Can retainers move teeth back into place if I stopped wearing them?

Retainers are designed to hold teeth in place, not to actively move them, so they are not a reliable way to correct teeth that have already shifted. If you stopped wearing a retainer and there has been only very slight, recent movement, a newly made retainer may still fit and can help stop things drifting further. But noticeable relapse usually needs orthodontic treatment (such as braces or aligners) to put right, not a retainer on its own. If your teeth have moved, it is best to see a dentist or orthodontist so they can assess what is actually needed.