The effect of various nanoparticle coating on the frictional resistance at orthodontic wire and bracket interface: A systematic review

This systematic review was aimed to test the null hypothesis that coating of orthodontic wires with nanoparticles does not affect the frictional properties at bracket--wire interface. Electronic database searches were performed up to September 2020. In vitro studies were considered for reviewing process. Study selection, data extraction, risk of bias assessment was performed during reviewing process. Only qualitative analyses of included literature were done due to the presence of heterogeneity among the studies. Out of 1,068 retrieved records, nine studies satisfied the inclusion criteria and included in this review. Studies were assessed at low risk to high risk of bias according to certain parameters. Wide variety of nanoparticles were used for surface coating of orthodontic wires of variable sizes, shapes, and materials like stainless steel, NiTi, and TMA and placed into the slots of different types of orthodontic brackets to evaluate the alteration in frictional and other mechanical properties. Most of the studies clearly indicate that coating with nanoparticles decreases the friction between wire and bracket interface under specified in vitro conditions. Furthermore, among the nine included studies, only two considered evaluation of effect of coated brackets on frictional and other mechanical properties and results were heterogeneous. The null hypothesis is rejected and it is concluded that the wires coated with nanoparticles might offer a novel opportunity to substantially reduce frictional resistance at bracket--wire interface during tooth movement. Further studies are necessary to strengthen the evidence regarding effect of coated brackets on frictional properties.