Yes. Most definitely. Retainers are for life and are usually worn at night time,
during sleep. There are different types of retainers,
some are permanently bonded to your teeth,
but generally most retainers are removable and worn during the night. When you stop wearing the retainers you will notice relapse which means the teeth are starting to shift back and move into a crowded position again. The only way to prevent this is to wear your retainers.