# Titanium Nitride Plating Reduces Nickel Ion Release from Orthodontic Wire
## 3 Results  
### TiN Coating of Orthodontic Wires Suppresses the Elution of Metal Ions from the Wire Surface  
The amount of metal ions released from the TiN-coated and uncoated wires after immersion in sterile water, physiological saline, HCl, or lactic acid for 30 min, are shown in Tables 1 and 2. All the data are shown as the mean \(\pm\) SD of four replicates. Following immersion in HCl for 30 min, the TiN-coated SS wire showed significantly reduced Cr, Mn, Fe, and Ni ion concentrations compared to the uncoated SS wire and the HCl-only immersion solution, which was used as a control (Figure 1a). On the other hand, following the immersion of the NiTi wire in HCl for 30 min, the concentrations of Ni and Ti ions were significantly reduced in the TiN-coated wire sample compared to the uncoated NiTi wire sample and the HCl-immersion-solution-only control (Figure 1b). Furthermore, the leaching of Ni ions from the uncoated SS and NiTi wire immersed in lactic acid for 30 min was significantly increased compared to the lactic-acid-only immersion solution control (Figure 1c,d). There were no significant differences in the amounts of metal ions released when the wires were immersed in sterile water or physiological saline for 30 min between the TiN-coated wire, the uncoated wire, and the immersion-solution-only control. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Wire**} & \multirow{2}{*}{**Solution**} & \multicolumn{2}{c}{**Immersion**} & \multicolumn{2}{c}{**Cr**} & \multicolumn{2}{c}{**Mn**} & \multicolumn{2}{c}{**Fe**} & \multicolumn{2}{c}{**Ni**} \\ \cline{3-10}  & & **Time (min)** & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** \\ \hline \multirow{5}{*}{TN-coated SS} & Sterile water & 0 & 4.78 & 6.83 & 0.76 & 0.54 & 49.26 & 52.90 & 0.43 & 0.28 \\  & & 30 & 3.08 & 2.85 & 0.51 & 0.31 & 22.07 & 17.00 & 0.48 & 0.26 \\ \cline{2-10}  & Physiological & 0 & 2.38 & 2.48 & 1.01 & 0.31 & 16.61 & 12.25 & 1.06 & 0.87 \\  & saline & 30 & 2.21 & 0.38 & 2.54 & 1.67 & 19.33 & 15.39 & 11.62 & 12.23 \\ \cline{2-10}  & Hydrochloric & 0 & 5.22 & 1.32 & 1.08 & 0.35 & 70.09 & 30.67 & 8.03 & 11.02 \\  & acid & 30 & 24,625,05 & 7557,31 & 2070,16 & 725,35 & 81,189,98 & 25,124,15 & 15,899,44 & 5752.39 \\ \cline{2-10}  & \multirow{2}{*}{Lactic acid} & 0 & 32.15 & 0.48 & 0.83 & 0.32 & 71.60 & 1.29 & 1.34 & 0.07 \\  & & 31.74 & 0.51 & 0.64 & 0.10 & 77.52 & 4.71 & 1.55 & 0.10 \\ \hline \multirow{5}{*}{Uncoated SS} & Sterile water & 0 & 4.78 & 6.83 & 0.76 & 0.54 & 49.26 & 52.90 & 0.43 & 0.28 \\  & & 30 & 3.29 & 2.27 & 0.86 & 0.40 & 33.03 & 14.57 & 2.25 & 1.72 \\ \cline{2-10}  & Physiological & 0 & 2.38 & 2.48 & 1.01 & 0.31 & 16.61 & 12.25 & 1.06 & 0.87 \\ \cline{1-1}  & saline & 30 & 3.89 & 2.72 & 1.52 & 0.24 & 22.22 & 11.94 & 17.36 & 22.61 \\ \cline{1-1} \cline{2-10}  & Hydrochloric & 0 & 5.22 & 1.32 & 1.08 & 0.35 & 70.09 & 30.67 & 8.03 & 11.02 \\ \cline{1-1}  & acid & 30 & 171,051,75 & 41,866,15 & 15,044,11 & 2118.26 & 653,585,22 & 116,232.28 & 82,007,05 & 15,393.43 \\ \cline{1-1} \cline{2-10}  & \multirow{2}{*}{Lactic acid} & 0 & 32.15 & 0.48 & 0.83 & 0.32 & 71.60 & 1.29 & 1.34 & 0.07 \\ \cline{1-1}  & & 30 & 32.33 & 0.58 & 0.77 & 0.20 & 81.63 & 2.24 & 4.14 & 3.49 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Metal ion release from SS wire (ug/L).