Assessment of frictional resistance and surface roughness in orthodontic wires coated with two different nanoparticles.

Several mechanical and biological factors may change the orthodontic wire frictional resistance (FR). Titanium dioxide (TiO 2 ) and silica dioxide (SiO 2 ) nanoparticle (NP) coatings may be used to improve the characteristics of materials, reducing FR between archwire and bracket. This in vitro study aimed to evaluate the FR of orthodontic wires with and without coating in both dry and wet environments and measure the surface roughness (SR). One hundred and eighty segments of rectangular Cr-Ni orthodontic wires (Morelli Co, Brazil) were divided into three groups according to the NP coating applied: TiO 2 group; SiO 2 group; and control group. The SR parameters were measured in an optical profilometer, the surface morphology was analyzed with scanning electron microscopy (SEM), and FR was performed in a universal testing machine in dry and wet environments (n = 30). The statistical analysis was performed using the Generalized Estimated Equations model with a Bonferroni post-test (α = 0.05). It was observed that SiO 2 NP coating decreased FR significantly when compared to the TiO 2 and control groups, in both environments (p < .001). The SiO 2 and TiO 2 groups presented statistically lower SR than the control group and were similar to each other (p < .001). The SiO 2 group presented the lower depth of Valley parameter than the TiO 2 group (p < .001). The SEM showed that the TiO 2 coating had the most heterogeneous surface morphology than the SiO 2 and control groups. The orthodontic wires with NP coating modified the FR and morphology. The SiO 2 coating reduced FR in both dry and wet environments and decreased SR. Titanium dioxide (TiO 2 ) and silica dioxide (SiO 2 ) nanoparticles coatings may be used to reduce frictional resistance (FR) between archwire and bracket as well as to improve surface morphology. The SiO 2 coating reduced FR in both dry and wet environments and decreased the SR of Cr-Ni orthodontic wire. The TiO 2 coating promoted the most heterogeneous surface morphology of Cr-Ni orthodontic wire.