Antimicrobial nanoparticles in restorative composites

Restorative composites are commonly used in dentistry, but they accumulate more dental plaques compared to amalgamation. As a result, bacterial adhesion, plaque, and secondary caries are often observed around these restorations. Although these materials improved substantially over the years, they do not possess antibacterial properties. Microleakage is another major drawback of restorative composites that antibacterial properties may compensate for. Thus, achieving antibacterial properties in restorative composites is a critical objective. Many endeavors to generate antibacterial restorative composites were reported. This goal may be achieved mainly through modifications made to the filler or matrix phases, which comprise restorative composites, using released or nonreleased antibacterial agents. Advantages and disadvantages of each modification to achieve antibacterial restorative composite are discussed in detail. To overcome the disadvantages of antibacterial materials based on releasing of antiseptic agents or small-molecule antimicrobial agents a possible solution is the usage of polymeric macromolecules with antimicrobial groups. Particularly, polycationic antimicrobials, which bear quaternary ammonium, have high charge density and excellent process ability, exhibiting high antimicrobial activity. Furthermore, usage of nanoparticles may be advantageous as active antibacterial groups, since their surface area is exceedingly outsized relative to their size and scope. Thus, nanoparticles may provide high activity even in cases when only a small dosage of the particles is added. Having this in mind, nanoparticles having quaternary ammonium groups were synthesized and incorporated in restorative composites. The nanoparticles were prepared from polyethyleneimine crosslinked at low degrees followed by alkylation and methylation of the amino groups to form quaternary ammonium residues. These cationic polymeric nanoparticles with quaternary ammonium groups when incorporated into restorative composites at low concentrations (1%-2%) have a strong antimicrobial activity upon contact that lasts for months without leach-out of the nanoparticles and without affecting the materials' biocompatibility.