I won't even get into what I think of your first orthodontist. But, to answer your question, a retainer for life is the way to go. People were being told that back in the 80's, and I'm still making new ones for people who go back to their ortho after 20-30 years.
Our teeth shift as we get older, and that goes for people who never had braces as well. Wisdom teeth could be a culprit, or just simple tiny shifts that shift something else that shifts something else, etc. People who had ortho treatment are more likely to shift back to where they were as teeth "remember" where they are supposed to be.
Hey labguy question if i may, seeing as you mentioned that you are in the business of retainers, can you answer this
How on earth does an ortho take impressions with braces on???
And also how readily available are those flossable retainers i really want that as my permanat one not that other one they offer???
Sorry to ambush the posting topic