Regardless of how teeth are moved, either by normal orthodontics, removable aligners or Cfast, if they are not held in position there is a strong possibility that they will start to move in time. Cfast provides two types of retainers; a fixed retainer which is permanently bonded to the inside of the teeth as well as a removable retainer that is worn overnight.
Your dentist will explain retainers in more detail when you attend your initial consultation.