Transmission electron microscopy (TEM) image of oxide nanoparticles. Image (A) shows ZnO nanoparticles (Sigma-Aldrich Chemical Company, St. Louis, MI, USA) using 80.0 kV and 42,000× magnification. In the previous study, these ZnO nanoparticles were used as inorganic fillers to confer antibacterial activity for a dental adhesive. Image (B) shows Fe3O4 (Sigma-Aldrich Chemical Company, St. Louis, MI, USA) using 80.0 kV and 26,000× magnification. In a previous study, these ZnO nanoparticles were used as inorganic filler of a dental adhesive to improve the µ-tensile bond strength under simulated pulpal pressure and magnetic field application.