Orthodontic appliances were traditionally made of metal or of a very hard, brittle synthetic material. The American orthodontist H.D. Kesling was the first to make use of the high resilience of synthetic flexible materials for moving teeth (1945). He found that those of his patients who were treated with fixed braces often did not look as good as they should have towards the end of their treatment or they needed a lot of appointments and work to achieve a good result. So he developed the ‘tooth-positioner’ in order to shorten the final phase of the treatment. Usually, at this stage of the process the position of the teeth was not perfect but the teeth had been loosened slightly. The Positioner was an appliance made out of rubber that encompassed both teeth quadrants simultaneously, very similar to a sports mouth guard.
The positioner was manufactured from impressions that were taken from the teeth with the fixed braces in place. These were then used to produce models in the dental laboratory whereby each individual tooth was cut out of the model and then re-positioned perfectly. These models with the correctly-positioned teeth were then used to manufacture the elastic positioners. At the patient’s next appointment the brackets were removed and then the positioner had to be worn all day. Since the teeth were looser than normal anyway as a result of treatment with the fixed brace, the positioner made it possible to achieve good results in just a single step. The degree of movement that is possible using a classical positioner is around one millimetre. But unfortunately this does not work so well for patients who have not had any prior orthodontic treatment and whose teeth are therefore rigid. This means that the positioner is always used in the final phase of treatment with a fixed brace. Kesling then had the idea of using a series of different positioners to achieve even greater movements of the teeth – all current aligner systems are based on this concept. There are now various categories of positioners including one-piece, two-piece and bespoke. Two-piece positioners are very similar to aligners.