A set of a first and a second preparation are intended to be mixed before or during an endodontic treatment to form an endodontic irrigation solution. The first preparation includes an oxidizing agent. The second preparation includes antibacterial nanoparticles treated to slow their oxidation by the oxidizing agent. The antibacterial nanoparticles are, for example, encapsulated in shells in a hybrid core-shell structure. In one variation, the antibacterial nanoparticles are made from an alloy of at least two elements, one of the elements being more resistant to oxidation than the other.