Why are my bottom teeth becoming crooked again? i wear my retainer day and night. i just don't get it.

Improper Fit: The most common cause of relapse is not using the retainer, followed by the retainer being used incorrectly. If, for example, the retainer was not placed correctly for a short period of time, the teeth would shift. Now it doesn't fit correctly, even if you are placing it in your mouth. See your orthodontist asap to see what can be done regarding the malposition..

Ortho consult: Have your retainer checked for proper fit. Some teeth have a great tendency for relapse. Make sure your retainer fits well. Talk to your orthodontist about a bonded retainer and see if this will work for you.

Late mandible growth: Late mandibular growth after teen years can contribute to relapse on the lower front teeth. If you still have wisdom teeth, some people think this might contribute also -- this is controversial though. :).

Relapse : This happens because either, 1- you had a fast orthodontic treatment , appliance was taken out too early. 2- late jaw development and growth, since you are 18, 3- the presence of wisdom teeth that can start growing and pushing forward leading to crowded anterior region. See your dentist.