Permanent retainer activation with the self-activated loop system.

labial bows require periodic tightening to maintain their activation. Without these adjustments, the activation loops at each end of the labial bow gradually open, reducing the force delivered by the appliance and often causing a relapse of anterior crowding. Since such relapse occurs gradually, the patient may be unaware of it until it has advanced to the degree that retreatment with fixed appliances is required. Loosening of the looped ends of the labial bows can adversely affect retention of the appliance in the mouth as well. This may lead the patient to wear the retainer less—another significant factor contributing to the relapse of orthodontic treatment results. Although the introduction of shape-memory wires in the early 1970s has revolutionized fixed appliance treatment,1 these wires have been difficult to incorporate into custom-made removable appliances. Retainer fabrication requires adaptation of wires to the patient’s dentition— something that is not easily accomplished with wires made of nickel titanium and other shapememory alloys. Recently, however, the development of preformed nickel titanium retainer loops has allowed the successful use of such alloys to eliminate the need for periodic tightening of retainers. The SAL System