Scroll through any of the before and after photos on social media, and it certainly looks like mail-in aligners work. There are hundreds of glowing reviews on Smile Direct's website , with patients saying that they're "ridiculously affordable" and "efficient." One Instagram user posted a photo of her results , and said that she was able to close a gap between her front teeth in just four months of her six-month treatment. Another Smile Direct reviewer said that the "improvement was almost immediate." But other people left reviews saying that the aligners didn't straighten their teeth as much as they would have liked. One wrote, "I am not sure if saving the money was worth not being able to have access to a dentist to ask questions to."