I had invisalign for 18 months with 3 refinements. I was meant to be a simple case but there was one tooth (canine) that wouldn't budge. I was impressed at first glance but when you look closely they are far from perfect! Infact I have now have a crooked tooth (central incisor) which was caused by ill fitting invisalign. I blame part of invisalign's failure on my dentist-I suspect he was inexperienced for various reasons. I want to try again- but I'm concerned that it will not work.