The influence of resin-based dental materials on oral biofilms developement

Resin-based composites (RBCs) are the most widespread restorative dental materials used nowadays. Nanotechnologies allowed the development and improvement of a new generation of RBCs which nevertheless still present many unsolved issues. The most important is secondary caries, which is the recurrence of dental caries in tissues close to the restoration. Dental caries disease is driven by a dysbiotic biofilm colonizing both natural and artificial surfaces. Many approaches have been developed in order to address this issue, mainly the development of bioactive surfaces with contact-active properties, the optimization of surfaces to obtain anti-adhesive properties and the synthesis of biomimetic materials. The aim of this PhD thesis was to explore the use of nanotechnologies in order to synthesize, evaluate and optimize the formulation of RBCs aimed at successfully controlling oral biofilms development. The experimental part explored all three previously mentioned approaches. Regarding the first approach, a lactose-modified Chitosan carrier for silver nanoparticles (nAg) was developed and used as a coating for RBCs in order to study the antibacterial behavior of a novel material possessing contact-killing properties. The results indicated an antibacterial activity of the coating related to nAg concentration, however rinsing procedures interfered with the coating and deprived nAg of their effect. The surface activation of RBC surfaces prior to coating application showed itself good antibacterial properties that are currently under examination. Considering the second approach, experimental resin-based dental materials differing in their compositions were extensively studied, hypothesizing that biofilm formation on the experimental materials may show a dependency on their surface characteristics and nanotexture. In this sense, the anti-adhesive properties of these materials were evaluated as a possible effective way to control biofilm formation without the need for biocidal agents. The results showed that both hydrophobicity of the resin matrix of RBCs and filler content can influence oral biofilm formation. The lowest values of cariogenic biofilm were reached by less hydrophobic resin and by nanofillers. The third approach evaluated the possibility that biomimetic materials (designed to positively interact with dental hard tissues) may have to control oral biofilms, without the need for specifically biocidal agents. Resin-functionalized nanoparticles of dicalcium phosphate dihydrate (nDCPD) were incorporated into an experimental RBC. Results showed that the RBC filled with functionalized nDCPD showed reduced biofilm formation when compared to a RBC filled with non-functionalized nDCPD. In conclusion, all these three approaches proved to significantly impact oral biofilm formation on RBCs surfaces, however the most interesting result suggests the possibility of influencing biofilm formation without necessarily adding biocidal compounds. In fact, recent studies regarding the human microbiome show that many diseases, including dental caries, are caused by an imbalance between host and biofilms. These diseases may be restored by modifying biofilms composition, without attempting to eradicate biofilms.