The Effect Of Direct Electric Resistance Heat Treatment On The Mechanical Properties Of Orthodontic NiTi Archwires

Objective:To study the effect of direct electric resistance heat treatment on the mechanical properties of nine different kinds of orthodontic NiTi archwires in oral temperature.Method:Selected nine different kinds of orthodontic NiTi archwires in different size(0.016" 3M Superelastic NiTi archwire,0.016" 3M Heat-Ativated NiTi archwire, 0.016" IMD Superelastic NiTi archwire,0.018*0.025" L&H Titan,0.018*0.025" Forestadent Biostarter,0.018*0.025"Tomy Heat-Activated NiTi archwire, 0.019*0.025"3M Superelastic NiTi archwire,0.019*0.025" IMD Superelastic NiTi archwire,0.019*0.025" YY NiTi archwire),8 each.The samples were heat-treated by Tomy SOARER-X for three times.Recorded the force-deflection curves by the deflection of 3mm by SANS Universal Testing Machine in 37±1℃water bath.Calculated the engagement forces at the deflections of 0.5mm,1.0mm.2.5mm and the working force at the deflection of 2.5mm,the hysteresis value at the deflection of 2.5mm,and the max engagement force during the whole process.All the differences in these variables were analysed by paired t-test in Oringin 7.5.Result:1. Before heat treatment,the max engagement forces of 9 NiTi orthodontic archwires are: 0.019*0.025" YY NiTi archwire>0.019*0.025" IMD Superelastic NiTi archwire>0.019*0.025 "3M Heat-Activated NiTi archwire>0.018*0.025 "Tomy Heat-Activated NiTi archwire>0.018*0.025" Forestadent Biostarter>0.018*0.025" L&H Titan>0.016" IMD Superelastic NiTi archwire>0.016" 3M Superelastic NiTi archwire>0.016" 3M Heat-Activated NiTi archwire;After direct electric resistance heat treatment, compared to the control group,the max engagement forces of 0.016" IMD Superelastic NiTi archwire and 0.018*0.025" L&H Titan increased, while the max engagement forces of 0.018*0.025" Forestadent Biostarter decreased.They have significant differences(p<0.05).2. Before heat treatment.the working forces of 9 NiTi orthodontic archwires at the deflections of 2.5mm are:0.019*0.025" YY NiTi archwire>0.019*0.025" IMD Superelastic NiTi archwire>0.018*0.025" Forestadent Biostarter>0.018*0.025"Tomy Heat-Activated NiTi archwire>0.019*0.025"3M Heat-Activated NiTi archwire>0.016" IMD Superelastic NiTi archwire>0.018*0.025" L&H Titan>0.016" 3M Superelastic NiTi archwire>0.016" 3M Heat-Activated NiTi archwire;After direct electric resistance heat treatment, compared to the control group,the working forces of 0.018*0.025" Forestadent Biostarter,0.019*0.025" IMD Superelastic NiTi archwire and 0.019*0.025" YY NiTi archwire decreased.They have significant differences(p<0.05).3. Before heat treatment,the hysteresis values of 9 NiTi orthodontic archwires at the deflections of 2.5mm are:0.019*0.025"3M Heat-Activated NiTi archwire>0.019*0.025" IMD Superelastic NiTi archwire>0.019*0.025" YY NiTi archwire>0.018*0.025"Tomy Heat-Activated NiTi archwire>0.018*0.025" Forestadent Biostarter>0.018*0.025" L&H Titan>0.016" IMD Superelastic NiTi archwire>0.016" 3M Superelastic NiTi archwire>0.016" 3M Heat-Activated NiTi archwire;After direct electric resistance heat treatment, compared to the control group, the hysteresis values of 0.016" IMD Superelastic NiTi archwire,0.018*0.025" L&H Titan,0.019*0.025" IMD Superelastic NiTi archwire and 0.019*0.025" YY NiTi archwire increased significantly(p<0.05).Conclusion:1. The size of archwire and the type of material are two key factors that decided the engagement force and working force of orthodontic NiTi archwires.The larger the size is,the greater the force is. Compared to Superelastic NiTi archwire in the same size,L&H Titan and Heat-Activated NiTi have lighter force.2. After direct electric resistance heat treatment,the mechanical properties of nine NiTi archwires changed differently.but the the superelasticity are all impaired to some extent.The times of direct electric resistance heat treatment make no differences.3. Direct electric resistance heat treatment doesn't strengthen the working force as expected. Instead of direct electric resistance heat treatment,the size of orthodontic NiTi archwire and the type of the material should be considered for clinical orthodontic requirement.