Clear aligners, also called invisible aligners, fix mal-aligned teeth and bites. They are a virtually invisible and removable alternative to braces designed around convenience and flexibility. The aligner trays are made of BPA-free plastic and are custom-made for every patient. Each tray discreetly moves the teeth in small increments. Aligner trays are routinely swapped out every 2 to 3 weeks until the teeth are straight and aligned. How many trays you need depends on the severity of teeth misalignment (also called malocclusion).