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This study was to analyze the stress of the orthodontic STS 304 steel round wires of JINSUNG IND. In diameter 0.9㎜ according to their bending methods we obtained the following conclusion after testing tensile strength and maximum stress, and checking deformation after bending wires to 90 degrees. 1. The tensile strength of the stainless steel round wires of JINSUNG IND., DENTAURUM and FORESTADENT was 1,808 ㎫, 1,824 ㎫ and 1,847 ㎫ respectively. The difference was not big. 2. The maximum stress occurred at the contact point of wires and R_(fix) after bending wires to 90 degrees. 3. The maximum stress increased as the bending angle reduced. The maximum stress of R_(fix) 4㎜ increased by 30%, compared with that of R_(fix) 0.2㎜.Especially R_(fix) lower than 0.5㎜ increased the possibility of fracture since the maximum stress (1,417 ㎫) got close to the yield strength (1,412 ㎫) of test material. 4. When R_(fix) of 0.2㎜, 0.5㎜, 1.0㎜, 2.0㎜ and 4.0㎜ were bent to 90 degrees, The deformation of R_(fix) 0.2㎜ is 62 degrees while that of R_(fix) 4㎜ is 59 degrees. All the cases had no big difference.
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