Abstract
Super-elastic NiTi alloy wire has special properties, i.e;shape memory effect, super-elasticity and spring-back property.Heat treatment is required to bend the super-elastic NiTi alloy wire and to control its super-elastic force value.The conditions of heat treatment for the forming of super-elastic NiTi alloy wire for use in removable orthodontic appliances were determined.After 90 minutes of heat treatment at 450℃(first stage of heat treatment), the load decreased and it became shape memory wire.By the second stage of heat treatment the same sample needs to be formed into a required shape so as to restore the original mechanical properties.The higher(510℃〜520℃)the heat treatment temperature was, the shorter the required time.On the contrary the lower(480℃〜490℃)the temperature was, the longer the required time.However, when the temperature exceeded 530℃, the excellent properties of NiTi alloy wire were lost.In conclusion, the optimum temperature of the second heat treatment was 480℃〜520℃ and load of the shaped wire could be changed according to the different heat treatment conditions.Therefore, the force level can be controlled for various orthodontic appliances.
