Secondary caries are considered the main cause of dental restoration failure. In this context, anti-biofilm and bactericidal properties are desired in dental materials against pathogens such as Streptococcus mutans. To this purpose, graphene based materials can be used as fillers of polymer dental adhesives. In this work, we investigated the possibility to use as filler of dental adhesives, graphene nanoplatelets (GNP), a non toxic hydrophobic nanomaterial with antimicrobial and anti-biofilm properties. Graphene nanoplatelets have been produced starting from graphite intercalated compounds through a process consisting of thermal expansion and liquid exfoliation. Then, a dental adhesive filled with GNPs at different volume fractions has been produced through a solvent evaporation method. The rheological properties of the new experimental adhesives have been assessed experimentally. The adhesive properties have been tested using microtensile bond strength measurements (µ-TBS). Biocidal activity has been studied using the colony forming units count (CFU) method. The anti-biofilm properties have been demonstrated through FE-SEM imaging of the biofilm development after 3 and 24 h of growth. A significantly lower vitality of S. mutans cells has been demonstrated when in contact with the GNP filled dental adhesives. Biofilm growth on adhesive-covered dentine tissues demonstrated anti-adhesion properties of the produced materials. µ-TBS results demonstrated no significant difference in µ-TBS between the experimental and the control adhesive. The rheology tests highlighted the necessity to avoid low shear rate regimes during adhesive processing and application in clinical protocol, and confirmed that the adhesive containing the 0.2%wt of GNPs possess mechanical properties comparable with the ones of the control adhesive.

Graphite nanoplatelets (GNPs) are bidimensional carbon nanostructures consisting of stacks of graphene sheets, having thickness in the range from one up to a few tens of nanometers, and lateral linear dimension in the micrometer range. These nanostructures represent a good candidate to replace carbon nanotubes in composites for electromagnetic applications. This paper proposes a new model based on the Maxwell-Garnett approach to compute the effective complex permittivity of GNP-filled nanocomposites. The effect of the dimensional probabilistic distribution of the nanofiller is investigated. To this purpose, an extensive experimental characterization of the morphological and physical properties of the GNPs after synthesis is performed. The proposed model is validated by comparison with the measured effective permittivity of GNP-composites with different concentrations, and it is used for the design of radar-absorbing materials in the frequency range 1-18 GHz.