Michanical Study On Leveling Spee's Curve With Reverse-curve Arch

Reverse-curve arch wire is a commonly used clinical orthodontic arch wire,because of the production simple,with comfortable,and the similar mechanical characteristics to MEAW(multi-Edgewise arch wire).So it's the favorite of the orthodontic doctors. Reverse-curve arch wire isn't only chosen when the bite is deep,but also seen in the treatment of difficult open-bite malocclusion cases,but seen in over-bite cases more often.It can be used alone or with the flat plates,and we can achieve very satisfactory results by it.Mechanical principle of reverse-curve arch wire whether in theory or in experiments has been confirmed, and in practice has been authorized by dentists.But in the face of all kinds of patients,how should we select a suit wire from a variety of materials,sizes,depth reverse-curve arch wire? Therefore,this paper focus on the relevant factors of reverse-curve arch wire mechanical properties and correlation between the stress of the premolar area and the different depth of Spee's curve.In the premolar area,the stress of four sizes(0.016″,0.018″,0.016″×0.022″,0.018″×0.025″) stainless steel and super-elastic nickel-titanium alloy orthodontic wires made to 2mm,4mm,6mm depth were tested by INSTRON-5544 single-performance desktop universal materials testing machines at the different depth of curve of Spee.Through statistical analysis found:1.Different depths,different sizes,different materials arch wires had different impact on the stress of the premolar area.There were significant differences(P＜0.001).With the increasing of the depth and the size,the stress of stainless steel wire were always larger than the super-elastic nickel-titanium wire,and there was the interaction among the three factors(P＜0.001).2.For super-elastic nickel-titanium wire,depth of curve of Spee and size(cross-sectional area) have the positive linear correlation with logarithm of the stress of the premolar area. Depth of reverse-curve arch wire has nonlinear correlation with stress.Optimal equation got through Stepwise regression analysis:(?)=-0.954+2.919X₁ + 0.127X₂3.For stainless steel wire,depth of curve of Spee,size(cross-sectional area) and depth of reverse-curve arch wire show positive linear correlation with logarithm of the stress of the premolar area.optimal equation:(?)=-0.749 + 4.203X₁+0.119X₂+0.015X₃Known from the experimental results,the mechanical properties of reverse-curve arch wire correlate with their depth,size,material.On using,the depth of curve of Spee also has an impact on stress.Therefore,when we open bite with reverse-curve arch wire,it should be selected carefully:when dentition is alignment,the depth of curve of Spee greater than 4mm, we had better select 0.016″,0.016″×0.022″super-elastic nickel-titanium wire,and 2mm,4mm and6 mm are suitable.When 2-4mm depth,whether 4mm deep 0.018″and 0.018″×0.025″ super-elastic nickel-titanium reverse-curve wire or 4mm deep 0.016″and 0.016″×0.022″stainless steel wire are suitable.0.018″and 0.018″×0.025″stainless steel straight wire is recommended.