If you are seen for a crown/veneer and a temporary is placed, it is important that it stays in place. Teeth are constantly moving/erupting if there isn't another tooth keeping it in place. When a tooth is shaped for a crown/veneer, some of the tooth structure is removed to make room for the new crown. If the temporary comes off while waiting for the permanent crown, the newly shaped tooth can shift/move now that it's a smaller structure. It's important to re-cement the temporary in a timely manner.
Dr. James L. Johnson