Metal Oxide Nanoparticles and Nanotubes: Ultrasmall Nanostructures to Engineer Antibacterial and Improved Dental Adhesives and Composites

Abstract

Advances in nanotechnology have unlocked exclusive and relevant capabilities that are being applied to develop new dental restorative materials. Metal oxide nanoparticles and nanotubes perform functions relevant to a range of dental purposes beyond the traditional role of filler reinforcement-they can release ions from their inorganic compounds damaging oral pathogens, deliver calcium phosphate compounds, provide contrast during imaging, protect dental tissues during a bacterial acid attack, and improve the mineral content of the bonding interface. These capabilities make metal oxide nanoparticles and nanotubes useful for dental adhesives and composites, as these materials are the most used restorative materials in daily dental practice for tooth restorations. Secondary caries and material fractures have been recognized as the most common routes for the failure of composite restorations and bonding interface in the clinical setting. This review covers the significant capabilities of metal oxide nanoparticles and nanotubes incorporated into dental adhesives and composites, focusing on the novel benefits of antibacterial properties and how they relate to their translational applications in restorative dentistry. We pay close attention to how the development of contemporary antibacterial dental materials requires extensive interdisciplinary collaboration to accomplish particular and complex biological tasks to tackle secondary caries. We complement our discussion of dental adhesives and composites containing metal oxide nanoparticles and nanotubes with considerations needed for clinical application. We anticipate that readers will gain a complete picture of the expansive possibilities of using metal oxide nanoparticles and nanotubes to develop new dental materials and inspire further interdisciplinary development in this area.

Keywords: adhesives; antibacterial; bioactivities; nanoparticles; resin composite.

Figure 1

Clinical photos illustrate the two most common pathways for the failure of resin-based materials, secondary caries (A) and restoration fracture (B). (A) The arrow in the photo shows the lesion’s location at the tooth-restoration interface presented by yellow to brown discoloration. (B) The arrow in the photo shows the fracture location at the proximal wall of the tooth structure, most probably due to the high mechanical load induced by the masticatory force.

Figure 2

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.

Figure 3

Image (A) illustrates a dental radiograph that shows a radiolucent line of interface between the tooth and the composite. The radiolucent area is the adhesive layer, formed by a dental adhesive without or with a low quantity of inorganic filler. Image (B) shows the radiopacity of a dental adhesive modified with different concentrations of cerium oxide particles. Different letters indicate statistical differences among groups (p < 0.05). Adapted from reference [65], with permission from Garcia et al., 2020.

Figure 4

Transmission electron microscopy (TEM) image of titanium dioxide nanotubes. The image was acquired using 80.0 kV and 67,000× magnification. It is possible to observe the lumen of the elongated structures. These nanotubes were used purely and carried an antibacterial molecule in a dental adhesive in a previous study [126].