The orthodontic applications of nanotechnology are numerous. Nanotechnology can assist in manufacturing orthodontic wires, brackets, orthodontic aligners and mini-/microimplants.
Orthodontic wires coated with nanoparticles exhibited well-controlled tooth movements and better anchorage, with less frictional forces, less root resorption and less bone/periodontal damage. Orthodontic nanorobots and nanoindented orthodontic wires both contributed directly to healthy periodontal tissues, fast tissue repair, short treatment duration, painless tooth movement and larger scale of orthodontic movements. Orthodontic brackets with nanoparticle coatings demonstrated high antimicrobial effects and bacterial adhesive properties to resist enamel demineralization and gum inflammation. Dental composites manufactured by nanotechnology had higher bond strength with stainless steel brackets compared to traditional composite materials. In addition, they were found to be easily shaped with a high degree of strength and resistance to abrasion.
Different silver derivatives were applied as surface coatings on orthodontic microimplants made of titanium. The chemical structures of such composites are tested through a series of laboratory tests such as energy-dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS); while the microstructures are examined with scanning electron microscopy.
The antibacterial mechanism of silver nanoparticles is described with the ability of such nanoparticles to release silver ions in aqueous solutions. In addition, silver ions are capable to react with bacterial cell membranes to produce reactive oxygen that kills bacteria. More importantly, silver nanoparticles have large surface area with higher bacterial contact and strong affinity against bacterial enzymes.
The amount and concentration of silver ions leached from the surface of microimplant are important determinants of the ability of the implant to create a clear zone around itself inhibiting bacterial invasion.
Polymers, although having weaker antibacterial effect than silver nanoparticles, could play synergistic role to increase the bactericidal effect of silver ions in the microimplants. Current in vitro trials adopt using biopolymers to stabilize the effect and release of silver nanoparticles, to prevent oxidation reactions and to increase the bioavailability and antimicrobial properties. Silver ions were found to have a pivotal role to promote immediate antibacterial effect while biopolymer can exert firm effect of the antibacterial coating. Concerns related to toxicity of silver ions in the oral tissues need to be justified prior to clinical usage.
There still exist surface-modification techniques that change the morphological structures and antimicrobial effects of these orthodontic devices. There are also several methods to enhance the sustainability of ion release and the long-term stability in the oral environment. These modifications will be exploited to improve the retention of these devices, and their coatings, in clinical application.