the most interesting approach.