How many aligners are there in a treatment?

Matthieu wants to know how many aligners are needed for a typical treatment? 

Typically, between 20 and 50 aligners are used. The first set of aligners brings the teeth as close as possible to their ideal position. 

It's a bit like a round of golf: the first shot gets you closer to the hole, but you're not quite there yet. 

There may be a series of revisions to adjust and refine the teeth to perfection.