If you’ve worn braces, you will need to wear a retainer afterwards.

• A retainer will keep your teeth in the correct position after braces have been removed.
• Without a retainer, your teeth will shift back to their original position and require corrective orthodontic work later on.
• In most cases, you will not need to wear your retainer while sleeping.

"Your teeth are vulnerable to shifting throughout your lifetime."

Read more about how retainers can ensure straight teeth:
https://yourdentalhealthresource.com/do-i-really-need-to-wear-my-retainer-forever-and-why/