Interesting 4d printing research from MIT last month. What do you think about the idea of using shape-shifting "4D printed" polymers in orthodontic aligners? Basically, the idea is that your print a next step aligner (or even the final aligner/retainer), then deform it to the current model and allow the heat in the mouth to slowly transform the aligner, reducing the number of steps needed in orthodontic alignment procedures.

Source: http://news.mit.edu/2016/3-d-printed-structures-remember-shapes-drug-delivery-solar-panel-0826