**2.4 Plasma ion implantation**

Attempts by some researchers to improve the corrosion and wear resistance of titanium implants have led to the development of a surface modification technique known as plasma ion implantation. In this technique, the surface of orthodontic miniscrews is coated with a thin film of titanium nitride (TiN) and/or zirconium nitride (ZrN) which acts as a protective layer (**Figure 6**). Kim et al. studied the mechanical and electrochemical changes on the surface of plasma ion implanted miniscrews [46]. Field emission SEM (FE-SEM) and EDS analysis showed that when compared to noncoated miniscrews, the TiN and ZrN coated miniscrews had a smoother surface owing to a decrease in the number of machined defects. Electrochemical tests revealed that coated miniscrews had a reduced corrosion current density. Later, on comparing the biologic stability of plasma ion implanted and SLA miniscrews in beagle dogs after a loading period of 3 and 12 weeks, Cho et al. concluded that since there was no difference in BSC, bone volume ratio or the number of osteoblasts around the miniscrews in both groups, they had similar biologic characteristics [47].
