These are removable braces made from flexible material without any wire elements. Introduced by Kesling in 1944, they resemble a sports mouth guard and encompass both teeth quadrants simultaneously although they are sometimes also used for a single teeth quadrant. They were originally made from rubber, although today they are generally made of silicone. The Positioner was originally a retention device based on the MB-Appliance (fixed brace) that allowed for small movements of the teeth. Better materials have now made it possible to correct larger deviations in the position of the teeth, something that could not really be done adequately with a fixed brace. Occasionally the suspicion arises that orthodontists who have had limited success with fixed braces try to compensate for this by using positioners. There is no doubt that the self-disciplined wearing of a Positioner can achieve significant improvements, but this is true of all removable braces that rely totally on the cooperation of the patient. Yet, after having their fixed braces removed, patients do not want any more inconvenience so they do not wear their positioners. Any actual assessment of the Positioner is therefore completely ambivalent.