Everyone needs some kind of retainer after they finish up with their braces or Invisalign treatment.
Your teeth have memory, and for most people, their teeth want to move back in the direction they came from. The amount of movement varies from person to person.
Our bodies change as we age, and that includes your teeth. They are not set in stone. You can generate a lot of force when you bite down. These forces are transmitted to the teeth and they can move the teeth around. This is especially true for people that grind their teeth (brux) in their sleep.The most common reason I see people in their 30s or 40s to get their teeth straightened for a second time is because they stopped wearing their retainers and their lower front teeth crowded up.
So retainer wear is a long term situation. However, most of our patients get to the point where they are wearing their retainers a night or two a week to keep everything straight. We have a blog post that has more information on retainers. Check it out.