Development of Clear Aligners

The use of clear aligners in orthodontic treatment for adults became possible as vacuum-formed clear thermoplastic sheets were introduced into orthodontics in the 1980s. These “suck-down” materials were used initially as retainers and still are important for this purpose. It became apparent rather quickly, however, that if teeth were reset slightly and the vacuum-formed sheet was made to fit the reset teeth, a tooth moving device rather than a retainer would be the result. The device now could be, and quickly was, called an “aligner” because the typical use was to bring mildly displaced teeth back into alignment, as, for instance, when mild irregularity of maxillary or mandibular incisors occurred in an orthodontic patient after retainers were discontinued.

Only small amounts of tooth movement are possible with a single aligner, however, because of the stiffness of the plastic material. To obtain more than minor changes, it was necessary either to reshape the aligner or make a new one on a new cast with the teeth reset to a greater degree.

Because the suck-down material is softened and becomes moldable when heated, it would be possible to alter the shape of an aligner with a heated instrument,2 and in an attempt to extend the use of aligners, a special heated pliers for this type of reshaping was offered as a way to avoid the cost and complexity of having to make multiple new aligners (Figure 10-11). This still allowed only minor tooth movement, and skill was required to obtain just the right amount of change in the aligner. A major limitation is that the plastic can only be stretched a maximum of about 3 mm (in 1 mm increments) before it becomes too thin to exert force. More recently, hard plastic bumps that snap into a hole in the aligner have been used to modify it for further tooth movement, which has the advantage that the plastic of the aligner is not stretched and thinned.