Abstract: An orthodontic system including an ultraelastic archwire having a transformation temperature of normal body temperature of about 37.degree. C. is provided. Only a small load is applied to the teeth when the orthodontic system is disposed in a patient's mouth. An increased load is applied to the teeth only when the temperature in the mouth is increased by placing a material having a higher than body temperature in the mouth. As a result, the temperature in the patient's mouth can be controlled without inflicting pain during natural every day actions. The orthodontic effect is available intermittently by raising the mouth temperature for producing higher stress or load which serves to move the teeth orthodontically. The ultaelastic alloy is preferably Ni-Ti alloy containing at least about 50.5 atomic percent of nickel and preferably about 50.7 atomic percent.