What happens if retainers arent worn after mouth braces have been out?

Teeth move. Teeth have a tendency to move back to where they came from. There can be jaw growth until about age 30 which can affect tooth position also. There are many adults out there who wish they had listened to their dentist/orthodontist and some are wearing braces a second time to get their beautiful smile back.
Protect investment. You worked so long and hard to produce a beautiful smile. It would be a shame to throw away all that hard work and money. Wear your retainers as directed to protect and preserve your orthodontic treatment result.
Movement. Of teeth back to previous places. Need retainer to help heal in place once they are straight.
Relapse. Retainers are an integral part of orthodontic treatment and are meant to stabilize teeth in their new positions. Failure to follow through with the retention program as directed by your doctor will result in adverse tooth movement, disappointment in the final outcome, and possibly further treatment time and expense to rectify the relapse.
So many times... So many times, I am putting adults in braces for the second time. It is expensive and it can cause root tips to shorten. Often referred to as root resorption. Please wear your retainers after going thru braces. It is a small price to pay compared to the costs and time involved with re-treating with braces.
Retainers. The purpose of retainers is to retain the teeth (hold them) in their new places. If you don't wear your retainers then your teeth will want to move back to where they were before braces. If they were crooked they'll get crooked again. If they were spaced then they'll move apart again.
Why risk it! Your teeth are like every other part of your body....They tend to change with age. Most of those changes are not desirable. Fortunately, unlike other parts of your body, retainers are able to minimize the negative changes in your teeth. Wouldn't it be awesome if you could do the same for your vision or waistline!!
The teeth can move. It is advisable to wear your retainer and if you lost it...Please have another appliance made asap.