Yes, since the bone and soft tissue have yet to fully mature around the new tooth positions.
For this reason, fixed retainers are recommended. These are thin wires glued to the back of the front teeth BEFORE the braces are removed to prevent them from shifting.
Removable retainers are usually prescribed together with fixed retainers as a backup system, in case the fixed retainer breaks or debonds.
There is no "safe" period of time after the braces come off when your teeth will no longer shift. It may take more time for the shifting to occur but it will still happen. Lifelong retainer wear is a must to ensure you maintain the results of your braces treatment.
