Effects Of Different Heat Treatment Conditions On The Mechanical Performance Of Orthodontic Stainless Steel Wire

The clinical application’s development of the orthodontic arch wiregoes through roughly the gold alloy wire,18-8nickel chromiumaustenitic stainless steel wire, Australia special steel wire, cobaltchromium alloy wire, nickel titanium alloy wire, beta titanium alloy wireand so on. Each kind of arch wire have their respective features and theirtiming of the orthodontic clinical application also are not identical.However, the stainless steel wire bears the key role in orthodontic clinicbecause of its cheap price, high strength, small friction coefficient, goodformability, and easy bending. If the size of orthodontic bracket groove iscertain, the larger the size of the arch wire, the greater the stiffness, butthe friction force in tooth movement is also larger at the same time.If we choose small size of the arch wire in order to reduce the friction, thestability of the arch wire can be difficult to guarantee in teeth movement.In the process of rectification, if we want to get smaller friction andalso want to maintain the stability of the dental arch form, we can use thelow temperature heat treatment technology to increase the stiffness of thearch wire. Low temperature heat treatment technology can make thealloy’s performance stable, reduce the breakage tendency in theapplication process and to a certain extent, can also increase its corrosionresistance.Objective: The rough content of this study is choosing fivedimensions of stainless steel arch wire which is commonly used in theclinic, doing different levels of electric heat treatments to them,and usingthree-point bending test to test their mechanical properties. Our purposeis making every effort to get the optimum parameters of heat treatment of stainless steel arch wire with different dimensions and providingorthodontic doctors a standardized clinical theoretical basis and supportof the heat treatment in stainless steel wire.Method: We selected American ORMAER stainless steel arch wirewhich are commonly used in orthodontic clinical of the stomatologicalhospital of Jilin university, including5clinical commonly usedsizes(0.016inch,0.018inch,0.017,0.018x0.025inches x0.025inches,0.019x0.025inches). For each size, wo did electric heat treatment atdifferent levels by TOMY arch wire forming machine-X which is made inJapan, then, according to the American orthodontic arch wire ISOstandards (15841:2006), we did three point bending test by AG-X Plus1KN from shimadzu electronic universal testing machine at roomtemperature to get the load-displacement curve of the arch wire andcompare the differences of the elastic modulus. Results: After the optimum heat treatment, the elastic modulus ofeach kind of arch wire are increased. Comparing with the untreated group,the difference between them has statistical significance. The elasticmodulus of Stainless steel round wire increased obviously than stainlesssteel square wire after the optimum heat treatment, but the differences ingrowth between them does not have statistical significance. The0.016inch stainless steel arch wire, heated under4gear for6seconds, has themaximum of elastic modulus,195.8820±4.14Gpa. Compared with theuntreated group (162.9000±2.59Gpa), the difference is statisticallysignificant(p＜0.05), but compared with4s,5s,6s in gear4,3s,4s,5s,6sin gear6and2s,3s,4s,5s,6s in gear8, the differences of the elasticmodulus are not statistically significant. The0.018inch stainless steelarch wire, heated under4gear for5seconds, has the maximum of elasticmodulus,193.5545±0.77Gpa. Compared with the untreated group (159.0940±2.53Gpa), the difference is statistically significant(p＜0.05),but compared with2s,3s,4s,6s in gear4,3s,4s,5s,6s in gear6and2s,3s,4s,5s,6s in gear8, the differences of the elastic modulus are notstatistically significant. The0.017×0.025inches stainless steel wire,heated under6gears for7seconds, has the maximum of elastic modulus,184.7590±3.00Gpa. Compared with the untreated group(168.5230±3.63Gpa), the difference is statistically significant(p＜0.05),but compared with10s,12s,14s,16s in gear4,3s,5s,6s in gear6and5s,6s,7s in gear8, the differences of the elastic modulus are not statisticallysignificant. The0.018×0.025inches stainless steel wire, heated under6gears for7seconds, has the maximum of elastic modulus,188.2403±1.44Gpa. Compared with the untreated group(162.4767±2.50Gpa), the difference is statistically significant(p＜0.05).The0.018×0.025inches stainless steel wire, heated under6gears for8 seconds, has the maximum of elastic modulus,180.9060±1.05Gpa.Compared with the untreated group (162.3510±1.86Gpa), the differenceis statistically significant(p＜0.05). The color of each size of the stainlesssteel arch wire is silver before the heat treatment. When the color of thearch wire turns to golden yellow or deep amber, the wire can obtain amaximum elastic modulus relatively.Conclusion:1.The modulus of elasticity of the orthodonticstainless steel wire after heat treatment will have varying degrees ofincrease, compared with the untreated group.2.The stainless steel archwire will get relatively large elastic modulus when its colour turns fromsilver to golden yellow or dark yellow partial brown during the heattreatment.3. When we heat the stainless steel arch wire by using JapaneseTOMY arch wire forming machine-X in clinic, we need to know thefollowing parameters. The0.016inch stainless steel round wire will achieve the maximum modulus of elasticity after it is heated in4files for6seconds. The0.018inch stainless steel round wire will achieve themaximum modulus of elasticity after it is heated in4files for5seconds.The0.017x0.025inches stainless steel square wire will achieve themaximum modulus of elasticity after it is heated in6files for7seconds.The0.017×0.025inches stainless steel square wire will achieve themaximum modulus of elasticity after it is heated in6files for7seconds.The0.018×0.025inches stainless steel square wire will achieve themaximum modulus of elasticity after it is heated in6files for7seconds.The0.019×0.025inches stainless steel square wire will achieve themaximum modulus of elasticity after it is heated in6files for8seconds.