Purpose : To understand the impact on the strength or restoration force by the change of heating temperature when soldering 18-8 stainless steel round wire which is the chrome-nickel class for dental orthodontic device production. Methods : The following conclusions were made upon the results from tensile strength test, 3 point bending test, and $90^{circ}$ bending fatigue test with 24 samples that had been applied with condition 1 (before heat treatment - natural) and condition 2 (after heat treatment - mooring 30 seconds after heating up to $500^{circ}C$, $700^{circ}C$, and $900^{circ}C$) to ${phi}0.4mm$, ${phi}0.7{eta}mm$, 18-8 stainless steel round wire (spring hard) by Jinsung Company. Results : When it was heat-treated at $900^{circ}C$, both ${phi}0.4mm$ and ${phi}0.7mm$ showed very low tensile strengths compared to the heat treated cases at $500^{circ}C$ and $700^{circ}C$ Yield strengths of both ${phi}0.4mm$ and ${phi}0.7mm$ showed very low compared to the heat treated cases at natural, $500^{circ}C$, and $700^{circ}C$, as well. Upon the results of 3 point bending test, the heat treated case at $900^{circ}C$ showed very low in both ${phi}0.4mm$ and ${phi}0.7mm$, compared to the heat treated cases at natural, $500^{circ}C$, and $700^{circ}C$. Tensile strength of both ${phi}0.4mm$ and ${phi}0.7mm$ as well, showed very low compared to the heat treated cases at natural, $500^{circ}C$, and $700^{circ}C$. Upon the results of $90^{circ}$ bending fatigue test, the heat treated case at $900^{circ}C$ showed the highest wave node resistance in both ${phi}0.4mm$ and ${phi}0.7mm$. Conclusion : This study concluded that heating temperature change during wire soldering impacts on the characteristics of orthodntic wire.